Peter Garrard, Associate Professor in Neurology, St George’s, University of London, talks to Cardio Debate about young onset dementia.
Definition and how to diagnose – any diagnostic markers available in everyday practice?
It’s somewhat arbitrary but we think of young onset dementia as dementia that occurs within working age, so under the age of 65 years. It’s a somewhat arbitrary definition and actually the statistics show demographically is that the instance and prevalence on dementia is very low in this working-age age group – so less than one per cent of the population. And then as people age the incidence increases by five per cent per year, so that over the age of 90 it’s estimated that around a quarter or even one third of people meet the criteria for dementia.
But the significance of this is that it is a disease of aging, for which ageing is one of the major risk factors. So when we see a patient in general practice with symptoms that are suggestive of cognitive failure – so memory impairment, language loss, behavior change, inability to navigate or use visual apparatus to perform the tasks of daily life – its always regarded as a low probability that they’re going to have anything seriously wrong with them.
Whereas in an older person, because the prior probability is so high, a diagnosis of dementia will be suspected much more often – so there’s often a delay.
I think the most important biomarkers to look out for at a clinical level, the characteristic symptom complex, characteristic symptom areas – is to realize that dementia doesn’t always present with memory loss or forgetfulness. It can present with difficulty in navigation, difficulty with using visual information – difficulty with reading, with driving, with navigating around the house. And this is quite frequently is dismissed as being a symptom of visual impairment, which it isn’t – it’s visual processing impairment. That must always be taken seriously.
And then there are language symptoms – changes in word finding ability, changes in ability to understand more complex words.
And there are these rather unusual behavioural symptoms, where people’s personalities change from being compatible with leading a normal life in social work environments, with beginning to exhibit bizarre behaviours.
Mechanisms of young onset dementia – is there a genetic background involved?
With regard to the underlying mechanism of these conditions, there are – we think of them in terms of underlying pathology – and overall the commonest the underlying pathology causing dementia is going to be Alzheimer’s disease.
But overall, and in a younger onset population, those patients with the underlying pathology of Alzheimer’s disease would account for maybe one third of the population, and of the remainder a large percentage will probably be caused by premature vascular disease, and then perhaps an equally large percentage with non-Alzheimer neurodegenerative conditions.
There are also groups of patients with non-neurodegenerative conditions, inflammatory conditions, toxic conditions, alcoholism, all presenting in that age group with cognitive decline.
But the non-Alzheimer neurodegenerative conditions fall into two distinct subtypes, and they are defined according to the protein that accumulates in the brain.
So with Alzheimer’s disease as everyone knows it’s Amyloid-Tau clots and tangles, and in the non-Alzheimer neurodegenerative cases there’s one group where Tau alone without Amyloid accumulates, and we call them tauopathies.
And there’s another group where the accumulating abnormal protein is something known as TDP43. And Tau and TDP43 both accumulate principally in frontal and temporal regions, so they’re front-of-brain neurodegenerative syndromes, whereas Alzheimer’s is more posterior.
So with Alzheimer’s we see more visual and memory problems, but with the anterior ones wee see more language and behavior problems.
Now, the mechanisms in the vast majority of all these underlying pathologies are unknown. But a proportion of them will be accounted for by having inherited a faulty gene, which are normally autosomally dominantly transmitted. So those ones will be easily recognized as they will give a very reliable and good family history, both of their own generation and their parents generation, possibly further back too.
But those only account for about 5 to 10 per cent, probably, of all the young onset dementias. Perhaps slightly more in the non-Alzheimer group. But by far the majority are sporadic, and the causes of sporadic neurodegenerative syndromes are totally unknown, and they are a source of intensive research across the world. And the first person who finds out a mechanism for sporadic Alzheimer’s or tauopathy or TDP43 will become very famous indeed, very quickly.
Prevention and management – New directions regarding diagnosis and treatment
I think treatment and prevention should be regarded as separate as indeed they are in cardiovascular disease. Though the risk factors for neurodegenerative disease are perhaps less well defined than they are for cerebrovascular disease.
Certainly hypertension, smoking, alcohol excess do lower one’s resistance to the development of neurodegenerative diseases as one ages. And similarly obesity, diabetes, lack of physical exercise are also risk factors.
So one can do a lot of good by these public health measures, but one will not eliminate the incidence of Alzheimer’s disease and the non-Alzheimer degenerative conditions either in the young onset group or later in life, even if you educated the entire population on these measures.
There’s very good evidence that homocystine is a potent risk factor for the development of Alzhiemer pathology. I know that in cerebrovascular disease and coronary vascular disease, there was at one time a lot of interest in whether we could prevent the incidences by lowering homocystine, and that hasn’t really proved particularity effective.
Whereas the evidence in Alzheimer’s disease – and it seems to act on the accumulation of Tau-protein in Alzheimer pathology – the evidence is that if you lower the homocystine in people who have above average levels, then that can stabilize their cognition. So that can be a very useful preventative measure but it needs a large clinical trial to prove its efficacy and of course it’s potential health/economic benefits.
So I think those are the preventative measures we can take. With regard to treatment, there is no proven disease-modifying treatment for Alzheimer’s Disease, but there are a lot of compounds in trial and there are a lot molecular targets – because so much now is understood about the molecular basis of all these degenerative conditions.
Now the target in all the Alzheimer trials will be to remove the amyloid, which has been successful using immunological mechanisms – immunization against amyloid. And that has been shown to remove the amyloid but not improve cognition, or stabilize cognition – suggesting that by the time you’ve got amyloid in the brain sufficient to give you a cognitive problem then you’ve missed the boat already. So the idea now is to treat amyloid, is to treat people as early as possible in their Alzheimer’s ‘career’.
So people with minimal or prodromal Alzheimer’s disease to see whether we can remove the amyloid and stabilize them that way.
Then there are new compounds coming along upstream for stopping the chemical change that changes normal Tau into toxic Tau. Those compounds are also being used in Alzheimer’s disease but also the tauopathies.
The TDP43 proteinopathies, as far as I know there are no compounds in trial but there are certainly molecular targets that will probably lead to trials coming upstream in the next five years.