Improving the diagnosis of 11β-hydroxylase deficiency using home-made MLPA probes: identification of a novel chimeric CYP11B2/CYP11B1 gene in a Sicilian patient

Purpose: 11β-Hydroxylase deficiency (11OHD) represents the second most common cause of congenital adrenal hyperplasia. It is caused by mutations in the CYP11B1 gene localized about 40 kb from the CYP11B2 gene with which it shares a homology of 95 %. The asymmetric recombination of these two genes is involved both in 11OHD and in glucocorticoid-remediable aldosteronism (GRA). Our objective was to set up an easy and rapid method to detect these hybrid genes and other kinds of deletions, to improve the molecular diagnosis of 11OHD. Methods: A set of 8 specific probes for both the CYP11B1 and the CYP11B2 genes to be used for multiplex ligation-dependent probe amplification (MLPA) analysis was designed to detect rearrangements of these genes. Results: The method developed was tested on 15 healthy controls and was proved to be specific and reliable; it led us to identify a novel chimeric CYP11B2/CYP11B1 gene in one patient that carried the known A306V mutation on the other allele. Specific amplification and sequencing of the hybrid gene confirmed the breakpoint localization in the second intron. Conclusions: The MLPA kit developed enables the detection of deletions, duplications or chimeric genes and represents an optimal supplement to DNA sequence analysis in patients with 11OHD. In addition, it can also be used to show the presence of the opposite chimaera associated with GRA.