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- Congenital condition associated with intellectual disability and an increased risk of multisystem medical problems
- System(s) affected: Neurologic (100%); Cardiac (40–50%); Gastrointestinal (GI) (8–12%)
- Etiology: Presence of all or part of an extra chromosome 21
- Synonym(s): Trisomy 21; Down syndrome (DS)
- Congenital heart disease is major cause of morbidity/mortality.
- Murmur may not be present at birth. Delay in recognition may lead to irreversible pulmonary hypertension.
- Life expectancy has increased to ~60 years.
- Age-related health issues occur at earlier age than in the general population.
- Communication difficulties may interfere with prompt recognition of some medical issues.
- The ACOG and ACMG recommend all pregnant women be offered prenatal screening and testing for DS:
- Maternal prenatal screening may be performed in the 1st or 2nd trimester.
- Prenatal diagnosis includes chorionic villus sampling or amniocentesis.
- Most, but not all, men with DS are believed to be infertile.
- Most women with DS are subfertile, but can conceive.
In the US, 1/691 live births, ~6,000 births/year (1)
~400,000 persons in the US
- DS occurs in all races with equal frequency.
- Chance of having an infant with DS increases with mother's age.
- Relatively more infants with DS are born to younger mothers because younger women are more likely to become pregnant.
- Prenatal diagnosis of DS is more common in older women, and a high percentage of such pregnancies are terminated.
- Online Mendelian Inheritance in Man (OMIM) #190685
- Inheritance: Most commonly sporadic nondisjunction resulting in trisomy 21
- Chance of having another child with DS is:
- 1% (or age risk, whichever is greater) after conceiving a pregnancy with nondisjunction trisomy 21
- 10–15% for mothers/sisters and 3–5% for fathers/brothers who carry balanced translocation with chromosome 21
- 100% if the parental translocation is 21:21 (45,t[21:21])
- Unclear after child with mosaic DS, but ~1%
- No prevention for nondisjunction trisomy 21
- Preimplantation diagnosis with in vitro fertilization (IVF), prenatal diagnosis and termination, and adoption are current options for expectant parents who do not wish to raise a child with DS.
- Trisomy 21: 95% of DS, an extra chromosome 21 is found in all cells due to nondisjunction, usually in maternal meiosis.
- Translocation DS: 3–4% of DS, extra chromosome 21q material is translocated to another chromosome (usually 13, 14, or 21); ~25% have parental origin.
- Mosaic trisomy 21: 1–2% of DS, manifestations may be milder.
Commonly Associated Conditions
- Congenital heart defects (40–50%)
- Feeding problems are common in infancy.
- Structural defects (12%)
- Gastroesophageal reflux
- Celiac disease (5%)
- Tracheal stenosis/tracheoesophageal fistula
- Pulmonary hypertension
- Obstructive sleep apnea (50–75%)
- Cryptorchidism, hypospadias
- Transient myeloproliferative disorder (10%): Generally resolves spontaneously; can be preleukemic (acute megakaryoblastic leukemia [AMKL]) in 20–30%
- Leukemia (AMKL or acute lymphoblastic leukemia [ALL]) in 0.5–1%
- Decreased risk of most solid tumors; increased risk of germ cell tumors
- Hypothyroidism: Congenital or acquired (4–18%)
- Atlantoaxial instability (15%): 2% symptomatic
- Short stature is common
- Scoliosis (some cases have adult onset)
- Hip problems (1–4%)
- Abnormal immune function with increased rate of respiratory infections
- Increased risk of autoimmune disorders, including Hashimoto thyroiditis, celiac disease, alopecia
- Intellectual disability ranging from near-normal to severe. Average is moderate intellectual disability.
- Autism spectrum disorder (<18%); autism (<6%)
- Seizures: (8%), typically occurring <1 year of age or >30 year of age
- Alzheimer disease: At least 25% at age 35 develop signs of dementia; percentage increases with age
- ADHD, obsessive-compulsive disorder (OCD), oppositional-defiant disorder, autism spectrum disorder increased frequency in children
- Generalized depression and anxiety more common young adults/adults.
- Hearing loss (75%): Mostly conductive due to high frequency of asymptomatic middle ear effusion; otitis media (50–70%)
- Visual impairment (60%): Mostly strabismus (refractive errors, 15%), nystagmus, cataracts (15%)
- Xerosis, eczema, palmoplantar hyperkeratosis, atopic or seborrheic dermatitis, onychomycosis, syringomas, furunculosis/folliculitis