Carrier detection and prenatal diagnosis of congenital adrenal hyperplasia must identify 'apparently mild' CYP21A2 alleles which associate neonatal salt-wasting disease.
OBJECTIVE
Couples at risk of severe congenital adrenal hyperplasia (CAH) may be offered prenatal treatment or preimplantation diagnosis. However, proper genetic counselling requires the accurate identification of apparently 'mild alleles' in partners of CAH-carriers/patients.


METHODS
CYP21A2 gene analyses were performed in 255 patients with severe 21-hydroxylase deficiency (21-OHD), 94 with mild 21-OHD, 752 parental samples, 233 clinically unaffected partners and 253 historic DNA samples. GENSCAN and ClustalX2.0 software were used for in silico analyses, and Epidat 3.1 software for statistical calculations.


RESULTS
Twenty-seven partners were carriers of p.Val282Leu (alias p.Val281Leu, allele frequency 11.7%, 7.4-16.1). 'Val282Leu alleles' were detected in 30 patients with salt-wasting (SW) disease, 21 with other pseudogene-derived and rare coding cis severe mutations, and 9 without. These CYP21A2 genes were compared to those of 94 fully characterized patients with mild deficiency carrying p.Val282Leu in compound heterozygosity with a severe allele. A rare intronic variant, c.292+5G>A, was detected in the nine 'severe Val282Leu alleles' and that was not seen in mild p.Val282Leu alleles, in other deficient alleles or in normal chromosomes. The in silico documented effect on splicing and the clinical association (p < 0.0001) confirmed p.Val282Leu; c.292+5G>A as a severe allele.


CONCLUSIONS
As only severe alleles require clinical intervention, CAH-carrier detection of p.Val282Leu should be followed by the analysis of c.292+5G>A.
Ezquieta
Begoña
B
Laboratorio de Diagnóstico Molecular, Hospital Universitario Gregorio Marañón, Madrid, Spain. bezquieta.hgugm@salud.madrid.org
Santomé
Luis
L
Barrio
Raquel
R
Barrionuevo
Jose L
JL
López-Siguero
Juan P
JP
Oliver
Antonio
A
Ramírez
Joaquín
J
Rodríguez
Ildefonso
I
Muñoz-Pacheco
Rafael
R
D000312:Adrenal Hyperplasia, Congenital / Q000175:diagnosis / Q000201:enzymology* / Q000235:genetics; D000483:Alleles; D004247:DNA / Q000737:chemistry / Q000235:genetics; D005260:Female; D005817:Genetic Counseling; D014644:Genetic Variation; D006579:Heterozygote; D006801:Humans; D007231:Infant, Newborn; D008297:Male; D018895:Microsatellite Repeats; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide; D011296:Prenatal Diagnosis / Q000379:methods*; D013255:Steroid 21-Hydroxylase / Q000235:genetics*
D004247:DNA; C531510:CYP21A2 protein, human; D013255:Steroid 21-Hydroxylase