Rare types of dementia

Over 850,000 people in the UK and 50 million people worldwide live with some form of dementia. While Alzheimer’s disease is the most common, there are actually over 400 different types of dementia, most of which few people have ever heard of. According to Rare Dementia Support, an estimated 5-15% of people with dementia have a rare type of dementia

A person is considered to have a form of dementia if they experience a progressive decline in their cognitive function. It is possible to have more than one type of dementia, and many of the rare types of dementia listed below are caused by more common types of dementia, particularly Alzheimer’s disease.

Familial Alzheimer’s disease (FAD)

2-3% of people with Alzheimer’s disease have a form called familial Alzheimer’s disease.

This type of Alzheimer’s disease passes down through genetics. People with the condition likely have a parent with familial Alzheimer’s disease. It is believed to be caused by a mutation in certain genes that promote the ‘clumps’ and ‘tangles’ of protein in the brain that are typical of Alzheimer’s disease.

Symptoms are alike to non-familial Alzheimer’s disease but are more likely to appear at a younger age. How young this is depends on which gene mutates. People who have mutations of the PS2 gene usually experience the onset of symptoms between ages 45-88. For the APP gene, it’s age 40-65, while people with mutations of the PS1 gene can experience symptoms as early as 35-55 years old.

There is also an inherited form of frontotemporal dementia (FTD), called familial frontotemporal dementia (fFTD). Up to 40% of people with the condition have fFTD.

Frontal variant Alzheimer’s disease (fvAD)

This is a form of Atypical Alzheimer’s disease, which is when someone has Alzheimer’s disease but not the usual symptoms because the plaques and tangles are on a different part of the brain. Usually, these plaques and tangles are on the temporal lobe, so symptoms are typically problems with memory, planning and problem-solving. Around 5% of people with Alzheimer’s are atypical.

Frontal variant Alzheimer’s disease is when the frontal lobe is affected; this occurs in around 2% of people with Alzheimer’s. This part of the brain is responsible for memory too, but also how we control and express ourselves, including emotional expression, sexual behaviours and language.

Posterior cortical atrophy (PCA)

Posterior cortical atrophy affects around 5% of people with Alzheimer’s disease, but because it is hard to diagnose, this number could be higher.

Atrophy is when the body breaks down its own tissue. Posterior cortical atrophy is when there is a breakdown of brain cells at the back of the brain, including the cerebellum and occipital lobes. These areas are responsible for processing visual information, coordination and some memory.

It is sometimes called visual variant Alzheimer’s disease, as the atrophy is usually caused by Alzheimer’s. It can be caused by other types of dementia such as Creutzfeldt-Jakob disease and corticobasal syndrome.

Symptoms can vary widely. It’s fairly common to have difficulty with sight, including visual-spatial awareness, reading and making sense of what they see. Other symptoms can include memory problems and hallucinations. Symptoms usually present in people aged 50 to 65.

Primary progressive aphasia (PPA)

Primary progressive aphasia is a group of three conditions that affect communication, usually in older people. These are semantic dementia, logophenic aphasia and progressive non-fluent aphasia.

It is much more common in men than women, with around twice as many men receiving this diagnosis. It is thought to be caused by mutated genes and people with learning disabilities are at higher risk of developing the condition.

Symptoms vary depending on which type of primary progressive aphasia the person has, but they can include misspelling or misreading words, poor grammar, repetition, difficulty with expressing what they are trying to say and understanding language, both verbally and written. People with primary progressive aphasia can eventually stop speaking altogether.

Corticobasal syndrome (CBS)

Corticobasal syndrome is a type of frontotemporal dementia. It is characterised by damage to the cortical and basal areas of the brain, which control movement, thinking, language and behaviour. Another term for it is atypical Parkinsonism.

While it shares symptoms with Parkinson’s disease, including slow, stiff movements and tremors, it also causes problems with movement, memory, problem solving and speech. There may be changes to personality and loss of inhibitions. One of the most common symptoms is gradually losing the use of one limb, known as limb apraxia.

Creutzfeldt-Jakob disease (CJD)

The cause of Creutzfeldt-Jakob disease is a protein called prion. The presence of too much prion in the brain can damage cells and lead to the progressive loss of cognitive and motor function. Up to 2 in every million people each year receive diagnoses with a form of CJD.

There are four types of Creutzfeldt-Jakob disease, including sporadic, varial, familial and iatrogenic. Sporadic is the most common, when normal proteins in the brain change into prion. 

Variant Creutzfeldt-Jakob disease is incredibly rare and caused by eating beef from a cow that had mad cow disease (bovine spongiform encephalopathy) in life.

Familial Creutzfeldt-Jakob disease is when someone inherits a mutation on the gene that produces prion. Iatrogenic means that the disease is caught from contaminated medical equipment.

Symptoms of Creutzfeldt-Jakob disease include changes in cognitive abilities, personality, movement, vision and speech.

Normal pressure hydrocephalus (NPH)

The brain and spinal cord are surrounded by a fluid called cerebrospinal fluid. This fluid acts as a cushion, helps the brain to stay buoyant and provides nutrients. Normal pressure hydrocephalus occurs when there is an excess of cerebrospinal fluid that builds up in the ventricles of the brain. This excess of fluid can be due to old age, or an infection, head injury or tumour.

Symptoms usually include difficulty with balance, walking, bladder control, confusion and mood changes.

The condition can often be successfully treated by draining the excess fluid. Unfortunately it is difficult to diagnose and very commonly misdiagnosed as another form of dementia.

Huntington’s disease (HD)

Huntington’s disease affects the nervous system, causing difficulties with memory, concentration, hand-eye coordination and spatial awareness. There are also physical symptoms such as difficulty with controlling movement, and many people experience involuntary twitches.

Huntington’s disease is caused by an inherited faulty gene. Symptoms usually appear between the ages of 30 and 50, but this can be earlier or later in life. Less than 10% of people with the gene develop symptoms before the age of 21, but those who do are diagnosed with Juvenile Huntington’s disease. This version of the illness can carry additional symptoms, such as seizures and behavioural problems. 

Progressive supranuclear palsy (PSP)

Progressive supranuclear palsy is a disorder that affects cognitive function, movement and eyes. It is thought to be caused by abnormal deposits of a protein called tau (the same protein that causes Alzheimer’s disease when it builds up in plaques and tangles) in the brain, particularly the brain stem. Other theories include genetic mutation, exposure to an unknown chemical or free radicals.

Symptoms can include blurred vision, involuntary eye movements, brain fog, poor memory, slow speech, dysphagia, muscle stiffness and significant changes in personality and mood.

Leukodystrophy

Leukodystrophy is the term for a range of over 52 (so far discovered) disorders that are caused by deterioration or malformation of white matter in the brain. This matter is responsible for insulating and protecting the nervous system. When it is inhibited, the brain cannot properly communicate with the nervous system.

Leukodystrophies are usually hereditary, and symptoms appear in childhood. Symptoms can include difficulty with breathing, balance and mobility, learning disabilities, behavioural issues, seizure, incontinence and impaired speech, hearing or vision. Some people with a form of leukodystrophy also experience progressive dementia, particularly metachromatic leukodystrophy and CADISAL, which impair memory, concentration, behaviour and other cognitive functioning.