ESPE Abstracts

Background: Congenital adrenal hyperplasia (CAH) is a group of inborn errors of steroidogenesis. It is mainly caused by steroid 21-hydroxylase coding gene (CYP21A2) mutations. More than 30% of the CYP21A2 mutations are deletions, with ethnic specific differences. The Bulgarian mutational spectrum of CYP21A2 gene is unknown.

Objective and hypotheses: To determine CYP21A2 mutation spectrum in Bulgarian CAH patients.

Method: Nineteen patients, picked up by the 17-OHP neonatal screening (nation-wide implementation 2010), were enrolled in the study. The multiplex ligation-dependent probe amplification (MLPA) was chosen as a first step genetic testing. In many cases targeted sequencing may prove point mutation detected by MLPA. Sequencing of the whole gene was chosen as a second step.

Results: The molecular genetic testing detected a heterozygous deletion of CYP21A2 gene in 47% (9/19) of the patients (23.5% allele frequency). The whole gene sequencing revealed the splice site mutation c.293-13A/C>G (allele frequency 57.8%), missense mutations – c.518T>A; p.I173N (13%); c.334G>A, p.Asp112Asn (2.6%), nonsense mutation 955C>T, p.Gln319* (2.6%) and frame shift mutation c.923dupT, p.Leu308Phefs*6 (2.6%). The total percent is more than 100 because one of the patients carries three mutations. This patient reveals classic salt-wasting CAH phenotype caused by a homozygous c.923dupT mutation and a heterozygous mutation c.334G>A. The double mutated allele was inherited from the mother and it is most probably formed due to non-allelic homologous recombination between the CYP21A2 and its pseudogene.

Conclusion: Our results showed that the screening in Bulgarian patients for CYP21A2 gene mutations should begin with screening for mutations c.293-13A/C>G and c.518T>A; p.I173N, followed by MLPA analysis and whole gene sequencing as a last step. Nevertheless, we should keep in mind that due to possible recombination some of the patients may carry more than two mutations in the CYP21A2 gene which is important for genetic testing in relatives and prenatal diagnosis.