ABSTRACT
The late 20th century saw much interest in the basal ganglia and frontostriatal system, while this century may be the turn of the cerebellum, the Last Great Unknown or Terra Incognita. Developmental disorders, unlike Angelman's, are typically a product of the interaction of genes and environment. The nature and extent of any genetic contribution, with respect to developmental disorders generally, is becoming clearer with the ability to perform genome-wide associative studies across many thousands of individuals. It is thus possible to identify genetic variation in single nucleotide polymorphisms, and determine the extent of chromosomal variants such as copy-number variations, which can lead to pathological increase or decrease of function. However, evidence to date suggests that developmental disorders tend to manifest as an apparent consequence of commonly-occurring variants at a large number of loci, even though any single variant may only have a small effect upon an overall polygenic disease risk.
