Microdeletion syndromes

Sub-microscopic deletion of a part of a chromosome (1-3 million bp) that are too small to see on standard microscopy.

Sometimes involves loss of a few contagious genes (contagious gene syndromes).

Sometimes involves micro duplications.

They can be detected using specific FISH testing, MLPA or CGH microarray.

 Examples of microdeletion syndromes:

• DiGeorge syndrome or velocardiofacial syndrome  – most common microdeletion syndrome.
• Prader–Willi syndrome.
• Angelman syndrome.
• Williams syndrome.
• Miller–Dieker syndrome.
• Smith–Magenis syndrome.
• Rubinstein–Taybi syndrome.
• Wolf–Hirschhorn syndrome.
  

- 47, XYY syndrome.

47, XYY syndrome

Also known as Jacobs syndrome

This affects 1 in 1000 live-born boys.

These males are phenotypically normal but tend to be tall.

But affected boys may have hypotonia, hand trembling or involuntary muscle movements, delayed or difficult speech and delayed motor skill development.

Intelligence is usually within normal limits but there is an increased incidence of behavioral abnormalities.

Treatment:

·       speech therapy for speech delay.

·       occupational therapy: for delayed motor skill development.

·       Educational therapy: for learning disabilities.

- Triple X syndrome (karyotype 47,XXX)

Triple X syndrome (karyotype 47,XXX)

Also called trisomy X

This affects 1 in 1000 live-born girls.

These patients show little phenotypic abnormality mostly hypertelorism and clinodactyly  but tend to be of tall stature.

Although intelligence is typically reduced compared with siblings it usually falls within normal or low–normal limits.

However, mild developmental and behavioral difficulties are more common. Fertility is normal but the incidence of early menopause is increased.

Delayed development of motor skills (such as sitting and walking), hypotonia, and behavioral and emotional difficulties are also possible, but these characteristics vary widely.

Seizures or kidney abnormalities occur in about 10 percent of affected females.

Treatment for triple X syndrome depends on which symptoms, if any, are present and their severity.