Genetic factors contribute substantially to the variations of various types of narcissism, stability of narcissism as well as its associations with other personalities, & the distinctions between different types of narcissism; environments (mostly non-shared by family members) also play important roles

The Etiology of Narcissism: A Review of Behavioral Genetic Studies. Yu L. L. Luo. Huajian Cai. In Handbook of Trait Narcissism pp 149-156, https://link.springer.com/chapter/10.1007/978-3-319-92171-6_16

Abstract: A great deal of research has delved into the etiology of narcissism via behavioral genetic methodologies in recent years. These studies have established that genetic factors contribute substantially to (1) the variations of various types of narcissism, (2) the stability of narcissism as well as its associations with other personalities, and (3) the distinctions between different types of narcissism. In the meantime, environments (mostly non-shared by family members) also play important roles in these situations. Together, these findings shed light on the origins of narcissism. Future studies may further examine how genetic and environmental factors interplay with each other in influencing narcissism and even what gene(s) is associated with narcissism.