After a normal pregnancy without hydramnios, delivery of a healthy-looking girl was uneventful. At four months of age, she had had a respiratory infection and was noted to have a weak cough. At eight months of age she was just able to keep her head in an upright position but was not able to sit unsupported. Her mother admitted that she had not been very active since birth, but there was no progressive muscle weakness and no swallowing difficulty. She was referred to a paediatric neurologist because of a suspected neuromuscular disorder. The parents were healthy and there was no consanguinity.