Her karyotype [46XX, inv(9)(p12q13), i(21)(q10)] included triplication of the gene for amyloid precursor protein and the Down syndrome critical region.
Modern research had proposed that the over expression of DYRK1A (Dual specificity tyrosine phosphorylation regulated kinase1A, a family of protein kinases, positioned within the Down's syndrome critical region (DSCR) on human chromosome 21causes phosphorylation of APP protein resulting in its cleavage to Aβ 40, 42 and tau proteins (regulated by beta and gamma secretase) which plays critical role in early onset of Alzheimer's disease (AD) detected in Down's syndrome (DS), leading to permanent functional and structural deformities which results ultimately into neuro-degeneration and neuronal death.
BACE2 is homologous to BACE1, a beta-secretase that is involved in the amyloidogenic pathway of amyloid precursor protein (APP), and maps to the Down syndrome critical region of chromosome 21.
Mapping to the Down syndrome critical region (chromosome 21) and identified as a homologue of BACE1, BACE2 also cleaves amyloid precursor protein at the beta-site.