Nowadays many different diseases are known. Some are caused by contamination from bacteria or viruses, some by radiation or toxic substances and others by genetic inheritance. Much knowledge has been acquired about a number of these genetic diseases, but there are still many diseases that are not common and about which not much is known. That is why not much research is done into these diseases and therefore the disease often cannot be cured or even treated. Most people with a rare disease have to learn to live with it and this is really no fun. One such rare disease is ADCA: a brain disease with many consequences.
What exactly is ADCA?
ADCA stands for Autosomal Dominant Cerebellar Ataxi. ‘Autosomal’ means that it does not determine sex: it is not the case that only men or only women can get it. ‘Dominant’ means that the disease is transmitted from parent to child: this chance varies from 50% to 75%. However, because it is a rare disease and in almost all cases there is only one heterozygous (one dominant allele and one recessive allele, instead of two dominant alleles*) parent, the chance of inheritance is 50% rather than 75%. ‘Cerebellar ataxi’ means that there is a disturbance in movement coordination due to damage to the small brain ( cerebellum ). In short, it is a progressive genetic disease in which the cerebellum shrinks. This shrinking means that the cells of this brain become damaged and/or die. This is very serious, because the cerebellum ensures the coordination and coordination of body movements.
The fact that this is a rare disease can be seen from its prevalence. The estimated minimum prevalence of ADCA is between 0.8 to 3.5 per 100,000 people in the Netherlands. Because of the 50% chance of inheritance, there is a good chance that the disease will remain in the family. The disease is dominant, so being a carrier of this disease is not possible . If a person has not inherited the disease, their children have a 0% chance of getting the disease. The disease usually manifests itself later in life, around the ages of 50-60. In general, people start to deteriorate physically around that age, but with ADCA it is worse.
What are the consequences of inheriting the genetic mutation that causes the disease?
More amino acids (glutamine) are produced than normal and this causes the brain cells of the cerebellum to die. This number of amino acids is inherited by the child, whereby the amino acids increase even more and this causes even greater complications. A complication that occurs is that the disease manifests itself at a younger age than in previous family members. A second complication is that the severity of the symptoms will increase, for example more severe spasm than their parent. This also causes more and more variations of the disease within a family. These variations differ in severity of symptoms and in which part of the nervous system is affected. For example, one person mainly has spastic problems, the other has serious hearing problems.
What are the consequences of the disease itself?
People with this disease eventually become unable to walk properly. They have trouble balancing, like a very drunk person has. A walker or even a wheelchair is then needed to get around. Another symptom that occurs in many people with ADCA is difficulty speaking. Because muscle coordination is affected, these people are very dependent on help from other people.
In addition to no longer being able to walk and speak properly, there are also other symptoms that often occur with different ADCA variants: hearing problems, vision problems (characteristic of unregulated eye movements or very slow eye movements), epilepsy, spasm, chewing – and swallowing problems and Parkinson-like symptoms. A certain ADCA variant can also relate to memory: dementia can also be a symptom. It can be hypothesized that each variant of ADCA affects a different part of the cerebellum. Hence, not every patient shows the same symptoms. All these symptoms have a major negative impact on the lives of ADCA patients and those around them, so the disease is a major problem.
How can ADCA be treated?
So far, no success has been found in curing the disease. Much more research and knowledge is needed for this. However, the symptoms can be treated, making the patient’s life a little easier. This is often done by administering medication. For example, Parkinson-like symptoms can be reduced with levodopa and/or dopamine agonists. Medicines such as clozapine and budipine are also used to reduce tremors (shaking of limbs). Other symptoms involving the muscles can also be treated with medication. Wearing a hearing aid can be a (temporary) solution for symptoms such as hearing problems. In addition, physiotherapy, speech therapy and/or occupational therapy are also used to make living with the movement-limiting symptoms easier.
Given the rarity of this disease, little research is done on it. That is why little is known about further treatment and possible prevention or cure of this disease. However, scientific research in June 2015 provided more light about the cause of the disease: the shrinking of the brain is related to the clumping of proteins. About thirty variants are known so far, of which SCA1 is the most severe form. Unfortunately, it is very difficult to find out which variant ADCA a patient has. It cannot be deduced from the variants that the family members have, because many different variants can occur even within the family. To find out which variant is present, it is necessary to investigate which gene the mutation is on. Unfortunately, it is very expensive to have a gene tested, which means that patients will sometimes never know which variant they actually have and this sometimes makes treatment more difficult. When research is done into the mutation on the genes, genes 1, 2, 3, 6 and 7 are normally checked first. The reason for this is that most mutations occur on these genes. If it is clear on which gene the mutation is located and what symptoms are associated with it, it is easier to treat the disease.
*an allele is a gene variant.
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