Rare variants are, by definition, present in < 1% of the population. While the vast majority of rare variants will have small effect, some rare variants have large effects on vulnerability. Some of the most, prominent, findings involve copy number variants (CNVs), small deletions or duplications of genetic material detectable with molecular techniques. Some, such as the 22q11 deletion, are associated with major psychiatric disorder.39 Chromosomal microarray (CMA) analyses can detect many of these CNVs. The CMA technique (along with fragile X testing) is now widely recommended as a first-line evaluation in the assessment and treatment of autism spectrum disorders.40–44
