Introduction

Down syndrome is the most prevalent genetic alteration (1:600 to 1:1000) and probably the commonest clinically classifiable condition associated with learning disability¹. Although the first published accurate description of the syndrome’s features belongs to Sir John L. Down (1866), it had presumably been described before by Esquirol (1838) and Seguin (1846)² In 1959, Lejeune and Jacobs independently determined the genetic origin of the alteration: trisomy of chromosome 21³.
Down syndrome is a congenital autosomal anomaly where part or all of chromosome 21 is duplicated^3,4. Often duplication involves band 22q of the chromosome. Approximately 95% of cases have true trisomy whereas the other 5% present different chromosomal abnormalities like translocation, partial trisomy or mosaicism³. The aetiology of this genetic anomaly is unknown but it is thought to be multifactorial. Maternal age plays an important role in its frequency^3,5.
There is wide variation among people with Down syndrome. Despite the numerous features that characterise the trisomy 21 phenotype, it is important to have a genetically verified diagnosis. Not every person with the syndrome presents every feature of the syndrome². Furthermore, it has been demonstrated that the syndrome may be underdiagnosed in diverse ethnic groups because of racial variation in physical characteristics^6,7.
Besides characteristic physical features, there are also systemic and cognitive conditions that may affect oral health and dental management. Knowledge of these aspects, as well as of the orofacial manifestations and the development of the oral structures in the syndrome, is necessary to plan an effective oral health programme.