Hyperinsulinemia in myotonic dystrophy: identity of the maternal factor causing the neonatal myotonic dystrophy syndrome.

An environmental factor acting on the fetus is thought to cause a neonatal syndrome characterized by marked muscular hypotonia, lack of respiratory drive and feeding difficulties, in some infants born to mothers with myotonic dystrophy. Mortality is high, especially amongst those babies born prematurely, but muscle strength and tone improve rapidly in survivors. Nevertheless, most survivors have physical deformities and mental retardation and are thought to develop myotonic dystrophy later. We propose that alterations in maternal insulin secretion (usual in myotonic dystrophy subjects) alter fetal blood glucose and amino acid levels and retard growth and maturation of fetal skeletal muscle. This leads to severe muscular hypotonia in affected infants. Also, we suggest that infants who die during the perinatal period may not have inherited the defective autosomal dominant gene that causes myotonic dystrophy.