Kok Kok RC RC Timmerman Timmerman MA MA Wolffenbuttel Wolffenbuttel KP KP Drop Drop SL SL de Jong de Jong FH FH Isolated 17,20-lyase deficiency due to the cytochrome b5 mutation W27X Isolated 17,20-lyase deficiency due to the cytochrome b5 mutation W27X J Clin Endocrinol Metab J Clin Endocrinol Metab 2010 2010 95 95 994 994 9 9 10.1210/jc.2008-1745 10.1210/jc.2008-1745 20080843 20080843. The gene discussed is CYB5A; the disease is hyperinsulinemic hypoglycemia, familial, 4.