FHL can be further subclassified into FHL2 caused due to perforin deficiency (FHL-2; MIM 603553) and genetic defects affecting proteins involved in transport, membrane fusion, or exocytosis of perforin containing lytic granules such as Munc 13-4 (FHL-3; MIM 608898), syntaxin 11 (FHL-4; MIM 603552), and syntaxin binding protein 2 (Munc 18-2) (FHL-5; MIM 613101) [4]. Here, STX11 is linked to hyperinsulinemic hypoglycemia, familial, 4.