Bruce Willis has been diagnosed with frontotemporal dementia, his family announced on Thursday.

The actor, 67, retired from his career spanning four decades in March after being diagnosed with the condition aphasia, which affects speech and language.

Now, his wife Emma Heming Willis, ex-wife Demi Moore and daughters Rumer, Scout, Tallulah, Mabel and Evelyn have shared "an update" to his health with a joint statement on Instagram.

"Our family wanted to start by expressing our deepest gratitude for the incredible outpouring of love, support and wonderful stories we have all received since sharing Bruce’s original diagnosis," the caption reads.

"In the spirit of that, we wanted to give you an update about our beloved husband, father and friend since we now have a deeper understanding of what he is experiencing.

"Since we announced Bruce’s diagnosis of aphasia in spring 2022, Bruce’s condition has progressed and we now have a more specific diagnosis: frontotemporal dementia (known as FTD).

"Unfortunately, challenges with communication are just one symptom of the disease Bruce faces. While this is painful, it is a relief to finally have a clear diagnosis."

Read more: Dementia could be prevented by regular hearing tests in your 30s, experts advise

The family also explained on the Association for Frontotemporal Degeneration website, "FTD is a cruel disease that many of us have never heard of and can strike anyone. For people under 60, FTD is the most common form of dementia, and because getting the diagnosis can take years, FTD is likely much more prevalent than we know.

"Today there are no treatments for the disease, a reality that we hope can change in the years ahead."

With them keen to "shine a light on this disease", here's what we know about the signs and symptoms of different types of dementia, including frontotemporal.

Watch: Bruce Willis diagnosed with frontotemporal dementia

What is dementia?

Dementia is a syndrome (a group of related symptoms) associated with an ongoing decline of brain function, according to the NHS. There are many different types, with many different causes, and it is not a natural part of ageing.

For example, Alzheimer's disease and vascular dementia are two different types, with both of them making up the majority of cases. Other types include frontotemporal dementia, dementia with Lewy bodies (DLB), young-onset, as well as mixed dementia (more than one at the same time).

The condition can affect memory, as well as the way you speak, think, feel and behave.

There are currently around 900,000 people with dementia in the UK, projected to rise to 1.6 million by 2040, according to the Alzheimer's Society.

The likelihood of developing dementia increases significantly with age. One in 14 people aged over 65 has the condition, which rises to one in six for those aged over 80. However, it can affect younger people too.

Alzheimer's disease

Alzheimer's disease is the most common cause of dementia in the UK. It is a progressive condition, meaning symptoms develop gradually over many years, slowly becoming more severe.

The exact cause isn't yet fully understood, though factors that can potentially increase your risk include age, a family history, untreated depression and lifestyle factors associated with cardiovascular disease.

The first sign is usually minor memory problems, such as forgetting about recent conversations or events, or forgetting the names of places and objects.

As the condition develops and symptoms become more severe, as listed by the NHS, these include:

• Confusion, disorientation and getting lost in familiar places

• Difficulty planning or making decisions

• Problems with speech and language

• Problems moving around without assistance or performing self-care tasks

• Personality changes, such as becoming aggressive, demanding and suspicious of others

• Hallucinations (seeing or hearing things that are not there) and delusions (believing things that are untrue)

• Low mood or anxiety

Read more: As Chris Hemsworth takes time off after discovering Alzheimer's risk, what is the disease?

Vascular dementia

Vascular dementia is a common type of the syndrome, caused by reduced blood flow to the brain, which often gets worse over time – though it's sometimes possible to slow it down. It can either start suddenly or begin slowly over time.

Symptoms listed by the NHS include:

• Slowness of thought

• Difficulty with planning and understanding

• Problems with concentration

• Changes to your mood, personality or behaviour

• Feeling disoriented and confused

• Difficulty walking and keeping balance

• Symptoms of Alzheimer's disease, such as problems with memory and language (many people with vascular dementia also have Alzheimer's disease)

This can make daily life increasingly hard for someone with the condition, eventually preventing them from being able to look after themselves.

Dementia with Lewy bodies (DLB)

DLB, also known as Lewy body dementia, is another common type of dementia. It is caused by the Lewy bodies, which are clumps of protein that appear in the nerve cells of the brain. As it shares symptoms with Alzheimer's disease and Parkinson's disease, it is often wrongly diagnosed.

Symptoms listed by the NHS include:

• Hallucinations – seeing, hearing or smelling things that are not there

• Problems with understanding, thinking, memory and judgement – this is similar to Alzheimer's disease, although memory may be less affected in people with dementia with Lewy bodies

• Confusion or sleepiness – this can change over minutes or hours

• Slow movement, stiff limbs and tremors (uncontrollable shaking)

• Disturbed sleep, often with violent movements and shouting out

• Fainting spells, unsteadiness and falls

Frontotemporal dementia

Generally speaking, frontotemporal dementia is an uncommon type of dementia. While dementia generally mostly affects people over 65, this type typically starts at a younger age. Most cases are diagnosed in people aged 45-65, though it can also present in younger or older people.

Frontotemporal dementia affects the front and sides of the brain, and causes problems with behaviour and language. Similar to other types of dementia, it usually develops slowly and gets gradually worse over a long period of time.

Symptoms listed by the NHS include:

• Personality and behaviour changes – acting inappropriately or impulsively, appearing selfish or unsympathetic, neglecting personal hygiene, overeating, or loss of motivation

• Language problems – speaking slowly, struggling to make the right sounds when saying a word, getting words in the wrong order, or using words incorrectly

• Problems with mental abilities – getting distracted easily, struggling with planning and organisation

• Memory problems – these only tend to occur later on, unlike more common forms of dementia, such as Alzheimer's disease

As well as mental symptoms, there may be physical ones too, such as slow or stiff movements, loss of bladder or bowel control, muscle weakness or difficulty swallowing. Frontotemporal dementia can also lead to someone being unable to care for themselves.

Read more: Dementia symptoms checklist as one in four show signs for two years before diagnosis

Young-onset dementia

Young- or early-onset dementia is defined as someone who develops the condition before the age of 65 (the usual age of retirement) with more than 42,000 people living with it in the UK.

Younger people with dementia may also experience a wide range of symptoms, with the overall condition caused by a range of different diseases. However, the support they need might vary, because it might affect them in different ways.

As listed by Alzheimer's Society, these include:

• A wider range of diseases cause young-onset dementia.

• A younger person is much more likely to have a rarer form of dementia.

• Younger people with dementia are less likely to have memory loss as one of their first symptoms.

• Young-onset dementia is more likely to cause problems with movement, walking, co-ordination or balance.

• Young-onset dementia is more likely to be inherited (passed on through genes) – this affects up to 10% of younger people with dementia.

• Many younger people with dementia don’t have any other serious or long-term health conditions.

Younger people living with dementia may also have concerns about how it will affect their family, relationships, finances, daily life, or the risk to future children.

When to see a GP

It's normal for memory to be affected by stress, tiredness, certain illnesses and medicine, but if you're becoming increasingly forgetful (or are experiencing other signs of dementia), particularly if you're over the age of 65, it's important to talk to a GP about it.

To distinguish normal memory loss from memory loss that could be a cause for concern, question whether it's affecting your daily life. If it's worrying you, or someone you know, don't delay in seeking advice.

Alzheimer’s Society has urged anyone worried about themselves or someone they love to take the first step and contact the charity for help. Support and more information about a diagnosis is just a phone call or a click away. Visit alzheimers.org.uk/memoryloss or call 0333 150 3456.

You can also use Alzheimer's Society's possible symptoms checklist to help with a medical appointment.

Additional reporting SWNS.