Congenital quiver, an inherited neurological defect in the chicken

A new neurological defect in the chicken, congenital quiver (CQ), is characterized by a continuous tremor. At hatching, affected chicks show a rapid tremor, while adult expression varies from a slight quiver to pronounced shaking. Genetic analysis showed the defect to be inherited as an autosomal recessive gene (cq) with complete penetrance. Livability of CQ birds is equivalent to that of their normal sibs. Affected females lay eggs and produce chicks; however, males are essentially sterile. Histologically, their testes show considerable cellular disorganization and a marked reduction in spermatogenic elements. Semen quality evaluations showed CQ males to be significantly inferior in respect to semen volume, sperm concentration, initial motility, and percent normal sperm. Histological examination of CQ brains revealed a number of pathological changes, including extensive degeneration of fiber tracts and neurons across the neuroaxis. There also is a diffuse loss of Purkinje cells in the cerebellar cortex with the remaining cell somas becoming extremely eosinophilic. In addition, many of the blood vessels throughout the white matter showed perivascular cuffing.