Infantile spinal muscular atrophy with respiratory distress type I (SMARD 1): an atypical phenotype and review of the literature.

Spinal muscular atrophy with respiratory distress (SMARD 1) is a very rare autosomal recessive motor neuron disorder that affects infants and is characterized by diaphragmatic palsy, symmetrical distal muscular weakness, muscle atrophy, peripheral sensory neuropathy and autonomic nerve dysfunction. SMARD 1 is inherited as an autosomal recessive trait and the mutations have been identified in the gene encoding immunoglobulin μ-binding protein 2 (IGHMBP2), located on chromosome 11q13. It is considered a fatal form of infantile motoneuron disease and most of the patients dies within the first 13 months of life. We present a female child with genetically confirmed SMARD 1 displaying a mild phenotype and no severe signs of respiratory involvement, typically found in this form, up to 38 months despite a diaphragmatic palsy diagnosed at 6 months of age. Therefore, our clinical observation suggests that respiratory failure is not secondary, in any case, to the diaphragmatic palsy but other pathogenetic mechanisms might be involved.