Neotenic complex syndrome is a syndrome that presents as an extreme form of developmental delay, with the defining characteristic being neoteny of the patient. It was named in 2017 by Walker et al., who discovered several genes implicated in the syndrome. Prior to 2015, when whole genome sequencing was used to identify some genes involved in NCS, the condition was labelled "Syndrome X" when it was first discovered in Brooke Greenberg. Thereafter, others afflicted with the developmental symptoms were sought out in order to find common genetic aberrations that could provide clues as to cause. To date, sevenhuman females have been diagnosed with NCS. In five patients, codingde novo mutations were found in five different genes which fall into similar functional categories of transcription regulation and chromatin modification.
Genetics
In most of the patients analyzed, researchers identifiedmissensede novo mutations in a set of genes. Mutations in three of these genes were shared with those found in databases of individuals with developmental delay or autism spectrum disorder. A mutation in one gene was identified in a large knockout mouse study as likely to result in disease in humans. In two patients, a small non-coding region of chromosome X was discovered to have a rare haplotype. This region appears to have regulatory functions and is in close proximity to several genes involved in mental retardation. The fact that NCS has so far only be found in females may be by chance or may be due to the X linkage of some of the genes and regions potentially responsible for NCS, in which the lack of a healthy copy on a second X chromosome could render the disease lethal in males. Whether or not these mutations contribute to NCS is unclear. Not enough research has been conducted, complicated by the rarity of the syndrome. Many genetic differences were noted to be insignificant, and the effects of mutations in some genes are currently beyond scientific understanding.
