Mystery Word

Mystery Word

My first is in apple but not found in plum,
My second’s in sibilant – sounds like that one.
My third is a vegetable, small green and round,
My fourth is a vowel, not a consonant sound.
My next is in rolling but not standing still,
While my sixth may be uttered when getting a thrill.
The next one in seven may be seen twice.
Letter five is repeated; isn’t that nice?
My whole forms the name of the doctor from Wien
And also a Syndrome that you must have seen.