So far, three studies have been able to analyze the SHM spectrum in the VH3-23 region of IGHM transcripts of purified CD19+CD27+ B cells using Sanger sequencing in human MSH6 deficiency (four patients, mean: 103 mutations), UNG deficiency (two patients, mean: 119 mutations), or PMS2 deficiency (two patients; 65 mutations on average) (25–27). Here, CD19 is linked to hyperinsulinemic hypoglycemia, familial, 4.