Detection of heterozygosity for the −13T → G mutation via Mwo I restriction endonuclease digestion of PCR-amplified DNA. (A) The −13T → G mutation creates a restriction site for Mwo I. Wild-type amplification products are not sensitive to Mwo I digestion, while digestion of mutant spectrin St Claude amplification products yields two fragments of 42 bp and 141 bp. (B) Mwo I digestion of PCR-amplified products showed heterozygosity in both parents (lanes F and M) and a brother (lane B) and homozygosity in the propositus (lane P). In the wild-type control (lane C), the PCR products were undigested after Mwo I digestion.