22q11.2 deletion syndrome is a microdeletion syndrome with an estimated prevalence of 1：2000-1：6000 live births. Various comorbidities and multimorbidity in physical, neurological, and intellectual aspects occur throughout life, resulting in poor quality of life（QOL）in individuals with 22q11.2 deletion syndrome. However, the relationship between multimorbidity and QOL remains unclear. This study investigated relationship between multimorbidity and QOL in individuals with 22q11.2 deletion syndrome using the National Database of Designated Incurable Diseases of Japan.

Information on comorbidities（e.g., congenital heart disease, immunodeficiency due to impaired thymic development, intellectual disability）and QOL such as social, daily, and physical function was obtained for 87 individuals with 22q11.2 deletion syndrome who were registered in the database from 2015 to 2020. The relationship between the binary variables of the total number of comorbidities（3 or less, 4 or more）and each item of QOL（with or without difficulties）was analyzed with the χ² test.

Those with 4 or more comorbidities were more likely to report difficulties with social function than those with 3 or less（87％ vs. 63％, p＝0.03）. Those with comorbidity 4 or more were also more likely to report difficulty with daily and physical function than those with comorbidity 3 or less, while not statistically significant.

To improve the daily function, which is a domain of QOL, of individuals with 22q11.2 deletion syndrome, it may be necessary to establish a support system for those with more severe comorbidities in addition to reducing multimorbidity through treatment and support for each comorbidity.