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Global hypotonia, difficulty swallowing, absent deep tendon reflexes, and tongue atrophy, with disease onset within the first 6 months of birth.
44%
1079/2457
Delayed motor milestones, scoliosis, and joint contracture, with disease onset around 6-18 months of age
14%
344/2457
Scoliosis, hand tremors, increased lumbar lordosis, and bilateral Trendelenburg lurch, with disease onset later in life (>18 months of age).
6%
158/2457
Any of the above
30%
735/2457
None of the above
4%
101/2457
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Spinal muscular atrophy (SMA) results from a homozygous deletion in the SMN1 gene on chromosome 5 and loss of the anterior horn cells of the spinal cord. This results in a spectrum of disease. Answers 1-3 describe SMA types 1-3, respectively. While all types lack SMN1 protein, the severity is thought to be inversely proportional to the number of remaining functional copies of the SMN2 gene, which produces a similar protein. The three general categories of disease, highlighted above in the answer choices, are Acute Werdnig-Hoffman (Type 1), Chronic Wernig-Hoffman (Type 2), and Kugelberg-Welander (Type 3) disease. Though later onset is associated with milder disease, all share common characteristics of hypotonia, hyporeflexia, proximal greater than distal muscle weakness, and fasciculations to varying degrees. Diagnosis is clinical, and molecular and genetic testing confirmatory. Mesfin et al. review the pathophysiology and orthopaedic manifestations of SMA. The authors discuss the presentation and management of scoliosis, hip instability, torticollis, flexion contractures of the lower extremities, and osteopenia resulting from immobility. Routine surveillance and multidisciplinary intervention are often necessary. Spinal fusion is often indicated early to address progressive scoliosis, however surgical management of contractures and hip instability remains controversial. Haaker et al. similar review the presentation of SMA and discuss the timing and necessity of orthopaedic intervention. The authors note that while orthopaedic treatment may have only a marginal influence on SMA type 1 due to its severity, timely and appropriate surgical management of manifestations of types II and III can dramatically decelerate disease progression and improve quality of life. Incorrect answers: Answers 1-3: Each is an individual type (1-3) of SMA, therefore all answers are possible with a homozygous SMN1 deletion. Answer 5: Any of the clinical scenarios is a possible manifestation of SMA.
1.8
(15)
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