Short rib polydactyly syndrome
Important diagnostic landmarks :
- Severe shortening of limbs leads to the group of lethal chondrodysplasia, i.e. a chondrodysplasia with narrow thorax severe enough to induce neonatal respiratory distress. Lethal chondrodysplasias are often discovered in the first or second trimester, and consist of a limited number of disorders.
- Within lethal chondrodysplasias, with a dominant pattern of narrow thorax and short ribs with polydactyly, the most likely diagnosis is Short ribs polydactyly syndrome.
Some important negative signs here are important to rule out other differentials of lethal chondrodysplasias:
- No curved limbs ("telephone handset"), especially femur (thanatophoric dysplasia)
- Normal bone density, no fractures (osteogenesis imperfecta in its early and lethal form).
- No classical widened metaphyses (metatropic dysplasia).
- No stippling of epiphyses (chondrodysplasia punctuata in its lethal form)
- Bones are identifiable here so obviously this is not an achondrogenesis
Note that Short ribs polydactyly syndrome is part of a spectrum of 4 ciliopathies which includes, for example, Ellis-van Creveld (EVC) syndrome and Jeune's asphyxiating thoracic dysplasia.
EVC shows the same pattern of short ribs + short limbs + postaxial polydactyly, and cardiac defects are a common feature. However, shortening of limbs are less severe and the prognosis is not lethal.
Jeune's syndrome shows also the same pattern of short ribs + short limbs, however, there is usually no postaxial polydactyly and no cardiac defect. Prognosis is lethal in most cases.
All syndromes in this spectrum are inherited (non de novo) in an autosomal recessive fashion. This is important for genetic counseling for the next pregnancy.