Role of genotype in the diagnosis of children with 21-hydroxylase deficiency

Background: Mutations of CYP21A2 gene are responsible of 21-hydroxylase deficiency (21-OHD), the most common enzymatic defect causing congenital adrenal hyperplasia (CAH). Objective and hypotheses: The aims of our study were: to confirm the diagnosis of 21-OHD by the analysis of CYP21A2 in infants with clinical features of 21-OHD; to analyze the genotype-phenotype relationship in these infants. Methods: We studied 21 children with clinical features of 21-OHD: 4 babies presented a salt-wasting form of CAH, 12 a premature pubarche and 5 an elevated 17-OHP level at newborn screening. All of them and their parents were submitted to genetic analysis of CYP21A2, performed by PCR, MLPA and exons and promoter sequencing. Patients were classified in 3 groups according to predict mutations’ severity: severe (group A), moderate (group B) or mild (group C). Results: The most frequent mutation in our population was V281L. All children in group A (2) and B (2) presented a salt-wasting form of CAH. Eight children were in group C and had a non classical form of CAH. Four infants were heterozygotes for 21-OHD and other 4 children did not present mutations in CYP21A2. A girl clinically presenting a non classical form of CAH was a compound heterozygote for Q318X and R25S, a new mutation whose residual enzymatic activity is not known, moreover she shown 4 genes at MLPA analysis. Analyzing the correlation between the 17-OHP levels after ACTH stimulation test and the genotype, we found an optimal relationship in patients of all three groups. All affected children presented a 17-OHP level after ACTH stimulation greater than 100 nmol/L. Conclusions: CYP21A2 analysis permitted to confirm the diagnosis of 21-OHD in 61.9% of our children. To improve this percentage we suggest to perform the analysis of CYP21A2 only when 17-OHP after ACTH stimulation is greater than 100 nmol/L. We confirm an optimal genotype-phenotype relationship in the 21-OHD patients.