[Genetic epidemiology of Duchenne muscular dystrophy in Japan]

Duchenne muscular dystrophy (DMD) is one of the most serious neuromuscular afflictions in childhood. The present analysis describes clinical, genetic and epidemiological features in a total of 675 DMD cases, 666 males and 9 females, reported from 20 national hospitals for muscle diseases in Japan. The results are as follows: 1) Average ages of milestones of progression were: onset at 3.6 +/- 1.7, Gower's sign 5.2 +/- 2.3, inability to walk 9.8 +/- 2.1, death 19.5 +/- 3.6 years old, respectively. The patients died 10.9 +/- 3.3 years after the age of inability to walk. 2) Proportion of selected abnormalities (knee contracture, ankle contracture, kyphoscoliosis) and abnormal findings in electrocardiograms increased with age, whereas pseudohypertrophy of the calves, abnormal findings of electromyograms, and mental retardation remained constant. 83-95% of patients were unable to turn the body in bed over 20 years old. 3) Survival rates at 20 and 27 years old were 63%, and 35%, respectively. The 50% survival rate was observed in 22-23 years of age. 4) The proportion of the sporadic cases was compatible with 1/3, as expected for on X-linked lethal trait assuming complete penetrance. 5) The incidence rate and prevalence rate among males were estimated to be 29.2 x 10(-5) and 6. 7 x 10(-5), respectively. The estimated mutation rates in egg and sperm were 9.2 x -5 and 10.9 x 10(-5)/gamete/generation, respectively.