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Patau syndrome

  • Patau syndrome, like Down syndrome, is a trisomy disorder. It is caused by the presence of a whole extra copy (or occasionally partial extra copy) of chromosome 13.
  • Occurrence in live births is about 1 in 9,500 (in the absence of any prenatal detection programme), and rises with increasing maternal age.
  • Patau syndrome is associated with a high rate of spontaneous loss of pregnancy (64% loss rate from 2nd trimester onwards) and very poor chances of survival in neonates (median survival is 10 days).
  • Clinical manifestations involve severe bodily deformities and mental retardation.
  • Prenatal diagnosis and appropriate counselling is available.

Clinical features

  • Most fetuses with Patau syndrome (64% from the 2nd trimester onwards) are miscarried spontaneously.
  • Fetal or congenital malformation is usual, with holoprosencephaly (the failure of the forebrain to develop into two hemispheres), microphthalmia (small eye), cleft lip and palate, and polydactyly (extra digits), each having a 60%-70% chance of occurrence in babies with the condition.
  • Cardiac malformations occur in over 80% of cases.
  • Severe growth, mental retardation and kidney malformations are also associated with the condition.
  • Live birth weight is low, and more than 50% of infants die within one month of birth. Only 8%-10% of patients survive beyond one year, but typically with severe learning disabilities. Long-term survival is most likely due to mosaicism (where the extra chromosome is not present in all cells), or due to only part of chromosome 13 being involved (partial trisomy 13).

Diagnosis

  • Diagnosis can often be made either antenatally from the abnormalities on a 20-week ultrasound scan or postnatally from the presence of the characteristic clinical features, but should always be confirmed by genetic testing.

Genetic basis

  • Patau syndrome, in 75%-90% of cases, is the result of the presence of a whole extra (third) copy of chromosome 13, hence its alternative name of trisomy 13 (or simple trisomy 13).
  • Patau syndrome is caused by a chromosomal translocation in 5%-10% of cases, and to mosaicism (whereby only some cells have the extra copy of chromosome 13) in 5%. In occasional cases, it is only a part of chromosome 13 that is extra (partial trisomy 13).
  • About 90% of cases of simple trisomy 13 are caused by non-disjunction in maternal meiosis, and the likelihood of occurrence rises with increasing maternal age.
  • For parents of a child with simple trisomy 13, the risk of recurrence for trisomy 13 or for the other major chromosomal abnormalities is usually very low (typically 1% unless the maternal age-dependent risk is already above 1%).
  • If one parent is a carrier of a balanced translocation, the risks are higher.

Clinical management

  • Due to the severity of this disorder, clinical management usually focuses on minimising discomfort and enabling feeding in infants.
  • For the small proportion who are longer-term survivors, management is individual according to the child’s needs.

Genetic testing

  • The definitive diagnosis in a newborn is by full karyotyping, although DNA-based techniques such as quantitative fluorescence PCR (QF-PCR) or fluorescent in-situ hybridisation (FISH) may be used simultaneously as an urgent initial way of detecting three copies of chromosome 13 material.
  • During pregnancy, QF-PCR and karyoptyping may be offered from a chorionic villus sample (CVS) or amniocentesis sample where serum screen or maternal age indicate a pregnancy at increased risk, or where there are abnormalities on fetal ultrasound scan.

 

This information is intended for educational use and was current in August 2013. For clinical management, it is recommended that local guidelines and protocols are used.