Whites here virtually too sick (6)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

The definition is the region whose wines are primarily white; but is the wordplay a reference to the disease ALS? It seems to me most unlikely, but I cannot come up with anything else. All suggestions welcome. Thanks to KVa @1, who came up with the parsing 5 minutes after I posted the blog.