Spinal muscular atrophy (SMA) is a rare neuromuscular disease that affects 1:10 000 people.1 It is caused by mutation that results in the non-expression of the survival motor neuron gene (SMN1) which leads to the degeneration of motor neurons in the spinal cord, with muscle weakness and atrophy. Here, SMN1 is linked to proximal spinal muscular atrophy.