BACKGROUND: Down syndrome comprises multiple malformations and is due to trisomy 
of chromosome 21. There is epidemiologic evidence that individuals with Down 
syndrome are at decreased risk for solid tumors including brain tumors. It has 
been suggested that some genes expressed on the extra copy of chromosome 21 act 
as tumor suppressor genes and contribute to protection against tumorigenesis.
CASE DESCRIPTION: We report the first case to our knowledge of a patient with 
Down syndrome, an 8-year-old boy, with an intracranial meningioma, in which the 
status of chromosome 21 was examined. The diagnosis was based on histologic 
examination of the surgically resected tumor. Postoperatively, the patient's 
neurologic status improved, and there was no tumor regrowth in the next 2 years. 
Fluorescence in situ hybridization for chromosome 22 confirmed high allele loss 
involving the neurofibromin 2 gene locus, a finding typical in meningiomas. 
Fluorescence in situ hybridization also revealed chromosome 21 heterogeneity in 
tumor cells; not only cells with trisomy 21 but also cells with disomy and 
monosomy 21 were present. All blood cells from the patient manifested trisomy 
21.
CONCLUSIONS: Deletion of the chromosome 21 allele may be associated with 
tumorigenesis of meningioma in Down syndrome. This supports the hypothesis that 
some genes whose expression is increased on the extra copy of chromosome 21 
function as tumor suppressor genes and that they contribute to the reduced tumor 
incidence in individuals with Down syndrome.