chromosome 1q deletion (MONDO_0022756) is a chromosome abnormality that occurs when there is a missing copy of the genetic material located on thelong arm (q) of chromosome 1. The severity of the condition and the signs and symptoms depend on the size and location of the deletion and which genes are involved. Features that often occur in people with chromosome 1q deletion include developmental delay, intellectual disability, behavioral problems, and distinctive facial features. Most cases are not inherited, but people can pass the deletion on to their children. Treatment is based on the signs and symptoms present in each person. Also known as: partial deletion of chromosome 1q, partial deletion of the long arm of chromosome 1, partial deletion of the long arm of chromosome type 1, partial monosomy of chromosome 1q, partial monosomy of the long arm of chromosome 1.