Core features of this disorder:
- impulsive eating, which can lead to being overweight
- compact body build
- undeveloped sexual characteristics
- poor muscle tone

Some Behaviors common with Autism:
- delays in motor development
- learning disabilities
- feeding problems 
- sleep disturbances
- skin picking
- temper tantrums

People who have this disorder are missing a portion of chromosome 15 but unlike Angelman Syndrome, receive this from the paternal side. 

Santa Clara University

This list includes disorders or conditions that are related to autism or autistic states/features but are not currently directly or officially included in the DSM. These disorders include:

- Williams Syndrome
- Fragile X Syndrome
- Landau - Kleffner Syndrome
- Prader - Willi Syndrome
- Angelman Syndrome
- Rett Syndrome
- Tardive Dyskinesia


List of Other Recognized Autism Spectrum and Related Disorders

No Author or Date. Related Disorders. Autism Research Institute. https://autism.org/related-disorders/#fragile-x-syndrome

Related Disorders 

A disorder characterized by fluent linguistic function but poor performance on standard IQ tests and great difficulty with spatial processing. This syndrome is caused by the absence of about 28 genes from one of the two chromosomes numbered 7.

Williams syndrome

Fragile X syndrome is perhaps the most common genetic form of intellectual disability. It results when the trinucleotide repeats (i.e., CGG repeats) in the long arm of the X chromosome number more than 200 repeats, as opposed to the normal 6-50 repeats. This extension of repeats leaves this region of DNA fragile, or prone to breakage. Specifically, the overexpansion causes methylation and transcriptional repression of the Fragile X Mental Retardation 1 gene (*FMR1*), which encodes an important RNA-binding protein that inhibits RNA translation into proteins known as fragile X retardation protein (FMRP). The condition affects 1 in 3600 males and 1 in 8000 females. The reason for this large discrepancy between incidences in biological sexes is due to the fact that genetic females have two X chromosomes rather than one X like genetic males do. Generally speaking, females have one normally functioning *FMR1* on the non-mutated chromosome in each cell, which allows their symptoms to be milder since the amount of abnormal *FMR1* is more variable than in males.

Fragile X Syndrome

Rett Syndrome is a rare X-linked disorder usually caused by spontaneous (de novo) mutations in the methyl-CpG-binding protein 2 (*MeCP2*) gene. It affects almost exclusively genetic females (1 in 10,000 females). This is because genetic males only have one X chromosome and therefore don’t have dosage compensation occurring, lessening the amount of the mutated gene circulating. Genetic males with the syndrome either die in utero or in infancy due to the severity of the mutation phenotype. For 6 - 18 months persons with Rett Syndrome experience normal development, hitting the usual developmental milestones, until said development suddenly stops and regression begins. There’s usually a mild improvement in some social skills at around age 5, but regression (mental and physical) will continue for the rest of the person’s life.


Rett Syndrome

A disorder characterized by involuntary movements, especially involving the face, mouth, lips, and tongue. Can be caused by prolonged use of antipsychotic drugs, like chloropromazine

Tardive Dyskinesia

A rare form of epilepsy that manifests through loss of language. It develops when the child is between 3-7 years old. It is twice as common in males than in females. Individuals generally lose their ability to comprehend first and then lose the ability to speak. 

Some autistic traits seen with this syndrome include aggression, poor eye contact, insistence on sameness, and sleep problems. 

The cause of LKS is not known but many suggest it could be a dysfunctional immune system, virus exposure, or brain trauma. 

Landau - Kleffner Syndrome

Initial symptoms manifest in the first year of life and become more visible during early childhood. 

It derives from a missing portion of chromosome 15 from the maternal side. 


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