Article: XYY syndrome

XYY syndrome is an aneuploidy (specifically a trisomy) of the sex chromosomes in which a human male receives an extra Y chromosome, producing a 47,XYY karyotype.

Some medical geneticists (Allanson & Graham 2002) question whether the term "syndrome" is appropriate for this condition because its phenotype is normal and the vast majority (an estimated 97% in the UK) of 47,XYY males do not know their karyotype.

Effects

Physical traits

Most often, this chromosomal change causes no unusual physical features or medical problems.

47,XYY boys and men are usually taller than average and several centimeters taller than their parents and siblings.

Severe acne was noted in a very few early case reports, but dermatologists specializing in acne (Plewig & Kligman 2000) now doubt the existence of a relationship with 47,XYY.

Testosterone levels (prenatally and postnatally) are normal in 47,XYY males. (Ratcliffe et al. 1994)

Most 47,XYY males have normal sexual development and usually have normal fertility.

Since there are no distinct physical characteristics, the condition usually is only detected during genetic analysis for another reason.

Behavioral characteristics

47,XYY boys have an increased risk of learning difficulties (in up to 50%) and delayed speech and language skills (Allanson & Graham 2002, Beltz 2005, Firth et al. 2005, Gardner & Sutherland 2004, Milunsky 2004, NLM 2006, Nussbaum et al. 2004). For context, surveys report 10% of all boys had a learning disability (NCHS 2006).

As with 47,XXY boys and 47,XXX girls, IQ scores of 47,XYY boys average 10–15 points below their siblings (Firth 2005, Guy's Hospital 2001, Milunsky 2004, Nussbaum 2004). It is important to realize that this amount of variation—an average difference of 12 IQ points—occurs naturally between children in the same family (Guy's Hospital 2001).

In 14 prenatally diagnosed 47,XYY boys from high socioeconomic status families, IQ scores available for 6 boys ranged from 100–147 with a mean of 120. For 11 boys with siblings, in 9 instances their siblings were stronger academically, but in one case they were performing equal to and in another case superior to their brothers and sisters (Linden & Bender 2001).

Developmental delays and behavioral problems are also possible, but these characteristics vary widely among affected boys and men, are not unique to 47,XYY and are managed no differently than in 46,XY males (Milunsky 2004, NLM 2006).

Aggression is not seen more frequently in 47,XYY males (Allanson & Graham 2002, Beltz 2005, Guy's Hospital 2001, Milunsky 2004, Nussbaum et al. 2004). ..

Cause

47,XYY is not inherited, but usually occurs as a random event during the formation of sperm cells. An error in cell division during meiosis II called nondisjunction can result in sperm cells with an extra copy of the Y chromosome. If one of these atypical sperm cells contributes to the genetic makeup of a child, the child will have an extra Y chromosome in each of the body's cells. (NLM 2006, Robinson & Jacobs 1999)

In some cases, the addition of an extra Y chromosome results from nondisjunction during cell division during a post-zygotic mitosis in early embryonic development. This can produce 46,XY/47,XYY mosaics. (NLM 2006, Robinson & Jacobs 1999)

The incidence of 47,XYY is not affected by advanced paternal (or maternal) age. (Allanson & Graham 2002, Firth 2005, Milunsky 2004)

Incidence

About 1 in 1,000 boys are born with a 47,XYY karyotype.

First case

The first published report (Sandberg et al. 1961) of a man with a 47,XYY karyotype was by Dr. Avery A. Sandberg and colleagues at Roswell Park Memorial Institute in Buffalo, New York in 1961. It was an incidental finding in a normal 44-year-old, 6 ft. [183 cm] tall man of average intelligence who was karyotyped because he had a Down syndrome daughter.

See also

• Klinefelter syndrome
• Triple X syndrome
• Turner syndrome
• 48,XXYY syndrome
• The XYY Man

Source

Public domain text from:

• NLM (2006). Genetics Home Reference: 47,XYY syndrome.