Motor neuron disease (MND) in a girl associated with neuropathy, mitochondrial abnormalities and centrometric deletion of survival motor neuron (smn) gene on chromosome 5q13

Childhood SMA is the most common MND. Homozygous centromeric survival motor neuron (SMN2) deletions are rarely described in SMA but are present in 36% of lower MND cases. We present a 12-year-old girl who manifested progressive walking difficulties at the age of 8. On examination peroneal gait, left leg hypotrophy, radicular pain, absent triceps sure jerks and bilateral Babinski sign were registered associated with extensive right leg angiokeratoma. Brain CT and MRI spinal scans were normal. Clinical and electromyographical progression of the neurogenic lesion with decreasing motor nerve conduction occurred over 4 years, followed by involvement of the left upper extremity and development of cavus foot on the right. Cerebrospinal fluid, immunologic tests and alpha-galactosidase activity (Fabry disease) were normal. Increased vascular resistance without stenotic abnormalities was recorded on both legs by Doppler ultrasonography. DNA analysis revealed SMN2 deletion. Muscle biopsy showed neurogenic atrophy and accumulation of abnormal mitochondria. Sural nerve biopsy showed a decreased number of myelinated axons with scarce onion bulbs. SMN2 deletion probably acts as factor of increased susceptibility for MND. Although SMN gene deletion detection is useful in atypical SMA, it might be a coincidental finding in MND associated with clinical features of other pathogenetic origin.