General information
The SALSA MLPA Probemix P495 CYP11A1-CYP11B1-CYP11B2 is a research use only (RUO) assay for the detection of deletions or duplications in the CYP11A1, CYP11B1 and CYP11B2 genes, which are associated with renal insufficiency, congenital adrenal hyperplasia and aldosteronism.

Cytochrome P450 family 11 genes CYP11A1, CYP11B1 and CYP11B2 encode enzymes which are involved in steroid biosynthesis in the mitochondria of the adrenal cortex. Steroid biosynthesis starts with the conversion of cholesterol into pregnenolone, which is catalysed by the cholesterol side-chain cleavage enzyme, also known as desmolase, encoded by CYP11A1. CYP11A1 disruption causes a block in all aspects of adrenal and gonadal steroid synthesis, leading to congenital adrenal insufficiency (Buonocore F and Achermann JC 2020; OMIM #613743). CYP11B1 encodes 11β-hydroxylase, which catalyses the conversion of 11-deoxycortisol to cortisol and the conversion of 11-deoxycorticosterone to corticosterone amongst others. A deficiency of 11β-hydroxylase causes autosomal recessive disorder 11β-hydroxylase-deficient congenital adrenal hyperplasia, 11-OHD CAH (OMIM #202010; 5-8% of CAH cases). This is the second most common form of CAH after (CYP21A2 related) 21-OHD CAH which accounts for ~90% of CAH cases. CAH involves a decreased synthesis of cortisol and corticosterone and an accumulation of their precursors, which leads to androgen excess and hypertension.

CYP11B1 and CYP11B2 share ~95% sequence homology and are located in close proximity (~31 kb) on chromosome 8q. CYP11B2 encodes aldosterone synthase, which is involved in the synthesis of aldosterone. Aldosterone synthase deficiency is inherited in an autosomal recessive manner and usually presents with salt wasting, hyperkalaemia and hypotension (Hui et al. 2014). Recombination of CYP11B1 and CYP11B2 by unequal crossing over between these highly homologous genes and their regulatory elements have been reported. On the allele lacking the normal copies of CYP11B1 and CYP11B2, the CYP11B chimeric gene results in CYP11B2 being regulated by adrenocorticotropic hormone (ACTH), which normally controls expression of CYP11B1. This chimeric variant can lead to autosomal recessive 11β-hydroxylase deficiency or aldosterone synthase deficiency (Portrat et al. 2001). On the duplication allele, a complementary chimeric CYP11B gene results in CYP11B1 being regulated by angiotensin II and potassium, which normally control expression of CYP11B2. This can cause amongst others autosomal dominant glucocorticoid-remediable aldosteronism (GRA) or hyperaldosteronism (Lifton et al. 1992; Menabò et al. 2016; OMIM #103900).

The CYP11A1 gene (9 exons) spans ~30 kb of genomic DNA and is located on 15q24.1, about 72 Mb from the p-telomere. The CYP11B1 and CYP11B2 genes (9 exons each) span ~7.5 kb and ~7.3 kb of genomic DNA, respectively, and are located on 8q24.3, about 144 Mb from the p-telomere (close to the q-telomere).

This SALSA MLPA probemix is not CE/FDA registered for use in diagnostic procedures. Purchase of this product includes a limited license for research purposes.

Probemix content
The SALSA MLPA Probemix P495-A1 CYP11A1-CYP11B1-CYP11B2 contains 38 MLPA probes with amplification products between 129 and 441 nucleotides (nt). This includes ten probes for the CYP11A1 gene, nine probes for the CYP11B1 gene and nine probes for the CYP11B2 gene. In addition, ten reference probes are included that detect autosomal chromosomal locations. Complete probe sequences and the identity of the genes detected by the reference probes are available online (www.mrcholland.com).

This probemix contains nine quality control fragments generating amplification products between 64 and 105 nt: four DNA Quantity fragments (Q-fragments), two DNA Denaturation fragments (D-fragments), one Benchmark fragment, and one chromosome X and one chromosome Y-specific fragment. More information on how to interpret observations on these control fragments can be found in the MLPA General Protocol and online at www.mrcholland.com.