Study of galactosidase as therapy for type IV galactosemia

INTERVENTION: Test twice per patient will be performed using crossover technique. group A: (lactose and galactosidase loading) , followed by (lactose loading) group B: (lactose loading) , followed by (lactose and galactosidase loading) Dose of lactose and galactosidase are 1.0 g/kg and 0.05 g/kg, respectively. Eight cases are devided to group A or B. CONDITION: D005693 type IV galactosemia ; galactosemia: galactose mutarotase: GALM PRIMARY OUTCOME: Blood galactose levels at 2 or 3 hours after lactose loading SECONDARY OUTCOME: Difference between peak level of blood galactose and minimum level of blood galactose after 30 minutes after lactose loading; Peak level of blood galactose; Peak level of urine galactitol INCLUSION CRITERIA: Patients are diagnosed to type IV galactosemia by genetic test (pathogenic variants in GALM gene are identified by exome or direct sequencing) or GALM enzyme activity test.