Pc 1 Duarte is a mutant brain protein present in 32% of the normal human population with 2.6% being homozygous. Preliminary studies suggest an increased frequency of this mutation in individuals with affective disease. To determine if this mutant was present in primates, 32 fetal (wild)-born baboons were examined. All 32 were homozygous for a Pc 1 Duarte-like protein.