Combining blood biomarkers and the German version of the Dementia Screening Questionnaire for Individuals with Intellectual Disabilities (DSQIID‐G) for diagnosing cognitive decline in Down syndrome

INTRODUCTION Individuals with Down syndrome (DS) are at risk for Alzheimer's disease (AD). However, diagnosis remains challenging due to variability of intellectual ability and symptom presentation. To investigate whether serum AD biomarkers enhance accuracy of the German version of the Dementia Screening Questionnaire for Individuals with Intellectual Disabilities (DSQIID‐G), we combined test scores with neurofilament light chain (NfL) and glial fibrillary acidic protein (GFAP) levels. METHODS Seventy‐eight DS individuals (49% female) completed the DSQIID‐G; previous cohort data were added for a pooled sample ( n = 164, 47% female). Serum NfL and GFAP were assessed using the automated microfluid Ella system. RESULTS Combining the DSQIID‐G with NfL or GFAP resulted in improved accuracy in every diagnostic subgroup. The Youden index in the pooled samples yielded a cut‐off score at 6.5. DISCUSSION The DSQIID‐G is a robust screening tool and its combination with AD blood biomarkers aids earlier identification of individuals requiring further diagnostics for DS‐associated AD.