Patau syndrome

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

This along with Down syndrome (T21) and Edward syndrome (T18) are the only three trisomies to be compatible with extra-uterine life. However few infants live more than a few days. 

Epidemiology

The estimated incidence is at ~ 1 : 6000. There can be an increased incidence with advanced maternal age.

Clinical spectrum

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
• intra uterine 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)
  • rockerbottom feet
  • clenched hands + / - overlapping digits
• abdominal wall abnormalities
  • bladder exstrophy
  • omphalocoele
• genitourinary anomalies
  • cryptorchidism
  • cystic renal dysplasia

Pathology

Three forms are known 

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

Risk factors

• increased maternal age

Markers

• reduced maternal serum alpha-feto protein (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 (commoner) or oligohydramnios
• evidence of IUGR : especially early IUGR
• increased nuchal thickness
• evidence of hydrops fetalis
• echogenic bowel ⁶
• echogenic chorda tendinae ⁷

Prognosis

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

Diffenential diagnosis

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