Hereditary 1,25-dihydroxyvitamin D-resistant rickets (HVDRR): clinical heterogeneity and long-term efficacious management of eight patients from four unrelated Arab families with a loss of function VDR mutation

Hereditary Rickets: A Quick Guide for the Pediatrician

With the increased discovery of genes implicated in vitamin D metabolism and the regulation of calcium and phosphate homeostasis, a growing number of genetic forms of rickets are now recognized. These are categorized into calciopenic and phosphopenic rickets. Calciopenic forms of hereditary rickets are caused by genetic mutations that alter the enzymatic activity in the vitamin D activation pathway or impair the vitamin D receptor action. Hereditary forms of phosphopenic rickets, on the other hand, are caused by genetic mutations that lead to increased expression of FGF23 hormone or that impair the absorptive capacity of phosphate at the proximal renal tubule. Due to the clinical overlap between acquired and genetic forms of rickets, identifying children with hereditary rickets can be challenging. A clear understanding of the molecular basis of hereditary forms of rickets and their associated biochemical patterns allow the health care provider to assign the correct diagnosis, avoid non-effective interventions and shorten the duration of the diagnostic journey in these children. In this mini-review, known forms of hereditary rickets listed on the Online Mendelian Inheritance in Man database are discussed. Further, a clinical approach to identify and diagnose children with hereditary forms of rickets is suggested.

X-linked Hypophosphatemic Rickets: Awareness, Knowledge, and Practice of Pediatric Endocrinologists in Arab Countries

X-linked hypophosphatemic rickets (XLHR) is a genetic disease caused by inactivating pathogenic variants in PHEX, which results in reduced mineralization of bone, teeth, and renal phosphate wasting. XLHR is traditionally treated by phosphate and vitamin D analogs. Recently, burosumab, a recombinant anti-fibroblast growth factor-23 (FGF-23) monoclonal antibody was approved as specific XLHR therapy. We aimed to assess the awareness, knowledge, and management of XLHR among members of the Arab Society for Pediatric Endocrinology and Diabetes (ASPED). Of the 97 physicians who answered the online questionnaire, 97% were aware of XLHR, and while 90% screen family members of the index case, only 29% manage children with XLHR. In children with rickets, 40% of participants measure serum/urine phosphate routinely, and 31% request serum FGF-23 in suspected XLHR cases. Almost all responders use conventional XLHR therapy, and 4% used Burosomab. Only 14% were satisfied with the conventional treatment, and 69% reported therapeutic complications in up to 25% of their patients. Multidisciplinary care for XLHR is practiced by 94%, but 82% of providers did not have transition clinics. Pediatric endocrinologists in ASPED countries are aware of XLHR but have variable practice and are unsatisfied with its conventional treatment. Raising awareness of the recognition and modern management of XLHR is needed.

Identification and analysis of 35 genes associated with vitamin D deficiency: A systematic review to identify genetic variants

Vitamin D deficiency is a public health concern associated with, but not limited to, skeletal anomalies, chronic diseases, immune conditions, and cancer, among others. Hypovitaminosis D is mainly associated with environmental and lifestyle factors that affect sunlight exposure. However, genetic factors also influence 25-hydroxyvitamin D (25[OH]D) serum concentration. Although there is available information of genes with clear biological relevance or markers identified by Genome-Wide Association Studies, an overall view and screening tool to identify known genetic causes of altered serum levels of 25(OH)D is lacking. Moreover, there are no studies including the total genetic evidence associated with abnormal serum concentration of 25(OH)D. Therefore, we conducted a de-novo systematic literature review to propose a set of genes comprehensive of all genetic variants reported to be associated with deficiency of vitamin D. Abstracts retrieved from PubMed search were organized by gene and curated one-by-one using the PubTerm web tool. The genes identified were classified according to the type of genetic evidence associated with serum 25(OH)D levels and were also compared with the few commonly screened genes related to vitamin D status. This strategy allowed the identification of 35 genes associated with serum 25(OH)D concentrations, 27 (75%) of which are not commercially available and are not, therefore, analyzed in clinical practice for genetic counseling, nor are they sufficiently studied for research purposes. Functional analysis of the genes identified confirmed their role in vitamin D pathways and diseases. Thus, the list of genes is an important source to understand the genetic determinants of 25(OH)D levels. To further support our findings, we provide a map of the reported functional variants and SNPs not included in ClinVar, minor allelic frequencies, SNP effect sizes, associated diseases, and an integrated overview of the biological role of the genes. In conclusion, we identified a comprehensive candidate list of genes associated with serum 25(OH)D concentrations, most of which are not commercially available, but would prove of importance in clinical practice in screening for patients that should respond to supplementation because of alterations in absorption, patients that would have little benefit because alterations in the downstream metabolism of vitamin D, and to study non-responsiveness to supplementation with vitamin D.