Down syndrome is associated with a wide range of comorbidities, but the most common is congenital heart disease, which affects up to 50% of babies born with the condition. Beyond the heart, people with Down syndrome face significantly elevated risks for thyroid disorders, Alzheimer’s disease, sleep apnea, hearing and vision problems, leukemia, and several gastrointestinal conditions. Many of these can be managed effectively with routine screening and early treatment, which is a key reason life expectancy has climbed from just 9 years in 1900 to over 60 years today.
Congenital Heart Disease
Heart defects are the single most common comorbidity in Down syndrome. Roughly half of all infants with Down syndrome are born with some form of congenital heart disease, compared to about 1% in the general population. The most frequent type is an atrioventricular septal defect, where the walls between the heart’s chambers don’t form completely. This defect, along with ventricular septal defects (holes between the lower chambers), accounts for about 76% of all heart disease seen in Down syndrome. Other structural problems include tetralogy of Fallot, a combination of four heart abnormalities, found in roughly 13% of cases.
Most of these defects are now identified through echocardiography shortly after birth, and surgical repair in infancy has become routine. The success of these surgeries is one of the biggest reasons life expectancy has improved so dramatically over the past several decades.
Alzheimer’s Disease
The link between Down syndrome and Alzheimer’s is one of the strongest genetic connections in medicine. The gene responsible for producing amyloid protein, the substance that builds up in the brains of people with Alzheimer’s, sits on chromosome 21. Because people with Down syndrome carry three copies of that chromosome instead of two, they overproduce amyloid throughout their lives. By age 40, virtually all people with Down syndrome show the brain changes associated with Alzheimer’s, and the lifetime risk of developing clinical dementia exceeds 95%.
The mean age of Alzheimer’s diagnosis in this population is around 53 to 54 years, roughly two decades earlier than in the general population. Between ages 40 and 49, an estimated 23% to 55% already have a clinical diagnosis. By ages 60 to 69, that figure rises to 75% to 88%. This early onset makes cognitive monitoring in middle adulthood essential for people with Down syndrome.
Thyroid Disorders
Thyroid dysfunction is extremely common in Down syndrome, and it can appear at any age. Congenital hypothyroidism (an underactive thyroid at birth) occurs in about 4% to 8% of newborns with Down syndrome, a rate 28 to 35 times higher than in the general population. Even more prevalent is subclinical hypothyroidism, a milder form where the thyroid is slightly underperforming. This affects anywhere from 7% to 40% of individuals with Down syndrome, with many studies reporting rates around 25% to 30%.
Autoimmune thyroid disease also plays a role. Antibodies that attack the thyroid gland are found in 13% to 34% of people with Down syndrome. Graves’ disease, which causes an overactive thyroid, occurs at about 0.66% in this population compared to 0.02% in the general population. Because thyroid problems can quietly affect growth, energy, weight, and cognition, the American Academy of Pediatrics recommends annual thyroid screening starting in infancy and continuing through adulthood.
Hearing and Vision Problems
Sensory impairments are among the most widespread but often underrecognized comorbidities. Up to 75% of children with Down syndrome have some degree of hearing loss, which can be present at birth or develop over time. The narrow ear canals common in Down syndrome make fluid buildup and middle-ear infections more likely, contributing to both temporary and permanent hearing changes. Guidelines recommend hearing screening at birth, again at six months, then every six months through early childhood, and annually after that.
Vision problems affect more than half of children with Down syndrome. Strabismus (misaligned eyes) occurs in 25% to 60% of cases. Cataracts, including types present at birth, are found in 4% to 30%. Farsightedness and nearsightedness are also significantly more common. A pediatric ophthalmology evaluation within the first six months of life is standard practice, with ongoing monitoring throughout childhood.
Obstructive Sleep Apnea
Sleep apnea is remarkably common in Down syndrome, driven by a combination of low muscle tone, a smaller airway, and a relatively large tongue. Current estimates place the prevalence around 50% to 100% in children, with rates approaching near-universal in adulthood. A large study of over 120 unselected patients with Down syndrome found that 66% had obstructive sleep apnea on a formal sleep study. A separate review of 144 sleep studies found the rate at 78%.
Untreated sleep apnea can worsen behavioral and learning difficulties, contribute to heart strain, and reduce quality of life. Because symptoms like snoring, restless sleep, and daytime fatigue can easily be attributed to other causes, sleep apnea in this population frequently goes undiagnosed without proactive screening.
Leukemia and Blood Disorders
Children with Down syndrome face a roughly 20-fold increased risk of developing acute leukemia compared to the general population. Both major types of childhood leukemia are overrepresented: acute lymphoblastic leukemia (the more common form) and acute myeloid leukemia. Interestingly, a transient form of leukemia unique to Down syndrome can appear in newborns and often resolves on its own within the first few months, though it requires monitoring because a small percentage of these infants go on to develop true leukemia later.
Despite the higher incidence, treatment outcomes for children with Down syndrome who develop leukemia have improved considerably, though these children can be more sensitive to certain chemotherapy side effects and often require adjusted treatment plans.
Gastrointestinal Conditions
Structural abnormalities of the digestive tract occur more frequently in newborns with Down syndrome. Duodenal atresia, where the first section of the small intestine is blocked or incomplete, is one of the most closely linked. Hirschsprung disease, where nerve cells are missing from part of the colon, is also overrepresented. When both conditions occur together, the odds are dramatically elevated: one large analysis found the combination was 122 times more common in infants with Down syndrome than in the general population.
Celiac disease is another notable association. People with Down syndrome have a higher rate of the autoimmune reaction to gluten, making screening worthwhile if symptoms like poor growth, chronic diarrhea, or abdominal discomfort develop. Gastroesophageal reflux and chronic constipation are also more frequent across all age groups.
Epilepsy
Seizure disorders follow a distinctive pattern in Down syndrome, with two peak periods of onset. The first occurs during the first two years of life, and the second after age 30. By age 50, nearly half of people with Down syndrome have epilepsy, often in connection with the onset of Alzheimer’s-related brain changes. Seizures in younger children may present differently than in older adults, and the later-onset form is closely tied to the progression of dementia.
Respiratory Infections
Immune system differences in Down syndrome lead to a significantly higher rate of respiratory infections, particularly in infancy. Babies with Down syndrome have a 62-fold higher rate of pneumonia during their first year of life compared to infants without the condition. Differences in airway anatomy, lower muscle tone affecting cough strength, and subtle immune deficiencies all contribute. This vulnerability decreases with age but remains elevated throughout life, making respiratory illness a persistent concern.
Why Routine Screening Matters
What stands out across all of these comorbidities is how many of them are either treatable or manageable when caught early. Heart defects can be surgically repaired. Thyroid disorders respond well to medication. Hearing aids and vision correction can prevent developmental setbacks. Sleep apnea can be treated with positive airway pressure devices or surgery. The American Academy of Pediatrics publishes detailed screening timelines for children with Down syndrome that cover thyroid function, hearing, vision, heart health, and more, starting at birth and continuing through early adulthood. Following these guidelines closely is one of the most impactful things families can do to support long-term health and quality of life.