The Hermansky-Pudlak syndrome. Evidence for a lowered 5-hydroxytryptamine content in platelets of heterozygotes.

A Dutch kindred with the Hermansky-Pudlak syndrome (HPS) is described. We show for the first time evidence of a lowered platelet 5-hydroxytryptamine content in obligate heterozygotes. Platelet ATP and ADP levels and ATP/ADP ratio were normal in these patients. Platelet aggregation with ADP, collagen and adrenaline was within the normal range. In contrast to the homozygous HPS patients the heterozygotes are normally pigmented and none has diaphanous irides, nystagmus or a bleeding tendency. All homozygous HPS patients have the typical triad of oculocutaneous albinism, pigmented macrophages in the bone marrow and a bleeding disorder, based on a platelet dysfunction. The platelets showed the typical characteristics of a storage pool deficiency. Their platelet factor 3 availability was decreased and the aggregation patterns showed an absent second wave with ADP, adrenaline and absent collagen aggregation. Platelet ADP levels were strongly decreased in all homozygous HPS patients, whereas ATP was lowered only in 3 out of 6 HPS patients. The 5-hydroxytryptamine content of their platelets was very low (15-20% of normal).