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What Chromosomes Are Affected In Autism

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How Is Asd Diagnosed

Advances in the Genetics of Autism

ASD symptoms can vary greatly from person to person depending on the severity of the disorder. Symptoms may even go unrecognized for young children who have mild ASD or less debilitating handicaps.

Autism spectrum disorder is diagnosed by clinicians based on symptoms, signs, and testing according to the Diagnostic and Statistical Manual of Mental Disorders-V, a guide created by the American Psychiatric Association used to diagnose mental disorders. Children should be screened for developmental delays during periodic checkups and specifically for autism at 18- and 24-month well-child visits.

Very early indicators that require evaluation by an expert include:

  • no babbling or pointing by age 1
  • no single words by age 16 months or two-word phrases by age 2
  • no response to name
  • excessive lining up of toys or objects
  • no smiling or social responsiveness

Later indicators include:

  • impaired ability to make friends with peers
  • impaired ability to initiate or sustain a conversation with others
  • absence or impairment of imaginative and social play
  • repetitive or unusual use of language
  • abnormally intense or focused interest
  • preoccupation with certain objects or subjects
  • inflexible adherence to specific routines or rituals

Why Is It Important To Know If You Have A Family Health History Of Autism Spectrum Disorder

Having a family health history of ASD makes you more likely to have a child with ASD, or to have ASD yourself. If you have a child with ASD, you are more likely to have another child with ASDexternal icon, especially if you have a daughter with ASD or more than one child with ASDexternal icon. Your other family members would also be more likely to have a child with ASD.

If you are pregnant or planning a pregnancy, tell your doctor if you or your partner have a family health history of ASD. This information can help your doctor determine how likely you are to have a child with ASD.

When collecting family health history information,

Indirect Evidence Suggesting A Contribution Of Environmental Factors


Prevalence studies of autism spectrum disorders conducted in recent years have been the source of an important debate because of a steady and highly significant increase of estimates of the total prevalence of pervasive developmental disorders. Indeed, while the prevalence was estimated at 6 per 1000 in a population of school children in 2005, recent studies have gone so far as to estimate the prevalence to be one child in 38.The last prevalence estimates in the United States, released by the Centers for Disease Control recently, reached 1 in 88 child in 2008, while their previous estimate was one in 110 in 2006. However, most of the studies are not comparable in method or in the populations studied. One hypothesis is that this increase is the result of enlargement of diagnostic criteria, and the growing importance of screening for ASDs. The results of an epidemiological study from England, based on a national sample from 2007, support this hypothesis. Indeed the authors found a rate of about 1% in adults across the entire age range, without a significant reduction in the older part of the sample, as one would expect if the prevalence had increased in recent years. However, another study suggested that diagnostic substitution, especially for the most severe cases, and better ascertainment, especially for children at the less severe end of the spectrum, explain only a part of the linear increase observed in the California registry.

Immune dysfunction


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Genetic Studies On Autism

Following extensive research on autism and genetic links, several genes have been found to potentially be connected to ASD. Rylaarsdam, et al. highlights various findings from genetic studies these are highlighted below:

At the genesis of genome studies, genetic studies on heredity have been conducted through twin studies, namely monozygotic twins and dizygotic twins. Monozygotic twins are derived from one fertilized egg that has split into two and dizygotic twins are derived from two separate eggs released at the same time fertilized by two separate sperm. It has been found that monozygotic twins are more likely to share a diagnosis than dizygotic twins, therefore suggesting a genetic influence.

Thanks to the growth of genetic research, genomic studies have increased with findings citing that the etiology of autism spectrum disorder is both multigenic and heterogeneous.

Large scale genetic studies have been conducted on patients with ASD as well as their families. Through these studies, several risk genes have been identified. Of these, two broad classes of proteins have been found to be related, namely: synapse formation and transcriptional regulation and chromatin-remodeling pathways. In addition, several studies have found a variety of changes in chromosome structure and number in some samples of autistic children.

Lets break down the two classes and why autism risk genes are found to be related with these classes:

What Causes Autism Spectrum Disorder


Although the cause of ASD is known in some people and not known in others, genetics, biology, and environment are all important factors. Having older parents, a difficult birth, or infections during pregnancy are all examples of factors that might increase the risk for having ASDexternal icon. Beyond these factors, certain people are at higher risk than others. For example, ASD is four times more common in males than femalesexternal icon. People with certain genetic disordersexternal icon, such as fragile X syndrome, tuberous sclerosisexternal icon, and Down syndrome, are more likely to have ASD.

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Do Symptoms Of Autism Change Over Time

For many children, symptoms improve with age and behavioral treatment. During adolescence, some children with ASD may become depressed or experience behavioral problems, and their treatment may need some modification as they transition to adulthood. People with ASD usually continue to need services and supports as they get older, but depending on severity of the disorder, people with ASD may be able to work successfully and live independently or within a supportive environment.

Genetics And The Environment

The causes of autism are extremely complicated.

The causes of autism are extremely complicated. In most cases, we believe that many factors contribute to its development, not just one thing or another, said epidemiologist Craig Newschaffer, PhD, in a 2017 interview with Autism Speaks.13

Researchers are continuing to study the role of environment in autism risk. Environment, in this context, means more than the natural world, although it does include exposure to pollution, pesticides, and hazardous chemicals. It also includes many other things, from the age of parents when they conceive a child a pregnant womans medical conditions, illnesses and nutrition and events that happen at and after a babys birth.

For example, studies have suggested that exposure to air pollution, farm pesticides, and hazardous chemicals increase autism risk.14-18 Children of older parents, and children whose mothers had problems during pregnancy, such as gestational diabetes and bleeding, also face a higher risk of developing autism.19

Interestingly, these changes in gene functioning can be passed from parent to child. For example, men make sperm throughout their lives, said Dr. Newschaffer, professor of epidemiology and biostatistics, and associate dean for research, at Drexel University. Their exposure to chemicals and other environmental factors may cause epigenetic changes to sperm that may affect their babies, he said.

Leo Kannerearly infantile autism

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How Is Autism Diagnosed

Diagnosis of autism is based on standardized testing plus a clinical evaluation by an autism specialist. These professionals are usually psychologists, psychiatrists, developmental pediatricians, pediatric neurologists or medical geneticists.

The diagnosis of autism is made when there are a specific number of symptoms as defined by the Diagnostic and Standard Manual of Mental Disorders . Some commonly used diagnostic tests are the CARS , the ABC and the GARS . Formal diagnosis by an autism specialist usually depends on completing the ADOS , and ADI-R . The CHAT is often used in pediatrician’s offices to screen for autism symptoms.

When physical features, small head size or brain malformations are present or there is a family history of relatives with autism, genetic testing such as chromosome analysis and single-gene testing is done.

Mutational Analysis Of Slitrk2 And Cxorf1

Research: Genetics Play Vital Role In Autism

We sequenced both strands of the genomic sequence coding for all available exons , flanking splice junctions and untranslated regions genome browser) of the CXORF1 and SLITRK2 genes. Primers were designed using genomic sequence information from UCSC genome browser and the Lasergene PrimerSelect program. The sequencing procedures for mutation detection were performed as published elsewhere.

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Genetic Bases Of Autism

Several psychiatric diseases have strong evidences of genetic involvement in their origin, and among them are schizophrenia, bipolar disturbance and autism. In 1977, a study with mono and dizygotic twins described for the first time the genetic predisposition of autism .

Nowadays, population studies suggest that the model that better describes DASs is multifactorial with a concordance of 60-92% in monozygotic twins and 0-10% in dizygotic twins . Differences found in studies between monozygotic twins support the multifactorial model, demonstrating the importance of environmental factors.

Several studies were performed to clarify genetic factors associated with the disease. Autism symptoms that suggest a strong genetic component are convulsions, mental deficiency, neurons and synapse decrease in amygdala, hippocampus and cerebellum, increased size of encephalon, and increased level of circulating serotonin. Even studies with monozygotic twins show a significant concordance, as opposed to dizygotic twins. Non-twin siblings present a risk of developing autism ranging from 0-30%, and this risk is much higher than in the general population .

The comparison of the mentioned populational groups, as well as the difference between men and women, shows epistatic effects that involve an interaction between several genes, suggesting the role of environmental factors .

Transcriptional Regulation And Chromatin

The processes that encompass transcriptional regulation and chromatin-remodeling are complex. In short, these two processes control which genes can be expressed to form the corresponding protein.

Accurate follow-through of these processes is important as, if any of the steps involved during either transcriptional regulation or in the chromatin remodeling pathway are affected, it will bring rise to the formation of risk genes, some of which have been potentially linked to autism.

For example, the process of transcriptional regulation converts DNA to RNA. Once RNA is transcribed, it goes through cellular processes to coordinate cellular activity. When RNA is transcribed, RNA editing or modification can occur whereby discrete changes can take place within the RNA molecule. In the study by Tran et al. , it was found that mutations such as FMRP and FXRP1 can cause abnormal RNA modification activity.

According to Rylaarsdam, et al. , the genes that impact transcription and chromatin-remodeling pathways include MeCP2, UBE3A, chromodomain helicase DNA binding protein 8 , activity dependent neuroprotector homeobox , pogo transposable element derived with ZNF domain , fragile X mental retardation protein , and RNA binding forkhead box genes.

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Asd And Associated Genetic Conditions

Autism Spectrum Disorder and features of ASD can occur as part of some genetic conditions. Approximately 20% of children with ASD will have a diagnosable genetic syndrome. These syndromes can be due to missing or extra stretches of DNA, misspellings in genes, or biochemical abnormalities.

Some of these conditions are easy for a general pediatrician to recognize , while other conditions can be subtle and require specialized testing . For this reason, the American College of Medical Genetics recommends that anyone with an ASD diagnosis receive an evaluation by a clinical geneticist. Accurate diagnosis is important because there can be other health implications for the affected child, as well as differences in the risk of having another child on the autism spectrum.

In addition to genetic causes of ASD, exposure to certain medications during pregnancy can cause ASD. During your childs visit with a clinical geneticist, they will review any medications that you may have taken during pregnancy.

Examples of genetic abnormalities that can be associated with ASD are listed below.

22q deletion syndrome

Angelman syndrome


Cornelia de Lange syndrome

Down syndrome

Duchenne Muscular Dystrophy

Fragile X

Fragile X syndrome is a genetic condition that causes a range of developmental delay. Usually males are more severely affected than females. Children may be hyperactive or have a secondary diagnosis of ADHD.

Prader-Willi syndrome

Rett syndrome

Smith-Lemli-Opitz syndrome

What Role Do Genes Play


Twin and family studies strongly suggest that some people have a genetic predisposition to autism. Identical twin studies show that if one twin is affected, then the other will be affected between 36 to 95 percent of the time. There are a number of studies in progress to determine the specific genetic factors associated with the development of ASD. In families with one child with ASD, the risk of having a second child with the disorder also increases. Many of the genes found to be associated with autism are involved in the function of the chemical connections between brain neurons . Researchers are looking for clues about which genes contribute to increased susceptibility. In some cases, parents and other relatives of a child with ASD show mild impairments in social communication skills or engage in repetitive behaviors. Evidence also suggests that emotional disorders such as bipolar disorder and schizophrenia occur more frequently than average in the families of people with ASD.

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Behaviour Analysis Of Asds

Although now a days knowledge concerning autism is much more prefound, it still surprises due to the diversity of characteristics that patients can show.

Usually, the autistic child has normal physical . However, these children also show an irregular profile of development that is detectable in the first three years of life, being present till adulthood. The Triade of Social Impediments is characterized by a strict and continuous pattern with intelligence levels varying from mental retardation to an extraordinary performance in certain cognitive domains or savant capacities . Although 80% of autistic children show mental retardation, savant capacities can exist, however the global intelligence ratio is low . The difference between mental retardation and autism should be pointed out: The first one shows a uniform development deficit while the last presents an irregular profile, with differentiated degrees of commitment.

The following classification and diagnosis systems allow to distinguish autism from other disorders: International classification of Diseases of the World Health Organization and the Manual of Diagnosis and Statistics of Mental Disorders from the American Academy of Psychiatry . In these systems the term Child Autism was replaced by Autistic Disturbance, officially separating it from Asperger syndrome .

What Is Autism Spectrum Disorder

Autism spectrum disorder refers to a group of complex neurodevelopment disorders characterized by repetitive and characteristic patterns of behavior and difficulties with social communication and interaction. The symptoms are present from early childhood and affect daily functioning.

The term spectrum refers to the wide range of symptoms, skills, and levels of disability in functioning that can occur in people with ASD. Some children and adults with ASD are fully able to perform all activities of daily living while others require substantial support to perform basic activities. The Diagnostic and Statistical Manual of Mental Disorders includes Asperger syndrome, childhood disintegrative disorder, and pervasive developmental disorders not otherwise specified as part of ASD rather than as separate disorders. A diagnosis of ASD includes an assessment of intellectual disability and language impairment.

ASD occurs in every racial and ethnic group, and across all socioeconomic levels. However, boys are significantly more likely to develop ASD than girls. The latest analysis from the Centers for Disease Control and Prevention estimates that 1 in 68 children has ASD.

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Chromosomal Abnormalities Play Substantial Role In Autism

Cell Press
Genome-wide scans of families affected by autism spectrum disorder have revealed new evidence that previously unknown chromosomal abnormalities have a substantial role in the prevalent developmental disorder.

Genome-wide scans of families affected by autism spectrum disorder have revealed new evidence that previously unknown chromosomal abnormalities have a substantial role in the prevalent developmental disorder, according to a new report. Structural variants in the chromosomes were found to influence ASD with sufficiently high frequency to suggest that genomic analyses be considered in routine clinical workup, according to the researchers.

“Historical studies in identical twins and their families have provided strong evidence for a genetic basis of autism,” said Stephen Scherer of The Hospital for Sick Children and the University of Toronto. “Last year, with the Autism Genome Project Consortium, we did an initial study to look at the rate of chromosomal changes in autism. Now, we’ve really pinned down those numbers.”

In the new study, the researchers examined structural abnormalities in 427 unrelated ASD cases using both microarray analysis and karyotyping. Microarrays can detect “unbalanced” genetic changes that alter the number of copies of a particular gene. Karyotyping, in which chromosomes are viewed under the microscope, can identify “balanced” translocations or inversions that might otherwise be missed by microarrays.

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Clinical Implications And Future Perspectives

Fighting Autism with Genetics Research

When autism was first described, it was hypothesized to be an environmentally caused disease. Decades of research have since revealed that autism is a highly heterogeneous and extremely complex genetic condition. Even though great progress had been made in identifying hundreds of risk genes, very little is known about the different types of modifiers that may exacerbate or ameliorate disease severity. Such modifiers could include epigenetics, sex-linked modifiers, CNVs, double-hit mutations, or environmental factors .

Figure 1. Genetic modifiers in autism spectrum disorder. Autism is estimated to be 4080% heritable. However, both genetic and non-genetic factors modulate the penetrance of risk genes, resulting in a highly heterogeneous disease phenotype for similar pathogenic variants. Examples of genetic modulators include CNV, epigenetics, and double-hit mutations. Examples of non-genetic modifiers include environmental exposures and sex-linked modifiers.

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