PHKA2 and hyperinsulinemic hypoglycemia, familial, 4: This mutation has been reported previously in a patient with XLG I who had a pronounced PhK deficiency in both liver and erythrocytes (PhK activity was 10.0 % of the control mean in both liver and erythrocytes) and in a patient with XLG II who had normal erythrocyte PhK activity (83.0 % of the control mean), therefore the significance of this mutation for biochemical function in specific tissues and clinical severity remains speculative [8].