PIK3R1 encodes p85α, the regulatory subunit of phosphoinositide 3-kinase (PI3K), an enzyme complex that produces signaling molecules controlling cell growth, proliferation, and survival. The protein normally stabilizes and inhibits the PI3K catalytic subunit and helps the complex respond to signals from cell-surface receptors, including insulin, so alterations in this gene are associated with insulin resistance. PIK3R1 acts as a tumor suppressor: mutations that disrupt its inhibitory function can lead to abnormally active PI3K/AKT signaling and are found in several cancers, most often glioblastoma, as well as endometrial, breast, and colorectal cancers.

This Likely Pathogenic classification reflects a frameshift expected to eliminate the p85alpha regulatory subunit through nonsense-mediated decay, the loss-of-function mechanism that causes PIK3R1-related immunodeficiency and SHORT syndrome. Because p85alpha normally restrains PI3K/AKT signaling, this variant's predicted loss of function is also consistent with the gene's tumor-suppressor role in cancers such as glioblastoma, endometrial, breast, and colorectal cancer.