A boy with<unk>  using a cordless drill to assemble a book case An eight-year-old boy with<unk>  Those with<unk>  nearly always have physical and intellectual disabilities. As adults, their mental abilities are typically similar to those of an 8- or 9-year-old. They also typically have poor immune function and generally reach developmental milestones at a later age. They have an increased risk of a number of other health problems, including congenital heart defect, epilepsy, leukemia, thyroid diseases, and mental disorders. Characteristics Percentage Characteristics Percentage Mental impairment 99% Abnormal teeth 60% Stunted growth 90% Slanted eyes 60% Umbilical hernia 90% Shortened hands 60% Increased skin on back of neck 80% Short neck 60% Low muscle tone 80% Obstructive sleep apnea 60% Narrow roof of mouth 76% Bent fifth finger tip 57% Flat head 75% Brushfield spots in the iris 56% Flexible ligaments 75% Single transverse palmar crease 53% Proportionally large tongue 75% Protruding tongue 47% Abnormal outer ears 70% Congenital heart disease 40% Flattened nose 68% Strabismus ~35% Separation of first and second toes 68% Undescended testicles 20% Physical Feet of a boy with<unk> , showing the deviated first toes People with<unk>  may have some or all of these physical characteristics: a small chin, slanted eyes, poor muscle tone, a flat nasal bridge, a single crease of the palm, and a protruding tongue due to a small mouth and relatively large tongue. These airway changes lead to obstructive sleep apnea in around half of those with<unk> . Other common features include: a flat and wide face, a short neck, excessive joint flexibility, extra space between big toe and second toe, abnormal patterns on the fingertips and short fingers. Instability of the atlantoaxial joint occurs in about 20% and may lead to spinal cord injury in 1–2%. Hip dislocations may occur without trauma in up to a third of people with<unk> . Growth in height is slower, resulting in adults who tend to have short stature—the average height for men is 154 cm (5 ft 1 in) and for women is 142 cm (4 ft 8 in). Individuals with<unk>  are at increased risk for obesity as they age. Growth charts have been developed specifically for children with<unk> . Neurological This syndrome causes about a third of cases of intellectual disability. Many developmental milestones are delayed with the ability to crawl typically occurring around 8 months rather than 5 months and the ability to walk independently typically occurring around 21 months rather than 14 months. Most individuals with<unk>  have mild (IQ: 50–69) or moderate (IQ: 35–50) intellectual disability with some cases having severe (IQ: 20–35) difficulties. Those with mosaic<unk>  typically have IQ scores 10–30 points higher than that. As they age, people with<unk>  typically perform worse than their same-age peers. Commonly, individuals with<unk>  have better language understanding than ability to speak. Between 10 and 45% have either a stutter or rapid and irregular speech, making it difficult to understand them. After reaching 30 years of age, some may lose their ability to speak. They typically do fairly well with social skills. Behavior problems are not generally as great an issue as in other syndromes associated with intellectual disability. In children with<unk> , mental illness occurs in nearly 30% with autism occurring in 5–10%. People with<unk>  experience a wide range of emotions. While people with<unk>  are generally happy, symptoms of depression and anxiety may develop in early adulthood. Children and adults with<unk>  are at increased risk of epileptic seizures, which occur in 5–10% of children and up to 50% of adults. This includes an increased risk of a specific type of seizure called infantile spasms. Many (15%) who live 40 years or longer develop Alzheimer's disease. In those who reach 60 years of age, 50–70% have the disease. Senses Brushfield spots, visible in the irises of a baby with<unk>  Hearing and vision disorders occur in more than half of people with<unk> . Vision problems occur in 38 to 80%. Between 20 and 50% have strabismus, in which the two eyes do not move together. Cataracts (cloudiness of the lens of the eye) occur in 15%, and may be present at birth. Keratoconus (a thin, cone-shaped cornea) and glaucoma (increased eye pressure) are also more common, as are refractive errors requiring glasses or contacts. Brushfield spots (small white or grayish/brown spots on the outer part of the iris) are present in 38 to 85% of individuals. Hearing problems are found in 50–90% of children with<unk> . This is often the result of otitis media with effusion which occurs in 50–70% and chronic ear infections which occur in 40 to 60%. Ear infections often begin in the first year of life and are partly due to poor eustachian tube function. Excessive ear wax can also cause hearing loss due to obstruction of the outer ear canal. Even a mild degree of hearing loss can have negative consequences for speech, language understanding, and academics. It is important to rule out hearing loss as a factor in social and cognitive deterioration. Age-related hearing loss of the sensorineural type occurs at a much earlier age and affects 10–70% of people with<unk> . Heart The rate of congenital heart disease in newborns with<unk>  is around 40%. Of those with heart disease, about 80% have an atrioventricular septal defect or ventricular septal defect with the former being more common. Mitral valve problems become common as people age, even in those without heart problems at birth. Other problems that may occur include tetralogy of Fallot and patent ductus arteriosus. People with<unk>  have a lower risk of hardening of the arteries. Cancer Although the overall risk of cancer in<unk>  is not changed, the risk of testicular cancer and certain blood cancers, including acute lymphoblastic leukemia (ALL) and acute megakaryoblastic leukemia (AMKL) is increased while the risk of other non-blood cancers is decreased. People with<unk>  are believed to have an increased risk of developing cancers derived from germ cells whether these cancers are blood- or non-blood-related. Blood cancers Leukemia is 10 to 15 times more common in children with<unk> . In particular, acute lymphoblastic leukemia is 20 times more common and the megakaryoblastic form of acute myeloid leukemia (acute megakaryoblastic leukemia), is 500 times more common. Acute megakaryoblastic leukemia (AMKL) is a leukemia of megakaryoblasts, the precursors cells to megakaryocytes which form blood platelets. Acute lymphoblastic leukemia in<unk>  accounts for 1–3% of all childhood cases of ALL. It occurs most often in those older than nine years or having a white blood cell count greater than 50,000 per microliter and is rare in those younger than one year old. ALL in<unk>  tends to have poorer outcomes than other cases of ALL in people without<unk> . In<unk> , AMKL is typically preceded by transient myeloproliferative disease (TMD), a disorder of blood cell production in which non-cancerous megakaryoblasts with a mutation in the GATA1 gene rapidly divide during the later period of pregnancy. The condition affects 3–10% of babies with Down. While it often spontaneously resolves within three months of birth, it can cause serious blood, liver, or other complications. In about 10% of cases, TMD progresses to AMKL during the three months to five years following its resolution. Non-blood cancers People with<unk>  have a lower risk of all major solid cancers, including those of lung, breast, and cervix, with the lowest relative rates occurring in those aged 50 years or older. This low risk is thought due to an increase in the expression of tumor suppressor genes present on chromosome 21. One exception is testicular germ cell cancer which occurs at a higher rate in<unk> . Endocrine Problems of the thyroid gland occur in 20–50% of individuals with<unk> . Low thyroid is the most common form, occurring in almost half of all individuals. Thyroid problems can be due to a poorly or nonfunctioning thyroid at birth (known as congenital hypothyroidism) which occurs in 1% or can develop later due to an attack on the thyroid by the immune system resulting in Graves' disease or autoimmune hypothyroidism. Type 1 diabetes mellitus is also more common. Gastrointestinal Constipation occurs in nearly half of people with<unk>  and may result in changes in behavior. One potential cause is Hirschsprung's disease, occurring in 2–15%, which is due to a lack of nerve cells controlling the colon. Other frequent congenital problems include duodenal atresia, pyloric stenosis, Meckel diverticulum, and imperforate anus. Celiac disease affects about 7–20% and gastroesophageal reflux disease is also more common. Teeth People with<unk>  tend to be more susceptible to gingivitis as well as early, severe periodontal disease, necrotising ulcerative gingivitis, and early tooth loss, especially in the lower front teeth. While plaque and poor oral hygiene are contributing factors, the severity
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