Spondylocostal dysostosis (SCDO), also known as Jarcho-Levin syndrome, is a rare genetic disorder that impacts the normal development of bones in the spine and ribs. This condition affects the axial skeleton, which includes the vertebral column and rib cage.
What is Spondylocostal Dysostosis?
Spondylocostal dysostosis is characterized by abnormalities in the vertebrae and ribs. These malformations are present at birth. The condition involves misshapen and abnormally joined vertebrae, which can lead to scoliosis.
Beyond the spine, some rib bones may be fused together or entirely missing. These rib anomalies, along with the vertebral defects, contribute to a shortened thorax. This constrained space can affect the ability of the lungs to expand, leading to various respiratory challenges.
Genetic Roots of the Condition
The condition can be inherited in different patterns. Most types follow an autosomal recessive inheritance pattern, meaning an individual must inherit two mutated copies of the gene, one from each parent, to develop the condition. Parents who carry one copy of the mutated gene typically do not show signs of the condition themselves. Rarer forms of spondylocostal dysostosis can be inherited in an autosomal dominant pattern, where only one altered gene copy is sufficient to cause the disorder.
Several genes are associated with spondylocostal dysostosis, including DLL3, MESP2, LFNG, HES7, and TBX6. These genes play a role in the Notch signaling pathway, important in embryonic development. Notch signaling directs the separation of future vertebrae and ribs during early development, called somite segmentation. When this pathway is disrupted, proper somite segmentation does not occur, resulting in the malformation and fusion of the spinal and rib bones.
Recognizing the Clinical Features
Individuals with spondylocostal dysostosis often present with a short trunk in proportion to overall height, along with a short and rigid neck. The limbs typically appear to be of relatively normal length.
The malformations of the vertebrae often lead to spinal deformities such as scoliosis and kyphosis (forward rounding of the back). These spinal curvatures can contribute to the shortened appearance of the torso. The abnormalities in the rib cage can reduce the chest cavity’s size.
Respiratory problems are a concern, as the small chest may not adequately expand, potentially causing life-threatening breathing issues in infants. The lungs may push down on abdominal organs, leading to an out-pouching around the lower abdomen, known as an inguinal hernia. Other associated features can include short stature and neural tube defects like spina bifida or Chiari malformation.
Diagnosis and Treatment Approaches
Diagnosing spondylocostal dysostosis involves imaging studies that reveal the characteristic vertebral and rib anomalies. X-rays are the initial diagnostic tool, showing the multiple segmentation defects of the vertebrae, along with rib fusions or reductions in number. Advanced imaging techniques like CT scans and MRI provide more detailed views of the skeletal structures and associated abnormalities.
Genetic testing plays a role in confirming the diagnosis and identifying the specific gene mutation responsible for the condition. This genetic information can be helpful for genetic counseling for families. Treatment approaches are supportive and involve a multidisciplinary team.
Managing respiratory issues is a focus, which may include oxygen therapy or ventilator support for severe breathing difficulties. Orthopedic interventions are necessary for spinal deformities, ranging from bracing to surgical procedures like spinal fusion or the use of vertical expandable prosthetic titanium ribs (VEPTR) to stabilize the spine and expand the chest cavity. Physical therapy also helps improve mobility and lung function.
Prognosis and Long-Term Outlook
The long-term outlook for individuals with spondylocostal dysostosis can vary widely, depending on the severity of the skeletal abnormalities and, importantly, the degree of respiratory compromise. While severe cases, especially those with significant breathing challenges, may have a more difficult prognosis, many individuals can lead fulfilling lives with appropriate medical management.
Early diagnosis is beneficial, allowing for prompt interventions to manage symptoms and complications. Ongoing, specialized care is important to monitor growth, spinal curvature, and respiratory function, and to address any evolving needs. With advancements in medical care, including respiratory support and orthopedic interventions, studies indicate a trend toward improved survival rates into adulthood for affected individuals.