Prevalence:

• 1 in 100 births in Blacks and 1 in 700 births in Whites.
• More common in males than in females: 2 to 1.

Ultrasound diagnosis:

• More than 5 digits with or without bony phalanx in the hand or foot.
• There are 2 types of polydactyly:
  • Postaxial (more common): sixth digit is on the ulnar or fibular side, after the fifth digit.
  • Preaxial (rare): sixth digit is on the radial or tibial side, before the thumb or toe.

Associated abnormalities:

• Chromosomal abnormalities: found in 75% of fetuses with trisomy 13.
• In most cases it is an isolated finding, with an autosomal dominant mode of inheritance. In some cases there is an association with genetic syndromes:
  • Meckel - Gruber syndrome: autosomal recessive; polydactyly, polycystic kidneys, occipital cephalocele.
  • Bardet - Biedl syndrome: autosomal recessive; postaxial polydactyly, enlarged hyperechogenic kidneys. Postnatally: obesity, retinopathy, hypogonadism, neurological disorders.
  • Short - rib polydactyly syndrome: autosomal recessive; short limbs, hypoplastic thorax, polydactyly, heart  and brain defects, polycystic kidneys.
  • Ellis – van Creveld syndrome: autosomal recessive; short limbs, postaxial polydactyly, narrow chest, heart defects.

Investigations:

• Detailed ultrasound examination.
• Invasive testing and array in non-isolated cases.
• Consultation with clinical geneticist.

Follow up:

• In isolated cases, follow-up should be standard.

Delivery:

• Standard obstetric care and delivery.

Prognosis:

• Isolated cases: good prognosis.

Recurrence:

• Isolated familial: 50%.
• Part of trisomy 13: 1%.
• Part of autosomal recessive syndromes: 25%.