Characteristics of hydrocephalus expression in the LEW/Jms rat strain with inherited disease

Materials and methods: The expression and severity of hydrocephalus was characterized in LEW/Jms rats with inherited hydrocephalus. Results: The frequency of overt disease (lethal) was 27.7%, but varied depending on breeding line. It increased to 31.5% when rats with mild disease were included. Most breeding pairs (48/51) produced hydrocephalic offspring with significantly more males than females affected. Some adult rats were also found to have mild (nonlethal) ventricular dilatation. When bred to Fisher F344 rats, 3% of the F₁ progeny had overt hydrocephalus, indicating that the trait is not recessive. Overt hydrocephalus was 9-20% in N₂ rats (F₁ rats × LEW/Jms). The frequency of hydrocephalus and the presence of an excess of hydrocephalic males, varied depending on the direction of the cross. Mild hydrocephalus in N₂ rats was 3.1%. Conclusion: It is concluded that the inheritance of hydrocephalus in LEW/Jms strain is probably not mendelian recessive but may be semidominant or involve more than one gene and has a male bias indicating possible linkage to sex chromosomes.