Sleep disturbances and tryptophan in patients with Alzheimer's disease

In his Dec 18/25 commentary,1Foley D Sorting out sleep in patients with Alzheimer's disease.Lancet. 1999; 354: 2098-2099Summary Full Text Full Text PDF PubMed Scopus (7) Google Scholar Daniel Foley discusses sleep disorders in patients with Alzheimer's disease. Various sleep disorders are apparent in patients who have mental illnesses.2McCurry SM Logsdon RG Teri L et al.Characteristics of sleep disturbance in community-dwelling Alzheimer's disease patients.J Geriatr Psychiatry Neurol. 1999; 12: 53-59Crossref PubMed Scopus (199) Google Scholar, 3Vitiello MV Bliwise DL Prinz PN Sleep in Alzheimer's disease and the sundown syndrome.Neurology. 1992; 42: 83-94PubMed Google Scholar The neurotransmitter 5-hydroxytryptamine (serotonin) is one of the main regulators of circadian sleep/wake cycles, and deficiency of serotonin is reported to be associated with a broad pattern of psychiatric/neurological disorders ranging from sleep disorders to depression and certain forms of dementia. A study we carried out in patients with Alzheimer's disease gives some causes of sleep disorders in these patients.4Widner B, Leblhuber F, Walli J, Tilz GP, Demel U, Fuchs D. Tryptophan degradation and immune activation in Alzheimer's disease. J Neural Trans (in press).Google Scholar We found that as a result of enhanced degradation, tryptophan concentrations were significantly decreased. And a higher tryptophan degradation rate was closely associated with a low Mini Mental State score. Low serum tryptophan concentrations probably interfere with the availability of serotonin. Our data suggest that sleep disorders in Alzheimer's disease may be associated with immune activation-induced tryptophan catabolism. Indeed, immune activation associated with enhanced tryptophan degradation and decreased serum tryptophan concentrations has been found in patients with HIV-1 who have sleep disturbances.5Wiegand M Möller AA Schreiber W et al.Nocturnal sleep EEG in patients with HIV infection.Eur Arch Psychiatry Clin Neurosci. 1991; 240: 153-158Crossref PubMed Scopus (56) Google Scholar The biochemical background of patients with Alzheimer's disease should be carefully studied, and it could provide an important starting point for a proper treatment of the sleep disorder.