We searched PubMed for articles in English published between Jan 1, 2010, and Oct 1, 2018, using the MeSH terms “sexual development” and “disorders of sex development”, and the search terms “intersex”, “differences of sex development”, and “ambiguous genitalia”. Preference was given to clinical practice guidelines, international consensus statements, and multicentre studies. Where necessary, groundbreaking highly cited older publications were included. Reference lists within papers from the
ReviewA clinical algorithm to diagnose differences of sex development
Introduction
Sex development of the human embryo is divided into three stages (figure 1). In the indifferent stage (from fertilisation to 6 weeks of gestation), male (XY) and female (XX) embryos are morphologically indistinguishable. During the next stage, sex determination, the bipotential gonads form testes or ovaries. In the XY embryos, testicular development depends on the presence of the Y chromosome gene SRY,1 which initiates a complex cascade of gene expression involving dozens of genes (figure 1, table). In the XX embryo, ovary development is achieved by active repression of genes in the testicular pathway and expression of pro-ovarian genes, through two principal pathways initiated by RSPO1 and FOXL2 (figure 1, table).2, 3 During the third stage, sex differentiation, the gonads produce hormones that differentiate the internal and external genitalia.
Alterations in gonad formation (indifferent stage and sex determination stage) or function (sex differentiation stage) can lead to differences (also referred to as disorders) of sex development (DSDs). DSDs are genetically complex and phenotypes range from hypospadias to completely masculinised or feminised genitalia with a discordant karyotype. Genetic mutations causing DSDs were discovered by genomic analysis of patients with atypical gonads or genitalia, or often randomly discovered in unrelated knockout or transgenic mouse models. For example, serendipitously, the CBX2 knockout mouse showed XY male-to-female sex reversal. However, the complete process of sex determination is not fully understood, and novel causative DSD genes are still being identified.4, 5, 6 DSDs are classified into three subclasses: (1) sex chromosome DSDs, which include Turner syndrome and Klinefelter syndrome, as well as 45,X/46,XY and 46,XX/46,XY individuals who cover a broad phenotypic spectrum; (2) 46,XY DSDs, which comprise disorders of gonadal development, disorders of androgen synthesis and action, persistent Müllerian duct syndrome, and other unclassified disorders; and (3) 46,XX DSDs, which consist of disorders of gonadal development, disorders of androgen excess, and unclassified disorders. Further division is based on the use of clinically descriptive terms, including the molecular basis of the disorder where known (eg, 46,XX testicular SRY-positive; see panel 1 for more examples).7, 8
The diagnosis and management of patients with ambiguous genitalia is challenging for clinicians. The incidence of patients with ambiguous genitalia is one in 4500.9 A study using data from a German registry of rare diseases identified 80 babies born with ambiguous genitalia over a 2-year period and reported a similar incidence (one in 5000).10 Overlapping phenotypes, genetic heterogeneity, psychosocial aspects such as gender assignment, and surgery management turn diagnosis and management into complex problems. Reaching a specific diagnosis is important for individualised management, genetic counselling, and prognostic prediction of fertility and for the risk of tumour development. Ideally, assessment is made by a multidisciplinary team that includes specialists in surgery, urology, endocrinology, psychology, psychiatry, radiology, nursing, and clinical genetics.11 Genetic information for improved DSD diagnosis, reviewed in detail elsewhere12, 13, 14, 15, 16 and summarised by the Sex Development: Genetics and Biology initiative, has changed the diagnostic approach toward DSD patients. In the past 4 years, five diagnostic algorithms have been published, mainly clinical in scope17, 18 or focused on molecular aspects.14, 19, 20
The purpose of this Review is to guide specialists involved in multidisciplinary teams who encounter newborn babies with a DSD. Even though most centres have access to a targeted DSD gene panel, not all do,21, 22, 23 and our aim is to provide a diagnostic algorithm that can be used worldwide. The Review takes a holistic approach by integrating traditional clinical practices, such as physical examination, biochemical analysis, imaging evaluation, and biopsy and laparoscopy, with molecular diagnosis and new and emerging technologies, such as whole exome sequencing and next-generation genome mapping. We divide the evaluation of a patient with ambiguous genitalia into three stages: initial assessment, follow-up, and application of emerging technologies. The novel algorithm we have devised follows this structure (figure 2). The initial assessment includes family history, physical examination, and evaluation of internal structures (figure 2) to identify what further studies are required.
Section snippets
Initial assessment
The first assessment of a neonate with a suspected DSD can be challenging. In many cases, the genital ambiguity is obvious. However, mild forms of DSD might present with less severe clinical manifestations that challenge the decision to regard the patient as having a DSD. An apparently female newborn with clitoromegaly and posterior labial fusion or an inguinal hernia requires assessment for DSDs. An apparently male newborn should be investigated if bilateral cryptorchidism, hypospadias
Follow-up assessment
Depending on the results of the initial assessment, many options for follow-up assessment can be considered at this stage. These include hormonal studies, endoscopy and laparoscopy, biopsy and histology, and molecular genetics (figure 2).
Emerging technologies
Genomic testing is becoming a priority for diagnosing DSDs and is recommended by the DSD-Translational Research Network (figure 2).113 DSDs are complex and heterogenous, so next-generation sequencing can be an efficient tool in the clinical diagnosis and discovery of novel causative gene variants. This technology enables massive parallel sequencing of multiple genes.70 Whole exome sequencing is the sequencing of the protein-coding portions of genes, whereas whole genome sequencing is the
Controversies
Although there has been considerable progress in the understanding of DSDs, there is no uniform vision in important topics such as sex assignment and surgery. Even the term DSD has been problematic, and using the word differences is preferred over disorders when talking about sex development.
Conclusions
DSDs are genetically heterogeneous and careful assessment by multidisciplinary teams is essential to accurately diagnose them. Molecular technologies can help to clarify the aetiology and facilitate the diagnosis of DSDs. However, many forms of DSD continue to be undiagnosed. It is essential that clinicians have a clear decision making path for the evaluation of patients with DSDs. The vast clinical variability in these disorders requires that each patient receives individualised management and
Search strategies and selection criteria
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Contributed equally