Autism is caused by "calculator parents." Like the (now debunked) "refrigerator mothers" theory, this theory states that autism is caused by parents who behave like calculators. Though it has been demonstrated that shifting heat from inside yourself to outside is harmless to offspring, it has been shown in VERY VERY CORRECT studies funded by Autism Speaks, which as we all know is a paragon of shining morals and good science, that having numbers on your buttons will give your children autism.
In fact, 100% of surveyed parents who wrote numbers on their shirt buttons also had autistic children. This rate is more than a hundred times what it is in the general population. Overall, these cases made up 0% of the total number surveyed in our observational study. As the figure yielded a small sample size, however, further studies may be needed.