Down’s syndrome

Down’s syndrome (or Down syndrome) is a genetic disorder which is typically associated with a degree of intellectual disability, along with particular physical characteristics. The condition affects approximately ~1 in every 1000 babies born today¹.

Down’s syndrome is the most commonly occurring chromosomal disorder and is the leading cause of mild-moderate intellectual disability worldwide^{1, 2}. 

In addition to intellectual impairment, Down’s syndrome is associated with increased risk of medical problems including congenital heart defects, reflux, hearing loss, obstructive sleep apnoea, visual impairment, thyroid disease, and dementia³.

Pathology and functional impact of Down’s syndrome

Various abnormalities in brain structure and function have been associated with Down's syndrome, including abnormalities of neurones and their synaptic connections in the cortex and hippocampus⁴, regions heavily involved in cognition.

The cerebellum, involved in motor co-ordination and some aspects of cognition, has also been commonly implicated. Current models of Down’s syndrome emphasise that it is ‘late-developing’ brain structures that are most affected, and that these regions do not show the expected development over time in people with the condition⁵.

The majority of individuals with Down’s syndrome have intelligence quotient (IQ) scores less than 70, consistent with generalised or ‘global’ cognitive problems; however, individuals also show more specific impairments in memory and cognitive flexibility⁵.

These findings highlight the importance of using sensitive neuropsychological assessment tools capable of fractionating specific cognitive domains. 
 

Research and development in Down’s syndrome

 

Children and adults with Down’s syndrome should have access to multi-disciplinary support, which can involve input from doctors, educational experts, speech and occupational therapists, and social workers⁶. Examples of medical interventions that may be needed include surgery to correct congenital heart defects or a special diet to minimise digestive problems⁷.

Cognitive deficits in Down’s syndrome represent a key target for novel treatments, in order to maximise everyday functioning and quality of life. This is relevant in view of the intellectual disability occurring generally with the condition, but also due to the association between Down’s syndrome and elevated risk of Alzheimer’s disease as individuals get older.

 

You might also be interested in…

Haydar T.F., and Reeves R.H., (2012). Trisomy 21 and early brain development. Trends Neurosci.

Edgin J.O. (2013). Cognition in Down syndrome: a developmental cognitive neuroscience perspective. Wiley Interdiscip Rev Cogn Sci.

Das D., et al (2014). Neurotransmitter-based strategies for the treatment of cognitive dysfunction in Down syndrome. Prog Neuropsychopharmacol Biol Psychiatry.

Deutsch S.I., et al (2014). Targeting the α7 nicotinic acetylcholine receptor to prevent progressive dementia and improve cognition in adults with Down's syndrome. Prog Neuropsychopharmacol Biol Psychiatry.

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1. _{Genes and human disease. World Health Organization, 2015.}
2. _{Global Down Syndrome Foundation, 2015.}
3. _{Centers for Disease Control and Prevention, USA. Data and statistics, Down Syndrome, 2014.} 
4. _{Haydar TF, Reeves RH. Trisomy 21 and early brain development. Trends Neurosci. 2012 Feb;35(2):81-91.}
5. _{Edgin JO. Cognition in Down syndrome: a developmental cognitive neuroscience perspective. Wiley Interdiscip Rev Cogn Sci. 2013 May;4(3):307-17.}
6. _{NIH Eunice Kennedy Shriver National Institute of Child Health and Human Development. What are common treatments for Down Syndrome? 2015.}
7. _{Das D, Phillips C, Hsieh W, Sumanth K, Dang V, Salehi A. Neurotransmitter-based strategies for the treatment of cognitive dysfunction in Down syndrome. Prog Neuropsychopharmacol Biol Psychiatry. 2014 Oct 3;54:140-8.}