Absence of familial association between dementia of Alzheimer type and down syndrome

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Abstract
The aim of this study was to test whether there is an excess of dementia of Alzheimer type (DAT) cases in Down syndrome (DS) relatives. We conducted a case-control study in families of DS children with classical trisomy 21. A control group was constituted of families of children referred to the same hospital for benign diseases. Families of 188 DS children and 185 controls were recruited. We obtained vital statistics on 1,850 (response rate 82%) grandparents and great-grandparents in the DS group and 1,525 (69%) in the control group. Rates of possible severe dementia were calculated on ancestors over age 60 years with available data on mental function, 1,336 in the DS group and 1,113 in the control group. Rates of possible severe dementia were similar in the two groups: 5.6% (78 cases) in DS and 6.2% (66 cases) in control. Dementia with insidious onset suggestive of DAT was observed in 2% (28 cases) of DS ancestors and 2.6% (28 cases) of control ancestors. Our results argue against an excess of dementia cases with insidious onset suggestive of DAT in families of children with classical trisomy 21.