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A Case Report and Brief Literature Review

John M. Ringman, MD; P. Nagesh Rao, PhD; Po H. Lu, PsyD; Stephen Cederbaum, MD

Arch Neurol. 2008;65(3):412-415.

Objective  To describe a case of young-onset Alzheimer disease (AD) due to mosaicism for trisomy 21.

Design  Case report of a single patient.

Setting  Tertiary referral dementia clinic.

Patient  A 55-year-old man with a mild degree of developmental delay but no previous diagnosis of Down syndrome and only minimal physical manifestations of Down syndrome presented with gradually progressive cognitive impairment consistent with probable AD.

Results  Fluorescent in situ hybridization analysis of interphase chromosomes revealed trisomy 21 in 10% of peripheral lymphocytes.

Conclusions  As mosaicism for trisomy 21 can present with no or minimal manifestations of Down syndrome, it may be underdiagnosed as a cause of early-onset AD. Occult mosaicism for trisomy 21 may explain in part the previously described association between family history of Down syndrome and risk of AD. Screening for mosaicism with fluorescent in situ hybridization is indicated in selected patients with mild developmental delay and those with AD of young onset.

Author Affiliations: Alzheimer's Disease Research Center, Department of Neurology (Drs Ringman and Lu) and Departments of Pathology and Laboratory Medicine (Dr Rao), Pediatrics (Drs Rao and Cederbaum), Psychiatry (Dr Cederbaum), and Human Genetics (Dr Cederbaum), University of California, Los Angeles.

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