Associate Professor Samantha M Loi ( left ) Neuropsychiatry , Royal Melbourne Hospital ; Department of Psychiatry , University of Melbourne , Parkville , Victoria .

Dr Monica Cations ( PhD ) ( right ) College of Education and Social Work , Flinders University , Adelaide , South Australia .

First published online on 24 February 2023

INTRODUCTION

YOUNG-onset dementia refers to

a dementia where symptom onset occurs in those aged younger than 65 . 1 It represents about 5-10 % of all dementia , with an estimated prevalence of 119 per 100,000 . 2 In Australia , this equates to around 28,000 people living with young-onset dementia . The only published Australian data reports a much lower prevalence of 68.2 per 100,000 . 3 , 4

The common types of young-onset dementia include Alzheimer ’ s disease , but metabolic and genetic causes are important in younger people . 1 , 4 , 5

Major challenges faced by people with young-onset dementia include delays to diagnosis , lack of appropriate services for younger people , challenges accessing the National Disability Insurance Scheme ( NDIS ), limited availability of appropriate accommodation and lack of evidence-based psychosocial interventions to slow functional and cognitive decline . 6-9

This How to Treat describes the aetiology , presentation and issues relevant to individuals with young-onset dementia . It aims to ensure GPs can appropriately refer , identify red flags for referral , and support individuals

and families with this neurodegenerative condition .

AETIOLOGY

PREVALENCE studies in young-onset dementia from the UK , Japan and Australia report that the most frequent causes are Alzheimer ’ s disease ( AD ), frontotemporal dementia ( FTD ), vascular dementia and alcohol-related dementias ( ARD ). 10-12

While AD , FTD and vascular dementias are important , the secondary causes of dementia , such as ARD , dementia from multiple sclerosis , human immunodeficiency virus ( HIV ) and traumatic brain injury are more common among younger people . 12 These dementias are potentially treatable if intervention occurs sufficiently early , emphasising the need for recognition .

Almost all people with Down syndrome develop the neuropathological changes of AD by 40 , and nearly 90 % will meet clinical criteria for AD by 65 . 13

There is a significant hereditary disposition compared with older-onset dementia , and the younger the onset , the greater the likelihood of a genetic component . 14

Some of the known genetic abnormalities implicated in young-onset dementia are autosomal dominant , meaning children have a 50 % risk of inheritance . About 15 % of cases of all young-onset dementia are attributed to autosomal-dominant inheritance . 15

In FTD , 20-50 % of people have a known genetic abnormality , with the C9orf72 , MAPT and GRN mutations the most common . 16 Gene testing has significant implications for the next generation ; a low threshold for genetic testing for individuals diagnosed with young-onset dementia is recommended , especially if a first-degree

17 , 18 relative is affected . Genetic causes of dementia are relatively uncommon . They are characterised by neuropsychiatric and neurological manifestations and dementia occurring at a young age , and include Niemann-Pick type C and Huntington ’ s disease . 19 , 20 The former is autosomally recessive with dementia onset in the 30s , while the latter is autosomally dominant with dementia onset in the 40s .

PRESENTATION

UNLIKE dementias occurring in older adults , where short-term memory

impairment is often the first symptom , young-onset dementia has a more variable presentation .

In young-onset AD , initial symptoms may still be amnestic but executive functioning deficits are also common . 21 In a posterior cortical atrophy variant , primarily involving deficits in visual processing , early symptoms can include difficulties with reading , depth perception and apraxia . 22 Frontotemporal dementias most commonly emerge in mid-life , and early presentation often includes behavioural and personality changes , executive dysfunction , and / or language difficulties ( particularly aphasia and anomia ). 23

In clinical practice , people with young-onset dementia and their families will commonly report increasing difficulty managing multiple demands at work , financial mismanagement , mood changes , forgetfulness and sometimes impulsivity .

A 2021 study reported that 21-36 % of inpatients eventually diagnosed with young-onset dementia had ‘ new-onset ’ psychotic and depressive symptoms . 5

People with young-onset dementia can be misdiagnosed with depression or anxiety , referred to psychiatrists or counsellors , and started on