- 1 in 100 births in Blacks and 1 in 700 births in Whites.
- More common in males than in females: 2 to 1.
- 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.
- 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.
- Detailed ultrasound examination.
- Invasive testing and array in non-isolated cases.
- Consultation with clinical geneticist.
- In isolated cases, follow-up should be standard.
- Standard obstetric care and delivery.
- Isolated cases: good prognosis.
- Isolated familial: 50%.
- Part of trisomy 13: 1%.
- Part of autosomal recessive syndromes: 25%.