Figure 1. Cognitive effects of copy number variant syndromes in full-scale intelligence quotient scores.

(A) The intelligence quotient (IQ) distribution curve in individuals with deletion 22q11.2 (red line) is shifted 2 SD to the left of the IQ distribution in the general population (mean 100; SD: 15; light blue line).³⁵ (B) Individuals with deletion 16p11.2 have a mean IQ of 76·1 (dark blue line), which is significantly lower than the mean IQ of their non-carrier first-degree relatives (108·3, green line).³⁶ The higher IQ of first-degree relatives compared to the general population was previously discussed by Zufferey and colleagues³⁶ as likely due to ascertainment bias. For both copy number variant syndromes, many deletion carriers have IQ scores within the normal range (>70); this is often referred to as incomplete penetrance when cognitive function is viewed as a qualitative, dichotomous trait (normal intelligence vs intellectual disability) based on a cutoff of 70 points of IQ (dotted line), but may be better interpreted as variable expressivity of a continuous, quantitative trait.