Some patients with spinal muscular atrophy (SMA) may present with characteristics that are not associated with the neuromuscular manifestations of the disease, as demonstrated by a case study published in BMC Neurology. This can complicate the diagnosis and treatment of the disease.
This case could help clinicians take advantage of the diagnostic experience of the study authors in complicated cases of SMA.
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The case presented here is that of a 7-month-old boy who was referred to the rehabilitation and neurology department. He displayed motor regression at 5 months of age accompanied by callosal hypoplasia, a small penis, and small testes.
Upon physical examination, his deep tendon reflexes were absent and he had proximal weakness and significant hypotonia. Nerve conduction studies showed some features of motor neuron disease.
He was also tested genetically and found to have a homozygous deletion in exon 7 of the SMN1 gene. No other pathogenic variants that could be linked to the malformations were identified.
Based on these findings, the patient was diagnosed with SMA.
He was treated with nusinersen for almost 2 years, and after the seventh injection, he was able to sit unaided, which he was unable to do before treatment. His condition continued to improve, and the researchers reported no adverse events or signs of hydrocephalus.
SMA is a rare genetic disease caused by a homozygous mutation in the SMN1 gene, which is the main gene from which SMN protein is produced. SMN is essential for the survival of motor neurons, and its deficiency leads to SMA. Humans have a second homologous gene called SMN2 from which some functional SMN protein can also be made. The copy number of the SMN2 gene is inversely correlated with the severity of the disease.
SMA can cause complications affecting the musculoskeletal system, dysphagia, heart failure, and metabolic and nutritional problems.
Hypoplasia of the corpus callosum is an abnormality in which the corpus callosum, the major junction between the 2 hemispheres of the brain, is underdeveloped or thin. Callosal hypoplasia has rarely been reported in association with SMA.
Reference
Zhu X, Li H, Hu C, et al. Spinal muscular atrophy with hypoplasia of the corpus callosum: a case report. BMC Neurol. Published online February 18, 2023. doi:10.1186/s12883-023-03121-w
