Rapid Molecular Genetic Diagnosis with Next-Generation Sequencing in 46,XY Disorders of Sex Development Cases: Efficiency and Cost Assessment

Lessons from 17β-HSD3 deficiency: Clinical spectrum and complex molecular basis in Chinese patients

17β-Hydroxysteroid dehydrogenase type 3 (17β-HSD3) deficiency is rarely reported in Chinese patients with 46, XY disorders of sexual development (DSD). Seven subjects with 17β-HSD3 deficiency were identified from 206 Chinese 46, XY DSD patients using targeted next-generation sequencing (NGS). Serum AD and T levels were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS). In silico and functional studies were performed to evaluate the enzymatic activity impairment of HSD17B3 variants. A minigene assay was performed in an exonic splicing variant. Our results showed that four novel and five reported HSD17B3 variants were identified in 7 unrelated patients. The patients showed cryptic presentation during childhood and classical virilization after puberty with T/AD ratio< 0.4. A heterozygous large deletion from the 5'UTR to exon 1 was identified in a patient with a monoallelic variant of p.N130S. Although predicted to be 'likely pathogenic', only p. S232P and p. S160F drastically reduced the enzymatic activity of 17β-HSD3. A previously reported 'missense' variant c 0.277 G>A (p. E93K) was revealed to have no impact on enzyme activity but resulted in aberrant splicing of exon 3 and was reclassified as an exonic splicing variant. In our study, one nonsense, one exonic splicing, one deletion, one large deletion and five missense variants were detected in patients with 17β-HSD3 deficiency, expanding the clinical and molecular profile of this disorder. In silico analysis should be cautiously interpreted when the heredity pattern and functional study are inconsistent.

Disorder of Sex Development Due to 17-Beta-Hydroxysteroid Dehydrogenase Type 3 Deficiency: A Case Report and Review of 70 Different HSD17B3 Mutations Reported in 239 Patients

The 17-beta-hydroxysteroid dehydrogenase type 3 (17-β-HSD3) enzyme converts androstenedione to testosterone and is encoded by the HSD17B3 gene. Homozygous or compound heterozygous HSD17B3 mutations block the synthesis of testosterone in the fetal testis, resulting in a Disorder of Sex Development (DSD). We describe a child raised as a female in whom the discovery of testes in the inguinal canals led to a genetic study by whole exome sequencing (WES) and to the identification of a compound heterozygous mutation of the HSD17B3 gene (c.608C>T, p.Ala203Val, and c.645A>T, p.Glu215Asp). Furthermore, we review all HSD17B3 mutations published so far in cases of 17-β-HSD3 deficiency. A total of 70 different HSD17B3 mutations have so far been reported in 239 patients from 187 families. A total of 118 families had homozygous mutations, 63 had compound heterozygous mutations and six had undetermined genotypes. Mutations occurred in all 11 exons and were missense (55%), splice-site (29%), small deletions and insertions (7%), nonsense (5%), and multiple exon deletions and duplications (2%). Several mutations were recurrent and missense mutations at codon 80 and the splice-site mutation c.277+4A>T each represented 17% of all mutated alleles. These findings may be useful to those involved in the clinical management and genetic diagnosis of this disorder.

Novel Genomic Variants, Atypical Phenotypes and Evidence of a Digenic/Oligogenic Contribution to Disorders/Differences of Sex Development in a Large North African Cohort

In a majority of individuals with disorders/differences of sex development (DSD) a genetic etiology is often elusive. However, new genes causing DSD are routinely reported and using the unbiased genomic approaches, such as whole exome sequencing (WES) should result in an increased diagnostic yield. Here, we performed WES on a large cohort of 125 individuals all of Algerian origin, who presented with a wide range of DSD phenotypes. The study excluded individuals with congenital adrenal hypoplasia (CAH) or chromosomal DSD. Parental consanguinity was reported in 36% of individuals. The genetic etiology was established in 49.6% (62/125) individuals of the total cohort, which includes 42.2% (35/83) of 46, XY non-syndromic DSD and 69.2% (27/39) of 46, XY syndromic DSD. No pathogenic variants were identified in the 46, XX DSD cases (0/3). Variants in the AR, HSD17B3, NR5A1 and SRD5A2 genes were the most common causes of DSD. Other variants were identified in genes associated with congenital hypogonadotropic hypogonadism (CHH), including the CHD7 and PROKR2. Previously unreported pathogenic/likely pathogenic variants (n = 30) involving 25 different genes were identified in 22.4% of the cohort. Remarkably 11.5% of the 46, XY DSD group carried variants classified as pathogenic/likely pathogenic variant in more than one gene known to cause DSD. The data indicates that variants in PLXNA3, a candidate CHH gene, is unlikely to be involved in CHH. The data also suggest that NR2F2 variants may cause 46, XY DSD.

A novel variant luteinizing hormone receptor in the first transmembrane helix of two homozygous Iranian patients: case report

Background

Leydig cell hypoplasia (LCH) is a rare autosomal recessive endocrine syndrome that affects the normal development of male external genitalia in 46, XY individuals and is one of the causes of disorder of sexual differentiation (DSD) in males. The responsible gene of LCH is LHCGR which is located on the chromosome 2 and its various mutations lead to different degrees of the disease ranging from micropenis to complete XY DSD.

Case presentation

In this study, we have investigated the clinical presentation and molecular findings of two siblings with complete male LCH and XY DSD. This is the first detailed report of individuals with LCH from Iran. It aimed to study the molecular and clinical characteristics of two sisters with type 1 LCH. Whole exome sequencing was used for these patients to find the underlying genetic cause of the disease. Our Iranian DSD patients had external genitalia (normal labia major and minor, the external opening of the urethra beneath the clitoris) and bilateral testicular tissues in the inguinal region, which were removed by surgical exploration.

Conclusions

Genetic sequencing showed the homozygous variants of the LHCGR gene in the patients, a novel duplication variant in exon 11, c.1091dupT -or pLeu365Profs*5. This mutation is described as likely pathogenic. We think that this case report can widen the genotypic spectrum of the LHCGR variants. Moreover, this study emphasizes the significant rule of Whole Exome Sequencing in differentiating various causes of disorder of sexual differentiation.

A rare cause of primary amenorrhea: LHCGR gene mutations

INTRODUCTION

The luteinizing hormone/choriogonadotropin receptor (LHCGR) plays a critical role in sexual differentiation and reproductive functions in men and women. Inactivating mutations in this gene lead to Leydig cell hypoplasia (LCH), and cause disorders of sex development (DSD) in patients with 46,XY. In this study, it was aimed to discuss the clinical, laboratory and molecular genetic analysis results of nine patients with 46,XY karyotype who had mutations in the LHCGR gene.

MATERIALS AND METHODS

The ages, complaints, anthropometric measurements and hormonal results (follicle stimulating hormone (FSH), luteinizing hormone (LH), testosterone) of the patients at the time of admission were recorded retrospectively from their medical records. The mutations in the LHCGR gene were investigated using the Sanger sequencing method.

FINDINGS

In this study, LHCGR gene mutations were detected in a total of nine patients as a result of the analysis of the index patients presenting with primary amenorrhea from four different families and the examination of the families. In the first three families with no consanguinity between, the same mutation was detected in seven patients in total (Homozygous c.161 + 4A > G). A different mutation was detected in the fourth family (Homozygous p.A483D c.1448C > A).

CONCLUSION

In this study, nine patients with karyotype 46,XY, most of whom presented with the complaint of delayed puberty/primary amenorrhea, were diagnosed with LCH. Especially in patients, in whom the elevation of LH is pronounced and there is no testosterone synthesis, LCH should be considered.

Disorders of Sex Development in a Large Ukrainian Cohort: Clinical Diversity and Genetic Findings

BACKGROUND

The clinical profile and genetics of individuals with Disorders/Differences of Sex Development (DSD) has not been reported in Ukraine.

MATERIALS AND METHODS

We established the Ukrainian DSD Register and identified 682 DSD patients. This cohort includes, 357 patients (52.3% [303 patients with Turner syndrome)] with sex chromosome DSD, 119 (17.5%) with 46,XY DSD and 206 (30.2%) with 46,XX DSD. Patients with sex chromosome DSD and congenital adrenal hyperplasia (CAH, n=185) were excluded from further studies. Fluorescence in situ hybridization (FISH) was performed for eight 46,XX boys. 79 patients underwent Whole Exome Sequencing (WES).

RESULTS

The majority of patients with 46,XY and 46,XX DSD (n=140), were raised as female (56.3% and 61.9% respectively). WES (n=79) identified pathogenic (P) or likely pathogenic (LP) variants in 43% of the cohort. P/LP variants were identified in the androgen receptor (AR) and NR5A1 genes (20.2%). Variants in other DSD genes including AMHR2, HSD17B3, MYRF, ANOS1, FGFR11, WT1, DHX37, SRD5A1, GATA4, TBCE, CACNA1A and GLI2 were identified in 22.8% of cases. 83.3% of all P/LP variants are novel. 35.3% of patients with a genetic diagnosis had an atypical clinical presentation. A known pathogenic variant in WDR11, which was reported to cause congenital hypogonadotropic hypogonadism (CHH), was identified in individuals with primary hypogonadism.

CONCLUSIONS

WES is a powerful tool to identify novel causal variants in patients with DSD, including a significant minority that have an atypical clinical presentation. Our data suggest that heterozygous variants in the WDR11 gene are unlikely to cause of CHH.

Generation and mutational analysis of a transgenic mouse model of human SRY

SRY is the Y-chromosomal gene that determines male sex development in humans and most other mammals. After three decades of study, we still lack a detailed understanding of which domains of the SRY protein are required to engage the pathway of gene activity leading to testis development. Some insight has been gained from the study of genetic variations underlying differences/disorders of sex determination (DSD), but the lack of a system of experimentally generating SRY mutations and studying their consequences in vivo has limited progress in the field. To address this issue, we generated a mouse model carrying a human SRY transgene able to drive testis determination in XX mice. Using CRISPR-Cas9 gene editing, we generated novel genetic modifications in each of SRY's three domains (N-terminal, HMG box, and C-terminal) and performed a detailed analysis of their molecular and cellular effects on embryonic testis development. Our results provide new functional insights unique to human SRY and present a versatile and powerful system in which to functionally analyze variations of SRY including known and novel pathogenic variants found in DSD.

Genetics of human sexual development and related disorders

PURPOSE OF REVIEW

The aim of this study was to provide a basic overview on human sex development with a focus on involved genes and pathways, and also to discuss recent advances in the molecular diagnostic approaches applied to clinical workup of individuals with a difference/disorder of sex development (DSD).

RECENT FINDINGS

Rapid developments in genetic technologies and bioinformatics analyses have helped to identify novel genes and genomic pathways associated with sex development, and have improved diagnostic algorithms to integrate clinical, hormonal and genetic data. Recently, massive parallel sequencing approaches revealed that the phenotype of some DSDs might be only explained by oligogenic inheritance.

SUMMARY

Typical sex development relies on very complex biological events, which involve specific interactions of a large number of genes and pathways in a defined spatiotemporal sequence. Any perturbation in these genetic and hormonal processes may result in atypical sex development leading to a wide range of DSDs in humans. Despite the huge progress in the understanding of molecular mechanisms underlying DSDs in recent years, in less than 50% of DSD individuals, the genetic cause is currently solved at the molecular level.

Towards improved genetic diagnosis of human differences of sex development

Despite being collectively among the most frequent congenital developmental conditions worldwide, differences of sex development (DSD) lack recognition and research funding. As a result, what constitutes optimal management remains uncertain. Identification of the individual conditions under the DSD umbrella is challenging and molecular genetic diagnosis is frequently not achieved, which has psychosocial and health-related repercussions for patients and their families. New genomic approaches have the potential to resolve this impasse through better detection of protein-coding variants and ascertainment of under-recognized aetiology, such as mosaic, structural, non-coding or epigenetic variants. Ultimately, it is hoped that better outcomes data, improved understanding of the molecular causes and greater public awareness will bring an end to the stigma often associated with DSD.

A large cohort of disorders of sex development and their genetic characteristics: 6 novel mutations in known genes

INTRODUCTION

Disorders of sex development (DSD) constitutes a group of congenital conditions that affect urogenital differentiation and are associated with chromosomal, gonadal and phenotypic sex abnormalities.

OBJECTIVE

To evaluate the clinical and genetic features of childhood DSD cases.

MATERIALS AND METHODS

DSD patients followed up between the years of 2002-2018 were evaluated in terms of their complaints, demographic, clinical features and genetic diagnoses.

RESULTS

Out of 289 patients, 143(49.5%) were classified as 46XY DSD, 62(21.5%) as 46XX DSD and 84(29%) as sex chromosomal DSD. Genetic diagnosis was achieved in 150 patients (51.9%). The distribution of the molecular diagnosis of the 46XY DSD patients were; 12 (26.6%) SRD5A2, 10 (22.2%) AR, 7 (15.5%) HSD17B3, 3 (6.6%) WT-1, 2 (4.4%) AMHR2, 2 (4.4%) AMH, 2 (4.4%) LHCGR, 2 (4.4%) HSD3B2, 1 (2.2%) NR5A1, 1 (2.2%) CYP17A1 and 1 (2.2%) SRY mutation. Fifty (80.6%) of the 46XX DSD patients received a diagnosis with clinical and laboratory findings. Twenty-four (38.7%) of them were 21-hydroxylase deficiency, 9(14.5%) Rokitansky-Küster-Hauser Syndrome, 4 (6.5%) 11-β hydroxylase deficiency, 3 (4.8%) gonadal dysgenesis and 2 (3.2%) aromatase deficiency. In 46XX group pathogenic mutations were detected in 21(33.8%) of the patients. Eighty-four (29%) patients were diagnosed as sex chromosomal disorder. Of these 66 (78.5%) were Turner Syndrome, 6 (7.2%) Klinefelter Syndrome and 10 (11.9%) mix gonadal dysgenesis. Gender re-assignment was decided in 11 patients. Malignant and pre-invasive lesions was diagnosed in 8 (2.7%) patients.

CONCLUSION

Many of DSD's are clinically similar and etiology of numerous of them still cannot be established. A multi-disciplinary approach and new rapid genetic diagnostic methods are needed in the process from diagnosis to gender assignment and follow-up.

Prevalence of gene mutations in a Chinese 46,XY disorders of sex development cohort detected by targeted next-generation sequencing

46,XY disorders of sex development (DSD) is characterized by incomplete masculinization genitalia, with gonadal dysplasia and with/without the presence of Müllerian structures. At least 30 genes related to 46,XY DSD have been found. However, the clinical phenotypes of patients with different gene mutations overlap, and accurate diagnosis relies on gene sequencing technology. Therefore, this study aims to determine the prevalence of pathogenic mutations in a Chinese cohort with 46,XY DSD by the targeted next-generation sequencing (NGS) technology. Eighty-seven 46,XY DSD patients were enrolled from the Peking Union Medical College Hospital (Beijing, China). A total of fifty-four rare variants were identified in 60 patients with 46,XY DSD. The incidence of these rare variants was approximately 69.0% (60/87). Twenty-five novel variants and 29 reported variants were identified. Based on the American College of Medical Genetics and Genomics (ACMG) guidelines, thirty-three variants were classified as pathogenic or likely pathogenic variants and 21 variants were assessed as variants of uncertain significance. The overall diagnostic rate was about 42.5% based on the pathogenic and likely pathogenic variants. Androgen receptor (AR), steroid 5-alpha-reductase 2 (SRD5A2) and nuclear receptor subfamily 5 Group A member 1 (NR5A1) gene variants were identified in 21, 13 and 13 patients, respectively. The incidence of these three gene variants was about 78.3% (47/60) in patients with rare variants. It is concluded that targeted NGS is an effective method to detect pathogenic mutations in 46,XY DSD patients and AR, SRD5A2, and NR5A1 genes were the most common pathogenic genes in our cohort.

High Molecular Diagnosis Rate in Undermasculinized Males with Differences in Sex Development Using a Stepwise Approach

Differences of sex development (DSDs) are a constellation of conditions that result in genital ambiguity or complete sex reversal. Although determining the underlying genetic variants can affect clinical management, fewer than half of undermasculinized males ever receive molecular diagnoses. Next-generation sequencing (NGS) technology has improved diagnostic capabilities in several other diseases, and a few small studies suggest that it may improve molecular diagnostic capabilities in DSDs. However, the overall diagnostic rate that can be achieved with NGS for larger groups of patients with DSDs remains unknown. In this study, we aimed to implement a tiered approach to genetic testing in undermasculinized males seen in an interdisciplinary DSD clinic to increase the molecular diagnosis rate in this group. We determined the diagnosis rate in patients undergoing all clinically available testing. Patients underwent a stepwise approach to testing beginning with a karyotype and progressing through individual gene testing, microarray, panel testing, and then to whole-exome sequencing (WES) if no molecular cause was found. Deletion/duplication studies were also done if deletions were suspected. Sixty undermasculinized male participants were seen in an interdisciplinary DSD clinic from 2008 to 2016. Overall, 37/60 (62%) of patients with Y chromosomes and 46% of those who were 46XY received molecular diagnoses. Of the 46,XY patients who underwent all available genetic testing, 18/28 (64%) achieved molecular diagnoses. This study suggests that the addition of WES testing can result in a higher rate of molecular diagnoses compared to genetic panel testing.

A clinical algorithm to diagnose differences of sex development

The diagnosis and management of children born with ambiguous genitalia is challenging for clinicians. Such differences of sex development (DSDs) are congenital conditions in which chromosomal, gonadal, or anatomical sex is atypical. The aetiology of DSDs is very heterogenous and a precise diagnosis is essential for management of genetic, endocrine, surgical, reproductive, and psychosocial issues. In this Review, we outline a step-by-step approach, compiled in a diagnostic algorithm, for the clinical assessment and molecular diagnosis of a patient with ambiguity of the external genitalia on initial presentation. We appraise established and emerging technologies and their effect on diagnosis, and discuss current controversies.

Update on the genetics of differences of sex development (DSD)

Human gonadal development is regulated by the temporospatial expression of many different genes with critical dosage effects. Subsequent sex steroid hormone production requires several consecutive enzymatic steps and functional hormone receptors. Disruption of this complex process can result in atypical sex development and lead to conditions referred to as differences (disorders) of sex development (DSD). With the advent of massively parallel sequencing technologies, in silico protein modeling and innovative tools for the generation of animal models, new genes and pathways have been implicated in the pathogenesis of these conditions. Here, we provide an overview of the currently known DSD genes and mechanisms involved in the process of gonadal and phenotypical sex development and highlight phenotypic findings that may trigger further diagnostic investigations.

Germ cell neoplasia in situ complicating 17β-hydroxysteroid dehydrogenase type 3 deficiency

17β-hydroxysteroid dehydrogenase type 3 (17βHSD3) deficiency is an autosomal recessive disorder of male sex development that results in defective testosterone biosynthesis. Although mutations in the cognate HSD17B3 gene cause a spectrum of phenotypic manifestations, the majority of affected patients are genetic males having female external genitalia. Many cases do not present until puberty, at which time peripheral conversion of androgen precursors causes progressive virilization. Measurement of the testosterone-to-androstenedione ratio is useful to screen for 17βHSD3 deficiency, and genetic analysis can confirm the diagnosis. As some individuals with 17βHSD3 deficiency transition from a female sex assignment to identifying as males, providers should ensure stable gender identity prior to recommending irreversible treatments. Gonadectomy is indicated to prevent further virilization if a female gender identity is established. The risk of testicular neoplasia is unknown, a point which should be discussed if patients elect to transition into a male gender role.

Novel Compound Heterozygous Variants in the LHCGR Gene in a Genetically Male Patient with Female External Genitalia

The LHCGR gene encodes a G-protein coupled receptor that plays a pivotal role in sexual differentiation in males, ovarian development in females and in fertility via its interaction with luteinizing hormone and chorionic gonadotropin. Inactive variants of the LHCGR gene cause Leydig cell hypoplasia (LCH), which is a rare disease and one of the causes of disorder of sexual differentiation (DSD) in males. The aim of this work was to clarify the clinical and molecular characteristics of a 2.75 year old patient with type 1 LCH. Whole exome sequencing was performed for the patient family and variants in the LHCGR gene were validated by Sanger sequencing. Pathogenicity of the missense variant was evaluated by multiple in silico tools. Our Chinese patient, who exhibited DSD, had female external genitalia (normal labia majora and minora, external opening of urethra under the clitoris and blind-ended vagina) and bilateral testis tissues in the inguinal region. Genetic sequencing revealed compound heterozygous variants in the LHCGR gene in the patient, including a novel missense variant in exon 4 (c.349G>A, p.Gly117Arg) and a novel nonsense variant in exon 10 (c.878C>A, p.Ser293*). The missense variant is in the first leucine-rich repeat domain of the LHCGR protein, which is predicted to affect ligand recognition and binding affinity and thus protein function. The patient is molecularly and clinically diagnosed with type 1 LCH, which is caused by novel, compound heterozygous variants of the LHCGR gene. We believe this report will serve to expand the genotypic spectrum of LHCGR variants.

Translating genomics to the clinical diagnosis of disorders/differences of sex development

The medical and psychosocial challenges faced by patients living with Disorders/Differences of Sex Development (DSD) and their families can be alleviated by a rapid and accurate diagnostic process. Clinical diagnosis of DSD is limited by a lack of standardization of anatomical and endocrine phenotyping and genetic testing, as well as poor genotype/phenotype correlation. Historically, DSD genes have been identified through positional cloning of disease-associated variants segregating in families and validation of candidates in animal and in vitro modeling of variant pathogenicity. Owing to the complexity of conditions grouped under DSD, genome-wide scanning methods are better suited for identifying disease causing gene variant(s) and providing a clinical diagnosis. Here, we review a number of established genomic tools (karyotyping, chromosomal microarrays and exome sequencing) used in clinic for DSD diagnosis, as well as emerging genomic technologies such as whole-genome (short-read) sequencing, long-read sequencing, and optical mapping used for novel DSD gene discovery. These, together with gene expression and epigenetic studies can potentiate the clinical diagnosis of DSD diagnostic rates and enhance the outcomes for patients and families.

Novel NR5A1 mutations found in Chinese patients with 46, XY disorders of sex development

OBJECTIVE

To analyze nuclear receptor subfamily 5 group A member 1 (NR5A1) gene mutations in a cohort of Chinese patients with 46, XY Disorders of Sex Development (DSD).

METHODS

Sixty 46, XY DSD patients were recruited at Peking Union Medical College Hospital. Targeted next-generation and Sanger sequencing were performed to investigate pathogenic gene variants and validate NR5A1 gene variants, respectively. In silico tools and in vitro function studies were used to analyze the pathogenicity of rare variants. The clinical and endocrinological characteristics of patients with NR5A1 variants were retrospectively analyzed.

RESULTS

A total of four novel and three recurrent NR5A1 variants were identified in seven 46, XY DSD patients. These variants widely spread almost all the functional domains. Functional studies showed that novel mutations including p.S32N, p.N44del and p.G91D reduced transactivation of CYP11A1, while the other missense variant p.A168E did not impact protein function. All patients with NR5A1 rare variants had normal adrenal function and showed genital defects. Results of the genitalia examination showed female external genitalia (three patients), ambiguous external genitalia (two patients), female external genitalia with clitoromegaly (one patient), and hypospadias (one patient). All seven patients had bilateral testis and five of seven patients lacked Müllerian structures.

CONCLUSIONS

Four novel mutations in the NR5A1 gene were identified in our cohort with 46, XY DSD, expanding the spectrum of NR5A1 gene mutations. All patients with NR5A1 rare variants had normal adrenal function and showed genital defects.

GENETICS IN ENDOCRINOLOGY: Approaches to molecular genetic diagnosis in the management of differences/disorders of sex development (DSD): position paper of EU COST Action BM 1303 ‘DSDnet’

The differential diagnosis of differences or disorders of sex development (DSD) belongs to the most complex fields in medicine. It requires a multidisciplinary team conducting a synoptic and complementary approach consisting of thorough clinical, hormonal and genetic workups. This position paper of EU COST (European Cooperation in Science and Technology) Action BM1303 ‘DSDnet’ was written by leading experts in the field and focuses on current best practice in genetic diagnosis in DSD patients. Ascertainment of the karyotpye defines one of the three major diagnostic DSD subclasses and is therefore the mandatory initial step. Subsequently, further analyses comprise molecular studies of monogenic DSD causes or analysis of copy number variations (CNV) or both. Panels of candidate genes provide rapid and reliable results. Whole exome and genome sequencing (WES and WGS) represent valuable methodological developments that are currently in the transition from basic science to clinical routine service in the field of DSD. However, in addition to covering known DSD candidate genes, WES and WGS help to identify novel genetic causes for DSD. Diagnostic interpretation must be performed with utmost caution and needs careful scientific validation in each DSD case.

New technologies to uncover the molecular basis of disorders of sex development

The elegant developmental biology experiments conducted in the 1940s by French physiologist Alfred Jost demonstrated that the sexual phenotype of a mammalian embryo depended whether the embryonic gonad develops into a testis or not. In humans, anomalies in the processes that regulate development of chromosomal, gonadal or anatomic sex result in a spectrum of conditions termed Disorders/Differences of Sex Development (DSD). Each of these conditions is rare, and understanding of their genetic etiology is still incomplete. Historically, DSD diagnoses have been difficult to establish due to the lack of standardization of anatomical and endocrine phenotyping procedures as well as genetic testing. Yet, a definitive diagnosis is critical for optimal management of the medical and psychosocial challenges associated with DSD conditions. The advent in the clinical realm of next-generation sequencing methods, with constantly decreasing price and turnaround time, has revolutionized the diagnostic process. Here we review the successes and limitations of the genetic methods currently available for DSD diagnosis, including Sanger sequencing, karyotyping, exome sequencing and chromosomal microarrays. While exome sequencing provides higher diagnostic rates, many patients still remain undiagnosed. Newer approaches, such as whole-genome sequencing and whole-genome mapping, along with gene expression studies, have the potential to identify novel DSD-causing genes and significantly increase total diagnostic yield, hopefully shortening the patient's journey to an accurate diagnosis and enhancing health-related quality-of-life outcomes for patients and families.

Prevalence of endocrine and genetic abnormalities in boys evaluated systematically for a disorder of sex development

STUDY QUESTION

What is the likelihood of identifying genetic or endocrine abnormalities in a group of boys with 46, XY who present to a specialist clinic with a suspected disorder of sex development (DSD)?

SUMMARY ANSWER

An endocrine abnormality of the gonadal axis may be present in a quarter of cases and copy number variants (CNVs) or single gene variants may be present in about half of the cases.

WHAT IS KNOWN ALREADY

Evaluation of 46, XY DSD requires a combination of endocrine and genetic tests but the prevalence of these abnormalities in a sufficiently large group of boys presenting to one specialist multidisciplinary service is unclear.

STUDY, DESIGN, SIZE, DURATION

This study was a retrospective review of investigations performed on 122 boys.

PARTICIPANTS/MATERIALS, SETTING, METHODS

All boys who attended the Glasgow DSD clinic, between 2010 and 2015 were included in the study. The median external masculinization score (EMS) of this group was 9 (range 1-11). Details of phenotype, endocrine and genetic investigations were obtained from case records.

MAIN RESULTS AND THE ROLE OF CHANCE

An endocrine abnormality of gonadal function was present in 28 (23%) with a median EMS of 8.3 (1-10.5) whilst the median EMS of boys with normal endocrine investigations was 9 (1.5-11) (P = 0.03). Endocrine abnormalities included a disorder of gonadal development in 19 (16%), LH deficiency in 5 (4%) and a disorder of androgen synthesis in 4 (3%) boys. Of 43 cases who had array-comparative genomic hybridization (array-CGH), CNVs were reported in 13 (30%) with a median EMS of 8.5 (1.5-11). Candidate gene analysis using a limited seven-gene panel in 64 boys identified variants in 9 (14%) with a median EMS of 8 (1-9). Of the 21 boys with a genetic abnormality, 11 (52%) had normal endocrine investigations.

LIMITATIONS, REASONS FOR CAUTION

A selection bias for performing array-CGH in cases with multiple congenital malformations may have led to a high yield of CNVs. It is also possible that the yield of single gene variants may have been higher than reported if the investigators had used a more extended gene panel.

WIDER IMPLICATIONS OF THE FINDINGS

The lack of a clear association between the extent of under-masculinization and presence of endocrine and genetic abnormalities suggests a role for parallel endocrine and genetic investigations in cases of suspected XY DSD.

STUDY FUNDING/COMPETING INTEREST(S)

RN was supported by the James Paterson Bursary and the Glasgow Children's Hospital Charity Summer Scholarship. SFA, RM and EST are supported by a Scottish Executive Health Department grant 74250/1 for the Scottish Genomes Partnership. EST is also supported by MRC/EPSRC Molecular Pathology Node and Wellcome Trust ISSF funding. There are no conflicts of interest.

TRIAL REGISTRATION NUMBER

None.