Genetic studies of neuraxonal dystrophy in the Morgan

A naturally occurring disease condition, neuraxonal dystrophy, was identified in 27 male and 15 female Morgans, many of which were closely related. Five-generation pedigrees were constructed for 33 of these horses and were compared with those for 29 randomly selected age- and sex-matched Morgans. Their mean coefficient of inbreeding was not statistically different (P greater than 0.1, 1 tailed t test; P less than 0.001, median test). Breeding of 2 severely affected and 2 normal stallions to 2 severely affected, 3 mildly affected, and 6 normal mares produced 10 mildly affected, 8 suspect affected, and 6 normal offspring. Breeding 4 normal stallions to 17 normal mares produced 22 normal offspring. Neuraxonal dystrophy seems to have a familial component, although neither a simple dominant not recessive mode of inheritance could be demonstrated. The condition could be inherited in a polygenic mode or as a dominant disorder with variable expression.