Percentages of whole chromosome 21 gain and loss in the brain vary within and among individuals
| Aneuploid karyotype | |||||||
|---|---|---|---|---|---|---|---|
| Age (years) | Cell type | % Disomy | % Tetrasomy | % Monosomy | % Trisomy | % Aneuploidy | Mean chromosome number |
| 2 | Frontal cortex cells | 94.3 | 2.5 | 1.7 | 1.5 | 3.2 | 2.05 |
| 15 | Occipital cortex cells | 93.8 | 2.4 | 2.2 | 1.6 | 3.8 | 2.04 |
| 35 | Frontal cortex cells | 93.9 | 2.4 | 1.8 | 1.8 | 3.6 | 2.05 |
| 48 | Frontal cortex cells | 93.8 | 2.6 | 1.6 | 2.0 | 3.6 | 2.06 |
| 77 | Hippocampal cells | 91.5 | 3.8 | 2.6 | 2.3 | 4.8 | 2.07 |
| 86 | Hippocampal cells | 92.4 | 2.4 | 3.0 | 2.2 | 5.2 | 2.04 |
| Average | Brain cells | 93.3 | 2.7 | 2.1 | 1.9 | 4.0 | 2.05 |
| 33 | Lymphocytes | 99.8 | 0.2 | 0.4 | 0.2 | 0.6 | 2.00 |
| <0 | Down's syndrome neural cells | 7.1 | 3.6 | 0 | 89.3 | 89.3 | 2.96 |
Lymphocytes and Down's syndrome cells were used to validate the counting criteria using chromosome 21 FISH probes.