Hermelin and O'Connor (1990) provide data about the abilities of a young autistic man. This young man also appears in a later study (Anderson et al., 1999), where he is given the name Michael. Michael has exceptional abilities in multiple areas, particularly mathematics. At the time reported in the 1990 study, Michael is, for example, "known to be able to factorize", apart from being able to "add, subtract, multiply and divide large numbers". Michael also has no speech at all, makes virtually no use of written words, and has no measurable vocabulary. Anderson et al. (1999) describe Michael as "without language ability".
Here is Hermelin and O'Connor (1990), writing about Michael, the "subject":
Both the subject's parents have degrees in mathematics although neither works as a professional mathematician. When they told us of their son's numerical ability we asked whether he could identify prime numbers. As he had not previously been confronted with such a task, some primes were slipped into a list of numbers which he was asked to factorize. In his mother's words, "When he came to these, he looked at me as if I were mad."
References:
Anderson, M., O'Connor, N., & Hermelin, B. (1999). A specific calculating ability. Intelligence, 26, 383-403.
Hermelin, B., & O'Connor, N. (1990). Factors and primes: a specific numerical ability. Psychological Medicine, 20, 163-169.