title: The 25-hydroxyvitamin D 1-alpha-hydroxylase gene maps to the pseudovitamin D-deficiency rickets (PDDR) disease locus.
abstract: Pseudovitamin D-deficiency rickets (PDDR) is an autosomal recessive disorder that may be due to impaired activity of 25-hydroxyvitamin D-1alpha-hydroxylase, a renal cytochrome P450 enzyme (P450[1alpha]) 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(1alpha) gene (hereafter referred to as 1alpha-OHase). We have used a probe derived from the rat 25-hydroxyvitamin D-24-hydroxylase (CYP24; 24-OHase) sequence to identify and clone the 1alpha-OHase cDNA. The full-length 1alpha-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 1alpha,25-dihydroxyvitamin D3 [1alpha,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 1alpha,25(OH)2D3 reduced 1alpha-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 1alpha-OHase gene mapped to 12q13.1-q13.3, providing strong evidence that a mutation in the 1alpha-OHase gene is responsible for the PDDR phenotype. The availability of a cloned sequence for 1alpha-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.
authors.affiliation: Shriners Hospital, and Department of Surgery, McGill University, Montréal, Québec, Canada.
authors.forename: R
authors.initials: R
authors.lastname: St-Arnaud
authors.forename: S
authors.initials: S
authors.lastname: Messerlian
authors.forename: J M
authors.initials: JM
authors.lastname: Moir
authors.forename: J L
authors.initials: JL
authors.lastname: Omdahl
authors.forename: F H
authors.initials: FH
authors.lastname: Glorieux
mesh_terms: D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase / Q000737:chemistry / Q000235:genetics*; D000595:Amino Acid Sequence; D000818:Animals; D002117:Calcitriol / Q000737:chemistry / Q000627:therapeutic use; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000737:chemistry / Q000235:genetics*; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics; D006801:Humans; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010281:Parathyroid Hormone / Q000627:therapeutic use; D051381:Rats; D017207:Rats, Sprague-Dawley; D015183:Restriction Mapping; D012279:Rickets / Q000201:enzymology / Q000209:etiology / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D013250:Steroid Hydroxylases / Q000737:chemistry / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics; D014162:Transfection; D014808:Vitamin D Deficiency / Q000201:enzymology / Q000235:genetics; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D018076:DNA, Complementary; D010281:Parathyroid Hormone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D015090:25-Hydroxyvitamin D3 1-alpha-Hydroxylase; D002117:Calcitriol