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ABSTRACT

Congenital adrenal hyperplasia (CAH) is a family of inherited disorders of adrenal steroidogenesis, most commonly due to deficiency of P-450 21-hydroxylase (21-OH). There are two genes for 21-OH on the short arm of chromosome 6, the A gene which is thought to be inactive, and the B gene. These genes appear as 3·2 and 3·7 kb TaqI fragments on Southern blots. In a study of DNA from 60 normal controls with TaqI and a 21-OH cDNA probe, 12% exhibited a homozygous deletion of the A gene, and 22 and 8% heterozygous deletions of A and B genes respectively. TaqI analysis of eight patients with CAH revealed four without A or B gene deletions, three with heterozygous deletions of the B gene and one with a homozygous deletion of the B gene. On further analysis with KpnI, EcoRI, PvuII and BglII, however, these genotypes were amended to two with heterozygous deletions of the B gene and two with possible B to A gene conversions. The genotypes of the four patients without deletions remained unchanged.

RNA from CAH and Cushing's adrenal tissue was also analysed using A and B gene-specific oligodeoxynucleotide probes. B gene transcripts were detected in both CAH and Cushing's adrenals, while no A gene transcripts could be detected in either tissue. The level of B gene-derived mRNA was greater in the Cushing's adrenal than in the CAH adrenal, which in turn was greater than that in the adrenal from a normal individual.

These results suggest that there is a high frequency of 21-OH gene deletions in the normal population, but that TaqI alone is not capable of unequivocally identifying such deletions. The results also suggest that CAH is caused by heterogenous defects of the B gene. The defective gene, however, is transcriptionally active, indicating that the defect is not within the regulatory region.

ABSTRACT

An abundant, seven trans-membrane domain receptor related to the calcitonin receptor has been studied by a number of groups without identification of its ligand. A recent report claimed that the receptor was a type 1 CGRP receptor (Aiyar et al J. Biol. Chem. 271 11325-11329 (1996)). We have studied the equivalent rat sequence in transfected cells. When expressed in 293 cells the receptor interacts with CGRP and adrenomedullin with KD values of 1.2 nM for CGRP and 11 nM for adrenomedullin. Both ligands cause an elevation of intracellular cAMP with EC₅₀ values of 4 nM and 20 nM respectively and these effects are inhibited by the antagonist CGRP_8-37. The receptor is expressed at high levels in the pulmonary vascular endothelium. Both the pharmacological data and the localisation are consistent with the conclusion that the orphan receptor is a type 1 CGRP receptor. However, when expressed in COS-7 cells, no receptor activity could be demonstrated suggesting that 293 cells contain a factor necessary for functional receptor expression.