To determine the impact of TMLD enzyme activity on the development of primary carnitine deficiency, we inactivated (knocked out) the Tmlhe gene (Tmlhe) in mice to study constitutive TMLD enzyme deficiency-induced changes in the levels of carnitine and its biosynthetic intermediates TML and γ-butyrobetaine (GBB) in plasma and brain tissue. This evidence concerns the gene TMLHE and systemic primary carnitine deficiency disease.