The researchers determined a 96% chance that if one twin has ASD, the other has it, too. However, symptom scores varied greatly between twins diagnosed with ASD. The researchers estimated that genetic factors contributed to only 9% of the cause of trait variation among these twins.
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.
In a similar way, only one identical twin can get ASD, even though they have the same genetic ingredients. One twin's brain environment may trigger ASD. But, the other twin's environment could be different enough to not trigger the identical set of genes.
The risk of complications in a multiple pregnancy is greater than carrying just one child, and it's not uncommon for one twin to be disabled and the other not.
Studies in twins have shown that autism has genetic origins: A child is more likely to have autism if his or her sibling or twin also has the disorder. But there is also evidence that factors other than genetics, collectively referred to as 'the environment,' play a role.
The researchers determined a 96% chance that if one twin has ASD, the other has it, too. However, symptom scores varied greatly between twins diagnosed with ASD. The researchers estimated that genetic factors contributed to only 9% of the cause of trait variation among these twins.
Among all families affected by autism, up to 19 percent have more than one child with the disorder, according to one large study. Multiplex families, especially those who have twins, have led to many of the breakthroughs in our understanding of autism.
Monoamniotic-monochorionic Twins
This is the rarest type of twin, and it means a riskier pregnancy as the babies can get tangled in their own umbilical cords.
Twins not only have a bestie from birth — they also live longer than singletons. And those two factors may be related, according to new University of Washington research.
Longer lives
When analyzing the data by gender, the researchers found that female identical twins lived, on average, about 63.4 years, whereas female fraternal twins lived about 61.4 years and the general Danish female population lived about 58.8 years, Sharrow said.
At age 7, the mean IQ score of twins was 5.3 points lower than that of singletons in the same family, and at age 9, the score was 6.0 points lower. The lower intelligence of twins in childhood may partly be a consequence of the reduced fetal growth and shorter gestations of twins, say the authors.
If someone in your family has autism spectrum disorder (ASD), you may be more likely to have a child with ASD. ASD can look very different from person to person, so taking a careful family health history can be important for early diagnosis.
Indeed, it is possible for one ADHD twin to have an additional major disorder while the other does not.
The chances of anyone in the general population having an autistic child are about 1 in 1000 or 0.1%. So, while the risk is real, the chances of you and your husband having an autistic child are still very low. As I said, autism most likely involves lots of genes.
Research reveals that when one identical twin develops an Autism Spectrum Disorder (ASD), the risk of the other developing it is substantially higher than it is for fraternal twins (approximately 88% higher).
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.
While there are risks associated with all twin pregnancies, dizygotic (fraternal) twin pregnancies usually bring about the least amount of complications, carrying the lowest risk of all types of twins. Worse complications are possible with monozygotic (identical) twins because the embryo is dividing.
With identical twins, it's possible for a blood vessel in a shared placenta to result in one baby receiving too much blood and the other too little. This is a serious complication for both babies that might result in heart complications and the need for fetal procedures while you're still pregnant.
Identical twins have identical genes, because they are born of an embryo that splits at a very early stage in development. Such twins are often indistinguishable in outward appearance. But over the course of time they may experience radically dissimilar health.
The Science of Fraternal Twins. Mixed-gender twins are the most common type of fraternals, some 50 percent are boy-girl.
While many people can't tell them apart, Mary-Kate and Ashley are not identical, but rather fraternal: Mary-Kate is one inch taller than her sister and is left-handed, while Ashley is right-handed.
The DNA of monozygotic twins tends not to be 100% identical, and epigenetic and environmental differences further widen the gap between twin pairs. It's not nature or nurture; it's a complex interaction between our genes, our environment, and our epigenetic markers that shape who we are and what illnesses befall us.
Children born to older parents are at a higher risk for having autism. Parents who have a child with ASD have a 2 to 18 percent chance of having a second child who is also affected. Studies have shown that among identical twins, if one child has autism, the other will be affected about 36 to 95 percent of the time.
The team found that mothers passed only half of their structural variants on to their autistic children—a frequency that would be expected by chance alone—suggesting that variants inherited from mothers were not associated with autism. But surprisingly, fathers did pass on substantially more than 50% of their variants.
Advanced parental age at time of conception. Prenatal exposure to air pollution or certain pesticides. Maternal obesity, diabetes, or immune system disorders. Extreme prematurity or very low birth weight.