XYYYY syndrome, also known as 49,XYYYY, is an exceptionally rare chromosomal disorder in which a male has three additional copies of the

Y chromosome The Y chromosome is one of two sex chromosomes (allosomes) in therian mammals, including humans, and many other animals. The other is the X chromosome. Y is normally the sex-determining chromosome in many species, since it is the presence or abse ...

. Only seven non-

mosaic A mosaic is a pattern or image made of small regular or irregular pieces of colored stone, glass or ceramic, held in place by plaster/mortar, and covering a surface. Mosaics are often used as floor and wall decoration, and were particularly pop ...

cases of the disorder have ever been recorded in the medical literature, as well as five mosaic cases, of which two had more 48,XYYY than 49,XYYYY cells. Due to the extreme rarity of the disorder, little is understood about it, and the

phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...

appears to be variable.

Phenotype

XYYYY syndrome is associated with developmental and skeletal anomalies that are also observed in other sex chromosome

aneuploidies Aneuploidy is the presence of an abnormal number of chromosomes in a cell, for example a human cell having 45 or 47 chromosomes instead of the usual 46. It does not include a difference of one or more complete sets of chromosomes. A cell with any ...

. Findings associated with the karyotype include

hypertelorism Hypertelorism is an abnormally increased distance between two organs or bodily parts, usually referring to an increased distance between the orbits (eyes), or orbital hypertelorism. In this condition the distance between the inner eye corners as ...

(wide-spaced eyes),

low-set ears Low-set ears are a clinical feature in which the ears are positioned lower on the head than usual. They are present in many congenital conditions. Low-set ears are defined as outer ears positioned two or more standard deviations lower than the p ...

radioulnar synostosis Radioulnar synostosis is a rare condition where there is an abnormal connection between the radius and ulna bones of the forearm. This can be present at birth (congenital), when it is a result of a failure of the bones to form separately, or follo ...

(fusion of the long bones in the forearm), and

clinodactyly Clinodactyly is a medical term describing the curvature of a digit (a finger or toe) in the plane of the palm, most commonly the fifth finger (the "little finger") towards the adjacent fourth finger (the "ring finger"). It is a fairly common iso ...

(incurved pinky fingers).

Intellectual disability Intellectual disability (ID), also known as general learning disability in the United Kingdom and formerly mental retardation, Rosa's Law, Pub. L. 111-256124 Stat. 2643(2010). is a generalized neurodevelopmental disorder characterized by signif ...

has been observed in all cases old enough to test and is in the mild to moderate range. Though other Y-chromosome

polysomy Polysomy is a condition found in many species, including fungi, plants, insects, and mammals, in which an organism has at least one more chromosome than normal, i.e., there may be three or more copies of the chromosome rather than the expected t ...

disorders are associated with tall stature, this does not appear to be true in XYYYY syndrome, with recorded heights ranging from the 10th to 97th percentile. Autism and

attention-deficit hyperactivity disorder Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characterised by excessive amounts of inattention, hyperactivity, and impulsivity that are pervasive, impairing in multiple contexts, and otherwise age-inappr ...

are both thought to be associated with the syndrome. External genitalia are normal, but testicular insufficiency appears to develop during childhood and lead to adult azoospermia.

History

Non-mosaic XYYYY syndrome was first recorded in 1981 in a 14-month-old boy, though a mosaic case with mixed 49,XYYYY and

45,X0 Turner syndrome (TS), also known as 45,X, or 45,X0, is a genetic condition in which a female is partially or completely missing an X chromosome. Signs and symptoms vary among those affected. Often, a short and webbed neck, low-set ears, low hair ...

cells had been recorded in 1968. This case was followed up at the age of seven, providing the only known long-term follow-up of the disorder. Only two adults with XYYYY syndrome have been described.

Prevalence

The disorder's prevalence is estimated to be below 1 in 1,000,000.

Notes

References

{{Chromosomal abnormalities Sex chromosome aneuploidies Chromosomal abnormalities Rare genetic syndromes

Phenotype

History

Prevalence

See also

Notes

References