I often use the language "condition". I know it is "softer" than saying "disorder" and know that some people do not consider their autism a "disorder", per se, but use the language "difference". Medical terminology can sometimes be off-putting, when the term "disorder", in this context, means something outside "the norm" or perhaps a certain number of standard deviations off from the mean.
I believe that most of us here are predominantly ASD-1/Asperger's variants. Some are ASD-2 variants with good communication skills on the computer.
To summarize, autism is a prenatal, genetic and/or epigenetic, neurodevelopmental disorder/condition that primarily affects behaviors, socialization, and communication, but can also affect fine motor skills, as well as specific hormonal, neurotransmitter, and immune responses. It is a medical condition, that unfortunately, science is still learning about, and as a result is diagnosed by symptomatology even though there clearly is a brain anatomy, physiology, and genetic component that needs to be studied more, but someday may be, in part, diagnosed by a neurologist and geneticist. Intelligence, per se, has little to do with autism, as some may have genius level, normal, or below normal IQs, and some may have asymmetrical intelligences, such as your brother, that may be "gifted" in a specific area.
Prenatal meaning it starts early in fetal development, as the primary areas that it effects include the thalamus, hypothalamus, and cerebellum that develop during the first and second trimester of pregnancy, and then to the cortex, which develops later in the second and third trimester. Genetics could be directly from the sperm and egg, or epigenetic where DNA and RNA alterations occur due to the intrauterine conditions (hormonal milieu, inflammatory reactions, infections, toxins, etc.). There are cases of identical twins, one with autism, the other not. Epigenetics.
At any rate, we can dig into all sorts of things here, but some things to think about.
