Patau syndrome (trisomy 13)

What it is

Patau syndrome is trisomy 13, the third most common autosomal trisomy. Incidence is about 1:7400 live births, and the karyotype is 47, XX, +13 or 47, XY, +13.

Causes and risk

Most cases are free trisomy 13 (75%). About 20% are trisomy 13 with a Robertsonian translocation. Free trisomy 13 correlates with maternal age.

How it presents

The child has a characteristic facies with microcephaly, microgenia and ear malformations, and severe mental and motor impairment.

• Midline defect and holoprosencephaly
• Aplasia cutis congenita (scalp lesions)
• Microphthalmia (small eyes) and coloboma
• Cleft lip and/or palate
• Postaxial polydactyly and a single transverse palmar crease
• Clenched fist
• Hypotonia
• Hypoplastic or absent ribs, abdominal wall defect
• Capillary hemangioma
• Deafness
• Urogenital malformations, for example polycystic kidney disease, and genital anomalies