A multi-national study (including both USA and Canadian collaborators) of false-positive screening results for succinylacetone when screening for TYR-I found that maleylacetoacetate isomerase deficiency (clinically insignificant) was a recognizable cause, and that a second-tier screening test with (urine) maleic acid (a biomarker for) might be useful to improve screening efficacy [116]. The gene discussed is GSTZ1; the disease is hyperinsulinemic hypoglycemia, familial, 4.