Complex sentence: They lived in the middle-class Notre-Dame-de-Grâce neighbourhood of Montreal from 1983 until 1994 when Layton was diagnosed with Alzheimer's disease.
Split into simpler sentences: They lived in the middle-class Notre-Dame-de-Grâce neighbourhood of Montreal from 1983 until the mid 1990s. In 1994, Layton was diagnosed with Alzheimer's disease.