Down Syndrome (DS) which is also known as trisomy 21, is defined by the National Down Syndrome Society (NDSS) as, “… When an individual has a full or partial extra copy of chromosome 21. … A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the centre of the palm – although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.”
There are three types of DS: trisomy 21, translocation and mosaicism. The common type of DS is trisomy 21, it accounts for 95% of cases. Translocation accounts for about four per cent of cases, where part of chromosome 21 separates during cell division and attaches itself to another chromosome. Although the total amount of chromosomes in the cells doesn’t change, the extra presence of chromosome 21 causes the characteristics of DS. Mosaicism happens when nondisjunction of chromosome 21 takes place in one, however not all of the primary cells divide after fertilization. Nondisjunction is the failure of homologous chromosomes to separate effectively during cell division. When this nondisjunction occurs, there is a mix of two types of cells in which some contain the usual 46 chromosomes and others contain 47. This type of DS accounts for about one per cent of all cases of DS.
Evidence has been found demonstrating that poor verbal short-term memory performance is associated with DS cases and these deficits would affect the person’s vocabulary development.
Servicio de Información y Noticias Científicas (SINC) reported that researchers led by Victoria Puig of the Instituto Hospital del Mar de Investigaciones Médicas (IMIM) conducted a study which observed the “neural bases of intellectual disability in mice with DS. The work, which also involved the Center for Genomic Regulation (CRG), has found that neural networks of brain circuits relevant to memory and learning are over-activated and that the circuit connectivity is poor.” Additionally, it was observed that the neural activity during sleep is also weakened, meaning it could be interfering memory consolidation.
Memory consolidation is a time-dependent process in which newly learned experiences are transformed into long-term memory by both structural and chemical changes in a person’s nervous system. The study also observed that these deficits can be corrected by continuous treatment with natural components of green tea (epigallocatechin gallate). In previous studies, it was also found that these natural components of green tea have improved executive function in adults with DS. “Both hyperactivity of neural networks and deficiencies in the connectivity of specific brain circuits are possible dysfunctional mechanisms that contribute to memory deficits in Down’s syndrome and, therefore, open up new therapeutic possibilities for the treatment of intellectual disability,” explains Puig.
According to Dr. Mara Dierssen from the Cellular and Systems Neurobiology lab at the CRG, “This study provides an in-depth description of the neurophysiological abnormalities present in different brain states in Down syndrome model mice and provides the keys for understanding the cellular mechanisms underlying the improved executive function observed in people with Down syndrome after chronic treatment with epigallocatechin gallate.”
DS was identified as a unique disorder by John Langdon Down in 1866 and the research towards this chromosomal abnormality hasn’t stopped. Institutes such as the Eunice Kennedy Shriver Institute of Child Health and Human Development (NICHD) have both conducted and supported DS research since it was founded in 1962. The NICHD explores all areas of DS, “including the development of animal models to help study the syndrome, examination of specific genes and gene groups that may play a role in the syndrome, understanding how maternal age plays a role in the disorder, and development of new methods of the diagnosis prenatally and postnatally.”