A boy was referred at the age of 2 years and 8 months because of frequent falls. This occurred several times per day and he had hurt his head on multiple occasions. Earlier major motor milestones had been delayed by several months. He had achieved rolling over at 9 months, crawling at 15, and independent walking just before his second birthday. Speech and language development were also behind as his first word had been heard around the age of 2 and he now mastered no more than ten. He was friendly in his behaviour and made good eye contact. Pregnancy and birth had been unremarkable. His mother was 5 months pregnant with her second child. Family history was unremarkable.

A 24-year-old man is the youngest of five children and of Turkish origin, who since the age of five years had noticed that he was not able to fully extend his arms. Furthermore, his Achilles tendons were taut. His previous history was unremarkable. An older brother had similar symptoms. Both had no cardiac symptoms. His parents were not affected.

A 23-year-old man gradually noticed slowly progressive difficulty running and climbing stairs and therefore he was referred. In retrospect, he had a hollow back since age 10, and when running, he had had difficulty keeping up with his peers. He had a younger brother with similar complaints. Serum CK activity was elevated (15 × ULN). EMG, which had been carried out by the referring neurologist, showed small motor unit action potentials.

A boy was born at 33 weeks’ gestational age via caesarean delivery because of a transverse position and difficulties in obtaining an adequate cardiotocography. Pregnancy had been complicated by fetal growth restriction with an abdominal circumference at p10, and polyhydramnios. His mother had noticed a reduction in fetal movements the day before delivery. Immediately after birth, he was hypotonic, pale, bradycardic, and without spontaneous breathing. Resuscitation was started with bag and mask ventilation and thoracic compressions. Heart rate and oxygen levels quickly normalized. However, breathing remained insufficient. Arterial CO2 levels rose to 14.0 kPa (ref 4.7–6.4) and he was intubated. He was the first child of unrelated parents. His mother had been diagnosed with obesity and gestational diabetes. The maternal grandmother had a sister whose daughter had a son who had died two days after birth more than 20 years earlier.