CUBN and hyperinsulinemic hypoglycemia, familial, 4: Primary elevation of 3‐MGCA occurs in defects of leucine catabolism, most notably 3‐methylglutaconyl‐CoA hydratase deficiency (MGA1), but also from deficiency of the more distal enzyme, 3‐hydroxy‐3‐methylgutaryl CoA Lyase (HMGCL).10