Steroid 21-hydroxylase deficiency is the major cause of congenital adrenal hyperplasia. Genotyping for deletions and nine point mutations in the CYP21 gene has been performed in 38 Spanish patients and their relatives by Southern blot analysis and allele-specific oligonucleotide hybridization. Three clinical variants were included in this study, viz., salt-wasting (SW, 21 patients), simple virilizer (SV, two patients), and late-onset (LO, 15 patients) forms. Twenty-three patient genotypes (16 SW, two SV, and five LO) were fully characterized. In both alleles, all but one of these severe forms (SW and SV) presented mutations that abolished or severely affected enzymatic activity. Patients with LO forms showed mutations that moderately impaired enzymatic activity in both alleles, or severe mutations in only one chromosome. Of 46 chromosomes from severe forms, 41 were characterized in this study (89%). The most frequent mutation was an aberrant splicing site (655 A or C to G) in intron 2, in 30% of these chromosomes. Deletions were found in 20%, and large gene conversions in 13% of these alleles. This screening allowed the characterization of 18 out of 30 LO chromosomes, the most frequent mutation being Val281Leu (37%). Severe mutations were found, in heterozygosis, in one third of LO patients.

Very young SGA children without spontaneous catch-up growth could benefit from GH treatment because growth was accelerated and no negative side effects were observed.

This study addresses the contributions of gene conversion and a founder effect to the distribution of the two most frequent severe point mutations of the 21-hydroxylase (21OH) gene causing congenital adrenal hyperplasia: the 655G splicing mutation at intron 2, and Gln318Stop in a Spanish population. Direct and indirect analyses of segregated mutant and normal 21OH genes in 200 Spanish families (classic and nonclassic 21OH deficiency) were performed. Both mechanisms were found to contribute to different degrees to the defective investigated alleles. The 655G splicing mutation (62 alleles, 15.5%) seemed to be almost exclusively related to recent conversion events, whereas Gln318Stop (33 alleles, 8.3%) is more likely to be due to the dissemination of remotely generated mutant alleles. Other severe defective alleles, 8 bp-deletion (13 alleles, 3.3%), 306insT (5 alleles, 1.3%), and gene deletions (43 alleles, 11%), as well as the mild mutation Val281Leu (120 alleles, 30%), also appear to be strongly associated with particular D6S273 alleles. Although gene conversion contributes to the generation of severe 21OH alleles, the high frequency of some severe mutations in different geographic areas is consistent with a founder effect.

ACTH-stimulated 17-OHP may predict the risk of severe mutations in compound heterozygosity in children (maximum predictive value 93% sensitivity and 83% specificity for a cut-off at 151 nmol l(-1)), although a certain overlap in individual values is observed and performance of molecular analysis should never be obviated in the genetic counselling of these patients.

Prenatal diagnosis and treatment of congenital adrenal hyperplasia due to steroid 21‐hydroxylase (21‐OH) deficiency has been proved to be effective. Screening for a panel of nine point mutations, deletions, and gene conversions allows the identification of most of the mutations, although 6–12 per cent of chromosomes remain uncharacterized. In the present study, microsatellite typing in the HLA region was performed in 23 21‐OH deficiency families to determine the usefulness of these markers in the indirect identification of disease alleles. Two Génèthon markers (D6S273 and D6S439) in the HLA complex, class III and II regions in 5′ and 3′, respectively to the CYP21 gene, were typed together with a microsatellite at intron 3 of the TAP1 gene also in 3′. The heterozygosity of these markers provided informativity in all but one family, in which only the father was informative. Direct genotyping of the chromosomes confirmed in each case the correct assignment of the disease alleles in the sibling. The indirect analysis of the 21‐OH gene through D6S273, TAP1, and D6S439 microsatellites provides useful information in the molecular analysis of steroid 21‐OH deficiency. © 1997 John Wiley & Sons, Ltd.