Previous studies have found that when one identical twin has ASD, chances are extremely likely that the other twin has it, too. The authors analyzed data from three previous studies comprising a total of 366 identical twin pairs with and without ASD.
Studies in identical twins have shown that autism has a strong genetic basis: If one identical twin has autism, the other one has it, too, as much as 90 percent of the time. The new work supports these estimates: In 64 of the 78 twin pairs, both twins have an autism diagnosis.
The twin rate weighted to number of children with autism, Asperger disorder, or PDD-NOS born per year was calculated to be 26/1,000. Thus, the rate ratio for multiple births comparing autism to total births is 1.35; when PDD-NOS, Asperger disorder, and autism are combined, the ratio is 1.15.
Mirror image: Identical twins are believed to be genetically identical, but one twin can have mutations not shared by the other. Identical twins can be genetically different, which could explain why they do not always share disorders such as schizophrenia or autism, according to a study published in March in PLoS One.
“Twin studies of major depressive disorder have showed that if one twin has the illness, a fraternal twin has an increased likelihood of developing the disorder and an identical twin's likelihood is even higher,” says Dr. Avari.
You can inherit genes that boost risk for ADHD from your mother, from your father or from both parents. In a recent Norwegian study, inherited risk was somewhat higher when a child's mother had ADHD compared to their father, but researchers weren't certain why that would be.
Identical twins share the same genomes and are always of the same sex. In contrast, fraternal (dizygotic) twins result from the fertilization of two separate eggs with two different sperm during the same pregnancy. They share half of their genomes, just like any other siblings.
The incidence of handicap was 3.7% in twins, 8.7% in triplets, 11.1% in quadruplets, and 10.0% in quintuplets. The risk of producing at least 1 handicapped child was approximately 1 in 13 pairs of twins (7.4%), 1 in 4 or 5 sets of triplets (21.6%), and 1 in 2 sets of quadruplet and quintuplets (50%).
Such twins, known scientifically as 'MoMo', an abbreviation for monoamniotic-monochorionic, are some of the rarest types of twins, making up less than one percent of all births in the United States, noted the statement. It also stressed that such MoMo twin pregnancies have a high risk of fetal complications.
Fraternal twins are more likely to both have autism than siblings who are not twins. Scientists theorize that may because they share the same prenatal environment. Identical twins, who have the same genes, have the highest rate of both having autism – 88 percent – among all siblings.
For starters, a recent study, partly funded by Autism Speaks, found that in families with one or more children with ASD, the chances that a baby sibling will develop autism are much higher than previously thought. In fact, the odds were around one in five, or 20 percent.
That's because twins are born prematurely 60 percent of the time and land in the costly neonatal intensive care unit more often than singletons. The article also mentions that these babies are more susceptible to mental retardation and learning disabilities.
Kathryn Morris talks about her twins' autism and how she's helping other families.
From the moment they were born, Flo and Kay Lyman were unlike any sisters on planet earth. Thought to be mentally disabled, they were tormented by kids and survived a near-death experience at the hands of their own mother.
Progress has been made toward understanding different environmental risk factors, and the clearest evidence involves events before and during birth, such as: Advanced parental age at time of conception. Prenatal exposure to air pollution or certain pesticides. Maternal obesity, diabetes, or immune system disorders.
If one identical twin is autistic and the other twin is not, it is possible that something in the child's environment or experience may be a factor in the child's ASD. Because of this, ASD is considered a complex genetic disorder, involving both genes and environmental factors .
If one identical twin has autism spectrum disorder (ASD), the other twin has a 76 percent chance of also being diagnosed with it. The numbers are lower for fraternal twins. The percentage of fraternal twins who each share an ASD diagnosis is 34 percent for same-sex twins and 18 percent for boy-girl pairs, Dr.
Types of Disability
Over three-quarters (76.8%) of people with disability reported a physical disorder as their main condition. The most common physical disorder was musculoskeletal disorder (29.6%) including arthritis and related disorders (12.7%) and back problems (12.6%).
These studies showed that IQ is very heritable (although the environment still plays a role in determining your IQ). We can tell this because the IQ of identical twins are almost always the same and non-identical twins are only sometimes the same.
Twins are more or less equally likely to be female or male. Contrary to popular belief, the incidence of twins doesn't skip generations.
Thus identical twins, though they start with the same genes, likely develop different personalities in the same environment partially based on how they interact with their environment.
Autism is very distinct from ADHD, but the core symptoms of ADHD-Combined type, i.e., attention deficit, impulsivity, and hyperactivity, would appear to also be features of autism. ASD and ADHD are neurobiological disorders characterized by similar underlying neuropsychological “deficits”.
Researchers have identified seven genetic variants common to autism and ADHD and five gene variants specific to only one of the two diagnoses. The study is the first to show that people with ADHD and autism are double-burdened with a genetic risk of receiving both diagnoses.
Causes of ADHD
Recent studies link genetic factors with ADHD. In addition to genetics, scientists are studying other possible causes and risk factors including: Brain injury. Exposure to environmental risks (e.g., lead) during pregnancy or at a young age.