This is a prospective, longitudinal study of children 2 -18 years of age who undergo aAntegrade Continence Enema (MACE) appendicostomy or cecostomy for treatmenthronic functional constipation as defined by the Rome IV criteria. Only patients withy on colonic manometry (CMS) will be included. The antegrade enema flushdication regimen will be randomized in 1:1 ratio of PEG 3350 and PEG3350 with electrolytes. The study statistician will create a blocked randomization schedule which will be uploadedREDCap. Glycerin and stimulant laxatives will be titrated as needed by a pediatric gastroenterologist in conjunction with the pediatric general surgery team. Neither patientviders will be blinded to laxative randomization as objective data in the form ofbiome composition is being evaluated.

Patients will have a pre-MACE placement stool sample obtained at time of colonic motilityudies and repeat stool samples collected at 1 month, 4 months and 8 months post-MACEd initiation of antegrade enemas. Post-MACE samples will be submitted at standardw-up appointments. All stool samples will be self-collected by patients. Samples will bed with the OMNIgene GUT kit which provides stabilization of DNA at room temperatureup to 60 days. Once the sample is collected by the research team, sample tubes will bed at -80 Celsius until all samples are collected and sent for sequencing. Pre-MACE stoolwill be collected while abstaining from osmotic laxative therapy for one week. Ifdo not spontaneously pass stool during the week of osmotic laxative abstention,will be collected from the first bowel movement after pre-CMS bowel flush with PEG 3350 with or without electrolytes has been initiated. Data regarding if stool collection occurred before or after receiving PEG 3350 with or without electrolytes for CMS bowel flush will beded. Patients will perform daily flushes after MACE placement and post-MACE stoolwill be collected within the first 10 minutes of flush initiation.