An example of a contiguous gene syndrome is Angelman syndrome. It is due to the loss of a series of genes from a region of chromosome 15 termed 15q13-15. (The syndrome is characterized by four cardinal features: severe developmental delay or mental retardation, severe speech impairment, gait ataxia (wobbliness) and/or tremulousness of the limbs; and a unique behavior with an inappropriate happy demeanor that includes frequent laughing, smiling, and excitability. In addition, microcephaly (abnormally small head) and seizures are common.)
In Angelman syndrome the genes that were lost prove always to have been from the mother. If they were from the father, an entirely different contiguous gene syndrome results called Prader-Willi syndrome.