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Uniparental Disomies

UPD

Clinical Features

When both homologous chromosomes or chromosome segments derive from a single parent, this is known as a uniparental disomy (UPD). The corresponding homologous chromosome from the other parent is missing. If the homologous chromosomes are of maternal origin, this is a maternal UPD (UPDmat); if the homologous chromosomes are of paternal origin, this is a paternal UPD (UPDpat).

The clinical features of uniparental disomy may be caused by a change in gene expression (subject to genomic imprinting) or by the homozygote presence of an autosomal recessive predisposition. Genomic imprinting refers to the fact that the expression of some genes is maternally or paternally imprinted, i.e. only one parent's genetic information is expressed. Aberrant chromosomal distribution in germ cell formation or post-zygotic mitosis are the causes of UPD. Carriers of a balanced, reciprocal or Robertsonian translocation have an increased risk of having a child with UPD. Trisomic rescue can make an originally trisomic cell disomic (normal karyotype); UPD is, however, a possible outcome of this process.

 

Examples of UPDs are:

  • maternal UPD 15: Prader-Willi Syndrome *
  • paternal UPD 15: Angelman Syndrome *
  • maternal UPD 7: Silver-Russell Syndrome *
  • paternal segmental UPD 11: Beckwith-Wiedemann Syndrom *
  • Uniparental disomies of chromosomes 2, 6, 14, 16, 20 and 22 can also lead to syndromal clinical features.

 

* please refer to the information on the clinical features of this disease provided by our website

 

Diagnostic

 

Indication

Suspicion of UPD

Method

Microsatellite analysis: the application of polymorphic markers provides information on the parental origin of tested chromosome segments and therefore on the possible existence of an UPD.

The MGC routinely performs testing for uniparental disomies 2, 7, 9, 11, 13, 14, 15, 16, 20 and 22; testing for a uniparental disomy of any other chromosome is available by arrangement.

Sample Requirement

2 - 4 ml of EDTA-blood of patient and parents

Duration

approx. 2 weeks



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