Issues with the Detection of Large Genomic Rearrangements in Molecular Diagnosis of 21-Hydroxylase Deficiency

More than 95% of congenital adrenal hyperplasia (CAH) cases are associated with mutations in the 21-hydroxylase gene (CYP21A2) in the human leukocyte antigen (HLA) class III area on the short arm of chromosome 6p21.3. In the diagnosis of 21-hydroxylase deficiency, CYP21A2 genotyping is a valuable complement to biochemical investigations. Genotyping can confirm the diagnosis (or carrier state) and, at the same time, provide accurate phenotype prediction in patients carrying severe mutations. In addition, the use of genetic testing is also helpful in prenatal diagnosis where the goal of prenatal treatment is preventing genital virilization of the female fetus. An in-depth knowledge of CYP21A2 genetics is essential to assure the correct interpretation of results obtained. To date, more than 200 small pathogenic variants of the CYP21A2 gene have been reported, showing good agreement between clinical phenotype and patient genotype. Recently, novel CYP21A2 deletions, involving one or more exons, have been reported in different populations. Since these rearrangements have never been described before in the genetic history of 21-hydroxylase deficiency, these new deletions have aroused particular interest. However, it is possible that these novel rearrangements are the result of incorrect interpretation of multiplex ligation-dependent probe amplification (MLPA).