Familial Hypertriglyceridemia (Type IV, Autosomal Dominant)

A 38-year-old man with BMI 30 kg/m² and type 2 diabetes presents with fasting triglycerides of 620 mg/dL, LDL cholesterol 108 mg/dL (normal), and HDL cholesterol 28 mg/dL. He has no eruptive xanthomas, lipemia retinalis, or history of pancreatitis. Detailed family history reveals isolated hypertriglyceridemia in his mother (TG 520 mg/dL), maternal grandfather (TG 610 mg/dL with pancreatitis at age 55), maternal aunt (TG 340 mg/dL), and siblings with similar lipid patterns. Male-to-male transmission is documented. The inheritance pattern shown in the diagram marked **A** is most consistent with which genetic disorder?