Asthma and genetics
Asthma is a chronic respiratory condition characterized by inflammation and narrowing of the bronchial tubes, leading to symptoms such as wheezing, tightness in the chest, and difficulty breathing. The development of asthma is influenced by a combination of genetic and environmental factors. Research indicates that an individual may inherit a predisposition to asthma, but symptoms are often triggered by environmental exposures, such as cigarette smoke and pollutants. More than one hundred genes have been associated with asthma, with significant candidate gene regions identified on several chromosomes, including 2, 5, and 6. This complex genetic landscape suggests that asthma inheritance does not follow a straightforward pattern.
While there is no definitive way to prevent asthma due to its multifactorial nature, individuals can manage their condition by avoiding known triggers and adhering to treatment plans that may include medications like inhaled corticosteroids and bronchodilators. Emerging research also points to the potential role of the gut microbiome in asthma, indicating that modifying it could offer new preventive strategies. Overall, understanding the interplay between genetics and environmental factors is crucial in addressing asthma and improving patient outcomes.
Asthma and genetics
DEFINITION Asthma is an inflammation and narrowing of the bronchial tubes. Air travels in and out of the lungs through these tubes.
Risk Factors
Patients should tell their doctors if they have any of the risk factors that increase their chance of developing asthma. These factors include living in a large urban area, regularly breathing in cigarette smoke (including secondhand smoke), and regularly breathing in industrial or agricultural chemicals. Other risk factors include having a parent who has asthma, having a history of multiple respiratory infections during childhood, low birth weight, being overweight, and having gastroesophageal reflux disease (GERD).
Etiology and Genetics
The causes of asthma are complex and poorly understood, but it is clear that both genetic and environmental factors are involved. The prevailing notion is that an individual inherits the tendency to develop asthma, but the disease itself is triggered by the exposure to environmental stimuli. According to John Rees, Dipak Kanabar, and Shriti Pattani, more than one hundred genes have been implicated in one way or another in the etiology of asthma. It is therefore not surprising that there is no clear pattern or predictability for the inheritance of the disease.
The eleven major candidate gene regions reported by American Academy of Allergy, Asthma, and Immunology in 2013 are found on chromosomes 2,5, 6, 9, and 17. Other genes that may contribute to a person’s susceptibility to asthma have been identified on chromosomes 11, 12, and 14. Of these, much research has concentrated on a gene cluster on chromosome 5 that encodes key molecules involved in the inflammatory response (cytokines and growth factor receptors) and on the major histocompatability cluster of related genes on chromosome 6. Preliminary research also suggests different genetic pathways for early childhood and adult asthma and for susceptibility to and severity of asthma.
Symptoms
Symptoms include wheezing, tightness in the chest, trouble breathing, shortness of breath, a cough, chest pain, self-limited exercise, and difficulty keeping up with one’s peers.
Screening and Diagnosis
The doctor will ask about a patient’s symptoms and medical history and will perform a physical exam. Tests may include a peak flow examination, in which a patient blows quickly and forcefully into a special instrument that measures the output of air; pulmonary function tests (PFTs), in which a patient breathes into a machine that records information about the function of the lungs; and bronchoprovocation tests—lung function tests performed after exposure to methacholine, histamine, or cold or dry air to stimulate asthma. These latter tests can help to confirm asthma in unclear cases. Other tests include exhaled nitric oxide (a marker of airway inflammation) to suggest the diagnosis and manage medications, and allergy tests, usually skin or sometimes blood tests, to find out if allergies may be contributing to the symptoms.
Treatment and Therapy
The treatment approach to asthma is fourfold: regular assessment and monitoring; control of contributing factors, such as gastroesophageal reflux and sinusitis, and avoidance of allergens or irritants; patient education; and medications.
Some medications are used to control the condition and avoid asthma attacks but are not used to treat an acute attack. These medications include inhaled corticosteroid, used daily to reduce inflammation in the airways. Long-acting beta agonists, such as inhaled salmeterol, can be used daily to prevent asthma attacks, but they should not be taken without an inhaled corticosteroid. Long-acting beta agonists may increase the risk of asthma-related death, intubation (putting a tube in the windpipe to breathe), and hospitalization. Patients who have any concerns about this medication should talk to their doctors.
Cromolyn sodium or a nedocromil sodium inhaler can be used daily to prevent asthma flare-ups or to prevent exercise-induced symptoms; zafirlukast, zileuton, and montelukast may be taken daily to help prevent asthma attacks; and omalizumab (Xolair), a monoclonal antibody against immunoglobulin E (IgE), may be given as an injection under the skin, used along with other medications. Theophylline may be taken daily to help prevent asthma attacks, but this drug is not as commonly used because of interactions with other drugs.
Some medications can be used to treat an asthma attack. Quick-acting beta agonists, such as inhaled albuterol or Xopenex (levalbuterol), relax a patient’s airways so that they become wider again and may be used to avoid exercise-induced asthma attacks. Anticholinergic agents, or inhaled medications, such as ipratropium, that function as a bronchodilator typically are used only in an emergency setting.
Corticosteroids in the form of pills, injections, or intravenous (IV) medications are given to treat an acute flare-up of symptoms. Pills may be taken for a longer period of time if the patient has severe asthma that is not responding to other treatments. A shot of epinephrine can be given to stop an asthma attack.
Prevention and Outcomes
There are no guidelines for preventing asthma because the cause is unknown. However, patients can help prevent asthma attacks by avoiding things that trigger the attacks. Some general guidelines include keeping windows closed; considering the use of high efficiency particulate air (HEPA) filters for heating/cooling systems and vacuum cleaners; keeping humidity in the house down; and avoiding strenuous outdoor exercise during days with high air pollution, a high pollen count, or a high ozone level. Patients should get a yearly flu shot and should treat allergies and sinusitis; they should not smoke, should avoid breathing in chemicals or secondhand smoke, and should not regularly use a wood-burning stove. Researchers have reported that heating systems that are more efficient and nonpolluting can help to reduce asthma symptoms in children. If allergies trigger a patient’s asthma attacks, he or she should ask the doctor about allergy shots.
Patients should also talk to their doctors about an appropriate level of exercise and about ways to track asthma; tracking will help patients to identify and treat flare-ups right away.
Research in the early 2020s has identified a connection between asthma and the patient's gut microbiome. Studies began on the possibility that editing the microbiome on the genetic level may help with new ways to treat or even prevent asthma. Researchers suggested that altering an infant's microbiome could help alter the child's health so they did not develop asthma and hoped to have a protocol ready for clinical trials before 2030.
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