Hereditary vitamin D rickets: a case series in a family.

Hereditary vitamin D-resistant rickets (HVDRR) is an autosomal recessive disorder characterized by end-organ resistance to 1α,25-dihydroxyvitamin D3 (1,25D3). Clinically, the syndrome is recognized by severe early onset rickets with bowing of the lower extremities, short stature, and often alopecia. Here, we report a case series on three siblings who had HVDRR with varied clinical findings.

[Genetic basis for skeletal disease. Hereditary rickets].

Hereditary rickets is caused by inborn error of vitamin D activation, vitamin D receptor (VDR) function or increased urinary phosphate excretion. Loss-of-function mutation of 1alpha-hydroxylase gene and loss-of-function mutation of VDR gene result in vitamin D-dependent rickets type I and type II, respectively. X-linked hypophosphatemic rickets (XLH) is the most common type of hypophosphatemic rickets, and autosomal dominant (ADHR) and negative (ARHR) types are rare. The diagnosis may be sometimes difficult and increasing cases of vitamin D deficiency must be distinguished.

[Rickets vitamin-D-dependent type 2]. / Raquitismo vitamina D dependente tipo II.

Rickets is a rare child disease especially in developed countries. Nutritional rickets remains the most prevalent condition, although congenital forms are well known. In the latest group, vitamin D dependent rickets type II is the rarest form and it can course with or without alopecia. There is a mutation on the receptor for vitamin D, with peripheral resistance to the vitamin D action. The authors present two clinical cases of vitamin D dependent rickets type II, in which the alopecia was a peculiar clinical sign that allowed the diagnoses. With prolonged calcium infusions, we achieved normal seric levels of calcium and correct bone disorders; alopecia persisted. This treatment is the most effective way to control the disease.

Hereditary hypophosphatemic rickets with hypercalciuria is caused by mutations in the sodium-phosphate cotransporter gene SLC34A3.

Hypophosphatemia due to isolated renal phosphate wasting results from a heterogeneous group of disorders. Hereditary hypophosphatemic rickets with hypercalciuria (HHRH) is an autosomal recessive form that is characterized by reduced renal phosphate reabsorption, hypophosphatemia, and rickets. It can be distinguished from other forms of hypophosphatemia by increased serum levels of 1,25-dihydroxyvitamin D resulting in hypercalciuria. Using SNP array genotyping, we mapped the disease locus in two consanguineous families to the end of the long arm of chromosome 9. The candidate region contained a sodium-phosphate cotransporter gene, SLC34A3, which has been shown to be expressed in proximal tubulus cells. Sequencing of this gene revealed disease-associated mutations in five families, including two frameshift and one splice-site mutation. Loss of function of the SLC34A3 protein presumably results in a primary renal tubular defect and is compatible with the HHRH phenotype. We also show that the phosphaturic factor FGF23 (fibroblast growth factor 23), which is increased in X-linked hypophosphatemic rickets and carries activating mutations in autosomal dominant hypophosphatemic rickets, is at normal or low-normal serum levels in the patients with HHRH, further supporting a primary renal defect. Identification of the gene mutated in a further form of hypophosphatemia adds to the understanding of phosphate homeostasis and may help to elucidate the interaction of the proteins involved in this pathway.