A contiguous gene syndrome is a syndrome caused by abnormalities of 2 or more gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s that are located next to each other on a chromosome

Chromosome

A chromosome is an organized structure of DNA and protein found in cells. It is a single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences. Chromosomes also contain DNA-bound proteins, which serve to package the DNA and control its functions.Chromosomes...

. Prader-Willi Syndrome

Prader-Willi syndrome

Prader–Willi syndrome is a rare genetic disorder in which seven genes on chromosome 15 are deleted or unexpressed on the paternal chromosome...

, which is caused by the microdeletion of 15q11-13, is a common example. Prader-Willi syndrome

Prader-Willi syndrome

Prader–Willi syndrome is a rare genetic disorder in which seven genes on chromosome 15 are deleted or unexpressed on the paternal chromosome...

 occurs when the deletion occurs on the paternal chromosome. If this deletion occurs on the maternal chromosome, it causes the Angelman syndrome

Angelman syndrome

Angelman syndrome is a neuro-genetic disorder characterized by intellectual and developmental delay, sleep disturbance, seizures, jerky movements , frequent laughter or smiling, and usually a happy demeanor....

. 22q11.2 deletion syndrome is a particularly well known example. WAGR syndrome (deletions of 11p13) is another example.