ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2016) 45 OC5.6 | DOI: 10.1530/endoabs.45.OC5.6

Cytochrome p450 side chain cleavage enzyme (CYP11A1) mutations: Phenotypic variability and identification of p.E314K as a recurrent, pathogenic variant

Avinaash Maharaj1, Federica Buonocore2, Eirini Meimaridou1, Tim Cheetham3, Caroline Brain2, Ewan Gray4, Jenifer Suntharalingham2, Niccolo Striglioni2, Helen Spoudeas2, Malcolm Donaldson4, John Achermann2 & Lou Metherell1

1Queen Mary University of London, London, UK; 2UCL Institute of Child Health, London, UK; 3Institute of Genetic Medicine, Newcastle University, Newcastle, UK; 4Royal Hospital for Sick Children, Glasgow, UK.

Background: CYP11A1 encodes the P450 side chain cleavage enzyme which initiates the steroidogenic cascade by conversion of cholesterol to pregnenolone. Severe (or classical) deficiency of this enzyme is characterised by disordered sexual differentiation in addition to adrenal and gonadal insufficiency. However partial loss-of-function mutations of CYP11A1 can present as isolated glucocorticoid deficiency (IGD). We describe 16 patients with both novel and known mutations in CYP11A1 who presented with varied clinical phenotypes.

Patients and methods: Whole exome or targeted (Haloplex) next generation sequencing (NGS) was performed in patients with adrenal insufficiency of unknown aetiology. The p.E314K variant (rs6161; c.940G>A) of CYP11A1 has a minor allele frequency of 0.0024 and is predicted benign. We postulated that it alters splicing and assessed its effect using an in vitro splicing assay.

Results: The following mutations in CYP11A1 were detected in 16 patients by NGS: homozygous p.A359V (2 non-pigmented sisters with IGD), homozygous p.R451W (1 classic patient), compound heterozygous mutations p.I279Yfs*9 and p.*522Rext*68 (2 siblings with IGD) and p.R120Q and p.Q395K (a patient diagnosed with lipoid adrenal hyperplasia). In the remaining 10 patients, with variable presentations, sequencing revealed the presence of compound heterozygosity for a p.E314K mutation with coexistent p.R424*, p.R439*, p.I279Yfs*9, c.990G> A (splice mutation), c.426-2A>G, p.L335P (2 siblings) or c.790_802del (3 brothers with pigmentation, low cortisol and salt loss but normal puberty). In all 16 cases the variants were biallelic and never seen together in parents or unaffected siblings. Although predicted benign the p.E314K variant is enriched in our patient cohort with an allele frequency =0.015 (P<0.01).

Conclusion: Previously considered a benign variant, the p.E314K occurs more frequently than expected in patients and we predict that it is pathogenic when in combination with a severe disruptive change on the other allele. We hypothesize that it affects the gene at the RNA level, perhaps altering splicing, or that it represents a marker for another deleterious change within the gene. This and other partially inactivating mutations of CYP11A1 often leads to mild phenotypic presentation including isolated hypocortisolaemia and normal sex development.