On the other hand, inter-familial phenotypic heterogeneity significantly delayed the identification of some founder variants shared by families e.g. we identified the same pathogenic founder INSR variant NM_000208.4:c.433 C > T;p.(Arg145Cys) in families where the phenotype ranged from classical hyperinsulinism to asymptomatic. This evidence concerns the gene INSR and hyperinsulinism.