Who said Willy Loman had Down’s syndrome?

I have a piece in today's Times on whether artists' private lives should determine how we regard their work. Here's an extract:

One by one, down they fall on their feet of clay. The latest liberal icon to be revealed in his true colours is Arthur Miller, theatrical voice of the tortured American psyche and “the moralist of a generation”, as The Guardian, speaking for the liberal intelligentsia who so revered Miller, puts it. 

...Miller’s private behaviour may, as Professor Bigsby implies, have added depth and insight to his work, but it is entirely irrelevant to its worth. Yes, we can understand more about a work of art when we understand more about its creator – Shostakovich’s Seventh Symphony is given an added dimension when we know that it was written in 1941, is called “The Leningrad” and was intended to mark the suffering of the city in the siege. But as a piece of art, it stands or falls on its own merit.

...The Miller revelation shows how fatuous judging artistic worth on the basis of artists’ behaviour can be. When Miller took his decision, attitudes to Down’s syndrome were different. What does that have to do with Willy Loman?