Pitt-Hopkins syndrome is a genetic disorder characterized by mental retardation

Mental retardation

Mental retardation is a generalized disorder appearing before adulthood, characterized by significantly impaired cognitive functioning and deficits in two or more adaptive behaviors...

, wide mouth

Mouth

The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

 and distinctive facial

Facial

A facial is a procedure involving a variety of skin treatments, including: steam, exfoliation, extraction, creams, lotions, facial masks, peels, and massage...

 features, and intermittent hyperventilation

Hyperventilation

Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...

 followed by apnea

Apnea

Apnea, apnoea, or apnœa is a term for suspension of external breathing. During apnea there is no movement of the muscles of respiration and the volume of the lungs initially remains unchanged...

. It is associated with an abnormality within chromosome 18

Chromosome 18 (human)

125px|rightChromosome 18 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 18 spans about 85 million base pairs and represents about 2.5 percent of the total DNA in cells.Identifying genes on each chromosome is an active area of genetic...

: specifically, it is caused by an insufficient expression of the TCF4

TCF4

Transcription factor 4, also known as immunoglobulin transcription factor 2 and TCF4, is a protein acting as a transcription factor. In humans this protein is encoded by the TCF4 gene.- Function :...

 gene.

Professor Phillip Beales, of the Institute of Child Health, has speculated that Peter the Wild Boy

Peter the Wild Boy

Peter the Wild Boy was a mentally handicapped boy from Hannover in northern Germany who was found in 1725 living wild in the woods near Hamelin , the town of Pied Piper legend...

suffered from Pitt-Hopkins Syndrome.