Rare diseases number at least 7,000 known to date, and it is estimated that numerous unknown diseases also exist. Prevalence is estimated at around 5% of the total population, with a significant number of patients remaining undiagnosed. To address this undiagnosed condition, comprehensive genome analysis projects for these patients are advancing in various countries. Among these undiagnosed diseases, glycan-related disorders have been confirmed to be included. In drug discovery research for rare diseases, for instance, the elucidation of the cause of familial hypo-/hyper-cholesterolemia has led to the development and commercialisation of treatments for common diseases. Glycan-related disorders tend to progress more readily from cause identification to therapeutic drug development research. Furthermore, new drug development for rare diseases such as glycan-related disorders holds the potential to yield blockbuster novel therapeutics. Among the genes involved in glycan synthesis and degradation, many remain unlinked to specific diseases. Addressing this requires not only genomic analysis but also functional studies and glycan analysis. Collaborative research integrating clinical expertise in symptoms with glycan-focused basic science is essential. Such collaborative research could lead to the elucidation of these links within the next decade.