Patau Syndrome, also known as trisomy 13 and trisomy D, is the least common and most severe of the viable autosomal trisomies. Median survival is fewer than 3 days. First identified as a cytogenetic syndrome in 1960, Patau syndrome is caused by an extra copy of chromosome 13, a medium-length acrocentric chromosome.

Patau syndrome is caused by the presence of an extra copy of chromosome 13, generally present at conception and transmitted to every cell in the body. Although the exact mechanisms by which chromosomal trisomies disrupt development are unknown, considerable attention has been paid to trisomy 21 as a model system for the autosomal trisomies.

Normal development requires 2 (and only 2) copies of most of the human autosomal genome; the presence of a third copy of an autosome is generally lethal to the developing embryo. Therefore, trisomy 13 is distinctive in that it is one of only 3 autosomal trisomies for which development can proceed to live birth. In fact, trisomy 13 is the largest autosomal imbalance that can be sustained by the embryo and yet allow survival to term. Complex physiologic structures, such as those found in the CNS and heart, appear to be particularly sensitive to chromosomal imbalance, either through the actions of individual genes or by the destabilization of developmental processes involving many genes in concert.

Patau syndrome is expressed prenatally and is fully evident at birth. A significant number of cases that are trisomic for chromosome 13 end in spontaneous abortion, fetal demise, or stillbirth. The mortality rate is very high among neonates. Children who survive the neonatal period continue to express developmental delays and exhibit a declining developmental quotient over time. This decline does not result from loss of developmental milestones but instead reflects a worsening developmental lag compared with other children. A report on a group of 21 individuals with Patau syndrome (3 mosaic and 18 nonmosaic) who survived past age 5 years showed the oldest to be aged 21 years.

Newborns with Patau syndrome typically present in the neonatal period with low Apgar scores and may have the following conditions:

  • Cleft lip
  • Cleft palate
  • Polydactyly (postaxial)
  • Microcephaly
  • Rocker-bottom feet
  • Microphthalmia
  • Scalp defects (cutis aplasia)
  • Omphalocele
  • Hernias
  • Neural tube defects

Stillbirth and in utero fetal demise are common pregnancy outcomes.

Cardiac defects occur in 80% of cases, accompanied by the following conditions:

  • Patent ductus arteriosus
  • Ventricular septal defect
  • Atrial septal defect
  • Dextrocardia

Holoprosencephaly, in which the brain does not divide completely into halves, is often present and is generally signaled by the presence of midline facial defects. Facial defects include the following:

  • Hypotelorism
  • Microphthalmia
  • Anophthalmia
  • Absent or malformed nose or proboscis
  • Severe clefting of the lip and/or palate
  • The clinical phenotypes of Patau syndrome and Edwards syndrome may seem similar to physicians who do not frequently encounter these syndromes.
  • Capillary hemangiomatas and polycystic kidneys or other renal malformations have been reported.

Median survival age for children with Patau syndrome is 2.5 days, with only one in 20 children surviving longer than 6 months. However, some children survive into their teens and seem to fare better than might be expected based on reports from those who die in the perinatal period. Reports of adults with Patau syndrome are rare.

Holoprosencephaly, a frequent brain malformation associated with Patau syndrome, is associated with severe neurological impairment; development of the structural features of the mid face is disrupted when holoprosencephaly is present. Serious cardiac anomalies are often present. Most common causes of death are cardiopulmonary arrest (69%), congenital heart disease (13%), and pneumonia (4%). Survivors with Patau syndrome exhibit severe mental retardation and developmental delays and are at increased risk for malignancy. Infants who survive the neonatal period have an average length of stay in a neonatal ICU of 10.8 days.

Medical management of children with Trisomy 13 is planned on a case-by-case basis and depends on the individual circumstances of the patient. Treatment of Patau syndrome focuses on the particular physical problems with which each child is born. Many infants have difficulty surviving the first few days or weeks due to severe neurological problems or complex heart defects. Surgery may be necessary to repair heart defects or cleft lip and cleft palate. Physical, occupational, and speech therapy will help individuals with Patau syndrome reach their full developmental potential.

Source: Wikipedia and Medscape