Health aspects of Down syndrome
Down syndrome is a genetic disease resulting from the presence of all or part of an extra 21st chromosome (trisomy 21). The medical consequences of this extra genetic material are highly variable and may affect the function of any organ system or bodily process. The health aspects of Down syndrome encompass anticipating and preventing effects of the disease, recognizing complications of the disorder, managing individual symptoms, and assisting the individual and his/her family in coping and thriving with the illness.
The most common manifestations of Down syndrome are the characteristic facial features, cognitive impairment, congenital heart disease, hearing deficits, short stature, and Alzheimer's disease. Other serious, but less common illnesses include leukemia, immune deficiencies, and epilepsy.
There are benefits as well as challenges:  People with Down syndrome have a reduced risk of developing most kinds of cancer, atherosclerosis, or diabetic retinopathy.
Down syndrome can result from several different genetic mechanisms. This results in a wide variability in individual symptoms due to complex gene and environment interactions. Prior to birth, it is not possible to predict the symptoms that an individual with Down syndrome will develop. Some problems are present at birth, such as certain heart malformations. Others become apparent over time, such as epilepsy.

# Individual symptoms

## Endocrinology and hematology
Individuals with DS are at increased risk for dysfunction of the thyroid gland, an organ which helps control metabolism. Low thyroid (hypothyroidism) is most common, occurring in almost a third of those with DS. This can be due to absence of the thyroid at birth (congenital hypothyroidism) or due to attack on the thyroid by the immune system. Reproduction is also affected by DS. Women with DS are less fertile and often have difficulties with miscarriage, premature birth, and difficult labor. However, women with DS are capable of having children without the extra chromosome 21 of DS. Men with DS are almost uniformly infertile, exhibiting defects in spermatogenesis.
Hematologic malignancies such as leukemia are more common in children with DS. In particular, the risk for acute lymphoblastic leukemia is at least 10 times more common in DS and for the megakaryoblastic form of acute myelogenous leukemia is at least 50 times more common in DS. Transient leukemia is a form of leukemia which is rare in individuals without DS but affects up to 20 percent of newborns with DS. This form of leukemia is typically benign and resolves on its own over several months, though it can lead to other serious illnesses. In contrast to hematologic malignancies, solid tumor malignancies are less common in DS, possibly due to increased numbers of tumor suppressor genes contained in the extra genetic material.

## Gastrointestinal and growth
Down syndrome increases the risk of Hirschsprung's disease, in which the nerve cells that control the function of parts of the colon are not present. This results in severe constipation. Other congenital anomalies occurring more frequently in DS include duodenal atresia, annular pancreas, and imperforate anus. Gastroesophageal reflux disease and celiac disease are also more common among people with DS.
Growth parameters such as height, weight, and head circumference are smaller in children with DS than with individuals of the same age. Adults with DS tend to have short stature  the average height for men is 5 feet 1 inch (157 cm) and for women is four feet 9 inches (144 cm). Individuals with DS are also at increased risk for obesity as they age.

## Axial Skeleton
Persons with down syndrome are at higher than normal risk for atlanto-axial instability, probably due to ligamental laxity. Periodic screening, with cervical x-rays, is recommended to identify this abnormality.

## Neurology
The neurologic consequences of DS manifest early in life. Infants with Down Syndrome have a decreased muscle tone and are more flexible. Mental retardation becomes apparent as individuals with DS grow and develop  sitting, walking, and talking are typically delayed. Children and adults with DS are at increased risk for developing epilepsy. The risk for Alzheimer's disease is increased in individuals with DS, with 10-25% of individuals with DS showing signs of AD before age 50, up to 50% with clinical symptoms  in the sixth decade, and up to 75% in the 7th decade. This sharp increase in the incidence and prevalence of dementia may be one of the factors driving the decreased life expectancy of persons with Down Syndrome.

## Ophthalmology and otolaryngology
Eye disorders are more common in people with DS. Almost half have strabismus, in which the two eyes do not move in tandem. Refractive errors requiring glasses or contacts are also common. Cataracts (opacity of the lens) and glaucoma (increased eye pressures) are also more common in DS.
Hearing loss affects more than half of individuals with DS, due to multiple factors. Frequent infections of the middle ear (otitis media) and obstructive sleep apnea are also more common DS. Instability of the atlanto-axial joint occurs in ~15% of people with DS and may lead to the neurologic symptoms of spinal cord compression.

# Prevention and screening
The American Academy of Pediatrics, among other health organizations, has issued a series of recommendations for screening individuals with Down Syndrome for particular diseases. These guidelines enable health care providers to identify and prevent important aspects of DS. All other typical newborn, childhood, and adult screening and vaccination programs should also be performed.

## Birth
Initial examination of newborns with DS should pay particular attention to certain physical signs which are more commonly found in DS. Evaluation of the red reflex can help identify congenital cataracts. Movement of the eyes should be observed to identify strabismus. Constipation should raise concerns for Hirschsprung's disease and feeding problems should prompt intense education to ensure adequate input and nutrition.
At birth, an ultrasound of the heart (echocardiogram) should be done immediately in order to identify congenital heart disease (this should be carried out by someone with experience in peadiatric cardiology). A complete blood count should be done in order to identify pre-existing leukemia. A hearing test using brainsteam auditory evoked responses (BAERS) testing should be performed and any hearing deficits further characterized. The thyroid function should also be tested. Early Childhood Intervention should be involved from birth to help coordinate and plan effective strategies for learning and development.

## Childhood and adulthood
As children with DS grow, their progress should be plotted on a growth chart in order to detect deviations from expected growth. Special growth charts are available so that DS children can be compared with other children with DS. Thyroid function testing should be performed at 6 months and 12 months of age as well as yearly thereafter. Evaluation of the ears for infection as well as objective hearing tests should be performed at every visit. Formal evaluation for refractive errors requiring glasses should be performed at least every two years with subjective vision assessments with each visit. After the age of three, an x-ray of the neck should be obtained to screen for atlanto-axial instability. As the child ages, yearly symptom screening for obstructive sleep apnea should be performed.

# Treatment
Treatment of individuals with Down Syndrome depends on the particular manifestations of the disease. For instance, individuals with congenital heart disease may need to undergo major corrective surgery soon after birth. Other individuals may have relatively minor health problems requiring no therapy.

## Plastic surgery
Plastic surgery has sometimes been advocated and performed on children with Down syndrome, based on the assumption that surgery can reduce the facial features associated with Down syndrome, therefore decreasing social stigma, and leading to a better quality of life. Plastic surgery on children with Down syndrome is uncommon, and continues to be controversial.  Researchers have found that for facial reconstruction, "...although most patients reported improvements in their child's speech and appearance, independent raters could not readily discern improvement...."  For partial glossectomy (tongue reduction), one researcher found that 1 out of 3 patients "achieved oral competence," with 2 out of 3 showing speech improvement.  Len Leshin, physician and author of the ds-health website, has stated, "Despite being in use for over twenty years, there is still not a lot of solid evidence in favor of the use of plastic surgery in children with Down syndrome."  The National Down Syndrome Society has issued a "Position Statement on Cosmetic Surgery for Children with Down Syndrome" which states that "The goal of inclusion and acceptance is mutual respect based on who we are as individuals, not how we look."

## Alternative treatment
The Institutes for the Achievement of Human Potential is a non-profit organization which treats children who have, as the IAHP terms it, "some form of brain injury," including children with Down syndrome. The approach of "Psychomotor Patterning" is not proven, and is considered alternative medicine.

# Lifespan
While there is evidence pointing to a  shortened life expectancy for people with Down syndrome, it is clear that persons with Down syndrome are living longer then they have previously. One study, carried out in the United States, showed an average lifespan of 49 years. , as opposed to 25 years of age before 1980, and approximately 10 years of age in 1929.
In the past congenital heart disease, leukemias,untreated hypothyroidism and infections contributed to mortality, where today the causes of death are more likely to be complications of Alzheimer's disease.
It remains to be seen what their ultimate life expectancy will be,but it seems unlikely to approach the national average, mainly because of the burden of the neurodegenerative disorders to which they are predisposed.