Spondyloepiphyseal dysplasia tarda (SEDT) is a rare, inherited skeletal disorder affecting the development of bones in the spine and the ends of long bones. The term “spondylo” refers to the vertebrae, while “epiphyseal” relates to the epiphyses, the ends of long bones. A characteristic of SEDT is its delayed onset, as the word “tarda” signifies that symptoms emerge in childhood, around ages four to eight, rather than at birth. The condition impacts the spine and large joints, leading to physical traits and health challenges that progress over time.
Genetic Causes and Inheritance
SEDT is caused by genetic mutations that disrupt the body’s instructions for creating healthy bone and cartilage. The most common form is X-linked, caused by variants in the TRAPPC2 gene located on the X chromosome. Because males have only one X chromosome, they are the ones who primarily develop symptoms of this form. These genetic errors interfere with the normal formation of cartilage and the maturation of the epiphyses, leading to the characteristic bone and joint abnormalities.
Other, rarer forms of SEDT exist. An autosomal dominant version has been linked to mutations in the COL2A1 gene, which provides instructions for making a component of type II collagen. In this inheritance pattern, a single copy of the mutated gene from one parent is sufficient to cause the disorder. There is also an autosomal recessive form, where an individual must inherit a mutated gene from both parents to be affected.
Characteristic Physical Signs
A noticeable physical sign of SEDT is disproportionate short stature that becomes apparent in late childhood. Individuals have a significantly short trunk, which contrasts with limbs of relatively normal length, resulting in an arm span greater than their height. A barrel-shaped chest is another common feature. Final adult height for males with the X-linked form ranges from 137 to 163 cm.
Pain is a predominant symptom, starting in the back, hips, and knees during late childhood or adolescence. The progressive joint issues often lead to the early onset of osteoarthritis, a degenerative joint disease. This can happen as early as a person’s 30s or 40s, particularly affecting the hip joints.
As the condition progresses, other signs may develop, including a waddling gait due to hip problems. Structural changes in the spine can also lead to scoliosis, an abnormal sideways curvature. Despite these skeletal issues, individuals with SEDT have normal intelligence and cognitive development.
The Diagnostic Process
Confirming a diagnosis of SEDT involves a physical evaluation, a review of family history, and specialized imaging. A physician will note characteristic physical signs and take a detailed medical history to identify any patterns of inheritance that might suggest a genetic disorder.
Radiological studies are used to make a definitive diagnosis. X-rays of the spine, pelvis, and limbs reveal specific abnormalities, such as flattened or abnormally shaped vertebrae, a condition known as platyspondyly. X-rays of the hips, shoulders, and knees will show small and irregular epiphyses. These imaging results provide clear evidence of the underlying skeletal development problem.
Genetic testing can finalize the diagnosis by identifying the precise mutation in a gene like TRAPPC2 or COL2A1. This confirmation provides valuable information about the inheritance pattern, which helps in counseling families about risks for other family members and future offspring.
Managing the Condition
Since there is no cure for SEDT, management focuses on alleviating symptoms, maintaining function, and improving quality of life. Treatment involves a combination of non-surgical and surgical approaches to manage pain and preserve joint mobility.
Non-surgical management includes physical therapy to maintain a good range of motion in the joints and strengthen surrounding muscles for better support. Pain management often involves medications to reduce discomfort from chronic pain and arthritis. Mobility aids like canes or walkers may become necessary to assist with walking and reduce stress on the hips and knees.
If joint degeneration becomes severe or spinal deformities progress, surgical interventions may be necessary. Hip replacement surgery is a common procedure, often required at a relatively young age to relieve pain from advanced osteoarthritis. If scoliosis becomes severe, a spinal fusion may be performed to correct the curvature and stabilize the spine. Despite lifelong challenges with chronic pain and degenerative joint disease, individuals with SEDT have a normal lifespan.