Medulloblastoma is the second-most frequent brain tumor in children after pilocytic astrocytoma and the most common malignant brain tumor in children, comprising 14.5% of newly diagnosed brain tumors. In adults, medulloblastoma is rare, comprising fewer than 2% of CNS malignancies.The rate of new cases of childhood medulloblastoma is higher in males (62%) than females (38%), a feature that is not seen in adults. Medulloblastoma and other PNET`s are more prevalent in younger children than older children. About 40% of medulloblastoma patients are diagnosed before the age of five, 31% are between the ages of 5 and 9, 18.3% are between the ages of 10 and 14, and 12.7% are between the ages of 15 and 19. Research models
Using gene transfer of SV40 large T-antigen in neuronal precursor cells of rats, a brain tumor model was established. The PNETs were histologically indistinguishable from the human counterparts and have been used to identify new genes involved in human brain tumor carcinogenesis. The model was used to confirm p53 as one of the genes involved in human medulloblastomas, but since only about 10% of the human tumors showed mutations in that gene, the model can be used to identify the other binding partners of SV40 Large T- antigen, other than p53. Recently a SHH-type mouse model with high incidence of medulloblastoma, a Patched 1 heterozygous mice knockout for the medulloblastoma suppressor Tis21 (Patched1+-/Tis21 KO). The high medulloblastoma frequency appears to be caused by the down regulation of Cxcl3, being Cxcl3 induced by Tis21.
Melanosis is a form of hyperpigmentation associated with increased melanin.It can also refer to:

Melanism
Ocular melanosis
Smokers melanosis
Oral melanosis
Riehl melanosis

See also
List of cutaneous conditions

References


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