The DNA polymerase chain reaction can be a powerful tool for amplifying selected segments of genomie DNA for investigation of point mutations that are inaccessible via classic restriction-fragment–length polymorphism analysis. We have applied this method to an analysis of the incidence of heterozygosity for the mutant insulin allele insulin Wakayama (A3 Val→Leu) in two unrelated Japanese families having the hyperinsulinemic mutant insulin syndrome. The results indicate that this method is simple, sensitive, and accurate and should be useful for screening larger (diabetic) populations to detect single-base substitutions in the insulin gene that lead to either altered (pro)insulin structure and/or insulin production.

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