MicroRNAs are also proposed to be involved.The dementia that occurs in Down syndrome is due to an excess of amyloid beta peptide produced in the brain and is similar to Alzheimers disease, which also involves amyloid beta build-up. Amyloid beta is processed from amyloid precursor protein, the gene for which is located on chromosome 21. Senile plaques and neurofibrillary tangles are present in nearly all by 35 years of age, though dementia may not be present. Those with Down syndrome also lack a normal number of lymphocytes and produce less antibodies which contributes to their increased risk of infection. Epigenetics
Down syndrome is associated with an increased risk of many chronic diseases that are typically associated with older age such as Alzheimers disease. The accelerated aging suggest that trisomy 21 increases the biological age of tissues, but molecular evidence for this hypothesis is sparse. According to a biomarker of tissue age known as epigenetic clock, trisomy 21 increases the age of blood and brain tissue (on average by 6.6 years). Diagnosis
Before birth
When screening tests predict a high possibility of Down syndrome, a more invasive diagnostic test (amniocentesis or chorionic villus sampling) is needed to confirm the diagnosis. The false-positive rate with screening is about 2–5% (see section Screening below). Amniocentesis and chorionic villus sampling are more reliable tests, but they increase the risk of miscarriage by between 0.5 and 1%. The risk of limb problems may be increased in the offspring if chorionic villus sampling is performed before 10 weeks.
Cognitive development
Hearing aids or other amplification devices can be useful for language learning in those with hearing loss. Speech therapy may be useful and is recommended to be started around nine months of age. As those with Down syndrome typically have good hand-eye coordination, learning sign language may be possible. Augmentative and alternative communication methods, such as pointing, body language, objects, or pictures, are often used to help with communication. Behavioral issues and mental illness are typically managed with counseling or medications.Education programs before reaching school age may be useful. School-age children with Down syndrome may benefit from inclusive education (whereby students of differing abilities are placed in classes with their peers of the same age), provided some adjustments are made to the curriculum. Evidence to support this, however, is not very strong. In the United States, the Individuals with Disabilities Education Act of 1975 requires public schools generally to allow attendance by students with Down syndrome.Individuals with Down syndrome may learn better visually. Drawing may help with language, speech, and reading skills. Children with Down syndrome still often have difficulty with sentence structure and grammar, as well as developing the ability to speak clearly. Several types of early intervention can help with cognitive development. Efforts to develop motor skills include physical therapy, speech and language therapy, and occupational therapy. Physical therapy focuses specifically on motor development and teaching children to interact with their environment. Speech and language therapy can help prepare for later language. Lastly, occupational therapy can help with skills needed for later independence.