CHRONIC ISOLATED MACROTHROMBOCYTOPENIA WITH AUTOSOMAL-DOMINANT TRANSMISSION - A MORPHOLOGICAL AND QUALITATIVE PLATELET DISORDER

We studied 47 subjects belonging to 13 unrelated families with a histo ry of mild haemorrhagic diathesis and chronic thrombocytopenia. 36 pat ients presented some degree of thrombocytopenia: 7/36 (19%) had slight thrombocytopenia (100-150x10(9)/L); 26/36 (72%) had mild thrombocytop enia (50-100x10(9)/L) and 3/36 (8%) had severe thrombocytopenia (<50x1 0(9)L). No correlation was observed between platelet count and the deg ree of haemorrhagic diathesis, which was mild in the majority of patie nts. Transmission was autosomal dominant. Platelet anisocytosis, incre ased percentage of large platelets and absence of leukocyte inclusions were observed in 26/30 (87%) of the examined blood smears. The ultras tructural appearance of platelets was normal. Megakaryocytes appeared normal in number in 10/10 patients, but showed asynchronous nuclear-cy toplasm maturation and mainly nonlobulated nuclei. Platelet aggregatio n was studied in 26 patients and either increased or decreased curves were variably observed in response to different aggregating agents. Pl atelet-associated IgG (PAIgG) was increased in 18/31 (58%) patients, w hile serum autoantibodies against platelet glycoproteins Ib/IX or IIb/ IIIa were demonstrable in only 1 case. An increased expression of plat elet surface glycoproteins Ib and IIb/IIIa, as studied by murine monoc lonal antibodies binding in 17 cases, was observed. Platelet survival performed by 111Inoxine-labelled autologous platelets was normal in th e 3 studied patients. Congenital macrothrombocytopenia confirms to be a distinct clinical disorder for which the name of ''chronic isolated hereditary macrothrombocytopenia'' is proposed.