A Novel Mutation in a Gene Causes Sclerosteosis in a Family of Mediterranean Origin.

Background and Objectives: Sclerostin is an SOST gene product that inhibits osteoblast activity and prevents excessive bone formation by antagonizing the Wnt signaling pathway. Sclerosteosis has been linked to loss of function mutations in the SOST gene. It is a rare autosomal recessive disorder characterized by craniotubular hyperostosis and can lead to fatal cerebellar herniation. Our aim is to describe the clinical and radiological features and the new underlying SOST mutation in a patient with sclerosteosis. Case: A 25-year-old female who was referred to the endocrine clinic for suspected excess growth hormone. The patient complained of headaches, progressive blurred vision, hearing disturbances, increased size of feet, proptosis, and protrusion of the chin. She had normal antenatal history except for syndactyly. Images showed diffuse osseous thickening and high bone mineral density. Biochemical and hormonal tests were normal. Due to progressive compressive optic neuropathy, optic nerve fenestration with decompression hemicraniotomy was performed. Sclerosteosis was suspected due to the predominant craniotubular hyperostosis with syndactyly. Using peripheral leucocyte DNA, genomic sequencing of the SOST gene was performed. This identified a novel deletion homozygous mutation in the SOST gene (c.387delG, p.Asp131ThrfsTer116) which disrupts sclerostin function, causing sclerosteosis. Conclusions: Discovery of the molecular basis of sclerosteosis represents an important advance in the diagnosis and management of this fatal disease.

Congenital radioulnar synostosis presenting in adulthood - a case report.

Congenital radioulnar synostosis is a rare developmental skeletal malformation of the upper limb, characterized by the fusion of the proximal ends of the radius and ulna from birth. The failure of prenatal longitudinal segmentation of the adjacent radius and ulna results in a fibrous bony bridge between the radius and ulna. We present a 23-year-old female who presented with pain and restricted mobility of the left elbow joint for 7 years. A plain X-ray was performed for the patient, revealing a diagnosis of congenital radio-ulnar synostosis. Careful evaluation of the anatomical relations and spatial orientation of bony structures is required for the diagnosis and treatment of such cases.

Clinical Characteristics of 90 Macrodactyly Cases.

PURPOSE: Macrodactyly is a rare, nonhereditary congenital deformity. Digital enlargement in macrodactyly involves all tissue types and presents alone or as part of a congenital deformity syndromes. Macrodactyly treatment largely depends on surgeons' experience and knowledge. Because there is a paucity of large cohort studies of macrodactyly in the literature, our goal was to retrospectively analyze macrodactyly cases in order to define a better system for diagnosis, classification, and prognosis. METHODS: Medical records of 90 Chinese macrodactyly patients, including demographic characteristics, clinical presentations, anatomical distributions, x-rays, pathological findings, and treatments, were reviewed. Genetic analyses of 12 patients were also reviewed. RESULTS: Disease incidence was similar across sex and geographical regions. Multiple-digit involvement was 2.6 times more frequent than single-digit involvement. The index finger, middle finger, and thumb were most commonly involved. Two digits were affected more often than 3, with the affected digits adjacent in most cases. The affected digit was in the median nerve innervation distribution in 79% of cases and was accompanied by enlargement and fat infiltration of the median nerve. Seven cases had syndactyly. Ten of the 12 cases subjected to PIK3CA mutation analysis were positive. CONCLUSIONS: Macrodactyly represents a heterogeneous group of conditions, without significant sex or geographical predilection, which is usually present at birth. A high PIK3CA mutation-positive rate in affected tissues suggests a similar cellular mechanism for overgrowth in patients with various clinical presentations. TYPE OF STUDY/LEVEL OF EVIDENCE: Prognostic IV.

Anatomical similarity between the Sost-knockout mouse and sclerosteosis in humans.

Sclerosteosis, a rare autosomal recessive genetic disorder caused by a mutation of the Sost gene, manifests in the facial skeleton by gigantism, facial distortion, mandibular prognathism, cranial nerve palsy, and, in extreme cases, compression of the medulla oblongata. Mice lacking sclerostin reflect some symptoms of sclerosteosis, but this is the first report of the effect on the facial skeleton. We used geometric morphometrics (GMM) to analyze the deformations of the murine facial skeleton from the wild-type to the Sost gene knockout. Landmark coordinates were obtained by surface reconstructions from micro-computed tomography. Centroid size, principal component scores in shape space and form space, and asymmetry were computed by the standard GMM formulas, and dental and skeletal jaw lengths were examined as ratios. We show here that, compared to wild type controls, mice lacking Sost have larger centroid size (effect size, p-value: 4.59, <.001), higher mean asymmetry (1.14, .065), dental and skeletal mandibular prognathism (1.36, .010 and 5.92, <.001), a smaller foramen magnum (-1.71, .015), and calvaria that are more highly curved (form space p = 4.09, .002; shape space p = 12.82, .002). These features of mice lacking sclerostin largely correspond to the changes of the facial skeleton observed in sclerosteosis. This alignment further supports claims that the Sost gene plays a fundamental role in bony facial development in rodents and humans alike.

Comparison of Vickers' Physiolysis With Osteotomy for Primary Correction of Clinodactyly.

Background: The purpose of this study was to compare the Vickers physiolysis procedure with osteotomy for correction of digital clinodactyly and determine which method provides better correction at final follow-up or whether the patient's age, preoperative angulation, or presence of syndactyly affects final outcomes. Methods: All patients of skeletal immaturity who underwent surgical correction of clinodactyly were evaluated with clinical examination and radiographs to determine the percentage and absolute change in the degree of clinodactyly pre- versus postoperatively, in addition to stratification based on the degree of deformity, age, and presence of syndactyly. Results: Vickers' physiolysis and osteotomy were undertaken in 30 and 11 digits, respectively. The angulation significantly improved from 43.0° to 23.9°, with a 46.2% correction of deformity in the Vickers group at 46.3 months. The angulation decreased from 39.2° to 22.4° in the osteotomy group, with a 55.3% correction of deformity at 55.3 months. There was better correction in those with isolated clinodactyly compared with those with concomitant syndactyly and better percentage of correction in patients with lesser deformity in the Vickers group. There were more reoperations in the osteotomy group. Conclusions: The use of osteotomy may lead to more revision cases, whereas the Vickers procedure has minimal complications and need for revision. The Vickers physiolysis procedure is more effective in those with angulation <55°.

SOST Deficiency Aggravates Osteoarthritis in Mice by Promoting Sclerosis of Subchondral Bone.

As the initial part in the development of osteoarthritis (OA), subchondral bone sclerosis has been considered to be initiated by excess mechanical loading and proven to be correlated to other pathological changes. Sclerostin, which is an essential mechanical stress response protein, is encoded by the SOST gene. It is expressed in osteocytes and mature chondrocytes and has been proven to be closely correlated to OA. However, the relationship and mechanism between the SOST gene and the development of OA remain unclear. The aim of the present study was to investigate the role of the SOST gene in OA pathogenesis in the subchondral bone. A knee anterior cruciate ligament transection (ACLT) mouse osteoarthritis (OA) model on SOST-knockout (SOST KO) and wild-type (WT) mice was established. The pathogenic and phenotypic changes in the subchondral bone were investigated by histology, micro-CT, immunohistochemistry, TRAP staining, Masson staining, and Toluidine blue staining. It was found that sclerostin expression decreased in both the calcified cartilage and mineralized subchondral structures during the development of OA. Joint instability induced a severe cartilage degradation phenotype, with higher OARSI scores in SOST KO mice, when compared to WT mice. SOST KO mice with OA exhibited a higher BMD and BV/TV ratio, as well as a higher rate of bone remodeling and TRAP-positive cell number, when compared to the WT counterparts, but the difference was not significant between the sham-operation groups. It was concluded that loss of sclerostin aggravates knee OA in mice by promoting subchondral bone sclerosis and increasing catabolic activity of cartilage.

In vivo measurements of kidney glomerular number and size in healthy and Os/+ mice using MRI.

The development of chronic kidney disease (CKD) is associated with the loss of functional nephrons. However, there are no methods to directly measure nephron number in living subjects. Thus, there are no methods to track the early stages of progressive CKD before changes in total renal function. In this work, we used cationic ferritin-enhanced magnetic resonance imaging (CFE-MRI) to enable measurements of glomerular number (Nglom) and apparent glomerular volume (aVglom) in vivo in healthy wild-type (WT) mice (n = 4) and mice with oligosyndactylism (Os/+; n = 4), a model of congenital renal hypoplasia leading to nephron reduction. We validated in vivo measurements of Nglom and aVglom by high-resolution ex vivo MRI. CFE-MRI measured a mean Nglom of 12,220 ± 2,028 and 6,848 ± 1,676 (means ± SD) for WT and Os/+ mouse kidneys in vivo, respectively. Nglom measured in all mice in vivo using CFE-MRI varied by an average 15% from Nglom measured ex vivo in the same kidney (α = 0.05, P = 0.67). To confirm that CFE-MRI can also be used to track nephron endowment longitudinally, a WT mouse was imaged three times by CFE-MRI over 2 wk. Values of Nglom measured in vivo in the same kidney varied within ~3%. Values of aVglom calculated from CFE-MRI in vivo were significantly different (~15% on average, P < 0.01) from those measured ex vivo, warranting further investigation. This is the first report of direct measurements of Nglom and aVglom in healthy and diseased mice in vivo.

A case report of Turner syndrome associated with fetal nuchal cystic hygroma and bilateral syndactyly of the hands and feet.

BACKGROUND: Turner syndrome (45,X), accounts for 1-2% of conceptions which typically miscarry early in the first trimester. Cases detected prenatally often present with cystic hygroma, which is an ultrasound marker for aneuploidy generally, but Turner syndrome particularly. In this study, we report a second trimester intrauterine fetal demise (IUFD), complicated by a marked cystic hygroma and bilateral syndactyly of the fingers and toes. CASE PRESENTATION: A 25-year-old woman presented for her first prenatal visit at 22-week gestation with IUFD. Color Doppler ultrasound revealed a septated nuchal lymphatic hygroma and hydrops fetalis, characterized by edema of the whole body, substantial pleural effusion and abdominal fluid. Pregnancy was further complicated by oligohydramnios. Following labor induction, a stillborn female baby was delivered at 22 weeks gestation. Autopsy confirmed the presence of huge nuchal cystic hygroma (10 cm × 10 cm × 6 cm) and generalized edema. Bilateral, partial syndactyly involving digits 2-5 of the fingers and toes were also observed. Chromosomal analysis revealed a 45,X karyotype. CONCLUSIONS: We investigated an unusual case of severe septated nuchal cystic hygroma associated with bilateral syndactyly of the fingers and toes in a stillborn infant with Turner syndrome. Although cystic hygroma has been frequently reported in 45,X the severity is marked in this case. In addition, syndactyly is not a typical complication of Turner syndrome. This case emphasizes the importance of early ultrasound in pregnancy.

A rare TTC30B variant is identified as a candidate for synpolydactyly in a Chinese pedigree.

BACKGROUND: Syndactyly type II (synpolydactyly, SPD) is a rare autosomal dominant inherited disease with higher incomplete penetrance. Currently, several variants in HOXD13 and one deletion in FBLN1 have been associated with SPD. However, the causative variants in several SPD families and their etiological mechanism are still largely unknown. METHODS: Whole exome and PCR-sanger sequencing followed by two-point linkage analysis were performed to identify the pathogenic variant in a six-generation Chinese pedigree. Homology modeling in combination with the RNAi and qRT-PCR experiments was used for revealing the pathogenic mechanism of the TTC30B variant. RESULTS: A six-generation SPD family was reported. The affected subjects in this family had no other clinical malformation beyond SPD. A rare missense variant c.1157C>T [p.Ala375Val] (chr2:178416368, hg19) in TTC30B was demonstrated to be responsible for this SPD family. The modeling structure indicated that the Ala375 was evolutionarily and structurally conserved. The variant p.Ala375Val was predicted to be deleterious for protein structure and/or stability. Two-point linkage analysis resulted in a maximum LOD score of 3.1444 (P = 0.000071). Furthermore, we found that TTC30B was regulated by the Shh signaling pathway and the abnormal expression of TTC30B will affect the activation of the Shh signaling pathway in human retinal pigment epithelial cells. CONCLUSIONS: This study demonstrates for the first time that an IFT (intraflagellar transport) - related gene TTC30B is implicated with SPD.

Two novel GJA1 variants in oculodentodigital dysplasia.

BACKGROUND: Oculodentodigital dysplasia (ODDD) is a rare disorder with pleiotropic effects involving multiple body systems, caused by mutations in the gap junction protein alpha 1 (GJA1) gene. GJA1 gene encodes a polytopic connexin membrane protein, Cx43, that is a component of connexon membrane channels. METHODS: We describe two unrelated female probands referred for a genetic review in view of a dysmorphic clinical phenotype. RESULTS: Two novel missense mutations in GJA1 that substitute conserved amino acids in the first and second transmembrane domains (NM_000165.5: c.77T>C p.Leu26Pro and NM_000165.5:c.287T>G p.Val96Gly) were detected through targeted sequencing of GJA1. These variants were detected in the heterozygous state in the two Maltese probands and segregated with the disease phenotype. CONCLUSION: This report further expands the mutational spectrum of ODDD.

Oculodentodigital Dysplasia: A Hypomyelinating Leukodystrophy with a Characteristic MRI Pattern of Brain Stem Involvement.

Oculodentodigital dysplasia, a rare genetic disorder caused by mutations in the gene encoding gap junction protein 1, classically presents with typical facial features, dental and ocular anomalies, and syndactyly. Oligosymptomatic patients are common and difficult to recognize, in particular if syndactyly is absent. Neurologic manifestation occurs in approximately 30% of patients, and leukodystrophy or T2 hypointensity of gray matter structures or both have been noted in individual patients. To investigate MR imaging changes in oculodentodigital dysplasia, we retrospectively and systematically reviewed 12 MRIs from 6 genetically confirmed patients. Diffuse supratentorial hypomyelination, T2-hypointense Rolandic and primary visual cortex, and symmetric involvement of middle cerebellar peduncle, pyramidal tract, and medial lemniscus was present in all, T2-hypointense pallidum and dentate nucleus in 2 patients each. This consistent, characteristic pattern of diffuse supratentorial hypomyelination and brain stem involvement differs from other hypomyelinating and nonhypomyelinating leukodystrophies with brain stem involvement, and its recognition should trigger genetic testing for oculodentodigital dysplasia.

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.

Sclerostin neutralization unleashes the osteoanabolic effects of Dkk1 inhibition.

The WNT pathway has become an attractive target for skeletal therapies. High-bone-mass phenotypes in patients with loss-of-function mutations in the LRP5/6 inhibitor Sost (sclerosteosis), or in its downstream enhancer region (van Buchem disease), highlight the utility of targeting Sost/sclerostin to improve bone properties. Sclerostin-neutralizing antibody is highly osteoanabolic in animal models and in human clinical trials, but antibody-based inhibition of another potent LRP5/6 antagonist, Dkk1, is largely inefficacious for building bone in the unperturbed adult skeleton. Here, we show that conditional deletion of Dkk1 from bone also has negligible effects on bone mass. Dkk1 inhibition increases Sost expression, suggesting a potential compensatory mechanism that might explain why Dkk1 suppression lacks anabolic action. To test this concept, we deleted Sost from osteocytes in, or administered sclerostin neutralizing antibody to, mice with a Dkk1-deficient skeleton. A robust anabolic response to Dkk1 deletion was manifest only when Sost/sclerostin was impaired. Whole-body DXA scans, µCT measurements of the femur and spine, histomorphometric measures of femoral bone formation rates, and biomechanical properties of whole bones confirmed the anabolic potential of Dkk1 inhibition in the absence of sclerostin. Further, combined administration of sclerostin and Dkk1 antibody in WT mice produced a synergistic effect on bone gain that greatly exceeded individual or additive effects of the therapies, confirming the therapeutic potential of inhibiting multiple WNT antagonists for skeletal health. In conclusion, the osteoanabolic effects of Dkk1 inhibition can be realized if sclerostin upregulation is prevented. Anabolic therapies for patients with low bone mass might benefit from a strategy that accounts for the compensatory milieu of WNT inhibitors in bone tissue.

Truncating mutations of HIBCH tend to cause severe phenotypes in cases with HIBCH deficiency: a case report and brief literature review.

3-hydroxyisobutryl-CoA hydrolase (HIBCH) deficiency is a rare inborn error of valine metabolism characterized by neurodegenerative symptoms and caused by recessive mutations in the HIBCH gene. In this study, utilizing whole exome sequencing, we identified two novel splicing mutations of HIBCH (c.304+3A>G; c.1010_1011+3delTGGTA) in a Chinese patient with characterized neurodegenerative features of HIBCH deficiency and bilateral syndactyly which was not reported in previous studies. Functional tests showed that both of these two mutations destroyed the normal splicing and reduced the expression of HIBCH protein. Through a literature review, a potential phenotype-genotype correlation was found that patients carrying truncating mutations tended to have more severe phenotypes compared with those with missense mutations. Our findings would widen the mutation spectrum of HIBCH causing HIBCH deficiency and the phenotypic spectrum of the disease. The potential genotype-phenotype correlation would be profitable for the treatment and management of patients with HIBCH deficiency.

Oculodentodigital Dysplasia with a Novel Mutation in GJA1 Diagnosed by Targeted Gene Panel Sequencing: A Case Report and Literature Review.

Oculodentodigital dysplasia (ODDD; MIM #164200), a rare genetic disorder characterized by abnormal craniofacial, dental, ocular, and digital features, is caused by mutations in the gap junction alpha-1 (GJA1) gene. We report a case of a 6-year-old male who presented with dysmorphic facial features (short palpebral fissure, thin nose with hypoplastic alae nasi, and flat face), bilateral syndactyly, abnormal dentition, and proportionate short stature with growth hormone deficiency. A novel de novo heterozygous missense mutation (c.221A>C, p.H74P) in GJA1 was identified by targeted gene panel sequencing. This is the first case report of a novel ODDD-causing mutation in GJA1 confirmed by genetic analysis in Korea.

The effects of microduplication 1q21.1 and in-utero isotretinoin exposure.

The impact of in-utero isotretinoin exposure has been widely reported, with many affected pregnancies failing to reach term.1 2 Due to the low numbers of in-utero isotretinoin exposed pregnancies, the interactions between this drug and rare genetic defects such as microduplication 1q21.1 are unclear, particularly how they might manifest phenotypically. We present this case of in-utero isotretinoin exposure occurring in a child with microduplication 1q21.1. The child was born with congenital abnormalities which did not fit into a single syndrome. Regrettably in-utero exposure to isotretinoin continues to occur. We hope this case will trigger further discussion on the dangers of dispensing Isotretinoin without ensuring stringent pregnancy testing and its potential interaction with genetic abnormalities, in particular with microduplication 1q21.1.

Case report of a novel nonsyndromic unilateral syndactyly of the hand.

Syndactyly is a cutaneous and/or bony digital malformation with possible webbing of adjacent fingers or toes and uni- or bilateral occurrence. We report an 84-year old woman with a novel non-syndromic congenital malformation of her left hand. Clinical examination showed that she only had four digits. Radiograph of the hand revealed synostosis of the second and third proximal phalanx, resulting in a triangular shaped bone with relatively normal articulations at both ends. The phalangeal base of the fused finger tapers distally and is broader than the middle phalangeal bases of the ring and little finger. This malformation does not fit in any of the known types of syndromic or non-syndromic syndactylies. Our case report highlights that radiological imaging is crucial for identification of bony syndactyly and correct classification of a given syndactyly. Knowledge of the different types of syndactylies is important because certain malformations may occur as a defining part of a syndromic disease.