Validation of a German version of the dementia screening questionnaire for individuals with intellectual disabilities (DSQIID‐G) in Down's syndrome

Abstract Background People with Down's syndrome (DS) are at high risk of developing Alzheimer dementia (DS‐AD) due to a triplication of the amyloid precursor protein gene. While several tools to diagnose and screen for DS‐AD, such as the dementia screening questionnaire for individuals with intellectual disabilities (DSQIID), are available in English, validated German versions of such instruments are scarce. Methods A German version of the DSQIID questionnaire (DSQIID‐G) was completed by caregivers before attending our specialist outpatient department for DS‐AD. All participants were assessed blind to DSQIID‐G scoring using clinical and neuropsychological examinations, including the Cambridge Examination for Mental Disorders of Older People with Down's Syndrome and Others with Intellectual Disabilities (CAMDEX‐DS). ICD‐10 and amyloid/tau/neurodegeneration (A/T/N) criteria were applied to detect and categorise cognitive decline. Results Of 86 participants, 43 (50%) showed evidence of cognitive decline. A definite diagnosis of DS‐AD was reached in 17 (19.8%) and mild cognitive impairment in seven (8.3%) participants. Secondary causes of cognitive decline were determined among 13 (15.1%) participants, and in six (7%) cases, the diagnosis remained unclassifiable due to co‐morbidities. Compared with cognitively stable individuals, participants with cognitive decline ( n = 43) displayed higher DSQIID‐G total scores [median (range): 3 (0–21) vs. 19 (0–48), P 7 provided a sensitivity of 0.94 against a specificity of 0.76, to discriminate DS‐AD and participants without cognitive decline according to ROC analysis. The convergent validity against the CAMDEX‐DS interview score was good ( r = 0.74), and split‐half reliability ( r = 0.96), internal consistency (Cronbach's α r = 0.96), test–retest reliability ( r = 0.88) ( n = 25) and interrater reliability ( r = 0.81) ( n = 31) were excellent. Conclusions The DSQIID‐G showed excellent psychometric properties, including concurrent and internal validity and reliability. The cut‐off value for screening was lower than in the original English validation study. For a screening instrument like DSQIID‐G, a lower cut‐off is preferable to increase case detection.