Abstract
The 21-OHase is encoded by 2 genes located in the HLA major histo compatibility complex on chromosome 6. While the 21-OHase B gene, corresponding to the 3.7 kb endonuclease Taq I fragment, is functional, the 21-OHase A gene, corresponding to the 3.2 kb Taq I fragment, is a pseudogene.
Using a relatively short 0.235 kb probe recognising the first 2 exons of the 5′end of both genes, we analysed genomic DNA of 12 patients with salt-wasting CAH, after digestion with U different restriction enzymes.
9 out of 12 patients shoved a change of normal molecular organisation: In 2 siblings and 3 other unrelated patients, we found a normal Taq I pattern but, at the same time, the loss of the A genc specific Hind III fragment. Another patient showed an increased B genc signal in the Taq I digest, whereas in the Eco R I digest the A gene signal was increased. Two HLA identical siblings, one with mild, the other with severe CAH, both surprisingly showed homozygous loss of the 3.7 kb Taq I fragment. However, Eco R I digest revealed that the B gene specific recognition sites were preserved. The same occured in another unrelated patient.
We infer frequent exchange between the 2 neighbouring 21-OHase A and B genes by either unequal crossing over or gene conversion resulting in hybrid genes that carry A- as well as B gene specific recognition sites in the gene or its' surrounding districts.
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Janssen, S., Knorr, D., Olek, K. et al. 19 EVIDENCE FOR RECOMBINED HAPLOTYPES IN THE AREA OF THE 21-HYDROXYLASE (21-OHase) A- AND B GENE IN CONGENITAL ADRENAL HYPERPLASIA (CAH). Pediatr Res 24, 520 (1988). https://doi.org/10.1203/00006450-198810000-00040
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DOI: https://doi.org/10.1203/00006450-198810000-00040