Spondylothoracic dysostosis

Alternate names

Spondylothoracic dysplasia; Jarcho-Levin syndrome

Definition

Spondylothoracic dysostosis (STD) is a rare condition that affects the bones of the spine and the ribs. The term “Jarcho-Levin syndrome” in many cases is used as a synonym for STD, and sometimes as a synonym for another condition known as spondylocostal dysostosis, which has several common features with STD. Also, the term “Jarcho-Levin syndrome” is often used for all radiologic features that include defects of the vertebrae and abnormal rib alignment.

Epidemiology

Spondylothoracic dysostosis affects about one in 200,000 people worldwide. However, it is much more common in people of Puerto Rican ancestry, affecting approximately one in 12,000 people.

Cause

The MESP2 gene provides instructions for a protein that plays a critical role in the development of vertebrae. Specifically, it is involved in separating vertebrae and ribs from one another during early development, a process called somite segmentation.

Gene mutation

Mutations in the MESP2 gene prevent the production of any protein or lead to the production of an abnormally short, nonfunctional protein. When the MESP2 protein is nonfunctional or absent, somite segmentation does not occur properly, which results in malformation and fusion of the bones of the spine and ribs seen in spondylothoracic dysostosis.

Inheritance

Autosomal recessive inheritance, a 25% chance

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Signs and symptoms

• Signs and symptoms of spondylothoracic dysostosis include spine and vertebral abnormalities, which result in a shortened spine, neck, and trunk, as well as rib anomalies including fused ribs. This combination of features result in a "crab-like" appearance to the rib cage. Although the neck and midsection of individuals with spondylothoracic dysostosis are shortened, the arms and legs grow normally. As such, individuals with spondylothoracic dysostosis have short stature and are said to have short-trunk dwarfism.
• The spine and rib abnormalities may cause other complications. Infants with this condition are born with a small chest that cannot expand appropriately. This often leads to life-threatening breathing problems. As the lungs expand, the narrow chest forces the muscle that separates the abdomen from the chest cavity (the diaphragm) down and the abdomen is pushed out. The increased pressure in the abdomen can cause a soft out-pouching around the lower abdomen (inguinal hernia) or belly-button (umbilical hernia).
• Most individuals with spondylothoracic dysostosis have normal intelligence and neurological problems are infrequent.
• Symptom severity may vary from patient to patient with spondylothoracic dysostosis; however, symptoms tend to be the worse for individuals who carry two E230X mutations in the MESP2 gene.

Diagnosis

• The diagnosis of SCDO is based on radiographic features. All vertebral segments show at least some disruption to form and shape.[1].
• SCDO2, caused by pathogenic variants in MESP2.
• The diagnosis of AR SCDO is established in a proband with the above radiographic features and identification of biallelic pathogenic variants in one of the genes listed in Table 1 on molecular genetic testing.
• The bones of the spine (vertebrae) do not develop properly, which causes 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.

Treatment

• There is no cure for spondylothoracic dysostosis. Treatment usually consists of intensive medical care, including early and aggressive treatment of respiratory infections, physical therapy, bone surgery, and orthopedic treatment.
• Surgery may then be needed for chest wall or spine deformities, such as severe scoliosis. An external bracing, for example, by use of an expandable prosthetic titanium rib may be used for some cases.

NIH genetic and rare disease info

• NIH info on Spondylothoracic dysostosis

Spondylothoracic dysostosis is a rare disease.

Spondylothoracic dysostosis Resources
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