G6PC3 deficiency resulting from homozygous inheritance of G6PC3 mutation G260R in 2 siblings with a multisystem syndrome involving severe congenital neutropenia and recurrent infections. P1 indicates affected brother; and P2, affected sister. (A) Family pedigree. Circles represent female; squares, male; filled symbols, affected; and unfilled symbols, unaffected. Numbers indicate subject ages. (B) DNA sequencing. Chromatograms from family members (father refused). (C) G6PC3 G260R is a complete loss-of-function mutation. G6PC3 activity was measured in lymphoblastoid cell lines from 2 healthy blood donors (HD1 and HD2) and both patients.