CONGENITAL ADRENAL HYPERPLASIA WITH COMPOUND HETEROZYGOUS I2 SPLICE AND P453S MUTATIONS

Abstract

Background

Congenital adrenal hyperplasia (CAH) is an autosomal recessive inherited disorder caused by congenital deficiency of enzymes involved in cortisol biosynthesis from cholesterol in the adrenal cortex. In this article, we aimed to present a 29-year-old female patient with I2 splice point mutation detected in one allele and P453S mutation on the other allele of CYP21A2 gene associated with 21-hydroxylase deficiency. Her further investigation revealed that her mother had P453S mutation and her father had I2 splice mutation.

Case report

A 29-year-old woman with CAH was admitted to our clinic with the request of pregnancy. Her physical examination revealed a height of 151 cm, weight 59 kg, body mass index 25.8 kg/m². According to Tanner staging, she had Stage 3 breast development and pubic hair. Her laboratory test results were as follows: Glucose: 79 mg/dL (70-100 mg/dL), Creatinine: 0.6 (0.5-0.95 mg/dL), Sodium: 138 mEq/L (135-145 mEq/L), Potassium: 4.4 mEq/L (3.5-5.1 mEq/L), Cortisol: 0.05 µg/dL, ACTH: <5.00 pg/mL (5-46 pg/mL), 17-OH progesterone: 7.67 ng/mL (0-3 ng/mL). Chromosome analysis revealed a 46, XX karyotype. CYP21A2 gene mutation analysis was performed for the patient whose clinical history and laboratory results were compatible with congenital adrenal hyperplasia. During the reverse dot blot analysis, I2 splice mutation in one allele and P453S mutation in the other allele were detected.

Conclusion

Although the I2 splice mutation detected in our case was mostly associated with a salt-wasting form of CAH, it was thought that the other P453S mutation detected may explain the relatively good clinical course in our case.

Introduction

Congenital adrenal hyperplasia (CAH) is an autosomal recessive inherited disorder caused by congenital deficiency of enzymes involved in cortisol biosynthesis from cholesterol in the adrenal cortex (1). Increased corticotrophin hormone (ACTH) and corticotropin releasing hormone (CRH) levels secondary to the reduction of cortisol levels cause hyperplasia by continuously stimulating the adrenal glands. Its incidence varies between 1:10.000 and 1:15.000 although it varies according to ethnic group (2). More than 90% of CAH cases result from 21-hydroxylase enzyme deficiency (1). Mutations in the CYP21A2 gene in the 21 subfamilies of the cytochrome P450 family play a key role in the 21-hydroxylase enzyme deficiency. The CYP21A2 gene encoding 21 hydroxylases is located in the HLA class III region in the short arm of chromosome 6p21.3 together with the CYP21A1P pseudogene (3-5). There is a genotype-phenotype correlation of CYP21A2 mutations, and its frequency and spectrum vary across different populations (4). CAH cases can be seen in three different clinical forms: salt-wasting and simple virilizing type (classic forms) and late onset type (non-classic form), depending on the severity of the enzyme deficiency (4, 6, 7). In the case of a compound heterozygous with two different mutations, it is generally assumed that the phenotype is determined by the less severely affected allele (2). In this article, we aimed to present a 29-year-old female patient with I4 splice point mutation detected in a CAH alleles and P453S mutation in the other allele associated with 21-hydroxylase deficiency. Her further investigation revealed that her mother had P453S mutation and her father had I2 splice mutation.

CASE REPORT

A 29-year-old woman with CAH was admitted to our clinic with the request of pregnancy. The patient had no history of consanguineous marriage and her brother had a history of dehydration, nausea and vomiting on the tenth day after delivery and a history of classic salt - wasting type of CAH. Our patient, who was 2 years old when her brother had CAH, had ambiguous genitalia and underwent vaginoplasty operations at the age of 3 and 10 years. She was on hydrocortisone for 15 years and dexamethasone 0.5 mg for the last 12 years. Her physical examination results were as follows: height:151 cm, weight: 59 kg, body mass index: 25.8 kg/m², waist circumference: 83 cm, and arm circumference: 30 cm. International Obesity Task Force (IOTF) references were used to determine overweight and obesity prevalence. According to Tanner staging, she had Stage 3 breast development and pubic hair. Her menarche age was 11. Her laboratory test results were given in Table 1.

Table 1.

Laboratory findings

Laboratory Parameters	Laboratory Results
Glucose (NVR: 70-100 mg/dL)	79
Creatinine (NVR: 0.5-0.95 mg/dL)	0.6
AST (NVR:0-35 U/L)	20
ALT (NVR:0-35 U/L)	11
Sodium (NVR:135-145 mEq/L)	138
Potassium (NVR:3.5-5.1 mEq/L)	4.4
Triglyceride (NVR: 0-150 mg/dL)	85
TSH (NVR: 0.38-5.33 mIU/L)	2.4
Free T4 (NVR: 0.61-1.3ng/dL)	0.87
17-OH progesterone (NVR:0-3 ng/mL)	7.67
ACTH (NVR: 5-46 pg/mL)	<5.00
FSH (NVR: 1.27-19.26 mIU/mL)	9.62
LH (NVR: 1.24-8.62 mIU/mL)	8.63
Cortisol (NVR: 3.09-22.4μg/dL)	0.05
Estradiol (NVR: 20-534pg/mL)	123.91
DHEA-S (NVR:35-430 ug/dL)	<15.00
1,4-Delta Androstenedione (ND:0.3-3.3 ng/mL)	0.57

^*(NVR: Normal Value Range).

Her abdominal ultrasonography revealed no detectable mass pathology in suprarenal locations. Uterus size was 46x34x70 mm and endometrial thickness was measured as 4 mm. The left ovary was 21x18x33 mm in size, and millimetric follicles were detected. The right ovary was 25x19x33 mm in size and a smooth-contoured, cystic lesion of 43 mm with thin wall and no septa or solid tissues was detected. Chromosome analysis revealed a 46, XX. CYP21A2 gene mutation analysis was performed for the patient whose clinical history and laboratory results were compatible with congenital adrenal hyperplasia. Gene deletions and large gene conversions were detected by nonradioactive Southern blotting of TaqI-, BglII-, and EcoRI/BglII-digested DNA hybridized with probes specific for the CYP21 and C4 genes. The patient was referred to Molecular Genetics Laboratory for congenital adrenal hyperplasia mutations examination. In the reverse dot blot analysis, I2 splice mutation in one allele and P453S mutation in the other allele were detected (Fig. 1). Her family history revealed that her mother had P453S mutation and her father had I2 splice mutation. The patient who had a pregnancy plan was told about the risks and was guided to genetic consultation. Genetic mutation screening of the patient’s husband was planned. The informed consent form was obtained from the patient for the publication of the article.

Figure 1.

In the reverse dot blot analysis, I2 splice mutation in one allele and P453S mutation in the other allele were detected.

DISCUSSION

CYP21A2 and CYP21A1P genes consist of 10 exons. The similarity between two genes is 98% in their exonic and 96% in the intronic sequences and two genes shows a high degree of homology. Most of the common mutations causing 21 hydroxylase deficiency are due to intergenic recombination between CYP21A2 and CYP21A1P. Approximately 5% of all CYP21A2 alleles resulting in disease are caused by rare mutations which are not originated from pseudogene. In our country, the most common mutation detected in CAH patients was V281L (8). The frequency of mutations varies according to ethnic backgrounds and populations. The most common mutations in CAH cases were point mutations and were found to be 70-75%of cases. Large gene conversions or deletions were also detected in approximately 25-30% of alleles of affected patients (9). The most common mutations according to clinical form are I2 splice in the classical salt-wasting type, I172N in simple virilizing type, and V281L in late-onset non-classical type. Even though there is a good genotype-phenotype correlation in CAH in compound heterozygous cases it is not easy to predict the exact clinical outcome of the patient.

Khan et al. found that the I2 splice mutation was associated with salt loss in the homozygous, while the I2 splice mutation in one allele was associated with the classic simple virilization form of the disease (10). Nils Krone et al. reported the compound heterozygous I2 G / P453S was previously reported as a nonclassical form of CAH in their study (11). In our case, I2 splice mutation in one allele and missense mutation P453S in the other allele were detected (12). Although I2 splice mutation is usually associated with the classical salt-wasting type form, it can rarely be seen in the form of simple virilizing type. Mutation P453S is rare and associated with a late-onset non-classical type (9). If there is a mutation in the husband of proband, prenatal diagnosis with chorionic villus sampling and molecular genetic analysis will be offered to the family. The treatment of the patient was planned since dexamethasone was not bound to sex hormone-binding globulin (SHBG) in the maternal blood and could not be metabolized in the placenta by the enzyme 11β-hydroxysteroid dehydrogenase. Dexamethasone suppresses ACTH secretion from mother to fetus via placenta (13). CAH is the most common genetic steroid disorder affecting fertility. Steroid hormones play a critical role in the functionality of sexual development and re-productivity. So, patients with either 21- hydroxylase or 11b-hydroxylase deficiency confront challenges related to their fertility. Subfertility is relative in non-classical adrenal hyperplasia; however, the incidence of spontaneous miscarriage is higher. Data regarding the fertility of non-classical adrenal hyperplasia patients are scarcely available. Many females with non-classical adrenal hyperplasia conceive spontaneously. The risk of spontaneous miscarriage, however, is higher in these females compared to normal ones (14). Although the I2 splice mutation detected in our case was mostly associated with a salt-wasting form of CAH, it was thought that the other P453S mutation detected may explain the relatively good clinical course in our case.

In conclusion, reports of a compound heterozygous mutation with the I2 splice mutation and the P453S mutation are extremely rare in the literature. More comprehensive studies are needed on this subject. In patients with CAH, genetic typing and genotype-phenotype correlation and genetic counseling are important and necessary.

Conflict of interest

The authors declare that they have no conflict of interest.