Enzyme replacement therapy reduces Gaucher cell burden but may accelerate osteopenia in patients with type I disease - a histological study.

Enzyme replacement treatment (ERT) is effective in controlling the clinical and biochemical manifestation of type I Gaucher disease. Little is known on the evolution of bone marrow histology caused by ERT. We compared the pretreatment trephine bone marrow biopsies in five patients (F32, F41, F50, M55, and M46) with the control biopsies performed after 26-32 months of imiglucerase treatment. The planimetric estimates revealed significant decrease in Gaucher cell burden in all the patients. The post-ERT values ranged from 24% to 65% of the initial total volumes occupied by the Gaucher cells. This resulted mainly from disappearance of Gaucher cells, and to a lesser extent from their shrinkage. Normal hemopoiesis was markedly increased in four of five patients, fat tissue in all the five patients. Surprisingly, the estimated volumes of trabecular bone in the control biopsies were significantly smaller than in the pre-ERT trephines (0.61%, 0.64%, 0.64%, 0.97%, and 0.22% of the initial volumes, P = 0.043). The bone loss correlated rather with the degree of reconstitution of normal hemopoiesis than with the decrease in the Gaucher cell burden. The histological response did not correlate strictly with initial clinical parameters and the genotype, with different reactions to ERT in two sibs (cases 3 and 4). Particularly, ERT alleviated bone manifestations in all four patients with previous bone pains or fractures. ERT may accelerate progress of osteopenia in men and premenopausal women. The clinical significance of this phenomenon remains to be established. Its mechanism may be linked to increased osteolytic activity exerted directly or indirectly by regenerating hemopoietic cells.