Cloning of human 25-hydroxyvitamin D-1 alpha-hydroxylase and mutations causing vitamin D-dependent rickets type 1

The secosteroid hormone, 1,25-dihydroxyvitamin D [1,25(OH)2D], plays a crucial role in normal bone growth, calcium metabolism, and tissue differentiation. The key step in the biosynthesis of 1,25(OH)2D is its 1 alpha-hydroxylation from 25-hydroxyvitamin D (25-OHD) in the kidney. Because its expression in the kidney is very low, we cloned and sequenced cDNA for 25-OHD-1 alpha-hydroxylase (P450c1 alpha) from human keratinocytes, in which 1 alpha-hydroxylase activity and mRNA expression can be induced to be much greater. P450c1 alpha mRNA was expressed at much lower levels in human kidney, brain, and testis. Mammalian cells transfected with the cloned P450c1 alpha cDNA exhibit robust 1 alpha-hydroxylase activity. The identity of the 1,25(OH)2D3 product synthesized in transfected cells was confirmed by HPLC and gas chromatography-mass spectrometry. The gene encoding P450c1 alpha was localized to chromosome 12, where the 1 alpha-hydroxylase deficiency syndrome, vitamin D-dependent rickets type 1 (VDDR-1), has been localized. Primary cultures of human adult and neonatal keratinocytes exhibit abundant 1 alpha-hydroxylase activity, whereas those from a patient with VDDR-1 lacked detectable activity. Keratinocyte P450c1 alpha cDNA from the patient with VDDR-1 contained deletion/frameshift mutations either at codon 211 or at codon 231, indicating that the patient was a compound heterozygote for two null mutations. These findings establish the molecular genetic basis of VDDR-1, establish a novel means for its study in keratinocytes, and provide the sequence of the key enzyme in the biological activation of vitamin D.

Renal dysplasia with secondary hyperparathyroidism and loose teeth in a young dog

In a dog with renal dysplasia and secondary hyperparathyroidism, loose teeth resulted from excessive resorption of alveolar bone. Sharpey's fibers, still anchored in the cementum, were lost in the replacing fibrous tissue and few fibers found their way to distant bone fragments. The alveolar bone is the site of predilection for the excessive, generalized resorption of bone in hyperparathyroidism. Clinical radiographic examination of the jaws is a valuable tool in the detection of the disease.

Jaw lesions resulting from renal hyperparathyroidism in a young dog--a case report

A five-month-old male Labrador retriever presented with massive bilateral jaw and facial swelling. Ulcers were found on the buccal mucosa and palate, and the jaws were flexible on firm palpation. The dog could eat only soft food and was underweight. Renal hyperparathyroidism was diagnosed based on serum chemistry screen, parathormone concentration, radiological findings and histopathology. The dog was euthanatized because of an extremely poor prognosis.