EB:
In Alvin H. Marill's book, The Films of Edw. G. Robinson, it mentions:
"Just over a year after Edward G. Robinson's death, his only son, Edward G. Robinson, Jr., who in his 1957 autobiography, My Father, My Son, chronicled his trouble-plagued life, also died. He was 40."
The only info IMdb gives is that Edward G. Robinson "had to deal with a psychologically troubled son."
And yet, if my mind isn't playing tricks on me, I recall "suicide" as the cause of death. But, I can't find anything in writing to substantiate that. If I find anything further in my collection, I'll let you know. Now, I'm curious.