Spondylothoracic dysostosis
Spondylothoracic dysostosis is a genetic condition characterized by malformations of the spine and ribs that result in a short torso and potential life-threatening breathing difficulties.
Overview
Spondylothoracic dysostosis is a condition characterized by malformation of the bones of the spine and ribs. The bones of the spine (vertebrae) do not develop properly, causing them to be misshapen and abnormally joined together (fused). The ribs are also fused at the part nearest the spine (posteriorly), which gives the rib cage its characteristic fan-like or "crab" appearance in x-rays.
Affected individuals have short, rigid necks and short torsos due to these bone malformations. Consequently, people with this condition have short bodies but normal-length arms and legs, a condition known as short-trunk dwarfism.
Symptoms
The spine and rib abnormalities are present from birth and lead to several health challenges:
- Small chest cavity: The chest cannot expand adequately, often leading to life-threatening breathing problems.
- Abdominal pressure: As lungs expand in the narrow chest, the diaphragm is forced down, pushing the abdomen out.
- Hernias: Increased abdominal pressure can cause soft out-pouchings, such as inguinal or umbilical hernias.
While breathing problems can be fatal early in life, some affected individuals live into adulthood. This condition is sometimes called spondylocostal dysostosis or Jarcho-Levin syndrome, though these are now considered distinct conditions.
Frequency
Spondylothoracic dysostosis affects approximately one in 200,000 people worldwide. It is significantly more common in individuals of Puerto Rican ancestry, affecting about one in 12,000 people.
Causes
The condition is caused by mutations in the MESP2 gene. This gene provides instructions for a protein critical to the development of vertebrae and the separation of vertebrae and ribs during early development, a process called somite segmentation. Mutations prevent the production of this protein or result in a nonfunctional version, leading to the characteristic bone malformations.
Inheritance
Spondylothoracic dysostosis is inherited in an autosomal recessive pattern. This means both copies of the gene in each cell must have mutations for the condition to occur. Parents of an affected individual typically each carry one copy of the mutated gene but do not show signs or symptoms of the condition.