Introduction

Spinal Muscular Atrophy- Lower Extremity Dominant Type 2 (SMALED2) is a subgroup of non-5q SMA that develops during antenatal period or early childhood. It is characterized  with more pronounced muscle weakness and atrophy in the proximal muscles of the lower extremities.

Case

3,5 year old boy brought for waddling gait which was first noticed when he was  15 months old. Physical examination revealed  muscle weakness and prominent atrophy in the lower extremities. Electromyographic (EMG) findings were consistent with anterior horn cell involvement. SMN gene analysis was found to be normal. Muscle biopsy was consistent with muscle involvement. Blood chemistry, creatine kinase levels and acyl carnitine panel were normal.Repeated EMG supported the second motor neuron involvement. Homozygous mutation of BICD2 gene was found and he was diagnosed with  SMALED2

Discussion

Mutations in the BICD2 gene lead to SMALED2 in the non-5q SMA group and hereditary spastic paraplegia. SMALED2 can present with findings ranging from antenatal to early childhood. Muscle atrophy in the lower extremity and prominent muscular weakness in the proximal muscles of lower extremities are typical. Joint contractures often accompany the disease. SMALED2 can be mistaken as SMA type 4 because of slowly progressive nature of the disease. In muscle biopsy, differences in muscle fiber diameter and  shape  and fibrousadipose changes can be seen.

Non-5q SMA subgroups should be kept in mind when SMN gene analysis is negative in patients with anterior horn motor neuron involvement.