Is it true that those afflicted with autism will not be held accountable for their deeds?

If the autism in a person reaches the level of mental retardation, then they are not held accountable by Islamic law. However, if they are rational and merely introverted, then they are accountable. Affliction with illness atones for sins and elevates ranks; for a Muslim, Allah expiates their sins through any hardship, illness, worry, sorrow, or harm that befalls them, even a thorn that pricks them. And no harm befalls a Muslim except that Allah expiates their sins by it, just as a tree sheds its leaves. Allah Almighty is merciful, good, and close to those afflicted with illness, to mend their hearts broken by the sickness.