Considering that chromosomal duplications lead to increased DSCAM expression in trisomy 21, our findings may help uncover novel mechanisms contributing to intellectual disability in Down syndrome.
The aim of this review is to present what is currently known about DSCAM (Down Syndrome Cell Adhesion Molecule) a protein that is directly connected to pathological changes in synaptic plasticity.
This work identifies DSCAM as a candidate causative gene in DS that is sufficient to modify synaptic transmission and synaptic plasticity and cause a DS behavioural phenotype.
We suggest a DS CHD candidate region on 21q22.2 (0.96Mb), being shared by most PT21 cases with CHD and containing three known protein-coding genes (DSCAM, BACE2, PLAC4) and four known non-coding RNAs (DSCAM-AS1, DSCAM-IT1, LINC00323, MIR3197).
Increased expression of Down Syndrome Cell Adhesion Molecule (Dscam) is implicated in the pathogenesis of brain disorders such as Down syndrome (DS) and fragile X syndrome (FXS).
Recently, it has been suggested that the facial gestalt of DS has been linked to the distal part of the DSCR whereas the proximal region harboring DSCR1/RCAN and DSCAM should be associated with the cardiac abnormalities.
We propose that impairment of the NMDA-mediated regulation of DSCAM translation may contribute to the alterations in dendritic morphology and/or synaptic plasticity in Down's syndrome.
In contrast, no comparable cardiac defects were detected in embryos of the more limited mouse trisomy model, Dp(16Cbr1-ORF9)1Rhr (Ts1Rhr), indicating that trisomy of the region syntenic to the Down's syndrome critical region, including the candidate genes DSCAM and DYRK1A, is insufficient to yield DS cardiac abnormalities.
The present case provides further support to the concept that there exists Down syndrome-associated congenital heart disease gene(s) on chromosome 21q22 and that over-expression of DSCAM may contribute to the cardiac defects of Down syndrome.
Given the homology of DSCAM to cell adhesion molecules involved in development and synaptic plasticity, and its demonstrated role in axon guidance, we propose that DSCAM overexpression contributes not only to the structural defects seen in these regions of the DS brain, but also to the defects of learning and memory seen in adults with DS.
We now report human molecular and cardiac data that narrow the DS-CHD region, excluding two candidate regions, and propose DSCAM (Down syndrome cell adhesion molecule) as a candidate gene.
The overexpression of DSCAM may also play a role in the mental retardation and the precocious dementia of DS patients, although the mechanism of neuronal dysfunction is undetermined.
Given its location on chromosome 21, its specific expression in the central nervous system and neural crest, and the homologies to molecules involved in neural migration, differentiation, and synaptic function, we propose that DSCAM is involved in neural differentiation and contributes to the central and peripheral nervous system defects in DS.