What is Olivopontocerebellar Atrophy?
Olivopontocerebellar atrophy (OPA) is a rare degenerative neurological disorder that affects the cerebellum. It is characterised by atrophy (wearing away) of the nerve tissue within the cerebellar region. OPA, or OPCA, incorporates a group of disorders and syndromes that have a degenerative effect on cerebellar nerve tissue. Examples include Fickler-Winkler OPA and pontocerebellar hypoplasia. Other related syndromes include MSA (multiple system atrophy) and SCA (spinocerebellar ataxia). All these conditions contribute to impaired balance, coordination problems and speech difficulties.
What causes OPA?
OPA can be inherited and the majority of inherited cases relate to SCA (spinocerebellar ataxia), which is a dominant autosomal disorder. This means that only one copy of the faulty gene is needed to develop SCA and it can be passed from either parent. Every time a baby is born, this means that there is a 50% chance of the baby developing SCA. Both males and females can be affected.
Pontocerebellar hypoplasia and Fickler-Winkler OPA are recessive autosomal disorders, meaning that both parents must pass on a defective gene in order for the baby to be affected. This means that with each pregnancy, there is a 25% chance of the child being affected, a 25% chance of the baby inheriting no defective genes and a 50% chance of the child being a carrier.
OPCA-X is what is known as an X-linked disorder. It follows recessive inheritance and mostly affects males. In this case, the defective gene is carried on the X chromosome. Females have 2 X chromosomes and males have one X and one Y chromosome. A female will be a carrier if she has a defective gene on one of the X chromosomes. Males only have one X chromosome and if the defective gene is present on the X chromosome, they will probably develop the disorder. With each pregnancy that involves a carrier female, there is a 25% chance of having a carrier daughter and a non-carrier daughter, a 25% chance of having an affected son and a 25% chance of the son not inheriting the defective gene. If the male is affected, all their daughters will be carriers, but the sons will not be affected, as the X chromosome is not passed from fathers to sons, only the Y.
How common is OPA?
OPA is rare. It affects both males and females and is thought to affect between 1 and 3 in every 100,000 people.
Symptoms of OPA
Symptoms of OPA are similar to many other degenerative neurological disorders and include:
- Ataxia: this is the most noticeable symptom of OPA. It relates to the inability to control voluntary muscular movements and may increase the risk of dropping things, losing balance and falling
- shakes and tremors
- slurred, slow speech
- neuropathy (damage to the nerves)
- stiffness in the muscles and a lack of fluidity in movement
- lack of balance
- gradual loss of coordination
- involuntary eye movements
- muscle spasms
- disturbed sleep patterns
- problems related to memory
Symptoms are caused by progressive damage to important parts of the brain, including the cerebellum, the pons and the inferior olivae. Damage affects the transmission of signals and the ability to control movement, balance and coordination. As the disease progresses, the symptoms may become more noticeable and profound.
OPA is often diagnosed based on symptoms and the results of tests. In the case of inherited disorders, genetic testing can be used to confirm a diagnosis. When there is no evidence of inheritance, a diagnosis of sporadic OPA is given and tests to reach this diagnosis may include blood tests, brain scans (MRI and CT scans) and EMG testing. This is used to examine electrical activity in the brain. A sample of cerebrospinal fluid may also be analysed. If diagnosis is made during pregnancy, genetic counselling will be made available.
Treatment for OPA
There is no cure for OPA and treatments are designed to alleviate symptoms and offer support for the individual. Patients with OPA are usually cared for by a multi-disciplinary team consisting of doctors and nurses who specialise in a range of fields and therapists, such as physiotherapists, speech therapists and occupational therapists.