In children with CM who were younger than 5 years at CM episode and 5 years or older at follow-up neurocognitive testing, plasma tau was associated with worse scores in attention (β = −1.08; 95% CI, −1.79 to −0.38; P = .003) and working memory (β = −1.39; 95% CI, −2.18 to −0.60; P = .001). This evidence concerns the gene MAPT and cutaneous mastocytosis.