The severity of myotonic dystrophy in 17 affected sibling pairs from 15 families in which 2 or more affected children were born to mothers with myotonic dystrophy is reported from the Hospital for Sick Children, London and the Prince of Wales Children’s Hospital, Sydney, Australia. In 13 of 17 sibling pairs the younger child was more severely affected than the older child. Increasing age difference between the affected siblings paralleled increasing age for each mother and showed a positive correlation with the difference in disease severity between siblings. Infants born to older mothers suffered more severe myotonic dystrophy. Maternal age at delivery correlated with the age at which the infant sat alone and walked alone. In addition, the incidence of neonatal feeding difficulties, neonatal respiratory difficulties, surgery for talipes, and scoliosis were directly related to maternal age at delivery. 
COMMENT. These findings have relevance in genetic counseling and suggest that maternal age and birth order are important in the relative severity of childhood onset myotonic dystrophy. The authors note that a normal infant born after a neonatally affected child is unlikely to develop myotonic dystrophy.
An increased risk of spontaneous abortion, cesarian section and neonatal death for women with myotonic dystrophy is reported from the Chicoutimi Hospital, Quebec Canada . The risk estimate that women with myotonic dystrophy will have a congenitally effected child is 3-9%. Among children surviving the neonatal period, 7.3% had congenital myotonic dystrophy and 7.3% had childhood onset myotonic dystrophy.