- Delayed speech and language development (HP:0000750): A degree of language development that is significantly below the norm for a child of a specified age. Evidence: IEA. (OMIM:300495)
- EEG abnormality (HP:0002353): Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp. Evidence: IEA. Frequency: Frequent (HP:0040282). (OMIM:300495)
- Mild intellectual disability (HP:0001256): Mild intellectual disability (ID) is defined as a type of ID characterized by mildly sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 50-69. Evidence: PCS. Frequency: 5/7. (PMID:14963808)
- Lack of peer relationships (HP:0002332): The state of not having relationships with peers outside of school or organized activity appropriate to developmental level. This may be caused by behavioral or physical barriers. Evidence: IEA. (OMIM:300495)
- Seizure (HP:0001250): A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain. Evidence: PCS. Frequency: 1/8. (PMID:14963808)
- Increased serum serotonin (HP:0003144): A increased concentration of serotonin in the blood. Evidence: IEA. Frequency: Frequent (HP:0040282). (OMIM:300495)
- Childhood onset (HP:0011463): Onset of disease at the age of between 1 and 5 years. Evidence: IEA. (OMIM:300495)
- Autistic behavior (HP:0000729): Persistent deficits in social interaction and communication and interaction as well as a markedly restricted repertoire of activity and interest as well as repetitive patterns of behavior. Evidence: PCS. Frequency: 4/10. (PMID:14963808;PMID:12669065)
- Restrictive behavior (HP:0000723): Behavior characterized by an abnormal limitation to a few interests and activities. Evidence: TAS. (OMIM:300495)
- Non-Mendelian inheritance (HP:0001426): A mode of inheritance that depends on genetic determinants in more than one gene. Evidence: IEA. (OMIM:300495)
- Motor stereotypy (HP:0000733): Use of the same abnormal action in response to certain triggers or at random. They may be used as a way to regulate one's internal state but must otherwise have no apparent functional purpose. Evidence: TAS. (OMIM:300495)
- Abnormal nonverbal communicative behavior (HP:0000758): Abnormalities in eye contact, communicative facial expressions, gesture use, or the use of others' bodies to communicate convey shared meanings within a culture that replace or supplement verbal communication. Evidence: TAS. (OMIM:300495)
- X-linked inheritance (HP:0001417): A mode of inheritance that is observed for traits related to a gene encoded on the X chromosome. Evidence: PCS. (PMID:12669065)
- Sporadic (HP:0003745): Cases of the disease in question occur without a previous family history, i.e., as isolated cases without being transmitted from a parent and without other siblings being affected. Evidence: IEA. (OMIM:300495)
- Plagiocephaly (HP:0001357): Asymmetric head shape, which is usually a combination of unilateral occipital flattening with ipsilateral frontal prominence, leading to rhomboid cranial shape. Evidence: PCS. Frequency: 2/5. (PMID:14963808)
- Inflexible adherence to routines (HP:0000732): A need to strictly adhere to repetitive routines or patterns of behavior which are created by the environment. One becomes upset or distressed when their routines are disrupted or altered. Evidence: IEA. (OMIM:300495)
- Lack of spontaneous play (HP:0000721). Evidence: IEA. (OMIM:300495)
These phenotypes are associated with the disease autism, susceptibility to, X-linked 2 (OMIM:300495).