Down syndrome

What is Down syndrome?

Down syndrome is also known as trisomy 21 syndrome. It is a genetic disorder that is characterised by recognisable physical features (mongolism), mental retardation and other associated medical problems. The way in which the syndrome expresses itself is highly variable between patients. About 15% of patients with severe Down syndrome die during the first year of life, whilst others show varying degree of signs and symptoms of the disease and can have a normal life expectancy.

Who gets Down syndrome and why?

It is estimated that Down syndrome occurs in approximately 1 in 700-800 live births. It is caused by a chromosomal disorder in which an error in cell division results in the presence of an additional third chromosome 21 or “trisomy 21”. Instead of the normal number of 46 chromosomes in each cell, the individual with Down syndrome has 47 chromosomes. This chromosome abnormality is called Standard Trisomy 21. It is the most common type of Down syndrome and occurs in 90-95% of cases. The two other variants of Down syndrome are called Translocation Trisomy 21 and Mosaic Down syndrome.

Apart from a few cases of Translocation Down syndrome, Down syndrome is not an inherited condition. A factor that does influence the incidence of Down syndrome is the age of the mother when she conceives. The incidence at various maternal ages is shown below.

Maternal age (years)	Incidence of Down syndrome (live births)
15-29	1 in 1500
30-34	1 in 800
35-39	1 in 270
40-44	1 in 100
Older than 45	1 in 50

What are the clinical features of Down syndrome?

The clinical features of Down syndrome include the characteristic physical, developmental and multisystem abnormalities. The physical features most recognised in patients with Down syndrome are:

Flattening of the back of the head
Slanting of the eyelids
Small skin folds at the inner corner of the eyes
Depressed nasal bridge
Stumpy limbs and loose joint ligaments

Skin disorders in Down syndrome

Patients with Down syndrome are affected more often by chronic skin conditions and skin infections than the general population.

A newborn with Down syndrome will often have blue hands and feet at birth due to decreased blood circulation. This may be apparent for a few days and in some cases may develop into cutis marmorata, a skin condition characterised by bluish mottling all over the skin. Although this condition is common in many newborns, it may last several months longer in infants with Down syndrome.

Usually up until the age of 5 years the skin is soft and velvety. From 5 years and onwards skin changes start to take place and can become a major physical feature of Down syndrome. Chronic skin conditions and skin infections occurring commonly in patients with Down syndrome are described in the following tables.

Chronic skin conditions	Features
Xerosis (dry skin)	Skin becomes abnormally dry, rough and inelastic between 5-10 years By 15 years, more than 70% show generalised xerosis of mild-to-moderate degree
Atopic dermatitis	Occurs in more than 50% of patients in childhood Red, scaly, itchy skin Most often appears on the cheeks, behind the ears, behind the knees, and in elbow creases Seborrhoeic dermatitis occurs in about 31% of patients
Palmoplantar keratoderma	Occurs in 40-75% of patients Growth of very thick skin on the palms and soles
Cheilitis	Fissures and red, scaly skin at the corners of the mouth and lips May be complicated by infection from bacteria or yeast (oral candidiasis) Incidence and severity increase with age
Syringoma	Benign skin tumours that arise from sweat ducts Occur in 18-39% of patients, with females affected more than twice as often as males Small multiple raised nodules usually found around the eyes, neck and chest
Oral lesions	Fissured tongue occurs in 80% of children with Down syndrome and is often associated with macroglossia (abnormally enlarged tongue) Geographic tongue occurs in about 11% of patients
Elastosis perforans serpiginosa	Deep red raised lesions appearing in a linear or circular pattern Most often occur on the back and sides of the neck, but also found on the chin, cheeks, arms and knees Usually appear during the second decade of life Males affected 4 times more often than females Lesions may last for well over 10 years before spontaneously disappearing
Vitiligo	Loss of pigmentation (colour) of the skin May occur anywhere on the body and at any age
Alopecia areata	Patchy hair loss occurs in 6-9% of patients (compared to 1-2% of the general population) Alopecia is unpredictable with patients experiencing several episodes of hair loss and regrowth during their lifetime

Skin infection	Features
Bacterial infections	A variety of bacterial skin infections affect patients with Down syndrome regardless of whether they have associated atopic dermatitis. Folliculitis Boils Impetigo
Fungal infections	These frequently occur in adolescents with Down syndrome who are institutionalised. Tinea pedis Onychomycosis (nail infection)
Parasitic infections	People with Down syndrome are predisposed to crusted scabies infestation.

What is the treatment for Down syndrome?

There is no specific treatment for Down syndrome. Treatment is directed at managing and preventing any complications that may arise.

Skin disorders are treated with various preparations, including emollients, topical medications and laser treatment. Click on individual skin disorders in the tables above for details on treatment options.

Related information

References:

OMIM – Online Mendelian Inheritance in Man (search term Down syndrome)
Book: Textbook of Dermatology. Ed Rook A, Wilkinson DS, Ebling FJB, Champion RH, Burton JL. Fourth edition. Blackwell Scientific Publications.
Down Syndrome – emedicine dermatology, the online textbook

On DermNet NZ:

Other websites:

Directory of Down Syndrome Internet Sites

Books about skin diseases:

See the DermNet NZ bookstore

Author: Vanessa Ngan, staff writer