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What is Mental Retardation?

Mental Retardation (MR) is a disorder with a wide variety of symptoms. It is characterized by an IQ of less than 70, and coincides with behavioural and/or adaptation problems in daily life.

Nothing is known about the causative factors of MR in a large part of the patient population. In 20-45% of the severe cases of MR, the cause of the disease is not known at all. This percentage increases to 80% for the moderate and mild cases.

Both genetic and environmental factors can play a role in those cases for which a cause can be determined. Environmental factors in these cases may be, among others: birth defects, infections and toxins.

The genetic factors can be divided into chromosomal and monogenic causes. Trisomy 21 is the most common chromosomal cause, while other forms of trisomy, monosomy and microdeletions can result in the development of (severe) MR.

Thanks to the enormous improvements in the fields of clinical genetics and molecular biology, the knowledge about monogenic disorders has greatly improved. Finding new genes and analysing their protein product gives us new insights in to how the brain develops and functions.