Down syndrome is a chromosomal disorder, trisomy 21, with distinct clinical features.
The prevalence is approximately 1 in 600 births but there is variation with maternal
age, so that at 40 years of age the incidence is about 1 in 40 births. However, the
numbers seen in any one country will vary depending on the prevailing attitude
towards prenatal screening and termination. The general physical features associated
with Down syndrome are a greater predisposition to cardiac defects, leukaemia of the
myeloid type, infective hepatitis infection (especially in institutionalized males),
although most children will have been vaccinated against viral forms. Coeliac disease
as well as thyroid disorders are also clinical features of this condition. Increasingly, a
form of early dementia, entitled disintegrative disorder is being recognized in
adolescents with Down syndrome. The features seen are of a progressive loss of
skills, both cognitive and physical and have obvious relevance in dentistry because of
the impact on personal oral care.
Varying degrees of mental retardation occur, and upper respiratory tract infections
and an inability to withstand infections generally are common. Physically,
predominant features are a rounded, small face with an under-developed mid-face
(1117HFig. 17.2), especially of the nasal bridge, an upward slant of the eyes with prominent
epicanthic folds, squints, cataracts, and Brushfield spots on the iris. The hands of
children with Down syndrome are stubby with a pronounced transverse palmar crease.
Intraorally the tongue is large, protruding, and sometimes heavily fissured (1118HFig. 17.3).
The palate may be high vaulted and narrow. There is usually a delay in the exfoliation
of primary teeth and in the eruption of permanent teeth, while some teeth may be
congenitally missing. Teeth that erupt are often microdont and/or hypoplastic (1119HFig.
17.4). There is a high prevalence of periodontal disease in the anterior alveolar
segments, especially in the mandible. This is probably due to impaired phagocyte
function in neutrophils and monocytes, combined with poor oral hygiene. Other
factors implicated in the pathophysiology of the extensive inflammation seen in Down
syndrome patients are enhanced PGE 2 production and increased activity of
plasminogen activators, and thus collagenase activity.
Key Points
Oral and dental features in Down syndrome:
- mid-face hypoplasia;
- large, fissured tongue;
- narrow, high-vaulted palate;
- delay in exfoliation/eruption;
- congenitally absent teeth;
- microdont/hypoplastic teeth;
Fragile X syndrome
Next to Down syndrome this is the most common cause of mental retardation. This
disorder is largely under-diagnosed; and people who have been classified as having
'mental handicap of unknown origin', especially if they are male, probably have
Fragile X syndrome. The condition is of particular significance because a high
proportion of affected individuals have congenital heart defects, usually mitral valve
prolapse, that may require antibiotic prophylaxis. Although males are predominantly
affected, milder versions of the disability may be seen in females.