Hereditary Vitamin D Resistant Rickets: Clinical, Laboratory, and Genetic Characteristics of 2 Iranian Siblings

Hereditary vitamin D resistant rickets (HVDRR) case series: phenotype, genotype, conventional treatment, and adjunctive cinacalcet therapy

INTRODUCTION

Hereditary vitamin D resistant rickets (HVDRR) is a rare autosomal recessive disorder marked by end-organ resistance of 1,25-dihydroxyvitamin D secondary to various mutations in the vitamin D receptor gene. The currently accepted treatment modality involves bypassing the affected receptors in the gut with high-dose intravenous calcium. In a few limited case reports, cinacalcet, a calcimimetic, has been used as an adjunctive therapy.

MATERIAL AND METHODS

Retrospective chart reviews were conducted to collect the clinical and biochemical data of 8 patients with HVDRR from 5 Saudi families. Four patients received only high-dose calcium, while the remaining 4 received adjuvant cinacalcet. Serum chemistry and PTH levels were measured before and during cinacalcet treatment. Gene sequencing was performed to identify the disease-causing mutation.

RESULTS

All 8 patients exhibited alopecia and secondary hyperparathyroidism. Other clinical and biochemical features of rickets were present to varying degrees. Genetic analysis revealed 3 distinct mutations: a ligand-binding domain mutation in 3 unrelated patients, a ligand-binding domain mutation in 2 sisters, and a missense DNA-binding domain mutation in 3 brothers. While the overall response to therapy was variable, none of the 4 patients who received adjunctive cinacalcet developed hypocalcaemia, and there was some initial promise in improving serum PTH levels.

CONCLUSIONS

This series provides new insight into the clinical and biochemical characteristics as well as treatment responses in Saudi children with HVDRR. The findings suggest that cinacalcet is a safe and potentially valuable adjuvant in this understudied population; however, further research is required to verify these results.

Intestinal Vitamin D Receptor Is Dispensable for Maintaining Adult Bone Mass in Mice With Adequate Calcium Intake

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3)-mediated intestinal calcium (Ca) absorption supplies Ca for proper bone mineralization during growth. We tested whether vitamin D receptor (VDR)-mediated 1,25(OH)2D3 signaling is critical for adult Ca absorption and bone by using mice with inducible Vdr gene knockout in the whole intestine (villin-CreERT2+/- × Vdrf/f, WIK) or in the large intestine (Cdx2-CreERT2+/- ×Vdrf/f, LIK). At 4-month-old, Vdr alleles were recombined (0.05 mg tamoxifen/g BW, intraperitoneally [i.p.], 5 days) and mice were fed diets with either 0.5% (adequate) or 0.2% (low) Ca. Ca absorption was examined after 2 weeks while serum 1,25(OH)2D3, bone mass, and bone microarchitecture were examined after 16 weeks. Intestinal and renal gene expression was measured at both time points (n = 12/genotype/diet/time point). On the 0.5% Ca diet, all phenotypes in WIK and LIK mice were similar to the controls. Control mice adapted to the 0.2% low-Ca diet by increasing renal Cyp27b1 mRNA (3-fold), serum 1,25(OH)2D3 level (1.9-fold), and Ca absorption in the duodenum (Dd, + 131%) and proximal colon (PCo, + 28.9%), which prevented bone loss. In WIK mice, low-Ca diet increased serum 1,25(OH)2D3 (4.4-fold) but Ca absorption remained unaltered in the Dd and PCo. Consequently, significant bone loss occurred in WIK mice (e.g., cortical thickness, Ct.Th, -33.7%). LIK mice adapted to the low-Ca diet in the Dd but not the PCo, and the effect on bone phenotypes was milder (e.g., Ct.Th, -13.1%). Our data suggest intestinal VDR in adult mice prevents bone loss under low Ca intake but is dispensable under adequate calcium intake.

Vitamin D-Resistant Rickets Diagnostics and Treatment Challenges at Muhimbili National Hospital, Tanzania

Introduction. Rickets is softening of bones caused by defective mineralization of the cartilage in the epiphyseal growth plate, causing widening of the ends of long bones, growth retardation, and skeletal deformities in children. It can be classified into calciopenic and phosphopenic, each type with various subclasses. Case Presentations. We presented 2 cases, first of a 1 year and 4-month-old male, with a history of recurrent episodes of cough for 8 months and bowing of the legs 6 months prior to admission. Clinical and laboratory investigation was suggestive of vitamin D-dependent rickets, and he started vitamin D treatment with minimal response. The second case is of a 4 years and 7-month-old male who presented with developmental delay, poor weight gain, and recurrent chest infection and worsening of bone pain since 9 months of age. Laboratory investigation was suggestive of phosphopenic rickets, and he was started on treatment at 9 months of age with little improvement and at 4 years, he sustained multiple fractures and succumbed to severe respiratory tract infection and died at 4 years and 7 months of age.

CONCLUSION

Rickets pose a diagnostic and treatment challenge in resource-limited countries, and clinical judgment and early initiation of treatment are important.

Biochemical parameters of rickets in Iranian children: A systematic review and meta-analysis

BACKGROUND

Many causes can lead to childhood rickets. We aimed to investigate the biochemical symptoms of childhood rickets with systematic review and meta-analysis.

MATERIALS AND METHODS

Seven articles published from 1975 to 2018 were recruited. The literature search was performed in the Scientific Information Database, Google Scholar, PubMed, and Elsevier databases using related keywords. For meta-analysis, the results of the studies were pooled using the random-effects model. The heterogeneity between the studies was checked using Q test and I 2 index.

RESULTS

The total sample population consisted of 933 children with biochemical symptoms of rickets (133 participants per article). According to our findings, the mean serum levels of PO4, Ca, and alkaline phosphatase in children with rickets were 4.18 (95% confidence interval [CI]: 3.75-4.61, I 2 = 98.3%, P < 0.001), 9.23 (95% CI: 8.78-9.68, I 2 = 99.6%, P < 0.001), and 1.33 (95% CI: 1.23-1.44, I 2 = 95.6%, P < 0.001), respectively.

CONCLUSION

Characterizing the biochemical symptoms of rickets in children can help to early diagnose and prevent the disease in children. Furthermore, educating parents about biochemical symptoms can lead to early diagnosis and successful treatment of rickets in children.