The 25‐hydroxyvitamin D 1‐alpha‐hydroxylase gene maps to the pseudovitamin D‐deficiency rickets (PDDR) disease locus

R St‐Arnaud, S Messerlian, JM Moir… - Journal of Bone and …, 1997 - academic.oup.com
R St‐Arnaud, S Messerlian, JM Moir, JL Omdahl, FH Glorieux
Journal of Bone and Mineral Research, 1997academic.oup.com
Pseudovitamin D‐deficiency rickets (PDDR) is an autosomal recessive disorder that may be
due to impaired activity of 25‐hydroxyvitamin D‐1α‐hydroxylase, a renal cytochrome P450
enzyme (P4501α) of the vitamin D pathway. The disease locus for PDDR has been mapped
by linkage analysis to 12q13‐q14, but the molecular defect underlying the enzyme
dysfunction has remained elusive due to the lack of sequence information for the P4501α
gene (hereafter referred to as 1α‐OHase). We have used a probe derived from the rat 25 …
Abstract
Pseudovitamin D‐deficiency rickets (PDDR) is an autosomal recessive disorder that may be due to impaired activity of 25‐hydroxyvitamin D‐1α‐hydroxylase, a renal cytochrome P450 enzyme (P450) of the vitamin D pathway. The disease locus for PDDR has been mapped by linkage analysis to 12q13‐q14, but the molecular defect underlying the enzyme dysfunction has remained elusive due to the lack of sequence information for the P450 gene (hereafter referred to as 1α‐OHase). We have used a probe derived from the rat 25‐hydroxyvitamin D‐24‐hydroxylase (CYP24; 24‐OHase) sequence to identify and clone the 1α‐OHase cDNA. The full‐length 1α‐OHase clone of 2.4 kb codes for a protein of predicted Mr 55 kDa. Functional activity of the cloned sequence was assessed using transient transfection, and the production of authentic 1α,25‐dihydroxyvitamin D3 [1α,25(OH)2D3] was confirmed using high performance liquid chromatography fractionation and time‐of‐flight mass spectrometry. The expression of the gene was analyzed in vitamin D–replete animals; treatment with 1α,25(OH)2D3 reduced 1α‐OHase transcript levels by 70%, while administration of parathyroid hormone led to a 2‐fold increase in the expression of the gene, thus confirming the hormonal regulation previously described using biochemical methods. The rat cDNA was used to obtain a human genomic clone. Interestingly, the human 1α‐OHase gene mapped to 12q13.1‐q13.3, providing strong evidence that a mutation in the 1α‐OHase gene is responsible for the PDDR phenotype. The availability of a cloned sequence for 1α‐OHase generates novel tools for the study of the molecular etiology of PDDR, and will allow the investigation of other disturbances of vitamin D metabolism.
Oxford University Press