Patau syndrome

Patau syndrome (also known as trisomy 13) is considered the 3^rd commonest autosomal trisomy.

Patau syndrome along with Down syndrome (trisomy 21) and Edward syndrome (trisomy 18) are the only three trisomies to be compatible with extrauterine life. However, few infants live more than a few days. 

Epidemiology

The estimated incidence is approximately 1:6,000. There may be an increased incidence with advanced maternal age.

Clinical presentation

Described features are protean and include

• congenital heart disease: 50-80%
  • hypoplastic left heart syndrome (HLHS)
  • ventricular septal defect (VSD)
• central nervous system/head and neck abnormalities: 70%
  • holoprosencephaly: most well known associated CNS anomaly: ~40-50% ⁹
  • microcephaly
  • fetal hydrocephalus
  • enlarged cisterna magna
  • agenesis of the corpus callosum
  • persistent stapedial artery ⁵
  • retinal dysplasia ³ 
• spinal anomalies
  • spina bifida
• intrauterine growth restriction (IUGR): tends to be early
• abnormal facies: 90%, strong marker
  • cleft lip +/- palate: ~45% ⁹
  • microphthalmia: rarely anophthalmia ¹⁰
  • micrognathia ⁶
  • hypotelorism
  • hypertelorism
  • cyclopia
  • proboscis
• skeletal abnormalities
  • polydactyly: 70% (tends to be post-axial)
  • rocker bottom feet
  • clenched hands +/- overlapping digits
• abdominal wall abnormalities
  • bladder exstrophy
  • omphalocele
• genitourinary anomalies
  • cryptorchidism
  • cystic renal dysplasia

Pathology

Three forms are known 

• free trisomy 13: classical form
• translocation trisomy 13
• mosaic trisomy 13

Markers

• reduced maternal serum alpha fetoprotein (MSAFP)
• reduced maternal beta HCG
• reduced PAPP-A

Associations

• single umbilical artery

Radiographic features

Antenatal ultrasound

Many of the individual clinical features listed above may be seen on ultrasound. Other general features include:

• abnormal liquor volumes: either polyhydramnios (more common) or oligohydramnios
• evidence of IUGR: especially early
• increased nuchal thickness
• evidence of hydrops fetalis
• echogenic bowel ⁶
• echogenic chorda tendinae ⁷

Treatment and prognosis

The syndrome carries a poor prognosis with most individuals not surviving beyond in utero or soon after birth. Management is mainly supportive.

Differential diagnosis

Clinically, individuals with Meckel-Gruber syndrome may carry some features similar to that of trisomy 13.