However, healthy relatives of P2 (B.II.3 and B.III.3) were found to be heterozygous for the Q463H mutation, suggesting that this allele (and possibly E320Q), like the previously reported L706S STAT1 allele [17], is associated with a partial form of STAT1 deficiency, with low clinical penetrance. Here, STAT1 is linked to hyperinsulinemic hypoglycemia, familial, 4.