Diseases like type 1 diabetes and sickle-cell anemia happen through a defect in a single gene. Sometimes all it takes is one wrong letter in the genetic code to create a life-threatening disease. If only autism were so easy to understand and treat.
Unlike diabetes, autism cannot be explained simply by proteins or genes. Diabetes has several obvious symptoms (frequent urination, excessive thirst, and exhaustion), it has one absent protein, and it has one mutated gene. Autism is in another world of complexity on several levels.
First of all, autism itself is a slippery disease to diagnose. Different people have different classic symptoms at different severities. Sometimes autism is mistaken for ADHD or language difficulties, and vice versa. There is no biological test for autism like there is for diabetes.
Second, in autism, there is no single gene that explains the symptoms. When we sequence the genomes of patients with a disease, sometimes we find one gene that is defective in all patients. Diabetes is a great example of this. We knew for decades that diabetics were incapable of making insulin, but only genetic sequencing could show that the cause was actually quite simple: the instructions for the insulin protein were mutated. Only about fifteen percent of autism cases across the spectrum can be pointed directly to genes. Multiple genes are involved, and some combinations of mutations seem to be worse than others. These relationships are too complex for even the smartest scientists to understand.
Twins can tell us a lot about the importance of genes in a disease. When one twin has autism, what are chances their identical twin also has autism? There is a 77% chance for males and 50% for females. Why don’t these other twins all have autism as well? Something must explain the difference.
The missing factor in autism is the environment. A similar relationship happens in cancer. Cancer runs in families, so part of a person’s risk for cancer comes from harmful genes. The other part of the risk comes from lifestyle. A person with resilient genes may avoid cancer by living cleanly, but could still get lung cancer if they smoke three pack a day. Likewise, someone with cancer genes can breathe only air their entire life and still develop cancer.
Viral infection is one non-genetic thing that can add to autism risk. A viral infection at a critical point in development before birth can alter the immune system of both mother and child, and eventually alter the fetus’s brain. Vaccines are probably a vital part of autism prevention.
A mother’s mental stress can explain some cases of autism. This is true before birth and during birth. For example, autism tends to increase after large groups of pregnant women experience disastrous events such as violent storms. The trauma causes the release of stress hormones, which activate the mother’s immune system and can harm the baby’s developing brain. Stress during birth can increase complications like low oxygen supply to the baby, which is of course harmful to the brain. The old wive’s tale that traumatizing a pregnant woman will harm the baby probably has a grain of truth.
Not only is autism a disorder of multiple genes, but lifestyle and environment of the mother are involved, too. Many connected factors come together to produce many complicated effects. It may turn out that the thing most affected in autism is the way our neurons are connected and knit together to send signals across the brain. One molecule injected in someone’s veins probably can’t fix that. However, by the time we understand autism enough to cure it, we will probably have understood it enough to lessen the burden we put on the autistic and maybe even appreciate what only they can add to our lives.