Respiratory failure in a patient with hypophosphatemic rickets: can an endobronchial stent make the difference?

Abnormalities associated with phosphate metabolism can lead to thoracic deformities that result in respiratory failure, which is conventionally managed by means of supplemental oxygenation, positive airway pressure and physiotherapy. However, when these measures fail, the clinician faces a dilemma, since many patients cannot tolerate a major surgical procedure. A minimally invasive technique, insertion of an endobronchial stent, might offer a solution.

Mutation update: Variants of the ENPP1 gene in pathologic calcification, hypophosphatemic rickets, and cutaneous hypopigmentation with punctate keratoderma.

ENPP1 encodes ENPP1, an ectonucleotidase catalyzing hydrolysis of ATP to AMP and inorganic pyrophosphate (PPi), and an endogenous plasma protein physiologically preventing ectopic calcification of connective tissues. Mutations in ENPP1 have been reported in association with a range of human genetic diseases. In this mutation update, we provide a comprehensive review of all the pathogenic variants, likely pathogenic variants, and variants of unknown significance in ENPP1 associated with three autosomal recessive disorders-generalized arterial calcification of infancy (GACI), autosomal recessive hypophosphatemic rickets type 2 (ARHR2), and pseudoxanthoma elasticum (PXE), as well as with a predominantly autosomal dominant disorder-Cole disease. The classification of all variants is determined using the latest ACMG guidelines. A total of 140 ENPP1 variants were curated consisting of 133 previously reported variants and seven novel variants, with missense variants being the most prevalent (70.0%, 98/140). While the pathogenic variants are widely distributed in the ENPP1 gene of patientsgen without apparent genotype-phenotype correlation, eight out of nine variants associated with Cole disease are confined to the somatomedin-B-like (SMB) domains critical for homo-dimerization of the ENPP1 protein.

Identification of ENPP1 Haploinsufficiency in Patients With Diffuse Idiopathic Skeletal Hyperostosis and Early-Onset Osteoporosis.

Homozygous ENPP1 mutations are associated with autosomal recessive hypophosphatemic rickets type 2 (ARHR2), severe ossification of the spinal ligaments, and generalized arterial calcification of infancy type 1. There are a limited number of reports on phenotypes associated with heterozygous ENPP1 mutations. Here, we report a series of three probands and their families with heterozygous and compound heterozygous ENPP1 mutations. The first case (case 1) was a 47-year-old male, diagnosed with early-onset osteoporosis and low-normal serum phosphate levels, which invoked suspicion for hypophosphatemic rickets. The second and third cases were 77- and 54-year-old females who both presented with severe spinal ligament ossification and the presumptive diagnosis of diffuse idiopathic skeletal hyperostosis (DISH). Upon workup, fibroblast growth factor 23 (FGF23) was noted to be relatively high in case 2 and serum phosphorous was low-normal in case 3, and the diagnoses of X-linked hypophosphatemic rickets (XLH) and ARHR2 were considered. Genetic testing for genes related to congenital hypophosphatemic rickets was therefore performed, revealing heterozygous ENPP1 variants in cases 1 and 2 (case 1, c.536A>G, p.Asn179Ser; case 2, c.1352A>G, p.Tyr451Cys) and compound heterozygous ENPP1 variants in case 3 constituting the same variants present in cases 1 and 2 (c.536A>G, p.Asn179Ser and c.1352A>G, p.Tyr451Cys). Several in silico tools predicted the two variants to be pathogeneic, a finding confirmed by in vitro biochemical analysis demonstrating that the p.Asn179Ser and p.Tyr451Cys ENPP1 variants possessed a catalytic velocity of 45% and 30% compared with that of wild-type ENPP1, respectively. Both variants were therefore categorized as pathogenic loss-of-function mutations. Our findings suggest that ENPP1 mutational status should be evaluated in patients presenting with the diagnosis of idiopathic DISH, ossification of the posterior longitudinal ligament (OPLL), and early-onset osteoporosis. © 2022 American Society for Bone and Mineral Research (ASBMR).

Prevalence of oral manifestations of hypophosphatemic rickets in patients treated in a peruvian pediatric hospital / Prevalencia de manifestaciones bucales del raquitismo hipofosfatémico de pacientes atendidos en un hospital pediátrico peruano

Objective: To describe the prevalence of oral manifestations of hypophosphatemic rickets in patients treated in a Peruvian referral pediatric hospital during the years 2012-2016. Material and methods: An observational, descriptive, retrospective, cross-sectional study was carried out. The sample consisted of patients diagnosed with hypophosphatemic rickets who attended the outpatient clinic of the Stomatology Service and the Genetics Service of the National Institute of Child Health (INSN), Lima, Peru, between the years 2012-2016. The research project was assessed and approved by the Research Ethics Committee of the Health Service. Medical records stored in a database of the health institution with the Code CIE E83.3, which corresponds to the diagnosis of Hypophosphatemic Rickets, were requested for the study. Results: Fifteen children received health care, of which only 10 were treated at the Stomatology Service. The distribution of the data was obtained from these 10 patients according to the proposed objective. A higher frequency of gingival lesions was found at the soft tissue level (41.18%); at the bone tissue level, only one case of dentigerous cyst was observed; and at the dental level, 90% of the patients had dental caries. Conclusion: The most frequent oral manifestations of hypophosphatemic rickets in pediatric patients treated at the National Institute of Child Health (2012-2016) were gingivitis and dental caries.

Objetivo:Describir la prevalencia de las manifestaciones bucales del raquitismo hipofosfatémico de pacientes atendidos en un hospital pediátrico de referencia peruano durante los años 2012-2016. Material y Métodos:Se realizó un estudio tipo observacional, descriptivo, retrospectivo, transversal. Para la selección de la muestra se consideró a los pacientes que acudieron a la consulta externa del Servicio de Odontoestomatología y el Servicio de Genética del Instituto Nacional de Salud del Niño, Lima, Perú; en el periodo comprendido entre los años 2012-2016 y que presentaron como diagnóstico Raquitismo Hipofosfatémico. El proyecto de investigación fue evaluado por un Comité de Ética en Investigación del servicio de salud. Se solicitaron las historias clínicas consignadas en una base de datos de la institución de salud con el Código CIE E83.3, que corresponde a este diagnóstico. Resultados: Fueron atendidos 15 niños, de los cuales solo 10 fueron tratados en el Servicio Odontoestomatología; siendo de estos 10 pacientes la distribución de los datos obtenidos según el objetivo propuesto. Se encontró mayor frecuencia de lesiones a nivel de tejido blando de gingivitis con 41.18%, a nivel de tejido óseo solo se presentó un caso de quiste dentígero; y a nivel de tejido dental el 90% de los pacientes presentó caries dental. Conclusión: Las manifestaciones bucales más frecuentes del raquitismo hipofosfatémico de pacientes pediátricos atendidos en el Instituto Nacional de Salud del Niño (2012-2016), fueron la gingivitis y caries dental.

Hypophosphatemic rickets: A rare complication of congenital melanocytic nevus syndrome.

We report the case of a child who presented with a giant melanocytic nevus with numerous satellite nevi at birth and developed hypophosphatemic rickets due to excessive secretion of the FGF23 hormone. A NRAS c.182A>G (Q61R) mutation was identified in the lesional skin. The functional outcome was favorable with medical treatment.

Molecular analysis of enthesopathy in a mouse model of hypophosphatemic rickets.

The bone tendon attachment site known as the enthesis comprises a transitional zone between bone and tendon, and plays an important role in enabling movement at this site. X-linked hypophosphatemia (XLH) is characterized by impaired activation of vitamin D, elevated serum FGF23 levels and low serum phosphate levels, which impair bone mineralization. Paradoxically, an important complication of XLH is mineralization of the enthesis (enthesopathy). Studies were undertaken to identify the cellular and molecular pathways important for normal post-natal enthesis maturation and to examine their role during the development of enthesopathy in mice with XLH (Hyp). The Achilles tendon entheses of Hyp mice demonstrate an expansion of hypertrophic-appearing chondrogenic cells by P14. Post-natally, cells in wild-type and Hyp entheses similarly descend from scleraxis- and Sox9-expressing progenitors; however, Hyp entheses exhibit an expansion of Sox9-expressing cells, and enhanced BMP and IHH signaling. These results support a role for enhanced BMP and IHH signaling in the development of enthesopathy in XLH.

Dentoalveolar Abscesses Not Associated with Caries or Trauma: A Diagnostic Hallmark of Hypophosphatemic Rickets Initially Misdiagnosed as Hypochondroplasia.

Hypophosphatemic rickets is a rare genetic disorder involving the regulation of fibroblast growth factor 23 (FGF23), a phosphaturic agent, clinically showing bowing of the legs, short stature and dentoalveolar abscesses. A 7-year-old boy, with previous hypochondroplasia diagnosis, was referred to our pediatric dentistry clinic presenting short stature, bone deformities and sinus tracts at deciduous teeth apex levels not related with trauma, restorations or dental caries. After deciduous teeth extraction, due to root resorption and mobility, light microscopy exhibited typical hypophosphatemic dentin, and micro-computed tomography revealed tubular clefts and porosities throughout the teeth. Laboratory tests confirmed the HR diagnosis, after which the treatment was initiated.

Hypophosphatemic rickets and craniosynostosis: a multicenter case series.

OBJECTIVE This study examines a series of patients with hypophosphatemic rickets and craniosynostosis to characterize the clinical course and associated craniofacial anomalies. METHODS A 20-year retrospective review identified patients with hypophosphatemic rickets and secondary craniosynostosis at 3 major craniofacial centers. Parameters examined included sex, age at diagnosis of head shape anomaly, affected sutures, etiology of rickets, presenting symptoms, number and type of surgical interventions, and associated diagnoses. A review of the literature was performed to optimize treatment recommendations. RESULTS Ten patients were identified (8 males, 2 females). Age at presentation ranged from 1 to 9 years. The most commonly affected suture was the sagittal (6/10 patients). Etiologies included antacid-induced rickets, autosomal dominant hypophosphatemic rickets, and X-linked hypophosphatemic (XLH) rickets. Nine patients had undergone at least 1 cranial vault remodeling (CVR) surgery. Three patients underwent subsequent surgeries in later years. Four patients underwent formal intracranial pressure (ICP) monitoring, 3 of which revealed elevated ICP. Three patients were diagnosed with a Chiari Type I malformation. CONCLUSIONS Secondary craniosynostosis develops postnatally due to metabolic or mechanical factors. The most common metabolic cause is hypophosphatemic rickets, which has a variety of etiologies. Head shape changes occur later and with a more heterogeneous presentation compared with that of primary craniosynostosis. CVR may be required to prevent or relieve elevated ICP and abnormalities of the cranial vault. Children with hypophosphatemic rickets who develop head shape abnormalities should be promptly referred to a craniofacial specialist.

Increased Probability of Co-Occurrence of Two Rare Diseases in Consanguineous Families and Resolution of a Complex Phenotype by Next Generation Sequencing.

Massively parallel sequencing of whole genomes and exomes has facilitated a direct assessment of causative genetic variation, now enabling the identification of genetic factors involved in rare diseases (RD) with Mendelian inheritance patterns on an almost routine basis. Here, we describe the illustrative case of a single consanguineous family where this strategy suffered from the difficulty to distinguish between two etiologically distinct disorders, namely the co-occurrence of hereditary hypophosphatemic rickets (HRR) and congenital myopathies (CM), by their phenotypic manifestation alone. We used parametric linkage analysis, homozygosity mapping and whole exome-sequencing to identify mutations underlying HRR and CM. We also present an approximate approach for assessing the probability of co-occurrence of two unlinked recessive RD in a single family as a function of the degree of consanguinity and the frequency of the disease-causing alleles. Linkage analysis and homozygosity mapping yielded elusive results when assuming a single RD, but whole-exome sequencing helped to identify two mutations in two genes, namely SLC34A3 and SEPN1, that segregated independently in this family and that have previously been linked to two etiologically different diseases. We assess the increase in chance co-occurrence of rare diseases due to consanguinity, i.e. under circumstances that generally favor linkage mapping of recessive disease, and show that this probability can increase by several orders of magnitudes. We conclude that such potential co-occurrence represents an underestimated risk when analyzing rare or undefined diseases in consanguineous families and should be given more consideration in the clinical and genetic evaluation.

The in vivo role of DMP-1 and serum phosphate on bone mineral composition.

Human DMP1 mutations or Dmp1-null (KO) mice display hypophosphatemia rickets, suggesting a causative role of low phosphate (P) in development of osteomalacia. To address the direct contribution of P to the in vivo bone mineralization we analyzed the properties of femurs obtained from Dmp1 null mice and wild type (WT) mice under a normal or high phosphorous (HiP) diet using combined assays, including histological examination, micro computed tomography (µCT), X-ray absorption near edge structure (XANES) spectroscopy and Raman spectroscopy. Histology and XANES indicate that WT mice have phosphate coordinated with Ca in the form of hydroxyapatite and tricalcium phosphate, while the KO mice have poorly coordinated soluble phosphates in their structure in both the normal and HiP diets. Raman spectroscopy and XANES indicate a higher carbonate/phosphate ratio and a low mineral/matrix ratio in the osteoid clusters in the KO femurs, which was only partially improved by HiP diets. Thus, we conclude that the hypophosphatemia induced osteomalacia phenotype in Dmp1 KO mice is contributed by at least two factors: the low Pi level and the DMP1 local function in mineralization.

Risk factors affecting the development of nephrocalcinosis, the most common complication of hypophosphatemic rickets.

The aim of the present study was to analyse the effects of combined treatment with calcitriol and phosphate, to find out the incidence of the nephrocalcinosis, and to elucidate the risk factor of nephrocalcinosis in patients with hypophosphatemic rickets. We followed six patients. The median age at diagnosis was 3.25 (0.75-10.5) years. The median follow-up duration was 8.25 (3.5-12.5) years. The mean dose of calcitriol and phosphate treatments was 39.1±8 ng/kg/day, 90.5±57.1 mg/kg/day, respectively. Nephrocalcinosis was detected in three patients (50%). The mean dose of phosphate taken by the patients found to have nephrocalcinosis was detected to be high with a statistically significant difference (p=0.041). No significant relationship was found the mean dose of calcitriol. We found no relationship between the development of nephrocalcinosis and the incidence of hypercalciuria or hypercalcemia episodes. We found the increased phosphate dose administered for treatment to play a role in nephrocalcinosis development.

[Medical treatment of children with hypophosphataemic rickets]. / Medicinsk behandling af hypofosfatæmisk rakitis hos børn.

Hypophosphataemic rickets is a rare, genetic disorder resulting in defect bone mineralisation and rickets. The current medical treatment consists of phosphate supplementation and alfacalcidol, but side effects such as secondary hyperparat-hyroidism and nephrocalcinosis are common. This treatment regimen often fails to prevent bone deformity and reduced final height. The rarity and complexity of these diseases call for centralised specialist care and international collaboration. Future medical treatment may be improved by addition of new promising experimental treatments.

A case report of nephrogenic diabetes insipidus with idiopathic Fanconi syndrome in a child who presented with vitamin D resistant rickets.

Fanconi syndrome is a complex of multiple tubular dysfunctions of proximal tubular cells, occurring alone or in association with a variety of inherited (primary) or acquired (secondary) disorders. It is characterized by aminoaciduria, normoglycemic glycosuria, tubular proteinuria without hematuria, metabolic acidosis without anion gap and excessive urinary excretion of phosphorous, calcium, uric acid, bicarbonate, sodium, potassium and magnesium. Diabetes insipidus is a disease of collecting tubules and children mainly present with dehydration and hypernatremia. We are reporting the first case of idiopathic Fanconi's syndrome along with nephrogenic diabetes insipidus in a child who presented to us with vitamin D resistant rickets. Medline search did not reveal any case of nephrogenic diabetes insipidus (NDI) associated with idiopathic Fanconi syndrome. We hypothesized that the NDI may be due to to severe hypokalemia induced tubular dysfunction.

Corrective osteotomy in femoral non-union in drug-induced hypophosphataemic osteomalacia.

Adefovir/tenofovir are commonly used antiviral agents in the treatment of chronic hepatitis B infection (CHB). We report a case of CHB-related cirrhosis presenting with sequential femoral neck fractures. Operative reduction and fixation was performed. Laboratory result and imaging was consistent with hypophosphataemic osteomalacia. He had bilateral femoral neck non-union and presented with a new left side subtrochanteric femoral fracture. Corrective osteotomy and cephalomedullary fixation was performed. The fractures healed in 6 months after correction of the hypophosphataemia.