The aims of the current study were to: (a) determine if perinatal maternal probiotic supplementation alters the concentration of TLSP, TGF-β1, TGF-β2 or TGF-β3 in breast milk at 10 days and 3 months postpartum and (b) investigate if these breast milk cytokines contribute to the preventative effect of maternal probiotic supplementation on the development of AD at 2 years of age through causal mediation analysis. This evidence concerns the gene KLK11 and Alzheimer disease.