Genetic linkage between the loci for colour blindness and Duchenne type muscular dystrophy.

Duchenne type muscular dystrophy is a condition which begins in infancy or early childhood, and is characterized by progressive muscle weakness leading to death in the late teens or early twenties (Walton and Nattrass, I954). This type of muscular dystrophy has been variously referred to as 'pseudohypertrophic muscular dystrophy' (Bell, I948), 'progressive muscular dystrophy of childhood' (Stephens and Tyler, 195i), and 'rapidly progressive muscular dystrophy of young boys' (Stevenson, I953). This type of muscular dystrophy will be referred to here as Duchenne type muscular dystrophy, in agreement with the suggestion made by Walton (I955, 1957) that this is probably the best designation for that type of muscular dystrophy which affects young boys and is inherited as an X-linked recessive trait. Evidence for X-linkage has been derived from several sources. In the few cases where affected males have lived long enough to have children, their sons have all been unaffected (Walton, I955; Morton and Chung, i959), though it is possible that these more benign cases represent a different disease, sometimes referred to as the Becker type of X-linked muscular dystrophy (Becker, I962). It has also been suggested that since several "affected children are known to have had the same mother but different fathers (Milhorat and Wolff, I943; Walton, I955) this may be used as evidence for X-linkage. However, this does not exclude autosomal inheritance with limitation to the male sex. Morton and Chung (I959) have provided statistical evidence, based on the proportion of sporadic cases, which does not agree with the hypothesis of an autosomal trait with sex-limitation but does agree with that of X-linkage. The fact that typical Duchenne muscular dystrophy has been described in two females with an XO sex chromosome con-