HistoryAn 8-month-old previously healthy boy was referred to our institution by the maternal child health center for progressive truncal hypotonia and developmental delay. This infant was born after an uncomplicated pregnancy with no perinatal complications. He was delivered at full term via spontaneous vaginal delivery. Two of his older male siblings died around 2-3 years of age due to pneumonia. According to the parents, these siblings also displayed reduced muscle tone, and one of them developed recurrent seizure.On physical examination, the child showed marked head lag and did not reach out to objects. Visual and auditory development were normal. His head circumference was below the third percentile, and his body weight was at the 10th percentile. His hair was sparse and coarse. A mild pectus excavatum deformity was present. Skull and chest radiographs were obtained (Figs 1, 2), and the patient underwent MRI of the brain (Fig 3).