Isolated exon 8 deletion in type 1 spinal muscular atrophy with bilateral optic atrophy: unusual genetic mutation leading to unusual manifestation?

Proximal spinal muscular atrophy (SMA) or type 1 SMA is a fatal autosomal recessive disorder usually caused by homozygous deletion of exons 7 and 8 in the survivor motor neuron (SMN) gene. Additional deletion of the neuronal apotosis inhibitory protein (NAIP) gene exacerbates the clinical severity. Isolated exon 8 deletion has been reported in a single case series of SMA types 2 and 3 and never with SMA type 1. While extraocular muscles are typically spared, there are a few case reports documenting associated external ophthalmoplegia. Optic atrophy is a hitherto unreported association of SMA. We report a 10-month-old male infant with SMA type 1 with optic atrophy due to isolated deletion of exon 8 of the SMN gene with intact exon 7 and NAIP gene.