The earlier autism is detected and intervened, the better the effect.
Many parents blame their children for autism.
01
Is autism inherited?
A study of 192 pairs of twins (including 54 pairs of identical twins and 138 pairs of fraternal twins) found that about 42.5% of male twins and 43% of female twins in identical twins suffer from autism; while among fraternal twins, about 12.9% of male twins and 20% of female twins suffer from autism.
People with a family history of autism are 50-175 times more likely to develop autism than those without a family history.
Even if there is no autism in the family, there may be similar diseases, such as language development disorders, neuropsychiatric disorders, mental retardation and extreme introversion, etc., which to some extent indicate that there is a significant genetic basis for the incidence of autism spectrum disorder, and heredity is a factor of autism, but it is not the only factor.
More and more researchers now believe that autism is the result of genetic and environmental interactions, but heredity plays a leading role.
Researchers have been working to find the genes that cause autism. However, except for a few subtypes of autism that have well-defined causative genes, such as Rhett syndrome, which is caused by a deletion of a fragment of the MECP2 gene.
But the vast majority (about 90%-95%) of autism diseases have not found a definitive causative gene. As research into the genetic factors of autism continues to deepen, the study has found nearly 400 genetic variants that increase the risk of autism.
This suggests that autism is not caused by one or a few genes, but by multi-gene interactions.
02
Why do non-autistic parents give birth to autistic children?
The proportion of parents with autism spectrum disorder who have a psychiatric disorder is about 18.6%, and normal parents may also have a child with autism.
On the one hand, in addition to genetic factors, environmental factors such as biological factors and immune factors in maternal pregnancy and perinatal period are also the causes of autism.
On the other hand, the mutated genes in children with autism may also be acquired in addition to being inherited from their parents.
This acquired mutation is called de novo mutation, and mutations inherited from parents are called hereditary mutations.
Whether it is a hereditary mutation or a newborn mutation, it may be derived from spontaneous base mismatch during DNA replication, or from the role of mutagens (such as the environment in the fetal period).
03
How do genes affect autism?
The abscissa coordinate is the IQ score of children with autism, and the total coordinate is a percentage of the number of newborn mutations.
The image above is a 2014 study that showed that the more harmful neonatal mutations, the lower the IQ of children with autism.
This suggests that the number of newborn mutations affects the IQ of children with autism. The study also found that the number of neonatal mutations in women was almost twice that of men, which is also in line with the fact that men have 4 times more autism than women, but women with more severe symptoms.
Neonatal mutations affect motor skills in addition to autistic IQ.
Many nascent mutations are copy number cariations (CNVs), which refer to deletions, insertions, repetitions, and variants of complex polytopes in the range of DNA fragments from kb to Mb.
There is also a mutation called Single Nucleotide Polymorphism (SNP), which refers to the change in DNA sequence caused by changes in a single nucleotide—A, T, C, or G—resulting in chromosomal genome diversity between species, including humans. 90% of the various genetic differences in human genes can be attributed to genetic variation caused by SNP. Both SNP and CNV may affect gene expression.
Because there are many genes that affect autism, and the function of each gene is different. This is also manifested in the diversity of symptoms of autism spectrum disorder.
04
What can genetic testing do?
On the one hand, the diagnosis and prevention of autism: some tests for CNV mutations, such as the absence of MECP2, can determine whether a child has Rhett syndrome.
Some tests for autism susceptibility genes cannot tell if a child has autism, but only indicate that a child is at greater risk of developing autism if they carry certain genetic mutations in the same environment.
Such an early warning may allow parents to detect their children's problems earlier, or expose children to less exposure to dangerous environments.
On the other hand is intervention in autism. There are many interventions for autism, but many are inconsistent in their effectiveness.
This may be because different children with autism carry different mutant genes, and the function of each gene is different, and the problems of each autism can be very different.
For example, MTHFR, VDR, and ASTM are all susceptibility genes for autism, which affect folate metabolism, vitamin D metabolism, and melatonin synthesis, respectively. But not every child with autism has mutations in these genes.
Some children with autism may simply have problems with MTHFR, while others with autism may simply have problems with ASTM.
How to blindly supplement vitamin D to all children with autism may lead to some side effects.
If it is possible to understand the metabolism of different nutrients in each autistic child, develop a personalized intervention plan for autistic children. The cost of trial and error for parents can be reduced.