Down syndrome (DS) (synonyms: trisomy 21; Down syndrome; Langdon-Down syndrome; Langdon-Down disease; mongolism; mongoloism; ICD-10-GM Q90.-: Down syndrome) is a variety of congenital mental and physical impairments associated with malformations. The synonyms Mongolism and Mongoloism come from the fact that the characteristic facial features as well as the eye shape resemble those of the Asian ethnic group.
More than 95% of Down syndrome is caused by a triplication of chromosome 21, in this case it is called free trisomy 21. For more information see Causes.
Sex ratio: Males to females is 1: 1.
Frequency peak: the risk of developing Down syndrome is directly related to an increasing age of the mother:
| Age of mother | Frequency in % |
| 20-38 | approx. 0.1 |
| 30-38 | 0,1-0,5 |
| 38-42 | 0,5-1,5 |
| 42-43 | 1,5-2 |
| 43-45 | 2-3,5 |
| > 45 | > 3,5 |
The prevalence (frequency of disease) is 0.125-0.2% (worldwide).
The incidence (frequency of new cases) is approximately 0.9 to 1 case per 100,000 population per year (worldwide).The prevalence (disease incidence) is 0.125-0.2% (worldwide).
Course and prognosis: The average life expectancy of a person with Down syndrome is about 60 years. Approximately every 10th affected person reaches the age of 70. The causes of mortality (number of deaths in a certain period of time, related to the number of the population concerned) differ from those of the normal population mainly in the aspects that an increased occurrence of general carcinomas (cancers) with a special focus on leukemias (blood cancers; e.g. acute lymphatic or myeloid leukemia) can be observed. Furthermore, dementia is 20 times more frequent as a cause of death than in the general population; approximately 70% of patients with Down syndrome die of dementia; among those with dementia, those with an ApoE4 allele died most frequently (7-fold increased risk of death).
Comorbidities: Depression and obstructive sleep apnea syndrome (OSA; breathing pauses during sleep caused by obstruction of the airways, often occurring several hundred times per night) are more common in children and adolescents with Down syndrome. Also can be considered a frequent occurrence of celiac disease with about 5% and autism spectrum disorder (ASD) with a probability of about 7%.