Epidemiology

Estimates of the prevalence and incidence of frontotemporal dementia (FTD) vary widely, due in part to methodological differences between studies.[24] The average age of onset is between 45 and 65 years, but there have been documented cases in patients below 30 years and in older people.[25] Prevalence peaks in the seventh decade.[1][4]​​​​​​ In a study in Cambridge, UK, data derived from the records of speciality clinics and hospitals in several communities showed a prevalence of 15 cases of FTD per 100,000 in adults aged 45-64 years.[1] In the Zuid-Holland province of the Netherlands, data derived from annual surveys of all neurologists and physicians gave a prevalence of 6.7 cases per 100,000 in people aged 45-64 years.[2] Age-specific prevalence rates were also calculated: 1.2 per 100,000 in people aged 40-49 years; 3.6 per 100,000 in people aged 50-59 years; 9.4 per 100,000 in people aged 60-69 years; and 3.8 per 100,000 in people aged 70-79 years.[2] These two studies reported mean age at onset to be 53 and 58 years, respectively.[1][2]​​​​​​

Behavioural variant FTD is reported to be four times as common as the primary progressive aphasias.[24]

One systematic review reported that FTD accounted for an average of 2.7% of all dementia cases in prevalence studies that included people aged 65 years and older, and 10.2% of dementia cases in studies that included only people younger than 65 years.[24] Analysis of brain bank data produced estimates that FTD accounts for 8% to 17% of all dementia cases, but brain bank samples are highly selected samples and so estimates derived from these sources are likely to be biased.[26][27]

The typical early age at onset does not imply that FTD is an exclusively early-onset form of dementia. In routine clinical practice, FTD is more often recognised in people aged over 65 years, although diagnosis may be delayed by up to 6 years from symptom onset.[28] A matched retrospective cohort study of patients with FTD presenting before the age of 65 years (19 patients) or after this age (11 patients) found that the older patients more often showed memory impairment, with more frequent hippocampal sclerosis, but had less severe frontal lobe atrophy.[29] A large retrospective cohort study found that the mean age of onset was earlier than 65 years in patients with mutations in the MAPT, GRN, or C9orf72 genes. The presence of a MAPT mutation was associated with earliest onset, with a mean age of onset of 49.5 years and earliest age of onset of 24 years. Age of onset in the second generation was lower than in the first generation.[30]

FTD has been reported to affect men and women equally in some studies, whereas other studies have shown a male preponderance.[3][24][31]​ One large retrospective cohort study reported a higher prevalence in women among FTD patients with GRN (but not MAPT or C9orf72) mutations, and that age at onset was later in women than in men among patients with GRN or C9orf72 mutations.[30] There is some evidence that the prevalence and severity of FTD may vary in different ethnic groups.[32][33]

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