Transmembrane protein 53 craniotubular dysplasia (OMIM # 619727): The skeletal disease and consequent blindness of this new disorder.

Craniotubular dysplasia, Ikegawa type (OMIM #619727) denotes the autosomal recessive skeletal disease identified in 2021 featuring blindness acquired in childhood. Five young members of four Indian families harbored a homozygous indel within TMEM53 (OMIM *619722), the gene that encodes transmembrane protein 53 (TMEM53). When intact, TMEM53 spans the nuclear envelope of osteoprogenitor cells, dampens BMP-SMAD signaling, and thereby slows bone formation. Consequently, defective TMEM53 accelerates osteogenesis. Herein, an American boy is compound heterozygous for a novel deletion and a novel missense mutation within TMEM53. His vision and sensorineural hearing became impaired. Radiographic survey revealed diploic thickening of his skull, broad calvarial and facial bones, skeletal modeling errors, vertebral body flattening, wide ribs, and osteopenia of expanded bones. DXA areal bone density (gm/cm2) Z-scores were low. His optic, auditory, and spinal canals were narrow. Mineral metabolism was intact. Serum alkaline phosphatase and osteocalcin levels were normal yet CTX was high. Iliac crest histomorphometry documented accelerated bone formation. His acute vision loss briefly improved following prednisone administration, optic canal decompression, and optic nerve sheath fenestration, but then progressed despite further surgeries and zoledronate treatment aimed to suppress bone turnover. Next generation sequencing of genes associated with elevated skeletal mass, including from high bone turnover, did not suggest an etiology. Whole genome sequencing then revealed within TMEM53: i) a paternally transmitted 54-base deletion, which included the mRNA splice acceptor site for exon 2 as well as 31 bases of exonic sequence (c. 62-23_92del), and ii) a maternally transmitted missense variant (c.650C > T, p.Ser217Leu: NM_024587.4/NP_078863.2) which is extremely rare in gnomAD (frequency = 0.000036), replaces Ser217 highly conserved across species, and is scored as damaging by SIFT and Mutation Taster. We call this new osteopathy TMEM53 craniotubular dysplasia.

Pediatric hypophosphatasia: avoid diagnosis missteps!

Hypophosphatasia (HPP) is the dento-osseous disorder caused by deactivating mutation(s) of ALPL, the gene that encodes the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP). In HPP, 3 natural substrates of cell-surface TNSALP accumulate extracellularly; phosphoethanolamine (PEA), inorganic pyrophosphate (PPi), and pyridoxal 5'-phosphate (PLP). Hypophosphatasemia together with elevated plasma levels of PEA, PPi, and PLP comprise its biochemical signature. PPi can inhibit mineralization and in extracellular excess can impair bone and tooth hardening and perhaps explain weak muscle. Autosomal dominant or autosomal recessive inheritance from among more than 400 mutations of ALPL largely accounts for HPP's broad-ranging severity, greatest among all skeletal diseases. Pediatric HPP spans life-threatening perinatal and infantile forms, childhood forms, and odonto-HPP selectively featuring premature loss of deciduous teeth. ALPL gene testing and TNSALP supplementation therapy have bolstered familiarity with HPP, but there are new considerations for diagnosis. Herein, diagnosis of a boy's mild childhood HPP was delayed by missteps involving his medical and dental history, physical examination, radiographic findings, and clinical laboratory studies. We review how pediatric HPP is now identified. Prompt diagnosis while appreciating the broad-ranging severity of HPP underlies the safe and effective management of this inborn-error-of-metabolism.

Drug-induced osteopetrosis.

Osteopetrosis (OPT) denotes the consequences from failure of osteoclasts to resorb bone and chondroclasts to remove calcified physeal cartilage throughout growth. Resulting impairment of skeletal modeling, remodeling, and growth compromises widening of medullary spaces, formation of the skull, and expansion of cranial foramina. Thus, myelophthisic anemia, raised intracranial pressure, and cranial nerve palsies complicate OPT when severe. Osteopetrotic bones fracture due to misshaping, failure of remodeling to weave the collagenous matrix of cortical osteons and trabeculae, persistence of mineralized growth plate cartilage, "hardening" of hydroxyapatite crystals, and delayed healing of skeletal microcracks. Teeth may fail to erupt. Now it is widely appreciated that OPT is caused by germline loss-of-function mutation(s) usually of genes involved in osteoclast function, but especially rarely of genes necessary for osteoclast formation. Additionally, however, in 2003 we published a case report demonstrating that prolonged excessive dosing during childhood of the antiresorptive aminobisphosphonate pamidronate can sufficiently block osteoclast and chondroclast activity to recapitulate the skeletal features of OPT. Herein, we include further evidence of drug-induced OPT by illustrating osteopetrotic skeletal changes from repeated administration of high doses of the aminobisphosphonate zoledronic acid (zoledronate) given to children with osteogenesis imperfecta.

Periarticular calcifications containing giant pseudo-crystals of francolite in skeletal fluorosis from 1,1-difluoroethane "huffing".

Inhalant use disorder is a psychiatric condition characterized by repeated deliberate inhalation from among a broad range of household and industrial chemical products with the intention of producing psychoactive effects. In addition to acute intoxication, prolonged inhalation of fluorinated compounds can cause skeletal fluorosis (SF). We report a young woman referred for hypophosphatasemia and carrying a heterozygous ALPL gene variant (c.457T>C, p.Trp153Arg) associated with hypophosphatasia, the heritable metabolic bone disease featuring impaired skeletal mineralization, who instead suffered from SF. Manifestations of her SF included recurrent articular pain, axial osteosclerosis, elevated bone mineral density, maxillary exostoses, and multifocal periarticular calcifications. SF was suspected when a long history was discovered of 'huffing' a computer cleaner containing 1,1-difluoroethane. Investigation revealed markedly elevated serum and urine levels of F-. Histopathology and imaging techniques including backscattered electron mode scanning electron microscopy, X-ray microtomography, energy dispersive and wavelength dispersive X-ray emission microanalysis, and polarized light microscopy revealed that her periarticular calcifications were dystrophic deposition of giant pseudo-crystals of francolite, a carbonate-rich fluorapatite. Identifying unusual circumstances of F- exposure is key for diagnosing non-endemic SF. Increased awareness of the disorder can be lifesaving.

Vitamin B6 deficiency with normal plasma levels of pyridoxal 5'-phosphate in perinatal hypophosphatasia.

Pyridoxal 5'-phosphate (PLP), the principal circulating form of vitamin B6 (B6), is elevated in the plasma of individuals with hypophosphatasia (HPP). HPP is the inborn-error-of-metabolism caused by loss-of-function mutation(s) of ALPL, the gene that encodes the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP). PLP accumulates extracellularly in HPP because it is a natural substrate of this cell-surface phosphomonoester phosphohydrolase. Even individuals mildly affected by HPP manifest this biochemical hallmark, which is used for diagnosis. Herein, an exclusively breast-fed newborn boy with life-threatening perinatal HPP had uniquely normal instead of markedly elevated plasma PLP levels before beginning asfotase alfa (AA) TNSALP-replacement therapy. These abnormal PLP levels were explained by B6 deficiency, confirmed by his low plasma level of 4-pyridoxic acid (PA), the B6 degradation product. His mother, a presumed carrier of one of his two ALPL missense mutations, had serum ALP activity of 50 U/L (Nl 40-130) while her plasma PLP level was 9 µg/L (Nl 5-50) and PA was 3 µg/L (Nl 3-30). Her dietary history and breast milk pyridoxal (PL) level indicated she too was B6 deficient. With B6 supplementation using a breast milk fortifier, the patient's plasma PA level corrected, while his PLP level remained in the normal range but now in keeping with AA treatment. Our experience reveals that elevated levels of PLP in the circulation in HPP require some degree of B6 sufficiency, and that anticipated increases in HPP can be negated by hypovitaminosis B6.

Non-endemic skeletal fluorosis: Causes and associated secondary hyperparathyroidism (case report and literature review).

Skeletal fluorosis (SF) is endemic primarily in regions with fluoride (F)-contaminated well water, but can reflect other types of chronic F exposure. Calcium (Ca) and vitamin D (D) deficiency can exacerbate SF. A 51-year-old man with years of musculoskeletal pain and opiate use was hypocalcemic with secondary hyperparathyroidism upon manifesting recurrent long bone fractures. He smoked cigarettes, drank large amounts of cola beverage, and consumed little dietary Ca. Then, after 5 months of Ca and D3 supplementation, serum 25(OH)D was 21 ng/mL (Nl, 30-100), corrected serum Ca had normalized from 7.8 to 9.4 mg/dL (Nl, 8.5-10.1), alkaline phosphatase (ALP) had decreased from 1080 to 539 U/L (Nl, 46-116), yet parathyroid hormone (PTH) had increased from 133 to 327 pg/mL (Nl, 8.7-77.1). Radiographs revealed generalized osteosclerosis and a cystic lesion in a proximal femur. DXA BMD Z-scores were +7.4 and +0.4 at the lumbar spine and "1/3" radius, respectively. Bone scintigraphy showed increased uptake in two ribs, periarticular areas, and proximal left femur at the site of a subsequent atraumatic fracture. Elevated serum collagen type I C-telopeptide 2513 pg/mL (Nl, 87-345) and osteocalcin >300 ng/mL (Nl, 9-38) indicated rapid bone turnover. Negative studies included hepatitis C Ab, prostate-specific antigen, serum and urine electrophoresis, and Ion Torrent mutation analysis for dense or high-turnover skeletal diseases. After discovering markedly elevated F concentrations in his plasma [4.84 mg/L (Nl, 0.02-0.08)] and spot urine [42.6 mg/L (Nl, 0.2-3.2)], a two-year history emerged of "huffing" computer cleaner containing difluoroethane. Non-decalcified histology of a subsequent right femur fracture showed increased osteoblasts and osteoclasts and excessive osteoid. A 24-hour urine collection contained 27 mg/L F (Nl, 0.2-3.2) and <2 mg/dL Ca. Then, 19 months after "huffing" cessation and improved Ca and D3 intake, yet with persisting bone pain, serum PTH was normal (52 pg/mL) and serum ALP and urine F had decreased to 248 U/L and 3.3 mg/L, respectively. Our experience combined with 15 publications in PubMed concerning unusual causes of non-endemic SF where the F source became known (19 cases in all) revealed: 11 instances from high consumption of black tea and/or F-containing toothpaste, 1 due to geophagia of F-rich soil, and 7 due to "recreational" inhalation of F-containing vapors. Circulating PTH measured in 14 was substantially elevated in 2 (including ours) and mildly increased in 2. The severity of SF in the cases reviewed seemed to reflect cumulative F exposure, renal function, and Ca and D status. Several factors appeared to influence our patient's skeletal disease: i) direct anabolic effects of toxic amounts of F on his skeleton, ii) secondary hyperparathyroidism from degradation-resistant fluorapatite bone crystals and low dietary Ca, and iii) impaired mineralization of excessive osteoid due to hypocalcemia.

Coalescing expansile skeletal disease: Delineation of an extraordinary osteopathy involving the IFITM5 mutation of osteogenesis imperfecta type V.

In 2003, we briefly reported the remarkable osteopathy of a 12-year-old boy who at age two months began fracturing his limbs with subsequent hyperplastic callus formation and expansion and fusion of appendicular bones. By age ten years he had coalesced his lumbosacral spine, pelvis, femurs, and leg and foot bones as a single structure. Computed tomography of expanded bone revealed a thin cortical shell, diminished irregular trabeculae, and cystic areas. Histopathology featured foci of woven bone, densely packed osteocytes, cartilage, fibrovascular tissue, and massive fat deposition in the marrow space lacking hematogenous precursor cells. Bone turnover markers indicated accelerated remodeling and the few radiographically assessable appendicular bones improved during brief adherence to alendronate therapy. Following puberty, serum multiplex biomarker profiling confirmed accelerated bone turnover. At age 23 years, macrospecimens from leg amputation revealed ossification along capsular tissue together with hyaline cartilage degeneration. Concurrently, the life-long course of this same disorder was delineated in an unrelated woman until her death at age 51 years. Both patients demonstrated the radiographic hallmarks and harbored the heterozygous point mutation (c.-14C>T) in the 5'-UTR of IFITM5 associated with osteogenesis imperfecta type V (OI-V). Herein, we detail the clinical, radiological, histopathological, biochemical, and molecular findings and discuss the etiology and pathogenesis of this extraordinary osteopathy that we call coalescing expansile skeletal disease.

Persistent idiopathic hyperphosphatasemia from bone alkaline phosphatase in a healthy boy.

Alkaline phosphatase (ALP) in humans comprises a family of four cell-surface phosphomonoester phosphohydrolase isozymes. Three genes separately encode the "tissue-specific" ALPs whereas the fourth gene encodes ubiquitous homodimeric "tissue-nonspecific" ALP (TNSALP) richly expressed in bone, liver, kidney, and developing teeth. TNSALP monomers have five putative N-linked glycosylation sites where different post-translational modifications account for this isozyme's distinctive physicochemical properties in different organs. Three bone-derived TNSALP (BALP) isoforms (B/I, B1, and B2) are present in healthy serum, whereas a fourth BALP isoform (B1x) can circulate in chronic kidney disease. Herein, we report a healthy boy with persistent hyperphosphatasemia due to BALP levels two- to threefold higher than age-appropriate reference values. High-performance liquid chromatography, electrophoresis, heat inactivation, catalysis inhibition, and polyethylene glycol precipitation revealed increased serum B/I, B1, and B2 differing from patterns found in skeletal diseases. B/I was ~23-fold elevated. Absence of mental retardation and physical stigmata excluded Mabry syndrome, the ALP-anchoring disorder causing hyperphosphatasemia. Routine biochemical studies indicated intact mineral homeostasis. Serum N-terminal propeptide of type I procollagen (P1NP) level was normal, but C-terminal cross-linking telopeptide of type I collagen (CTX) level was elevated. However, radiological studies showed no evidence for a generalized skeletal disturbance. Circulating pyridoxal 5'-phosphate, a TNSALP natural substrate, was not low despite the laboratory hyperphosphatasemia, thereby suggesting BALP phosphohydrolase activity was not elevated endogenously. Mutation analysis of the ALPL gene encoding TNSALP revealed no defect. His non-consanguineous healthy parents had serum total ALP activity and BALP protein levels that were normal. Our patient's sporadic idiopathic hyperphosphatasemia could reflect altered post-translational modification together with increased expression and/or impaired degradation of BALP.

Juvenile Paget's Disease From Heterozygous Mutation of SP7 Encoding Osterix (Specificity Protein 7, Transcription Factor SP7).

Juvenile Paget's disease (JPD) became in 1974 the commonly used name for ultra-rare heritable occurrences of rapid bone remodeling throughout of the skeleton that present in infancy or early childhood as fractures and deformity hallmarked biochemically by marked elevation of serum alkaline phosphatase (ALP) activity (hyperphosphatasemia). Untreated, JPD can kill during childhood or young adult life. In 2002, we reported that homozygous deletion of the gene called tumor necrosis factor receptor superfamily, member 11B (TNFRSF11B) encoding osteoprotegerin (OPG) explained JPD in Navajos. Soon after, other bi-allelic loss-of-function TNFRSF11B defects were identified in JPD worldwide. OPG inhibits osteoclastogenesis and osteoclast activity by decoying receptor activator of nuclear factor κ-B (RANK) ligand (RANKL) away from its receptor RANK. Then, in 2014, we reported JPD in a Bolivian girl caused by a heterozygous activating duplication within TNFRSF11A encoding RANK. Herein, we identify mutation of a third gene underlying JPD. An infant girl began atraumatic fracturing of her lower extremity long-bones. Skull deformity and mild hearing loss followed. Our single investigation of the patient, when she was 15 years-of-age, showed generalized osteosclerosis and hyperostosis. DXA revealed a Z-score of +5.1 at her lumbar spine and T-score of +3.3 at her non-dominant wrist. Biochemical studies were consistent with positive mineral balance and several markers of bone turnover were elevated and included striking hyperphosphatasemia. Iliac crest histopathology was consistent with rapid skeletal remodeling. Measles virus transcripts, common in classic Paget's disease of bone, were not detected in circulating mononuclear cells. Then, reportedly, she responded to several months of alendronate therapy with less skeletal pain and correction of hyperphosphatasemia but had been lost to our follow-up. After we detected no defect in TNFRSF11A or B, trio exome sequencing revealed a de novo heterozygous missense mutation (c.926C>G; p.S309W) within SP7 encoding the osteoblast transcription factor osterix (specificity protein 7, transcription factor SP7). Thus, mutation of SP7 represents a third genetic cause of JPD.

Healing of vitamin D deficiency rickets complicating hypophosphatasia suggests a role beyond circulating mineral sufficiency for vitamin D in musculoskeletal health.

Hypophosphatasia (HPP) is the metabolic bone disease caused by loss-of-function mutation(s) of the ALPL gene that encodes the cell-surface tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). In HPP, extracellular accumulation of inorganic pyrophosphate (PPi), a TNSALP natural substrate and inhibitor of biomineralization, often leads to rickets or osteomalacia despite normal or sometimes elevated circulating levels of calcium (Ca) and inorganic phosphate (Pi). We report an infant girl with vitamin D deficiency rickets subsequently healed by cholecalciferol administration alone before receiving TNSALP-replacement therapy for accompanying HPP. Throughout her clinical course, circulating Ca and Pi levels were normal or elevated. At presentation with failure-to-thrive at age six months, radiographs revealed severe rickets and serum 25(OH)D was 8 ng/mL (Nl, 30-100), yet low ALP activity 55 U/L (Nl, 124-341), normal Ca 9.3 mg/dL (Nl, 8.5-10.1) and Pi 6.4 mg/dL (Nl, 3.5-7.0), and low-normal parathyroid hormone 21 pg/mL (Nl, 14-72) were instead consistent with HPP. At age nine months, after 1000 IU of cholecalciferol orally each day for six weeks, serum 25(OH)D was 86 ng/mL, strength markedly better, and radiographs documented significant improvement of rickets. At age 18 months, with fully healed vitamin D deficiency rickets, findings of underlying HPP included a waddling gait and Gower sign, metaphyseal "tongues" of radiolucency, elevated serum pyridoxal 5'-phosphate 121 ng/mL (Nl, 2-33), and bi-allelic ALPL missense mutations. Then, nearly complete restoration of strength and radiographic healing of her remaining skeletal disease from HPP occurred during asfotase alfa enzyme replacement treatment. At no time, including presentation, were circulating Ca or Pi levels compromised. Instead, and in keeping with HPP, high-normal or elevated serum Ca and Pi concentrations were consistently documented. Thus, our findings suggest some role for vitamin D in musculoskeletal health beyond assuring circulating mineral sufficiency.

Bruck syndrome 2 variant lacking congenital contractures and involving a novel compound heterozygous PLOD2 mutation.

Bruck syndrome (BRKS) is the rare disorder that features congenital joint contractures often with pterygia and subsequent fractures, also known as osteogenesis imperfecta (OI) type XI (OMIM # 610968). Its two forms, BRKS1 (OMIM # 259450) and BRKS2 (OMIM # 609220), reflect autosomal recessive (AR) inheritance of FKBP10 and PLOD2 loss-of-function mutations, respectively. A 10-year-old girl was referred with blue sclera, osteopenia, poorly-healing fragility fractures, Wormian skull bones, cleft soft palate, congenital fusion of cervical vertebrae, progressive scoliosis, bell-shaped thorax, restrictive and reactive pulmonary disease, protrusio acetabuli, short stature, and additional dysmorphic features without joint contractures. Iliac crest biopsy after alendronate treatment that improved her bone density revealed low trabecular connectivity, abundant patchy osteoid, and active bone formation with widely-spaced tetracycline labels. Chromosome 22q11 deletion analysis for velocardiofacial syndrome, COL1A1 and COL1A2 sequencing for prevalent types of OI, and Sanger sequencing of LRP5, PPIB, FKBP10, and IFITM5 for rare pediatric osteoporoses were negative. Copy number microarray excluded a contiguous gene syndrome. Instead, exome sequencing revealed two missense variants in PLOD2 which encodes procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (lysyl hydroxylase 2, LH2); exon 8, c.797G>T, p.Gly266Val (paternal), and exon 12, c.1280A>G, p.Asn427Ser (maternal). In the Exome Aggregation Consortium (ExAC) database, low frequency (Gly266Val, 0.0000419) and absence (Asn427Ser) implicated both variants as mutations of PLOD2. The father, mother, and sister (who carried the exon 12 defect) were reportedly well with normal parental DXA findings. BRKS2, characterized by under-hydroxylation of type I collagen telopeptides compromising their crosslinking, has been reported in at least 16 probands/families. Most PLOD2 mutations involve exons 17-19 (of 20 total) encoding the C-terminal domain with LH activity. However, truncating defects (nonsense, frameshift, splice site mutations) are also found throughout PLOD2. In three reports, AR PLOD2 mutations are not associated with congenital contractures. Our patient's missense defects lie within the central domain of unknown function of PLOD2. In our patient, compound heterozygosity with PLOD2 mutations is associated with a clinical phenotype distinctive from classic BRKS2 indicating that when COL1A1 and COL1A2 mutation testing is negative for OI without congenital contractures or pterygia, atypical BRKS should be considered.

Hypophosphatemic osteosclerosis, hyperostosis, and enthesopathy associated with novel homozygous mutations of DMP1 encoding dentin matrix protein 1 and SPP1 encoding osteopontin: The first digenic SIBLING protein osteopathy?

The SIBLINGs are a subfamily of the secreted calcium-binding phosphoproteins and comprise five small integrin-binding ligand N-linked glycoproteins [dentin matrix protein-1 (DMP1), secreted phosphoprotein-1 (SPP1) also called osteopontin (OPN), integrin-binding sialoprotein (IBSP) also called bone sialoprotein (BSP), matrix extracellular phosphoglycoprotein (MEPE), and dentin sialophosphoprotein (DSPP)]. Each SIBLING has at least one "acidic, serine- and aspartic acid-rich motif" (ASARM) and multiple Ser-x-Glu/pSer sequences that when phosphorylated promote binding of the protein to hydroxyapatite for regulation of biomineralization. Mendelian disorders from loss-of-function mutation(s) of the genes that encode the SIBLINGs thus far involve DSPP causing various autosomal dominant dysplasias of dentin but without skeletal disease, and DMP1 causing autosomal recessive hypophosphatemic rickets, type 1 (ARHR1). No diseases have been reported from gain-of-function mutation(s) of DSPP or DMP1 or from alterations of SPP1, IBSP, or MEPE. Herein, we describe severe hypophosphatemic osteosclerosis and hyperostosis associated with skeletal deformity, short stature, enthesopathy, tooth loss, and high circulating FGF23 levels in a middle-aged man and young woman from an endogamous family living in southern India. Both shared novel homozygous mutations within two genes that encode a SIBLING protein: stop-gain ("nonsense") DMP1 (c.556G>T,p.Glu186Ter) and missense SPP1 (c.769C>T,p.Leu266Phe). The man alone also carried novel heterozygous missense variants within two additional genes that condition mineral homeostasis and are the basis for autosomal recessive disorders: CYP27B1 underlying vitamin D dependent rickets, type 1, and ABCC6 underlying both generalized arterial calcification of infancy, type 2 and pseudoxanthoma elasticum (PXE). By immunochemistry, his bone contained high amounts of OPN, particularly striking surrounding osteocytes. We review how our patients' disorder may represent the first digenic SIBLING protein osteopathy.

New explanation for autosomal dominant high bone mass: Mutation of low-density lipoprotein receptor-related protein 6.

LRP5 encodes low-density lipoprotein receptor-related protein 5 (LRP5). When LRP5 with a Frizzled receptor join on the surface of an osteoblast and bind a member of the Wnt family of ligands, canonical Wnt/ß-catenin signaling occurs and increases bone formation. Eleven heterozygous gain-of-function missense mutations within LRP5 are known to prevent the LRP5 inhibitory ligands sclerostin and dickkopf1 from attaching to LRP5's first ß-propeller, and thereby explain the rare autosomal dominant (AD) skeletal disorder "high bone mass" (HBM). LRP6 is a cognate co-receptor of LRP5 and similarly controls Wnt signaling in osteoblasts, yet the consequences of increased LRP6-mediated signaling remain unknown. We investigated two multi-generational American families manifesting the clinical and routine laboratory features of LRP5 HBM but without an LRP5 defect and instead carrying a heterozygous LRP6 missense mutation that would alter the first ß-propeller of LRP6. In Family 1 LRP6 c.602C>T, p.A201V was homologous to LRP5 HBM mutation c.641C>T, p.A214V, and in Family 2 LRP6 c.553A>C, p.N185H was homologous to LRP5 HBM mutation c.593A>G, p.N198S but predicting a different residue at the identical amino acid position. In both families the LRP6 mutation co-segregated with striking generalized osteosclerosis and hyperostosis. Clinical features shared by the seven LRP6 HBM family members and ten LRP5 HBM patients included a broad jaw, torus palatinus, teeth encased in bone and, reportedly, resistance to fracturing and inability to float in water. For both HBM disorders, all affected individuals were taller than average for Americans (Ps < 0.005), but with similar mean height Z-scores (P = 0.7606) and indistinguishable radiographic skeletal features. Absence of adult maxillary lateral incisors was reported by some LRP6 HBM individuals. In contrast, our 16 patients with AD osteopetrosis [i.e., Albers-Schönberg disease (A-SD)] had an unremarkable mean height Z-score (P = 0.9401) lower than for either HBM group (Ps < 0.05). DXA mean BMD Z-scores in LRP6 HBM versus LRP5 HBM were somewhat higher at the lumbar spine (+7.8 vs +6.5, respectively; P = 0.0403), but no different at the total hip (+7.9 vs +7.7, respectively; P = 0.7905). Among the three diagnostic groups, only the LRP6 HBM DXA BMD values at the spine seemed to increase with subject age (R = +0.7183, P = 0.0448). Total hip BMD Z-scores were not significantly different among the three disorders (Ps > 0.05), and showed no age effect (Ps > 0.1). HR-pQCT available only for LRP6 HBM revealed indistinct corticomedullary boundaries, high distal forearm and tibial total volumetric BMD, and finite element analysis predicted marked fracture resistance. Hence, we have discovered mutations of LRP6 that cause a dento-osseous disorder indistinguishable without mutation analysis from LRP5 HBM. LRP6 HBM seems associated with generally good health, providing some reassurance for the development of anabolic treatments aimed to enhance LRP5/LRP6-mediated osteogenesis.

No vascular calcification on cardiac computed tomography spanning asfotase alfa treatment for an elderly woman with hypophosphatasia.

Hypophosphatasia (HPP) is the inborn-error-of-metabolism characterized enzymatically by insufficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP) and caused by either mono- or bi-allelic loss-of-function mutation(s) of the gene ALPL that encodes this cell surface phosphomonoester phosphohydrolase. In HPP, the natural substrates of TNSALP accumulate extracellularly and include inorganic pyrophosphate (PPi), a potent inhibitor of biomineralization. This PPi excess leads to rickets or osteomalacia in all but the most mild "odonto" form of the disease. Adults with HPP understandably often also manifest calcium PPi dihydrate deposition, whereas enthesopathy and calcific periarthritis from hydroxyapatite (HA) crystal deposition can seem paradoxical in face of the defective skeletal mineralization. In 2015, asfotase alfa (AA), a HA-targeted TNSALP, was approved multinationally as an enzyme replacement therapy for HPP. AA hydrolyzes extracellular PPi (ePPi) and in HPP enables HA crystals to grow and mineralize skeletal matrix. In direct contrast to HPP, deficiency of ePPi characterizes the inborn-errors-of-metabolism generalized arterial calcification of infancy (GACI) and pseudoxanthoma elasticum (PXE). In GACI and PXE, deficiency of ePPi leads to ectopic mineralization including vascular calcification (VC). Therefore, in HPP, ectopic mineralization including VC could hypothetically result from, or be exacerbated by, the persistently high circulating TNSALP activity that occurs during AA treatment. Herein, using a routine computed tomography (CT) method to quantitate coronary artery calcium, we found no ectopic mineralization in the heart of an elderly woman with HPP before or after 8 months of AA treatment. Subsequently, investigational high-resolution peripheral quantitative CT and dual-energy X-ray absorptiometry showed absence of peripheral artery and aortic calcium after further AA treatment. Investigation of additional adults with HPP could reveal if the superabundance of ePPi protects against VC, and whether long-term AA therapy causes or exacerbates any ectopic mineralization.

Absence of an osteopetrosis phenotype in IKBKG (NEMO) mutation-positive women: A case-control study.

BACKGROUND: NF-κB essential modulator (NEMO), encoded by IKBKG, is necessary for activation of the ubiquitous transcription factor nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB). Animal studies suggest NEMO is required for NF-κB mediated bone homeostasis, but this has not been thoroughly studied in humans. IKBKG loss-of-function mutation causes incontinentia pigmenti (IP), a rare X-linked disease featuring linear hypopigmentation, alopecia, hypodontia, and immunodeficiency. Single case reports describe osteopetrosis (OPT) in boys carrying hypomorphic IKBKG mutations. METHOD: We studied the bone phenotype in women with IP with evaluation of radiographs of the spine and non-dominant arm and leg; lumbar spine and femoral neck aBMD using DXA; µ-CT and histomorphometry of trans-iliac crest biopsy specimens; bone turnover markers; and cellular phenotype in bone marrow skeletal (stromal) stem cells (BM-MSCs) in a cross-sectional, age-, sex-, and BMI-matched case-control study. X-chromosome inactivation was measured in blood leucocytes and BM-MSCs using a PCR method with methylation of HpaII sites. NF-κB activity was quantitated in BM-MSCs using a luciferase NF-κB reporter assay. RESULTS: Seven Caucasian women with IP (age: 24-67 years and BMI: 20.0-35.2 kg/m2) and IKBKG mutation (del exon 4-10 (n = 4); c.460C>T (n = 3)) were compared to matched controls. The IKBKG mutation carriers had extremely skewed X-inactivation (>90:10%) in blood, but not in BM-MSCs. NF-κB activity was lower in BM-MSCs from IKBKG mutation carriers (n = 5) compared to controls (3094 ±â€¯679 vs. 5422 ±â€¯1038/µg protein, p < 0.01). However, no differences were identified on skeletal radiographics, aBMD, µ-architecture of the iliac crest, or bone turnover markers. The IKBKG mutation carriers had a 1.7-fold greater extent of eroded surfaces relative to osteoid surfaces (p < 0.01), and a 2.0-fold greater proportion of arrested reversal surface relative to active reversal surface (p < 0.01). CONCLUSION: Unlike mutation-positive males, the IKBKG mutation-positive women did not manifest OPT.

Asfotase alfa for infants and young children with hypophosphatasia: 7 year outcomes of a single-arm, open-label, phase 2 extension trial.

BACKGROUND: Our previous phase 2, open-label study of 11 infants and young children with life-threatening perinatal or infantile hypophosphatasia showed 1 year safety and efficacy of asfotase alfa, an enzyme replacement therapy. We aimed to report the long-term outcomes over approximately 7 years of treatment. METHODS: We did a prespecified, end of study, 7 year follow-up of our single-arm, open-label, phase 2 trial in which children aged 3 years or younger with life-threatening perinatal or infantile hypophosphatasia were recruited from ten hospitals (six in the USA, two in the UK, one in Canada, and one in the United Arab Emirates). Patients received asfotase alfa (1 mg/kg three times per week subcutaneously, adjusted to 3 mg/kg three times per week if required) for up to 7 years (primary treatment period plus extension phase) or until the product became commercially available; dosage adjustments were made at each visit according to changes in the patient's weight. The primary objectives of this extension study were to assess the long-term tolerability of asfotase alfa, defined as the number of patients with one or more treatment-emergent adverse events, and skeletal manifestations associated with hypophosphatasia, evaluated using the Radiographic Global Impression of Change (RGI-C) scale (-3 indicating severe worsening, and +3 complete or near-complete healing). Respiratory support, growth, and cognitive and motor functions were also evaluated. All efficacy and safety analyses were done in all patients who received any asfotase alfa (full-analysis population). This study and extension phase are registered with ClinicalTrials.gov, number NCT01205152, and EudraCT, number 2009-009369-32. FINDINGS: 11 participants were recruited between Oct 6, 2008, and Dec 4, 2009. Ten patients completed a 6 month treatment period and entered the extension phase; nine received asfotase alfa for at least 6 years and completed the study, with four being treated for more than 7 years. Skeletal healing was sustained over 7 years of treatment; all evaluable patients had RGI-C scores of at least +2 at year 6 (n=9; median score +2·0 [range 2·0-3·0]) and year 7 (n=7; median score +2·3 [2·0-3·0]). No patient who completed the study required respiratory support after year 4. Weight Z scores improved to within normal range from year 3 to study end; length or height Z scores improved but remained below normal. Age-equivalent scores on gross motor, fine motor, and cognitive subscales of the Bayley Scales of Infant and Toddler Development also improved. All 11 patients had at least one treatment-emergent adverse event. The most common adverse events were pyrexia (eight [73%] of 11 patients), upper respiratory tract infection (eight [73%]), craniosynostosis (seven [64%]), and pneumonia (seven [64%]). Serious adverse events related to asfotase alfa occurred in three (27%) patients (severe chronic hepatitis; moderate immediate post-injection reaction; and severe craniosynostosis with severe conductive deafness). INTERPRETATION: Patients with perinatal or infantile hypophosphatasia treated with asfotase alfa for up to 7 years showed early, sustained improvements in skeletal mineralisation. Respiratory function, growth, and cognitive and motor function also improved, and asfotase alfa was generally well tolerated. FUNDING: Alexion Pharmaceuticals, Inc.

Sclerosteosis: Report of type 1 or 2 in three Indian Tamil families and literature review.

Sclerosteosis (SOST) refers to two extremely rare yet similar skeletal dysplasias featuring a diffusely radiodense skeleton together with congenital syndactyly. SOST1 is transmitted as an autosomal recessive (AR) trait and to date caused by ten homozygous loss-of-function mutations within the gene SOST that encodes the inhibitor of Wnt-mediated bone formation, sclerostin. SOST2 is transmitted as an autosomal dominant (AD) or AR trait and to date caused by one heterozygous or two homozygous loss-of-function mutation(s), respectively, within the gene LRP4 that encodes the sclerostin interaction protein, low-density lipoprotein receptor-related protein 4 (LRP4). Herein, we investigated two teenagers and one middle-aged man with SOST in three families living in the state of Tamil Nadu in southern India. Next generation sequencing of their genomic DNA using our high bone density gene panel revealed SOST1 in the teenagers caused by a unique homozygous nonsense SOST mutation (c.129C > G, p.Tyr43X) and SOST2 in the man caused by homozygosity for one of the two known homozygous missense LRP4 mutations (c.3508C > T, p.Arg1170Trp). He becomes the fourth individual and the first non-European recognized with SOST2. His clinical course was milder than the life-threatening SOST1 demonstrated by the teenagers who suffered blindness, deafness, and raised intracranial pressure, yet his congenital syndactyly was more striking by featuring bony fusion of digits. All three patients were from consanguineous families and heterozygosity for the SOST mutation was documented in the mothers of both teenagers. Thus, on the endogamous genetic background of Indian Tamils, SOST1 from sclerostin deficiency compared to SOST2 from LRP4 deactivation is a more severe and life-threatening disorder featuring complications due to osteosclerosis of especially the skull. In contrast, the syndactyly of SOST2 is particularly striking by involving bony fusion of some digits. Both the SOST and LRP4 mutations in this ethnic population likely reflect genetic founders.

Unique Variant of NOD2 Pediatric Granulomatous Arthritis With Severe 1,25-Dihydroxyvitamin D-Mediated Hypercalcemia and Generalized Osteosclerosis.

Pediatric granulomatous arthritis (PGA) refers to two formerly separate entities: autosomal dominant Blau syndrome (BS) and its sporadic phenocopy early-onset sarcoidosis (EOS). In 2001 BS and in 2005 EOS became explained by heterozygous mutations within the gene that encodes nucleotide-binding oligomerization domain-containing protein 2 (NOD2), also called caspase recruitment domain-containing protein 15 (CARD15). NOD2 is a microbe sensor in leukocyte cytosol that activates and regulates inflammation. PGA is characterized by a triad of autoinflammatory problems (dermatitis, uveitis, and arthritis) in early childhood, which suggests the causal NOD2/CARD15 mutations are activating defects. Additional complications of PGA were recognized especially when NOD2 mutation analysis became generally available. However, in PGA, hypercalcemia is only briefly mentioned, and generalized osteosclerosis is not reported, although NOD2 regulates NF-κB signaling essential for osteoclastogenesis and osteoclast function. Herein, we report a 4-year-old girl with PGA uniquely complicated by severe 1,25(OH)2 D-mediated hypercalcemia, nephrocalcinosis, and compromised renal function together with radiological and histopathological features of osteopetrosis (OPT). The classic triad of PGA complications was absent, although joint pain and an antalgic gait accompanied wrist, knee, and ankle swelling and soft non-tender masses over her hands, knees, and feet. MRI revealed tenosynovitis in her hands and suprapatellar effusions. Synovial biopsy demonstrated reactive synovitis without granulomas. Spontaneous resolution of metaphyseal osteosclerosis occurred while biochemical markers indicated active bone turnover. Anti-inflammatory medications suppressed circulating 1,25(OH)2 D, corrected the hypercalcemia, and improved her renal function, joint pain and swelling, and gait. Mutation analysis excluded idiopathic infantile hypercalcemia, type 1, and known forms of OPT, and identified a heterozygous germline missense mutation in NOD2 common in PGA (c.1001G>A, p.Arg334Gln). Thus, radiological and histological findings of OPT and severe hypercalcemia from apparent extrarenal production of 1,25(OH)2 D can complicate NOD2-associated PGA. Although the skeletal findings seem inconsequential, treatment of the hypercalcemia is crucial to protect the kidneys. © 2018 American Society for Bone and Mineral Research.

Validation of a Novel Scoring System for Changes in Skeletal Manifestations of Hypophosphatasia in Newborns, Infants, and Children: The Radiographic Global Impression of Change Scale.

Hypophosphatasia (HPP) is the heritable metabolic disease characterized by impaired skeletal mineralization due to low activity of the tissue-nonspecific isoenzyme of alkaline phosphatase. Although HPP during growth often manifests with distinctive radiographic skeletal features, no validated method was available to quantify them, including changes over time. We created the Radiographic Global Impression of Change (RGI-C) scale to assess changes in the skeletal burden of pediatric HPP. Site-specific pairs of radiographs of newborns, infants, and children with HPP from three clinical studies of asfotase alfa, an enzyme replacement therapy for HPP, were obtained at baseline and during treatment. Each pair was scored by three pediatric radiologists ("raters"), with nine raters across the three studies. Intrarater and interrater agreement was determined by weighted Kappa coefficients. Interrater reliability was assessed using intraclass correlation coefficients (ICCs) and by two-way random effects analysis of variance (ANOVA) and a mixed-model repeated measures ANOVA. Pearson correlation coefficients evaluated relationships of the RGI-C to the Rickets Severity Scale (RSS), Pediatric Outcomes Data Collection Instrument Global Function Parent Normative Score, Childhood Health Assessment Questionnaire Disability Index, 6-Minute Walk Test percent predicted, and Z-score for height in patients aged 6 to 12 years at baseline. Eighty-nine percent (8/9) of raters showed substantial or almost perfect intrarater agreement of sequential RGI-C scores (weighted Kappa coefficients, 0.72 to 0.93) and moderate or substantial interrater agreement (weighted Kappa coefficients, 0.53 to 0.71) in patients aged 0 to 12 years at baseline. Moderate-to-good interrater reliability was observed (ICC, 0.57 to 0.65). RGI-C scores were significantly (p ≤ 0.0065) correlated with the RSS and with measures of global function, disability, endurance, and growth in the patients aged 6 to 12 years at baseline. Thus, the RGI-C is valid and reliable for detecting clinically important changes in skeletal manifestations of severe HPP in newborns, infants, and children, including during asfotase alfa treatment. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Gnathodiaphyseal dysplasia: Severe atypical presentation with novel heterozygous mutation of the anoctamin gene (ANO5).

Gnathodiaphyseal dysplasia (GDD; OMIM #166260) is an ultra-rare autosomal dominant disorder caused by heterozygous mutation in the anoctamin 5 (ANO5) gene and features fibro-osseous lesions of the jawbones, bone fragility with recurrent fractures, and bowing/sclerosis of tubular bones. The physiologic role of ANO5 is unknown. We report a 5-year-old boy with a seemingly atypical and especially severe presentation of GDD and unique ANO5 mutation. Severe osteopenia was associated with prenatal femoral fractures, recurrent postnatal fractures, and progressive bilateral enlargement of his maxilla and mandible beginning at ~2months-of-age that interfered with feeding and speech and required four debulking operations. Histopathological analysis revealed benign fibro-osseous lesions resembling cemento-ossifying fibromas of the jaw without psammomatoid bodies. A novel, de novo, heterozygous, missense mutation was identified in exon 15 of ANO5 (c.1553G>A; p.Gly518Glu). Our findings broaden the phenotypic and molecular spectra of GDD. Fractures early in life with progressive facial swelling are key features. We assessed his response to a total of 7 pamidronate infusions commencing at age 15months. Additional reports must further elucidate the phenotype, explore any genotype-phenotype correlation, and evaluate treatments.