ILLEGITIMATE TRANSCRIPTION - ITS USE FOR STUDYING GENETIC ABNORMALITIES IN LYMPHOBLASTOID-CELLS FROM PATIENTS WITH GLANZMANN-THROMBASTHENIA

Glanzmann thrombasthenia is the most common inherited disorder of plat elets that may induce severe bleeding complications. Molecular biology techniques have offered the possibility to assess the basis of this c hronic haemorrhagic disease at the molecular level. However, the acces sibility of mRNA in platelets is limited by the availability of the pa tient's blood samples and the relatively weak amount of this material in these cells. Taking advantage of the genetic phenomenon of illegiti mate transcription, we have demonstrated that glycoprotein IIb and gly coprotein IIIa mRNA could be detected in lymphoblastoid cell lines iss ued from normal EBV-transformed lymphoblasts. We further analysed the sequences of the two glycoprotein transcripts in lymphoblastoid cell l ines from two previously characterized patients presenting with Glanzm ann thrombasthenia. The results showed that illegitimate transcripts p resented similar molecular abnormalities to those found in platelets. These data demonstrated that the nucleotide sequences of illegitimate transcripts were identical to tissue-specific mRNA found in platelets. We applied this methodology to screen for the genetic defect in a new thrombasthenic patient, and found a homozygous nonsense mutation GCA- ->TGA converting Arg8 to stop in the glycoprotein ma gene. This immort alized source of genetic material is therefore particularly useful for molecular genetic studies in inherited platelet disorders, avoiding r epetitive and large blood samplings in frequently anaemic patients.