Clinical Reasoning: A 19-Month-Old Girl With Infantile-Onset Myopathy and White Matter Changes.

We describe the case of a 19-month-old girl presenting with gross motor delays, hypotonia, diminished deep tendon reflexes, hyperCKaemia, extensive white matter changes on MRI brain, and electromyography studies consistent with myopathy. The differential diagnosis for infantile-onset hypotonia and muscle weakness is broad. It includes numerous subtypes of genetic disorders, including congenital muscular dystrophies, congenital myopathies, congenital myasthenic syndromes, spinal muscular atrophy, single-gene genetic syndromes, and inborn errors of metabolism. We outline our clinical approach leading to the diagnosis of a distinctive genetic neuromuscular condition essential for neurologists and geneticists working with patients of all ages to recognize.