PMM2 and heart disorder: HCM has been reported in PMM2‐CDG, ATP6V1A‐CDG, and ATP6V1E1‐CDG.19 Recent studies have shown that abnormal glycosylation, for example, abnormal sialylation or reduced hybrid/complex N‐glycosylation, is related to heart disease.19, 20, 21 However, future investigations are required to understand the clinical relevance of these findings.