Childhood mastocytosis and lymphomatoid papulosis are mostly spontaneously regressive diseases.Mastocytosis is a clonal myeloproliferative disease; whereas cutaneous forms may regressspontaneously especially in childhood, the disease is chronic among adults. KIT mutations aredifferent between children and adults. We showed in vivo that children with mastocytosis displaydecreased telomerase expression with shorter telomere length. In vitro, using infected cells withdifferent KIT mutants, "paediatric" or "adult " one, we found longer telomere among adult mutant withdecreased senescence compared to paediatric mutant, without significant differences of telomeraseexpression and activity. These observations could explain the regression in paediatric mastocytosis.Lymphomatoid papulosis is a primary cutaneous CD30+ T-cell lymphoproliferative disorder.Cutaneous lesions are spontaneously regressive but association with a T-cell lymphoma is observed in10 to 20% of cases. We studied PDGFRβ expression to explain proliferative phase and telomerebiology to understand the regressive phase of the disease. Our result showed that PDGFRβ expressionin CD30+ cells was associated to short telomeres. In conclusion, we showed for the first time thattelomere length in mastocytosis and lymphomatoid papulosis seemed to be correlated with diseaseoutcome; on the other hand, we identify a mutation potentially aggressive. Taken together, werecommend to systematically look for KIT mutation among each patient with mastocytosis in order tocarefully monitor them when the cutaneous lesions are persistent and/or progressive.
