An isolated and substantially pure nucleic acid sequence located between D20S119 and D20S178 on human chromosome 20q13, the nucleic acid sequence including: a nucleic acid sequence coding for a glucose transporting protein and having the sequence shown in SEQ ID NO: 1; or a nucleic acid sequence having at least 70% sequence identity with the nucleic acid sequence shown in SEQ ID NO: 1. The disclosed nucleic acid sequences map to a locus associated with human Type II diabetes mellitus and, therefore, therapeutic and diagnostic screening methods, which accommodate naturally and artificially occurring polymorphisms, are also disclosed.