BASICS

DESCRIPTION

• Down syndrome is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome and is named after John Langdon Down who described it in 1866.

• It is also called Trisomy 21.

EPIDEMIOLOGY

Incidence

• Down syndrome occurs worldwide in all ethnic groups and economic classes.

• In 2006, the Centers for Disease Control and Prevention estimated the rate as 1 per 733 live births in the US (5,529 new cases per year).

RISK FACTORS

• Advanced maternal age. At maternal age 20–24 years, the probability is 1 in 1,562, at age 35–39 years, the probability is 1 in 214, and above 45 years the probability is 1 in 19.

• 8% of children with Down syndrome are born to women under the age of 35 reflecting the fertility in this group.

• Paternal age over 42 years also increases the risk.

Genetics

Chromosomal abnormality characterized by the presence of an extra copy of genetic material on the 21st chromosome. If whole, it is Trisomy 21, which is caused by a meiotic nondisjunction event.

GENERAL PREVENTION

Screening can be performed during pregnancy and includes amniocentesis, chorionic villus sampling, or percutaneous umbilical cord blood sampling.

COMMONLY ASSOCIATED CONDITIONS

• Males are usually infertile exhibiting defects in spermatogenesis and females have significantly lower rates of conception.

• Hematologic malignancies

• Thyroid disorders

• Gastrointestinal disorders

• Epilepsy

• Alzheimer’s disease tends to develop at an earlier age, often before age 50 years, and shortens the life expectancy.

DIAGNOSIS

HISTORY

Maternal and paternal age

PHYSICAL EXAM

• Small chin (microgenia)

• Round face

• Protruding or oversized tongue (macroglossia) associated with a small oral cavity

• Short neck

• Brushfield spots (white or grayish/brown) in the periphery of the iris

• Epicanthal eyelid folds causing an almond shaped appearance

• Upward slanting palpebral fissures

• Shorter limbs

• A single palmar fold

• Poor muscle tone (hypotonia)

• Mental retardation

• Speech delay

• Short stature

• Strabismus

• Cataracts

• Increased obesity with age

DIAGNOSTIC TESTS & INTERPRETATION

Diagnostic Procedures/Other

• Prenatal diagnosis possible if gene mutation known

• Albinism is a clinical diagnosis that can be confirmed in some cases with DNA testing

• Optical coherence testing (OCT) demonstrates macular hypoplasia

• Multichannel visual evoked potentials demonstrate excessive decussation of retinal ganglion cell axons at the chiasm in most cases

• Molecular genetic testing may determine the specific mutations and thus helps identify the subtype of oculocutaneous albinism

• Tests for OCA1, OCA2, and OA1 are available clinically

• Tests for other genes only for research purposes

TREATMENT

ADDITIONAL TREATMENT

General Measures

Medical and surgical treatment as indicated for any associated conditions.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Childhood intervention, vocational training, a supportive environment, and medical treatment can improve the development of children with Down syndrome and improve the quality of life. Cognitive ability can be improved with education.

PATIENT EDUCATION

National Down Syndrome Society (NDSS): www.ndss.org

PROGNOSIS

• The life expectancy of people with Down syndrome has increased in recent years.

• In 1980 it was 25 years. In 2002 it was 49 years. The causes of death have changed. Those who survive into their 40s and 50s often develop chronic neurodegenerative disease (Alzheimer’s).

ADDITIONAL READING

• Center for Disease Control and Prevention (CDC). Improved national prevalence estimates for 18 selected major birth defects, United States, 1999–2001. MMWR Morb Mortal Wkly Rep 2006;54(51):1301–1305.

• Huether CA, Ivanovich J, Goodwin BS, et al. Maternal age specific risk estimates for Down syndrome among live births in whites and other races from Ohio and metropolitan Atlanta, 1970–1989. J Med Genet 1998;35(6):482–490.

• National Down Syndrome Center. http://www.ndsccenter.org/resources/package.

CODES

ICD9

• 379.99 Other ill-defined disorders of eye

• 743.69 Other congenital anomalies of eyelids, lacrimal system, and orbit

• 758.0 Down’s syndrome

CLINICAL PEARLS

• Risk factors for Down syndrome include advanced maternal and paternal age.

• Ophthalmic features of Down syndrome include Brushfield spots, or grayish brown spots on the peripheral iris, and cataracts.

• The life expectancy has increased in recent years.

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