Clinical Report: Type IV Spinal Muscular Atrophy with Gastrocnemius Pseudohypertrophy

Overview

This report presents a case of Type IV spinal muscular atrophy (SMA) caused by SMN1 gene deletion, characterized by gastrocnemius pseudohypertrophy. The findings highlight the importance of accurate diagnosis and genetic counseling in adult-onset SMA cases, including the role of the SMN2 gene in disease progression.

Background

Spinal muscular atrophy (SMA) is a rare genetic neuromuscular disorder primarily affecting infants and children, but Type IV SMA can present in adults, often leading to misdiagnosis. Accurate identification of SMA is crucial for appropriate management and genetic counseling, particularly in cases with atypical presentations such as gastrocnemius pseudohypertrophy. The incidence of SMA ranges from 1 in 10,000 to 1 in 6,000, with a carrier frequency of 1 in 70 to 1 in 40.

Data Highlights

No numerical data or trial data presented in the article, indicating a need for further research.

Key Findings

• The patient, a 51-year-old male, exhibited progressive weakness in all four limbs over 16 years, initially presenting with lower limb weakness.
• Initial misdiagnosis included cervical spondylotic myelopathy and muscular dystrophy.
• Whole-exome sequencing confirmed a homozygous deletion of the SMN1 gene.
• The patient presented with gastrocnemius muscle pseudohypertrophy, a rare manifestation of Type IV SMA.
• Despite recommendations for disease-modifying therapy, the patient refused treatment.

Clinical Implications

Clinicians should consider SMA in adults presenting with unexplained muscle weakness and atypical features such as pseudohypertrophy. Genetic testing for SMN1 deletions is essential for accurate diagnosis and management, emphasizing the need for early intervention.

Conclusion

This case underscores the need for heightened awareness of Type IV SMA and the importance of genetic counseling in adult patients with neuromuscular symptoms, particularly those with atypical presentations.

References

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