Non-classical 11β-hydroxylase deficiency caused by compound heterozygous mutations: a case study and literature review

Congenital adrenal hyperplasia (CAH) is a common genetic endocrine metabolic disorder, of which 21-hydroxylase deficiency (21OHD) is the most common type, accounting for 90–99% of all CAH cases. The second most common type of CAH is 11β-hydroxylase deficiency (11OHD), which accounts for 0.2–8% of cases [1]. Steroid 11b-hydroxylase defects lead to reduced conversion of 11-deoxycortisol (S) and 11-deoxycorticosterone (DOC) to cortisol and corticosterone, thereby leading to accumulation of the two steroid precursors mentioned above. In addition, an increase in metabolic products towards sex steroids corresponds to the typical clinical presentation including low renin hypertension, hypokalemia, hyperandrogenemia, and genital ambiguity in affected females. Current reports in the literature relevant to 11βOHD mostly involve classical 11OHD, and there are relatively few reports on non-classical 11OHD because of its mild symptoms.

The patient was a 23-year-old female (46, XY karyotype) diagnosed with hypertension (180/120 mmHg) since age 14 and a BMI of 20.8 kg/m². There was no obvious masculinization, and her parents stated that there were no obvious abnormalities in vulva development at birth. Antihypertensive drug therapy (nifedipine sustained-release tablets) had been taken continuously, and blood pressure was controlled to 130–140/80–90 mmHg. The patient sought treatment at our hospital due to menstrual disorders. The patient is the only child of non-consanguineous healthy parents from Northeast China. The study was approved by the ethics committees of China Medical University, and informed consent was obtained from the patient and her parents.

11βOHD is an autosomal recessive genetic disease. Over 100 mutations of CYP11B1 have been reported in the literature to date. There are more homozygous than compound heterozygous mutations (69.1% vs. 29.8%), and there are few single heterozygous mutations (1.1%), possibly because mutations in other exons have not yet been discovered [2, 3]. In the past, it was believed that mutations that cause 11βOHD are mostly concentrated in exons 2, 6, 7, and 8 [2, 4, 5]. However, our statistics revealed that most causative mutations are located in exons 3 and 8 (40%), and that the distribution in the other exons is actually more average. Patients carrying mutations in exon 8 account for the highest proportion among all patients, and patients carrying the R448H mutation are the most numerous (Fig. 2a) [5‐12]. Because the highly conserved amino acid sequence near C450 is located in exon 8, the normal structure of this region is essential for maintaining normal enzymatic activity [2]. Thus, most point mutations in exon 8 result in severe reduction of enzymatic activity, thereby resulting in classical 11βOHD. Although there are many mutations in exon 3, most cause a partial reduction in enzymatic activity and thus result in non-classical 11βOHD (Fig. 2c) [5, 7, 13‐23]. Thus, the probability of a mutation appearing in each exon is similar, but because the mutations reduce enzymatic activity to different degrees, different severities of clinical presentation are observed, and there is a high probability of misidentifying the disease for mutations in certain exons. The R448H mutation and 8 other mutations are the most frequently reported and account for approximately 40% of all cases (Fig. 2b). CYP11B1 mutation shows significant race specificity. For example, the R448H mutation mentioned above is common among Moroccan Jews [6]. Tunisians often carry the two mutations, G379 V and Q356X [24], of which Q356X is also common among sub-Saharan Africans and African-Americans [2, 3, 24‐26]. The T318 M mutation is most common among Yemenis [2, 27, 28], and some new mutations such as c.53_54insT, G206 V, W260X, R448P, and H465L are often found in Saudi Arabs [29‐31]. The R454C mutation has only been reported among the Chinese [8, 10, 32].

The case reported in this paper is a patient carrying the compound heterozygous mutations Y195H and R453Q located in exons 3 and 8, respectively, which are mutation hotspots. Of these mutations, R453Q has been reported in one individual of European descent and 3 Chinese individuals [8, 23, 33], and is likely to be more common among the Chinese [33]. The residue R453 is located in the L-helix and is adjacent to the Cys-pocket motif. This domain is highly conserved in the P450 family of enzymes, and causes 11-hydroxylase activity to decrease to approximately 1% of the wild-type activity [23]. The Y195H mutation has not been reported previously. Y195 is located in the E helix. Homology alignments indicate that this amino acid sequence is relatively conserved, and predictions using PolyPhen-2 and SIFT/Provean indicate that this mutation may impair protein function. A mutation in the neighbouring amino acid T196 has been reported previously (T196A). This mutation can lead to a 30–50% loss in enzymatic activity and can result in non-classical 11OHD [15]. Three-dimensional structural models show that Y195 and T196 are located in the middle segment of the E helix and are close to L463-L464 in the L helix, which is involved in heme binding [34]. This suggests that Y195H and T196A are similar and may affect enzymatic activity by indirectly affecting the structure of the L helix, but to a small degree; it is thus a mutation that causes non-classical 11OHD.

Because the clinical presentation of non-classical 11OHD is atypical and highly variable, its prevalence may be underestimated and it may be misdiagnosed. Some patients may be misdiagnosed as having polycystic ovary syndrome because of the mildly elevated androgen levels [13, 16], and there are patients that only present with hypertension with mineralocorticoid features [15]. After the ACTH stimulation test, the degree of increase in 17-hydroxyprogesterone can be used to differentiate from non-classical 21OHD, but there is still no consensus on the diagnostic standards for non-classical 11OHD [4, 17, 21]. Baseline and stimulated 11-deoxycortisol measurements, 11β-hydroxylase activity assays, and urinary steroid profiling using LC-MS/MS are recommended to avoid missing the diagnosis of non-classical 11OHD [16, 35]. However, 11-deoxycortisol measurement and ACTH medications are currently unavailable in most Chinese hospitals, which hinders the diagnosis of 11OHD, especially non-classical 11OHD. As the cost of genetic diagnosis decreases, genetic testing of CYP11B1 in suspected patients may make the diagnosis of non-classical 11OHD convenient and accurate.

Non-classical 11OHD patients may develop hypertension [14, 16], but this is highly variable, and its incidence and extent are still not clear [35]. The patient in our case developed severe hypertension at an early age, but because her diagnosis was never confirmed, antihypertensive therapy was irregular and she developed left ventricular myocardial hypertrophy and arteriosclerosis-like changes in the lower limbs, indicating the importance of early diagnosis and antihypertensive therapy. The use of mineralocorticoid receptor antagonists such as spironolactone or eplerenone for antihypertensive therapy is recommended in such patients [14]. The patient in this case was given spironolactone therapy, which controlled the blood pressure to normal.

In summary, the present study reports the case of a Chinese patient with non-classical 11OHD and presenting with early-onset hypertension, and carrying compound heterozygous mutations in CYP11B1, of which one mutation is reported for the first time. We also analysed and summarised over 170 cases that were previously reported in the literature and found that exons 3 and 8 were mutation hotspots. Mutations in exon 3 often result in non-classical 11OHD, whereas mutations in exon 8 more often result in complete loss of enzymatic activity and classical 11OHD. The possibility of non-classical 11OHD should be considered in hypertensive patients with hyperandrogenism or elevated mineralocorticoids. Such patients should be carefully identified and given an early diagnosis and treatment to avoid the adverse outcomes caused by hyperandrogenism or long-term hypertension.