Mutations in the vitamin D receptor gene in four patients with hereditary 1,25-dihydroxyvitamin D-resistant rickets

Abstract

Mutations in the vitamin D receptor (VDR) are associated to the hereditary 1,25-dihydroxivitamin D-resistant rickets. The objectives of this work are: search for mutations in the VDR and analyze their functional consequences in four Brazilian children presented with rickets and alopecia. The coding region of the VDR was amplifi ed by PCR e direct sequenced. We identifi ed three mutations: two patients had the same mutation in exon 7 at aminoacid position 259 (p.Q259E); one patient had a mutation in exon 8 at codon 319 (p.G319V) and another one had a mutation in exon 3 leading to a truncated protein at position 73 (p.R73X). Functional studies of the mutant receptors of fi broblast primary culture, from patients' skin biopsy treated with increasing doses of 1,25(OH) 2 vitamin D showed that VDR mutants were unable to be properly activated and presented a reduction in 24-hydroxylase expression level.

Transcriptional activation of the wild-type and mutant vitamin D receptors by vitamin D3 analogs

“…Furthermore, none of the tested VD 3 analogs exerted significantly higher mVDR (I314S) activation than calcitriol. According to previous reports, four patients identified with Q259E, H305Q, G319V, and R391C mVDRs presented various VDDRII symptoms such as leg deformation and alopecia, which were mitigated by administering high doses of calcitriol (Whitfield et al 1996, Malloy et al 2004, Macedo et al 2008. The results of this study show that for G319V, calcitriol stimulation at the high dose of 10.0 nM increased receptor transcriptional activity by 29.5 ± 0.5-fold, demonstrating almost the same efficacy as with the WT-VDR.…”

“…Among VDDRII patients with LBD mutations, I314S carriers could be treated with pharmacological doses of VD 2 , and Q259E, H305Q, G319V, and R391C carriers responded to high doses of calcitriol (Macedo et al 2008). However, patients with I268T and E420K showed no improvement in symptoms even when high calcitriol doses were administered (Malloy et al 2002(Malloy et al , 2004.…”

“…Mutation positions are indicated in Fig. 1A: Q259E on helix 4 (Macedo et al 2008), I268T on helix5 (Malloy et al 2004), H305Q on the loop connecting two α-helices (Malloy et al 1997), I314S and G319V on helix 7 (Whitfield et al 1996, Macedo et al 2008, R391C on helix 10 (Whitfield et al 1996), and E420K on helix 12 (Malloy et al 2002). The WT and mutant receptors were subcloned into the pCMX, and the WT receptor was pCMX-VP16 vectors described previously (Umesono et al 1991, Tagami et al 1999 for in vitro transcription/translation and transient expression in transfected cells.…”

Identification of a Novel Nonsense Mutation in the Ligand-Binding Domain of the Vitamin D Receptor Gene and Clinical Description of Two Greek Patients with Hereditary Vitamin D-Resistant Rickets and Alopecia

“…Approximately 100 HVDRR cases have been described so far, sharing 48 different mutations [1,7,8,9,10,11,12,13,14,15]. Several efforts have been made to design a well-defined correlation between the genotype and the phenotype of the patients using criteria such as the site of the mutation in the gene and the severity of the syndrome, the presence of alopecia or the successful response to treatment [18,19,20].…”

“…Several mutations, at least 48, have been identified throughout the coding region of the VDR gene - most of them missense and nonsense and to a lesser extent splice site mutations and partial (or single) nucleotide deletions - leading to a nonfunctional VDR [1,7,8,9,10,11,12,13,14,15]. The human VDR protein consists of 427 amino acids organized in two distinguishable functional domains, the N-terminal DNA-binding domain (DBD) and the C-terminal ligand-binding domain (LBD), separated by a hinge region.…”