Precisely defined, a genetic disorder is considered to have occurred when there is a mutation in the previously normal sequence of genes. While there is a great deal that has been discovered about the human genome and how genes form and mutate, there is still much research left to be done.
Definition & Facts
Professional geneticists view genetic disorders in three classes: monogenetic disorders, multifactorial inheritance disorders, chromosome disorders. Monogenetic disorders arise when one solitary gene mutates. Here, the mutation may be on one or both chromosomes (strand of DNA). Some common examples of monogenetic disorders include sickle-cell anemia, polycystic kidney disease, and cystic fibrosis.
Multifactorial inheritance disorders are inherited when a small contingent of genes interact in specific ways with environmental triggers (such as the presence of tobacco smoke, poor diet and abuse of alcohol). It is thought that alcoholism, Alzheimer's disease, and obesity all have a multifactorial inheritance component, although at this time it is not known how much of a contributing factor this may be. Some common examples of multifactorial inheritance disorders include certain types of cancer, diabetes and heart disease.
Chromosome disorders can result from the absence or overabundance of genetic material on a strand of chromosome. In addition, if a gene is not functioning (termed "non-expressive"), this can also give rise to chromosome disorders. And if genes exchange their material (termed chromosomal translocation), this can cause a new mutated gene to form and develop into a disorder of its own. Some common examples of chromosome disorders include Down syndrome and some forms of leukemia.
Thanks to the National Human Genome Research Institute (NHGRI) and many other advocacy and research organizations, it is now known that many diseases in humans can be triggered or worsened by genetic mutations. Some of these diseases are considered common to humans, while others are still considered relatively rare. Similarly, some identified diseases are well known, thanks in large part to education and advocacy efforts, while other diseases are rarely mentioned.
Some examples of fairly well known genetic disorders: Fragile X syndrome, Down syndrome, autism, breast cancer, Parkinson's disease, prostate cancer, skin cancer, Tay-Sachs disease. Examples of some little known genetic disorders: osteogenesis imperfecta, Progeria, Trimethylaminuria, Factor V Leiden, Charcot-Marie-Tooth disease.
Symptoms & Complaints
A genetic disorder occurs when a gene mutates, and there are two types of genetic mutations: heritable and acquired.
As the name suggests, heritable mutations are "inherited" from the parents. They are commonly called "germ-line" mutations. This is because they are rampant throughout the body in every cell. The risk of developing a heritable genetic disorder can grow if both parents possess a particular mutation, which then gets passed down to the children.
Acquired mutations are picked up at some point during the affected individual's lifetime. One of the most common acquired genetic mutations is the alteration of skin cells through exposure to the harmful UV radiation in the sun's rays. If a mutation occurs in cells not associated with the individual's reproductive cells, it won't be heritable and passed on to offspring.
Diagnosis & Tests
There are a number of genetic tests that can be used to diagnose the possibility or presence of mutations. Some tests can predict for future genetic disorders while others are primarily used to diagnose current genetic issues.
- Preimplantation genetic diagnosis (PGD). These tests are done on in-vitro embryos to decide which are suitable for implantation for in vitro fertilization (IVF).
- Prenatal testing. A prenatal test can be done to determine if the developing fetus may be experiencing genetic mutations while in utero. This can help parents decide whether to permit the fetus to grow to term.
- Newborn screening. Newborn screening tests can be done just after the baby is delivered to detect more common genetic disorders that may arise in the future.
- Diagnostic testing. The most common use of these tests is to make a definitive diagnosis when symptoms of a possible genetic disorder are already beginning to appear. It can only be done for certain disorders at this time.
- Carrier testing. When carrier tests are done, they are typically done on both partners prior to pregnancy to see if there is a risk the child might inherit a genetic disorder requiring both parents to contribute a certain mutation.
- Predictive testing and pre-symptomatic testing. These tests can be helpful to predict whether an individual might develop a serious genetic disorder at some point in the future.
Treatment & Therapy
As with causes, symptoms and diagnosis, the type of treatment and therapy prescribed can vary greatly depending on the specific type of genetic disorder diagnosed. The most important step here is to make a definitive diagnosis so that the right course of treatment and therapy can be swiftly initiated.
Prevention & Prophylaxis
Genetic testing for breast cancer risk is one example in which the study of genetic disorders has empowered people to take preventive steps to mitigate their risks. Women who test positive for the BRCA mutation which increases breast cancer risk may opt to have more frequent cancer screenings or even prophylactic surgery in the form of a preventive mastectomy.
If a baby is diagnosed with a genetic disorder shortly after birth, treatment can begin swiftly to prevent the progress of the disease or complications. Most states require newborns be tested for phenylketonuria, which can be managed with careful attention to the baby's diet. Genetic testing in these cases guides treatment and prevention of harm to the baby. As more is learned about genetic mutations and its effects on the human body, it is hoped that fewer debilitating genetic diseases will affect people.