Juvenile myelomonocytic leukemia is a rare neoplastic disorder
occurring in early childhood often showing an aggressive
progression. We report a case of a twin pair with concordant JMML
but an extremely different disease course. Both twins presented with
somatic aberrations of chromosome 7 and mutations in PTPN11.
Analysis of sorted BM and PB cell populations revealed the clonal
nature of the disease and indicated that genomic aberrations arise
from common hematopoietic precursor cells. PTPN11 mutations
in oral swab specimens of both patients during the active phase
of the disease were attributed to monocytes infiltrating the oral
mucosa and not to the presence of mosaic tissue mutations. This
study provides evidence that the discordant clinical disease course
in the twins is associated with a distinct gene expression profile