Autosomal Recessive Definition Explained
Definition
It is etymologically connected to two ancient Greek words AUTOS which means independent and SOMA which means body and translating it would mean that it is autonomic body, the body that doesn't depend on any other body. But that definition wouldn't be accurate.
According to today's knowledge that we have we can dispose this word in two explainations:
1) It is something that has characteristic of autosome
2) or something that is transmitted by an autosome to any condition.
To understand the meaning of Autosomal we must though understand what is AUTOSOME according to the previous explaination.
Autosome is according to medicine research any chromosome that is not a sex chromosome and that appears as a homologouls pair in a somatic cell. Depending from literature to literature some writers call it euchromosome. More explained it means that from human 22 pairs of chromosomes that they have, autosomes transmit all genetic traits and conditions that are not sex linked.
Understanding that what we said above we can simplify the definition as pertaining to a chromosome that is any chromosome except chromosome that defines sex and that it is relating to any of the chromosomes except sex ones.
People in their normal stage have 22 pairs of autosomes which means 44 autosomes in each cell together with two sex chromosomes from which XY are male sex chromosomes and XX are female sex chromosomes.
Autosomal VS sex related dominance
In humans and many other species sex gender is determinated by two sex chromosomes that are X and Y chromosome. Human female chromosome pair is XX and male XY. The remaining pairs of chromosome are found in both sexes and are called autosomes, and genetic traits that are contained in those autosomes we call autosomal. They have two main abilities according to which we identify them.They can be dominant or recessive.
Genetic traits on the X and Y chromosome are important because they carry the sex and all characteristics related to sex. Females have two copies of every gene position found on the X chromosome because they have double X (XX pair of chromosomes) and the autosomes are also in two copies due to that. Males we call hemizygous because they have only one copy of X chromosomes (XY pair of chromosomes) which means that their autosomes are only in one copy.
Dominance rules for sex gene position is determined by their behavior in the female. Because male has only one allele, that allele is always expressed, regardless of whether it is dominant or recessive.
Dominant and Recessive
Dominant is one of various ways that a trait or disorder can be passed down trough families.If a disease is dominant, it means that you only need to get the abnormal gene from one parent in order for you to inherit the disease. One of the parents may often have the disease. To inherit a disease, condition of disease or trait of disease on gene depends on the type of chromosome that was affected by disease (if that was autosomal or sex chromosome), it also depends if the gene itself is dominant or recessive.
A single abnormal gene that is carrier of disease if it is found on one of the first of 22 pairs of non sex chromosomes from either parent can cause an autosomal disorder.
Dominant inheritance means that an abnormal gene from one of parents is capable of causing disease, even though the matching gene from other parent seems normal.
In this case the abnormal gene takes domination of the pair of genes. Example:If just one parent has a dominant gene defect, each child has 50% chance to inherit the same disorder.
One more example: If four children are born to a couple that one of the parents has an abnormal gene for a dominant one and it carries a disease, it is great probability that two children will inherit the abnormal gene and two other children wont. Children who do not inherit the abnormal gene will not be carriers of abnormal gene in the future.
If someone has an abnormal gene that is inherited in an autosomal dominant matter, then he should be tested for the abnormal gene.
Dominant disorders can cause two diseases if genes are abnormal. Those are Huntington's disease and Neurofibromatosis-1.We will explain each of them.
Huntington's disease or Huntington chorea
Huntington's disease is a disorder passed down trough families in which certain nerve cells in the brain waste away or degenerate.
It is named by an american doctor George Huntington who was the first to describe this disease in the year of 1872.
According to his studies this disease is caused by a genetic defect on chromosome #4. This defect causes a part of DNA that is called CAG to repeat and to occur many more times that it suppose to. In normal conditions this section of DNA is repeated from 10 up till 35 times. But in persons with this anomaly it is repeated from 36 up to 120 times. As the gene is passed from one generation to the next the number of repeats (CAG repeat expansion) tends to get larger. The larger the number of repeats, the greater is the chance of developing symptoms at an earlier age. That is one very important proof that the disease exists in one family, it becomes more evident at younger and younger ages.
There are two forms of Huntington's disease:Adult-onset and Early-onset.
Most common is Adult-onset Huntington's disease. Persons with this form usually develop symptoms in their mid 30s and 40s.
An Early-onset form of Huntington's disease is mostly sporadic and almost extincted and begins in childhood or adolescence. Symptoms for early-onset form can resemble on those of Parkinson's disease with rigidity, slow motions and tremor.
Note: If one of your parents has Huntington's disease, you have 50% chance to get the gene for the disease. Testing is recommended because if you got the gene from your parents you will develop the disease at some point in your life and that has also 50% chance to pass on your children. If you don't have the gene from your parents, then you can't pass that gene on your children.
Symptoms
Huntington's disease can be manifested even before motion's problems.
Earliest stage includes symptoms like:
- Antisocial behaviors
- Hallucinations
- Irritability
- Moodiness
- Restlessness or fidgeting
- Paranoia
- Psychosis
- Head turning to shift eye position
- Facial movements, including grimaces
- Slow, uncontrolled movements
- Quick, sudden, sometimes wild jerking movements of the arms, legs, face, and other body parts
- Unsteady gait
- Loss of memory
- Loss of judgment
- Speech changes
- Personality changes
- Disorientation or confusion
- Anxiety, stress, and tension
- Difficulty swallowing
- Speech impairment
In childhood symptoms are following:
- Rigidity
- Slow movements
- Tremor
Exams & tests
The doctor will perform a physical exam and may ask questions about the patient's family history and symptoms. A neurological exam will also be done. The doctor may see signs of:
- Dementia
- Abnormal movements
- Abnormal reflexes
- "Prancing" and wide walk
- Hesitant speech or poor enunciation
A head CT scan may show loss of brain tissue, especially deep in the brain.
Other tests that may show signs of Huntington's disease include:
- Head MRI scan
- PET (isotope) scan of the brain
DNA marker studies may be available to determine whether you carry the gene for Huntington's disease.
Treatment
Unfortunately there is no cure for Huntington's disease and there is no known way to stop the disease from getting worse. The main cause of treatment is to slow down the course of the disease and to help the patient to function for as long as it is possible.
Medication vary depending on symptoms.
Dopamine blockers may help reduce abnormal behaviors and movements. Drugs such as haloperidol, tetrabenazine, and amantadine are used to try to control extra movements. There has been some evidence to suggest that co-enzyme Q10 may also help slow down the course of the disease.
Depression and suicide are common among persons with Huntington's disease. It is important for all those who care for a person with Huntington's disease to monitor for symptoms and treat accordingly.As the disease progresses, patients will need assistance and supervision. They may eventually need 24-hour care.
Huntington's disease causes disability that gets worse over time. Persons with this disease usually die within 15 to 20 years. The cause of death is often infection, although suicide is also common.
It is important to realize that the disease affects everyone differently. The number of CAG repeats may determine the severity of symptoms. Persons with few repeats may have mild abnormal movements later in life and slow disease progression, while those with a large number of repeats may be severely affected at a young age.
Possible Complications
- Loss of ability to care for self
- Loss of ability to interact
- Injury to self or others
- Increased risk of infection
- Depression
- Death
Prevention
Genetic counseling is advised if there is a family history of Huntington's disease. Experts also recommend genetic counseling for couples with a family history of this disease who are considering having children.
Neurofibromatosis-1 or Von Recklinghausen neurofibromatosis
Neurofibromatosis-1 is an inherited disorder in which nerve tissue tumors (neurofibromas) form in the skin, bottom layer of skin (subcutaneous tissue), and nerves from the brain (cranial nerves) and spinal cord (spinal root nerves).
Causes
NF1 is an inherited disease. If either parent has NF1, each of their children has a 50% chance of having the disease.NF1 also appears in families with no previous history of the condition, as a result of a new gene change (mutation) in the sperm or egg. NF1 is caused by abnormalities in a gene for a protein called neurofibromin.
Symptoms
Neurofibromatosis causes unchecked growth of tissue along the nerves. This can put pressure on affected nerves and cause pain, severe nerve damage, and loss of function in the area served by the nerve. Problems with sensation or movement can occur, depending on the nerves affected.The condition can be very different from person to person, even among people in the same family who have the NF1 gene.
The "coffee-with-milk" (café-au-lait) spots are the hallmark symptom of neurofibromatosis. Although many healthy people have 1 or 2 small café-au-lait spots, adults with 6 or more spots greater than 1.5 cm in diameter are likely to have neurofibromatosis. In most people with the condition, these spots may be the only symptom.
Other symptoms may include:
- Blindness
- Convulsions
- Freckles in the underarm or groin
- Large, soft tumors called plexiform neurofibromas, which may have a dark color and may spread under the surface of the skin
- Pain (from affected peripheral nerves)
- Small, rubbery tumors of the skin called nodular neurofibromas
Exams and Tests
Diagnosis is made by a doctor familiar with NF1, including a neurologist, geneticist, dermatologist, or developmental pediatrician. The diagnosis will usually be made based on the unique symptoms and signs of neurofibromatosis.Signs include:
- Colored, raised spots (Lisch nodules) on the colored part (iris) of the eye
- Fracture of the long bones of the leg in early childhood
- Freckling in the armpits, groin, or underneath the breast in women
- Large tumors under the skin (plexiform neurofibromas), which can affect the appearance and put pressure on nearby nerves or organs
- Many soft tumors on the skin or deeper in the body
- Mild cognitive impairment, attention deficit hyperactivity disorder, learning disorders
- Soft nodules under the skin
Tests may include:
- Eye exam by an ophthalmologist familiar with NF1
- Genetic tests to find a change (mutation) in the neurofibromin gene
- MRI of the affected site
- Other specific tests for complications
Treatment
There is no specific treatment for neurofibromatosis. Tumors that cause pain or loss of function may be removed. Tumors that have grown quickly should be removed promptly as they may become cancerous (malignant). Experimental treatments for severe tumors are under investigation.
Some children with learning disorders may need special schooling.
Outlook (Prognosis)
If there are no complications, the life expectancy of people with neurofibromatosis is almost normal. With the right education and job expectations, people with neurofibromatosis can live a normal life.
Although mental impairment is generally mild, NF1 is a known cause of attention deficit hyperactivity disorder in a small number of patients. Learning disabilities are a common problem.
Some people are treated differently because they have hundreds of tumors on their skin.
Patients with neurofibromatosis have an increased chance of developing severe tumors. In rare cases, these can shorten a person's lifespan.
Possible Complications
- Attention deficit hyperactivity disorder (ADHD)
- Blindness caused by a tumor in an optic nerve (optic glioma)
- Break in the leg bones that does not heal well
- Cancerous tumors
- Loss of function in nerves that a neurofibroma has put pressure on over the long term
- Pheochromocytoma, which causes very high blood pressure
- Regrowth of NF tumors
- Scoliosis, or curvature of the spine
- Tumors of the face, skin, and other exposed areas
When to Contact a Medical Professional
Call your health care provider if:
- You notice coffee-with-milk colored spots on your child's skin or any of the signs listed here.
- You have a family history of neurofibromatosis and are planning to have children, or would like to have your child examined.
Prevention
Genetic counseling is recommended for anyone with a family history of neurofibromatosis.
Annual eye exams are strongly recommended.
Resources
What to Expect the Toddler Years
Still Alice
What to Expect the First Year
Pocket Medicine: The Massachusetts General Hospital Handbook of Internal Medicine (Pocket Notebook Series)
Caring for Your Baby and Young Child, 5th Edition: Birth to Age 5 (Shelov, Caring for your Baby and Young Child, Birth to Age 5)
Your Baby's First Year (Second Edition)
Kaplan Medical USMLE Master the Boards Step 3 (Kaplan USMLE)
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