LEPR and diabetes mellitus: Furthermore, a congenic strain of the SDT rat, the SDT-fatty rat (SDT Leprfa), was established by introducing a fatty (fa) allele of the Zucker Diabetic Fatty (ZDF fa/fa ) rat, into the genome of the SDT rat deficient in the leptin receptor gene (Leprfa), such that the homozygous fa/fa strain develops diabetes earlier, from five weeks of age, while heterozygous and wildtype strains develop diabetes at 20 weeks [80].