Evaluation and characterization of the hypothyroid hyt/hyt mouse. I: Somatic and behavioral studies.

Mice homozygous for the autosomal-recessive gene hypothyroid (hyt) had congenital hypothyroidism of fetal onset after 15 days postconception. Neonatal hyt/hyt mice had reduced serum thyroxine ranging from 1/5 to 1/6 of normal as well as significantly delayed somatic and behavioral development. Delayed somatic development included retarded eye opening and ear raising, and reduced body length and body weight. The hyt/hyt animals compared to their normal littermates demonstrated delayed reflexive behavior and abnormal motor and adaptive behavior. The somatic and behavioral measures clearly distinguished hyt/hyt animals from their normal littermates even without T4 determination. The somatic and reflexive behavioral abnormalities in the hyt/hyt mouse were similar to other rodent models of human congenital hypothyroidism. The hyt/hyt mouse provided an ideal model for exploring the effect of severe primary inherited hypothyroidism related to deficient autonomous fetal thyroid function and was consistent with the hypothesis that thyroid hormone deficit in utero and in the early neonatal period significantly altered functional development.