Differences of Sex Development (DSD) and Infertility Panel

Infertility is a disorder of the reproductive system defined by the failure to achieve a clinical pregnancy after 12 months or more of regular unprotected sexual intercourse. It affects 10-20% of couples worldwide and is generally attributed to males and females equally. In humans, sexual development and reproductive function occur by the actions of the hypothalamin-pituitary-gonadal axis induced by gonadotropin-releasing hormone (GnRH). Aberrations in this axis can lead to pubertal and reproductive deficiencies. Diagnoses of infertility include hypogonadotropic hypogonadism, hypergonadotropic hypogonadism, and obstructive disorders (Layman. 2002. PubMed ID: 11897813). Patients with hypogonadotropic hypogonadism present with absent or deficient puberty and poorly defined secondary sexual characteristics owing to low serum gonadotrophin, follicle stimulating hormone (FSH), and luteinizing hormone (LH), while infertility in patients with hypergonadotropic hypogonadism is usually caused by gonadal defect (primary amenorrhea and premature ovarian failure in females; oligospermia, azoospermia , or other abnormalities of sperm morphology or motility in males). 46,XX testicular disorder of sex development is also a cause of infertility in phenotypical normal males.

Disorders of sex development (DSD) are congenital conditions with atypical development of chromosomal, gonadal, or anatomic sex (Hughes et al. 2006. PubMed ID: 18947601). This group of disorders are highly heterogeneous and range in severity from hypospadias (1 in 250 boys), ambiguous genitalia (1 in 4,500 live births), to complete XX or XY sex reversal (1 in 20,000 births; Park et al. 2006; Ohnesorg et al. 2014. PubMed ID: 24504012).

Three subtypes of DSD are generally recognized: sex chromosome DSD, 46,XY DSD, and 46,XX DSD. Sex chromosome DSDs include Turner syndrome (45,X), Klinefelter syndrome (47,XXY), mosaic 45,X/46,XY mixed gonadal dysgenesis, and 46,XX/46/XY ovotesticular DSD.

46,XY DSD include complete and partial gonadal dysgenesis (CGD) and result from incomplete intrauterine virilization. It is characterized by a 46,XY karyotype, ambiguous or "female" external genitalia, variable gonadal dysgenesis, hypospadias, azoospermia, and müllerian structures that range from absence to presence of a uterus and fallopian tubes (Mohnach et al. 2016. PubMed ID: 20301714). The main cause is pathogenic variants or deletions of SRY, which have been identified in 15% of individuals with 46,XY CGD.

46,XX DSD relate to excess androgen and are characterized by ambiguous or "male" external genitalia, müllerian aplasia, hyperandrogenism, and primary amenorrhea (Knarston et al. 2016. PubMed ID: 26846580). These include 46,XX testicular and ovotesticular DSD, as well as 46,XX gonadal dysgenesis. Known etiologies include SRY translocation and SOX9 or SOX3 gene CNVs.

Clinical management of DSD is often difficult, and currently only 13% patients receive an accurate clinical genetic diagnosis (Arboleda et al. 2013. PubMed ID: 22435390). An accurate diagnosis is critical to predict the occurrence of life-threatening crises, response to hormone replacement therapy, eventual gender, fertility, and recurrence risk.

It is estimated that genetic abnormalities including both chromosomal and single-gene alterations can account for up to 30% of cases of infertility (Hotaling. 2014. PubMed ID: 24286764). Apart from chromosomal abnormalities, alterations in reproductive function can be caused by gene defects at various levels of the hypothalamin-pituitary-gonadal axis. Mendelian forms may be inherited in an autosomal dominant (AD), autosomal recessive (AR), X-linked (XL), or Y-linked (YL) manner or may arise de novo. At least 35 genes have been shown to cause hypogonadotropic hypogonadism; 14 genes are involved in gonadal failure in females with hypergonadotropic hypogonadism (Layman. 2013. PubMed ID: 23499866). Moreover, single or multiple gene defects in other clinical conditions, such as cryptorchidism, premature ovarian failure, and spermatogenic failure, have also been recently described.

DSD are complex conditions caused by a wide range of genetic anomalies. They can be inherited in an AD, AR, XL, or YL manner or may arise de novo, depending on the gene involved. To date, more than 60 genes have been showed to be involved in DSD (Baxter et al. 2015. PubMed ID: 25383892; Eggers et al. 2016. PubMed ID: 27899157). These genes are implicated in sex determination, sex differentiation, and hypogonadism.

Androgen insensitivity is the most common form of DSD and is caused by a mix of missense, protein-truncating variants, and deletions in the AR gene. Pathogenic variants in the AR gene have been reported in 9.4% (26/278) of 46,XY DSD patients. Beyond the AR gene, pathogenic variants in NR5A1, SRD5A2, ZFPM2, HSD17B3, DHH, MAP3K1, SRY, CYP21A2, SOX9, duplication of NR0B1, and deletion of DMRT1 have also been frequently detected in DSD patients (Baxter et al. 2015. PubMed ID: 25383892; Eggers. et al. 2016. PubMed ID: 27899157).

Sex chromosome aneuploidy, structural abnormality, and copy number variants (CNVs) are common genetic causes of DSD and infertility. Deletions or duplications have been reported in the SOX3, LHCGR, SRY, NR0B1, DMRT1, NR5A1, GATA4, WT1, WNT4, FGFR2, and DPY19L2 genes in patients with DSD and infertility. For this reason, genetic testing to detect large cytogenetic events and CNVs is recommended in the case of a patient with ambiguous genitalia, other suspected disorder of sex development, or infertility. Our CNV detection via analysis of NGS data enables these large cytogenetic abnormalities as well as many exon-level CNVs to be identified.

See individual gene summaries for information about molecular biology of gene products and spectra of pathogenic variants.

This panel analyzes genes involved in syndromic and non-syndromic disorders of sex development (DSD), and male or female infertility. A genetic diagnosis in 35-43% of patients with 46,XY DSD and 17% of patients with 46,XX DSD were due to variants in 64 genes in this panel. Pathogenic variants in 28 genes cause hypogonadotropic hypogonadism in about 40-50% of patients. Pathogenic variants in 14 genes cause gonadal failure in 15% of females with hypergonadotropic hypogonadism (Layman. 2013. PubMed ID: 23499866).

This test is performed using Next-Gen sequencing with additional Sanger sequencing as necessary.

This panel typically provides 99% coverage of all coding exons of the genes plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define coverage as ≥20X NGS reads or Sanger sequencing.

Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).