Autism Spectrum Disorders
Contents
Autism Spectrum Disorders
Basic Characteristics
- Description
Autism Spectrum Disorders is a clinical description of the developmental disorders which are characterized by impaired language development, social development, and learning.
They include:
Children with ASD have extremely delayed development. Symptoms of this disorder usually start to appear between 12 to 36 months and consist of not reaching normal development benchmarks such as not babbling by 12 months, not speaking by 16 months, or a gradual loss of language or social skills. All children with ASD show deficits in social interactions, verbal and nonverbal communication. They may also show repetitive behaviors and interests, or aggressive behavior.
Although all children with ASD show similar deficits, the depth of these deficits can range drastically. Some have very mild deficits like in Asperger's Syndrome, where children have high levels of vocabulary and language skills. Others may have little to no spoken language functionality.
- Causes
Scientists have not found the exact cause of ASD, although all would agree that there is a genetic basis. The causes of some disorders in the spectrum have been found already and there are simple diagnostic tests that can be done to see if the child has this specific disorder, such as in Rett Syndrome.
The difficulty in finding the cause of ASD partially lies in its definition, and partially on the complex interplay between genes that happens during development. ASD, like most other behavioral disorders, is diagnosed based off of observable characteristics of the child. However, these diagnosis offer no direction as to which specific genes are defective. Furthermore, two patients with ASD can present very similar symptoms and yet have different defective genes or causes. For example, Rett Syndrome is caused by mutations in the gene MeCP2 while Tuberous Sclerosis is caused by mutations in TSC1 and TSC2. It should be noted that both Rett Syndrome and Tuberous Sclerosis are very rare.
- History
Prior to the 1970's, many people thought Autism Spectrum Disorders were a result of psychological causes, such as having an aloof mothering style. However, during the 1980's people began to note that chromosomal disorders and rare syndromes often co-occurred with ASD. As a result, people began to suspect that ASD could have genetic underpinnings. These suspicions were confirmed when, after the development of the ADI-R and ADOS as diagnostic tools and other technical advances, the first candidate gene association and resequencing studies, followed by whole-genome linking studies were done in the late 1990's. These studies were used to identify loci of potential interest.
Core Deficits
Those who have ASD have identifiable core deficits recognized by scientists and clinicians.
- Core Deficit of Joint Attention
- Core Deficit of Social Communication
- Repetitive behaviors or interests
Treatments
There are no drugs that can “cure” ASD. There are a variety of treatments available which aim to improve social and communication skills. Because of the complexity of ASD, there is no one treatment that works equally well for all people with ASD. Some common treatments are:
- Applied Behavior Analysis interventions
- Joint Attention interventions
Some clinicians may prescribe medications to target certain symptoms.
Neuroimaging
Genetics
A host of genes of interest have been identified through gene association studies, resequencing and, recently, the assessment of copy number variation (CNV).In particular, given the pathology of ASD, genes dealing with electrical conductance and neural transmission have been popular sites of study since synaptic dysfunction has been suggested as a unifying theme behind the various disorders in ASD.
Most approaches to finding loci of interest are under one of two hypotheses:
- ASD is a result of interplay between many genes
- There is one principle gene which contributes to many aspects of the disease.
The idea that the symptoms of ASD is a result of the interaction of many different genes has been supported by linkage studies, and the fact that although many genes have been identified with causing ASD symptoms, each of these individual genes do not cause more than 1-2% of over all ASDs. However, data mining techniques such as hierarchical clustering and principle components analysis find that it is highly likely that there is 1 continuously distributed factor contributing to many aspects of ASD, thereby validating the existence of the second hypothesis. Additionally, statistical analysis of ASD family data suggest a large portion of ASDs may be the result of dominant de novo mutations that have reduced penetrance in families.
Some likely candidate genes that have been explored include
| Gene | Function | Location |
|---|---|---|
| UBE3A | transcribed protein is an enzyme that works in protein degradation | 15q11-q13 |
| GABRB3 | encodes a member of of a ligand gated ionic channels responsible for inhibition in nervous system | 15q11-q12 |
Successful linkage studies in the past have been mostly based on affected sibling-pair designs in multiplex families. However, there were no genome wide significant results probably because of small effect sizes that were a result of any single gene. Even large scale studies showed only minor overlap, likely because of variety of phenotypes in ASD. Recently though, use of endophenotypes and QTL mapping have increased the power of linkage and association studies.
Related Information
- Task or test associated with this construct (vote for your favorite, or nominate a new one by editing this page):
- Indicators (dependent variables, conditions, or contrasts; measurement variables used for analysis) associated with this construct (vote or nominate by editing this page):
- Closely related pages (vote or nominate related pages by editing this page):
- CNP Level
- Syndrome
External Resources
- Links out:
- Google: ADHD
- Wikipedia: ADHD
- PubMed: ADHD
- -ucla cognitive atlas- (coming soon!)
- Database links
