Macrothrombocytopenia and Hemolysis Associated with Phytosterolemia

Phytosterolemia is a rare autosomal recessive sterol storage disease, characterized by increased serum concentrations of plant sterols (phytosterols). It is caused by gene mutations of ABCG5 and ABCG8. The patients suffer from xanthomas and premature atherosclerosis. In this study we demonstrate that macrothrombocytopenia and hemolysis are intrinsic features in four unrelated patients with phytosterolemia, and their clinical and pathogenesis are investigated.

Erythrocyte and platelet morphology was examined under light microscope. Platelet aggregation was measured turbidometrically. Platelet glycoproteins were analyzed using flow cytometry. Biochemistry was analyzed by routine methods. The plasma sterol levels were measured by HPLC method. ABCG5 and ABCG8 genes were directly sequenced to identify mutations, Restriction endonuclease analysis was used to exclude the possibility of gene polymorphism.

All the four patients presented xanthomas, macrothrombocytopenia, hemolysis and splenomegaly. The blood smears showed large platelets, some as large as erythrocytes and abnormal erythrocyte shapes, such as stomatocytes. All the patients had bleeding tendency. There were mild defect in aggregation induced by ADP and ristocetin. The red cells showed an increased osmotic fragility. Plasma concentrations of phytosterols including sitosterol, stigmasterol and cholestanol were markedly elevated (30 fold) in the affected patients. Patient 1 was found to be homozygous for C→T mutation at nucleotide 64 in exon 1 of the ABCG5 gene, which results in the premature termination of the ABCG5 protein at amino acid 22 (Gln22X). Patient 2 was homozygous for C→T mutation at nucleotide 1336 in exon 10 of the ABCG5 gene, which results in the premature termination of the ABCG5 protein at amino acid 446 (Arg446X). Patient 3 was compound heterozygous for a large fragment deletion at nucleotide 1842 to 1883 in exon 12, and a complex mutation of del 1938C–1939G/ins1938T in exon 13 of ABCG8. Patient 4 was also compound heterozygous for C→T mutation at nucleotide 1336 in exon 10 and A→G mutation at classical cut locus in intron 9.

In this study, we identified four patients with phytosterolemia who had macrothrombocytopenia and stomatocytic hemolysis in addition to common increased plasma plant sterols and xanthomas. Gene analysis confirmed the diagnosis. We suggest that the coexisting macrothrombocytopenia and stomatocytic hemolysis represent a new subtype of phytosterolemia, and plasma phytosterols should be measured in patients who have stomatocytic hemolysis and macrothrombocytopenia (so called“Mediteranean macrothrombocytopenia/ stomatocytosis”).

No relevant conflicts of interest to declare.