Sex Chromosome Abnormalities


In human subjects, the sex chromosomes are the X and the Y chromosomes. Normally, a complement of two X chromosomes (46,XX) is seen in females and one X and one Y (46,XY) in males. The X‐chromosome includes about 1500 genes, only a few of which are involved in sex development. The Y‐chromosome contains very few genes, but one gene, SRY, is the most important gene in male sex development. Multiple autosomal genes are also involved in sex development. Abnormalities of sex chromosomes can involve errors in the number of sex chromosomes, such as 45,X0 (Turner syndrome), 47,XXX, 47,XXY (Klinefelter syndrome), 47,XYY or mosaicism. Sex chromosome abnormalities also include aberrations of a single gene of the sex chromosome, leading to a disorder of sex development (DSD). This can result in 46,XX DSD and 46,XY DSD.

Key Concepts

  • Turner syndrome occurs when females have a missing sex chromosome (45,X0) or have a mosaic complement of cells with one or more lines missing a sex chromosome.
  • Girls with Turner syndrome have a variety of congenital anomalies, the most striking being short stature and premature ovarian failure.
  • Klinefelter syndrome boys (47,XXY) have tall stature, marfinoid habitus, and may have difficulty with language development and verbal IQ (intelligent quotient).
  • 46,XY complete gonadal dysgenesis, or Swyer syndrome, describes patients who have both external and internal female organs with a 46,XY chromosome complement.
  • 46,XY disorders of sex development encompass a wide range of disorders including androgen insensitivity, partial gonadal dysgenesis and many more.
  • 46,XX disorders of sex development can result from a multitude of virilising disorders or the presence of Y‐chromosome material.
  • Patients with disorders of sex development and intra‐abdominal gonads may be at risk for gonadoblastoma, depending on their underlying disorder.
  • Assignment of sex, timing of surgery and medical management of patients with disorders of sex development is controversial.

Keywords: Turner syndrome; Klinefelter syndrome; triple X syndrome; the 47,XYY syndrome; 46,XX DSD; 46,XY DSD; gonadal dysgenesis; androgen insensitivity; Swyer syndrome

Figure 1. Sex differentiation pathway.


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Pappas, Kara B, and Migeon, Claude J(Jan 2017) Sex Chromosome Abnormalities. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0005943.pub2]