Abstract • 129

Whatever the platelet function altered, inherited platelet disorders are often not distinguishable from their hemorrhagic symptoms. The diagnostic strategy of these heterogeneous disorders in children profit of the development of two modern and complementary tools: flow cytometry and molecular genetic technics. Using these tools, we have characterized GT (12 patients) X-linked familial thrombocytopenia (X-LFT) (3 patients), Fechtner syndrome (1 patient) or Gray platelet Syndrome like (GL) (1 newborn) in children and their families. The main glycoproteins of the platelet membrane, GPIIbIIa and GPIbIXV complexes, and P-selectin have been quantified by flow cytometry in resting and activated platelets using kits Platelet GP (Biocytex) and Cytoquant (Diagnostica Stago). The genetic abnormalities have been characterized from platelet RNA and/or genomic DNA using successively PCR-SSCP and sequencing (directly or after sub-cloning). We have used too an Allele Specific Oligonucleotides Technic that we had previously developed for the identification of the gipsy mutation (Blood, 1995, 86, 977-82). Cytometric studies confirmed the severe GPIIbIIIa deficiency in thrombasthenic children and gave new data : low levels of GPIIbIIIa and GPIb and functional defect of the small platelets of the children with XLFT, about double the normal levels of GPIIbIIIa and GPIb and strong functional capacities of the giant platelets of the "Fechtner patient" and a reduced platelet reactivity of the "GL patient". Molecular genetic studies allowed to identify the gipsy mutation in all the 10 gipsy children (homozygotes) and in the gipsy heterozygotes and two different new mutations in the other two thrombasthenic families (Thromb Haemost, 1997, supplt, 360, 1476 abstr.). They also characterized the genetic defect associated with XLFT in 3 children (J Pediatr, 1996, 129, 56-62).

Flow cytometry using this quantifying method gives quickly safe and key data from a very small volume of blood and therefore is particularly helpful for the diagnosis of inherited platelet disorders in neonates and children and is of high interest for the management of these patients. Genetic studies are "a must" for the understanding of the molecular mechanisms of these inherited disorders in children, genetic counselling and prenatal diagnosis.