Abstract
Steroid 21OHD is a monogenic, HLA-linked, recessively inherited condition. The homozygous affected state is not necessarily lethal. Penetrance is complete by criteria of ACTH-stimulated hormonal response. We report a distortion of the expected Mendelian ratio of 1 homozygous affected:2 heterozygous:1 homozygous unaffected amongst families studied with both ACTH-stimulation and HLA-typing. Specifically, we have observed a paucity of homozygous unaffected individuals. The mendelian ratio of 1:2:1 held true if HLA typing alone was considered. However, 50% of offspring predicted by HLA type to be unaffected tested hormonally as heterozygotes, indicating that extremely frequent chromosomal recombination had occurred. Neither paternal nor maternal transmission distortion was observed; nor was haplotype transmission distorted by specific HLA associations. Using hormonal criteria solely, there was a 35% increase over the expected number of heterozygotes (p < .005), resulting in a comparable decrease in homozygous unaffected individuals who had been ACTH-tested. Excluding one proband per family, there was no deviation from the expected proportion of homozygous affected individuals even when deceased sibs were included.
Conclusion:: In light of the excess number of heterozygotes and fewer than expected unaffected indi iduals among 21OHD families, it appears that there is some pressure to transmit the haplotype segment bearing the gene for 21OHD. Whether this can be attributed to the 21OHD gene itself remains to be proven.
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Speiser, P., New, M. 83 MENDELIAN RATIO DISTORTION IN STEROID 21-HYDROXYLASE DEFICIENCY (210HD). Pediatr Res 19, 617 (1985). https://doi.org/10.1203/00006450-198506000-00103
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DOI: https://doi.org/10.1203/00006450-198506000-00103