The weaning process is a critical phase in patients undergoing mechanical ventilation. This process can be hampered by numerous causes, such as neuromuscular diseases and spinal muscular atrophy (SMA). We present a 6-month-old boy with respiratory distress, fever, marked hypotonia without motor developmental milestones, and areflexia. The patient showed progressive respiratory distress requiring mechanical ventilation. Definitive weaning was not achieved and the boy died from respiratory failure. Partial autopsy was performed with a diagnosis of SMA and genetic study of the parents. Neuromuscular diseases are an infrequent cause of respiratory insufficiency in suckling infants. The differential diagnosis is made between axonal and motor neuron diseases. The diagnosis was confirmed by muscular biopsy and genetic study.