Some of these occur in an autosomal dominant manner. The cause of the remaining cases is unclear. If otherwise normal parents have one child with the condition, the next child has a 4% risk of being affected. Genetics
Several genes and specific regions on chromosomes (loci) have been shown or suggested to be associated with Hirschsprungs disease:
The RET proto-oncogene accounts for the highest proportion of both familial and sporadic cases, with a wide range of mutations scattered along its entire coding region. A proto-oncogene  can cause cancer if it is mutated or overexpressed. RET proto-oncogene
RET is a gene that codes for proteins that assist cells of the neural crest in their movement through the digestive tract during the development of the embryo. Those neural crest cells eventually form bundles of nerve cells called ganglions. EDNRB codes for proteins that connect these nerve cells to the digestive tract. Thus, mutations in these two genes could directly lead to the absence of certain nerve fibers in the colon. Research suggests that several genes are associated with Hirschsprungs disease. Also, new research suggests that mutations in genomic sequences involved in regulating EDNRB have a bigger impact on Hirschsprungs disease than previously thought.RET can mutate in many ways and is associated with Down syndrome. Since Down syndrome is comorbid in 2% of Hirschsprungs cases, a likelihood exists that RET is involved heavily in both Hirschsprungs disease and Down syndrome. RET is also associated with medullary thyroid cancer and neuroblastoma, which is a type of cancer common in children.
Zoophilia
The term zoophilia was introduced into the field of research on sexuality in Psychopathia Sexualis (1886) by Krafft-Ebing, who described a number of cases of "violation of animals (bestiality)", as well as "zoophilia erotica", which he defined as a sexual attraction to animal skin or fur. The term zoophilia derives from the combination of two nouns in Greek: ζῷον (zṓion, meaning "animal") and φιλία (philia, meaning "(fraternal) love"). In general contemporary usage, the term zoophilia may refer to sexual activity between human and non-human animals, the desire to engage in such, or to the specific paraphilia (i.e., the atypical arousal) which indicates a definite preference for animals over humans as sexual partners. Although Krafft-Ebing also coined the term zooerasty for the paraphilia of exclusive sexual attraction to animals, that term has fallen out of general use. Zoosexuality
The term zoosexual was proposed by Hani Miletski in 2002 as a value-neutral term. Usage of zoosexual as a noun (in reference to a person) is synonymous with zoophile, while the adjectival form of the word – as, for instance, in the phrase "zoosexual act" – may indicate sexual activity between a human and an animal. The derivative noun "zoosexuality" is sometimes used by self-identified zoophiles in both support groups and on internet-based discussion forums to designate sexual orientation manifesting as sexual attraction to animals. Bestiality
The legal term bestiality has three common pronunciations: [ˌbestʃiˈæləti] or [ˌbistʃiˈæləti] in the United States, and [ˌbestiˈæləti] in the United Kingdom.