ADSL and hyperinsulinemic hypoglycemia, familial, 4: Enzyme assay in erythrocyte lysates was not completely reliable due to the tissue heterogeneity of the ADSL defect [87] and residual activity (>2% of normal) could be detected in the lymphocytes or cultured fibroblasts of patients presenting a lethal fetal and early neonatal form of ADSL deficiency [88].