A 15 year old male patient presents with the chief complaint of pain in abdomen. General examination reveals xanthomas present in clusters on back, buttocks and arms, legs. On percussion, hepatomegaly and splenomegaly can be appreciated. What is the most probable diagnosis for this child?
Primary Hyperlipoproteinemias Causing Hypertriglyceridemia
Familial Chylomicronemia Syndrome (Type I Hyperlipoproteinemia)
Biochemical abnormalities:

Lipoprotein Lipase (LPL) or Apo CII defect.
Lipoprotein Lipase is required for hydrolysis of TGs in Chylomicrons and VLDL. Apo CII is the cofactor for Lipoprotein Lipase.
Lipoprotein accumulated is Chylomicron and VLDL, but chylomicron predominates.
Fasting Triglycerides is > 1000 mg/dL.
Fasting cholesterol is elevated to a lesser degree.

Clinical Presentation:

Present in childhood with recurrent abdominal pain due to acute pancreatitis.
On fundoscopic examination, opalescent retinal blood vessels (lipemia retinalis).
Lactescent plasma.
Eruptive xanthoma (small yellowish-white papules appear in clusters on backs, buttocks, extensor surfaces of arms and legs. These are painless skin lesions may become pruritic).
Hepatosplenomegaly.
Premature CHD is not a feature of FCS.

Diagnosis:
Assaying triglyceride lipolytic activity in post heparin plasma (IV heparin injection to release the endothelial-bound LPL).
Key Concept:
Xanthomas (present in clusters on back, buttocks and arms, legs) and hepatomegaly and splenomegaly (on percussion) with the chief complaint of pain in abdomen in children is the clinical presentation of Type I Hyperlipoproteinemia.
Type I Hyperlipoproteinemia
Autosomal Dominant Hypercholesterolemia Type I (ADH Type I)
Autosomal Recessive Hypercholesterolemia (ARH)
Abetalipoproteinemia