X-linked centronuclear myopathy as a cause of floppy baby.

Two families with X-linked recessive centro-nuclear myopathy (XLR-CNM) are described. Evidence is accumulating that XLR-CNM forms a distinct entity, in contrast to the commoner later-onset forms. Family history often provides a clue to the diagnosis. Pregnancy is very often complicated by hydramnios and reduced fetal movements. We describe two families with five affected male babies who all died. An isolated case with severe fetal brady-arrhythmias in combination with acute increase in polyhydramnios is mentioned. The neonatal mortality in all recorded cases is 80 percent, with respiratory insufficiency as the cause of death. An attempt is made to establish early prenatal diagnosis and the possibility of carrier detection is briefly discussed.