Of course, this depends on what you call a "specific disability". Autism is known as a spectrum with a wide range of different characteristics. Many would not consider it a "disability" at all...
In the UK, within the Department of Health, there is currently a minister for "Minister of State for Mental Health, Suicide Prevention and Patient Safety". If autism can be considered a specific disability, then perhaps "mental ill-health" can also be considered as such. If so the UK has a Junior Minister with such specific responsibility.
There is also a "Minister of State for Disabled People, Work and Health" within the Department of Work and Pensions.
It's not unusual for a Junior Minister to have specfic responsibilty for one aspect of a departmental brief, especially if there is a legislative programme or specific spending around an area. It is also not unusual for there to be different departments that work with one group of people. A (fictional but memorable) example is in the Harry Potter books, where there is a "Werewolf support services" (as part of the Beings Division) and a "Werewolf capture unit" (as part of the Beast Divsion).
I don't have the google-fu to find any other examples of a "Minster for Autism" (but that is partly due to the controversy that Bernie Finn has gotten into with posting abelist memes) Such a specific brief is rare, but it may indicate that the opposition have a program of planned legislation on autism (and therefore would need a minister to guide this) or that Bernie Finn had a prior interest in autism, and asked this to be a named part of his brief, in order to raise awareness in Victoria.