The Diagnosis and Management of an Adult 46xy Female with Isolated 17, 20-Lyase Deficiency due to a Novel Mutation P. Y35xi Cytochrome B5a Gene

Case Report

Austin J Obstet Gynecol. 2014;1(1): 4.

The Diagnosis and Management of an Adult 46xy Female with Isolated 17, 20-Lyase Deficiency due to a Novel Mutation P. Y35xi Cytochrome B5a Gene

Tracy Wing Yee Yeung1*, Angel on Kei Chan2, Raymond Hang Wun Li1, Chi Chung Shek2, Pak Chung Ho1 and Ernest Hung Yu Ng1

1Department of Obstetrics & Gynecology, The University of Hong Kong, People's Republic of China

2Department of Pathology, Queen Mary Hospital, People's Republic of China

*Corresponding author: Tracy Wing Yee Yeung, Department of Obstetrics and Gynecology, The University of Hong Kong, Queen Mary Hospital, Pokfulam Road, Hong Kong

Received: June 20, 2014; Accepted: July 22, 2014; Published: July 23, 2014


Objective: To report the diagnosis and clinical management of an adult Chinese 46 XY woman due to isolated 17,20-lyase deficiency resulting from a homozygous Cytochrome B5A mutation p.Y35X with non-consanguineous parents.

Design: Case Report.

Setting: Gynaecological endocrine clinic in a University Hospital.

Patients: A 29 year-old Chinese woman with 46XY Disorder of Sex Development (DSD) resulting from isolated 17, 20-lyase deficiency and her parents.

Intervention: Investigations with serum hormonal profiles, urine steroid profile, serum methaemoglobin, mutational analyses of the CYP17A1 and CYB5A by polymerase chain reaction (PCR) and DNA sequencing, surgical correction for ambiguous genitalia.

Main outcome measure: Steroid hormones and methaemoglobin levels, urine steroid profile, serum mutational analyses of CYP17A1 and CYB5A genes and post-operative clinical outcomes.

Result: Steroid hormone levels and urine steroid profile suggested isolated 17,20-lyase deficiency with elevated methaemoglobin level. Mutational analysis confirmed a homozygous novel mutation p.Y35X in the CYB5A gene. Correctional surgery restored normal female external genitalia.

Conclusion: Urine steroid profiling is a useful test in pinpointing the exact error of testosterone metabolism and serum methaemoglobin level may be used to screen for abnormal Cytochrome B5 function. Surgical treatment aims at restoring normal external genitalia of the assigned gender.

Keywords: 46XY female; isolated 17,20-lyase deficiency; novel mutation p.Y35X; Cyt B5 gene; urine steroid profiling; methaemoglobin level; investigation; clinical management


P450c17 is an essential enzyme in the steroidogenesis pathway. It is expressed in microsomes in steroidogenic tissues including the adrenal cortex, testis and ovary. It is the single enzyme that catalyzes both the 17 alpha-hydroxylase reaction to produce glucocorticoid, cortisol, as well as the subsequent 17,20-lyase reaction leading to production of sex steroids. While electron donation from P450- oxidoreductase (POR) is essential for proper functioning of P450c17, cytochrome B5 acts as an allosteric cofactor to facilitate electron transfer and ensure optimal 17,20-lyase function [1,2]. Isolated 17,20-lyase deficiency resulting in impaired production of testosterone is an exceedingly rare cause for 46XY Disorder of Sex Development (DSD). Only a few cases of mutations in CYP17A1 gene and cytochrome P450 oxidoreductase (POR) mutations have been identified and reported as the cause [3-7]. Kok et al [8] first reported a homozygous p.W27X mutation leading to aberrant cytochrome B5 (CytB5) protein as a cause of impaired 17,20-lyase activity in a newborn male presenting with ambiguous genitalia. The consanguineous parents carried heterozygous p.W27X mutation.

In this article, we reported the diagnosis and management of an adult woman with 46XY DSD due to a novel homozygous mutation in CYB5A inherited from her non-consanguineous parents resulting in defective testosterone production and ambiguous genitalia. We highlighted the important steps in arriving at the diagnosis and presented the surgical outcomes in the correction of external genitalia.

Case Presentation

The patient was presented to our Gynaecological Endocrinology Clinic at the age of 29 for further management of "testicular feminisation". She was noted to have ambiguous genitalia at birth with gonads being palpable at the vulva. Karyotyping revealed 46XY and gonadal biopsy confirmed the presence of testicular tissue. Diagnosis of testicular feminisation was made and she was advised to have surgical removal of gonads at puberty. However, the patient defaulted follow up since early childhood and only presented to our clinic at age 29 for clarification of the condition. She started to have breast development at 12 and axillary and pubic hair growth at 13. She had primary amenorrhea and has never attempted coitus. Physical examination revealed a body height of 170cm and weight of 48kg. Breast development was at Tanner stage IV. Axillary hair was shaved and she had a normal female pattern of pubic hair. Pelvic examination revealed clitoromegaly of 1 x 1 x 1.5 cm. A 3 x 2 cm firm mass was detected in the left labia majora and another firm mass of 2 x 2 cm was noted at the right groin, being mobile along the distal inguinal canal and right labia majora. Labia minora and vaginal mucosa were normal looking. A short blind-ended vaginal pouch of 2 cm long was detected upon gentle probing. Rectal examination revealed no palpable cervix or uterus. Ultra sonography of inguinal and groin regions confirmed the presence of testicular masses, while magnetic resonance imaging (MRI) of pelvis failed to detect any uterus or cervix.

Hormonal analysis in serum

Serum 17-alpha hydroxyprogesterone (17OHP), progesterone, testosterone, androstenedione, dehydroepiandrosterone sulphate (DHEA-S), follicle-stimulating hormone (FSH), luteinizing hormone (LH), estradiol (E2), anti-Mullerian hormone (AMH) and cortisol were measured.

Urinary steroid profiling

Urinary steroid profiling was performed by gas chromatography-mass spectrometry on a 24-hour urine collection.

Stimulation Tests

Short synacthen test and Human Chorionic Gonadotrophin (HCG) stimulation test were performed to demonstrate the extent of enzyme deficiency.

Molecular confirmation

Molecular analysis for the confirmation of the diagnosis of 17, 20-lyase deficiency was performed after obtaining written consent from the patient and her parents. DNA was extracted from peripheral whole blood using standard procedures. All the coding exons and exon-flanking introns of the CYP17A1 (NG_007955.1) and CYB5A (NG_023211.1) genes were amplified by polymerase chain reaction using the following conditions: one cycle of 94°C for 12 min; 40 cycles of denaturation at 94°C for 30 s, annealing at 63°C for 45 s, and an extension at 72°C for 45 s using the primers listed in Supplementary Table I. The reaction mixture of final volume 25 μL contained 100 ng DNA template, 1x PCR buffer (Applied Biosystems, Foster City, CA), 2.0mmol/L MgCl2, 0.2 μmol/L dNTP, 12.5 pmol of each primer, and 0.625U AmpliTaq Gold DNA polymerase. The PCR products were then purified for bidirectional DNA sequencing.


Reduction clitoroplasty and bilateral gonadectomy were performed with an aim to restore normal female external genitalia and reduce the risk of gonadoblastoma.

The operation was performed under general anaesthesia. Clitoromeglay was noted with the clitoral glans measuring 1 x 1 cm and the clitoral body measuring 3 cm long. Urethral opening was identified in its normal position. A blind-ended vaginal opening was seen below the urethral opening and was partially covered by genital fold. It admitted one finger and was ~2 cm deep. Gonads were identified at left labia majora and right groin as described above (Figure 1a).