Many parents are worried about the possibility of their child having a gene disorder. In some cases, this worry can stem from the fact that a couples fertility issues are the result of a gene disorder they themselves have. Concern for passing on a disorder may result in meeting with a genetic counselor for advice and testing. However, not all gene disorders are caused by genetics. Knowing more about genes and how they contribute to fetal development can help you better understand whether or not your child is at risk.
What is a Gene Disorder?
Gene disorders are caused by an altered or flawed gene or set of genes. Gene disorders can be inherited when a child receives an altered gene or abnormal chromosome from her parents or from a combination of genetic and environmental factors. There are four main types of gene disorders: single gene disorders, chromosome abnormalities, mitochondrial disorders and multifactorial disorders. Some common disorders caused by altered genes include cystic fibrosis, sickle cell anemia, hemophilia and Tay Sachs disease.
What are Genes?
Every cell in your body contains approximately 30,000 genes. Genes are the chemical units composed of deoxyribonucleic acid (DNA) that influence your physical characteristics, personality and intelligence as well as your susceptibility to disease. Genes are found in the chromosomes of a cell. Each person has 23 pairs of chromosomes, one set you inherit from your mother and the other from your father. The sex chromosomes X and Y determine whether you became a girl (XX) or a boy (XY).
Occasionally, the DNA of genes becomes mutated due to an error in cell division, cells divide too quickly or the number or structures of the chromosomes are altered. For example, the genetic disorder Down syndrome is caused by an extra chromosome in the DNA. People with Down syndrome have 47 instead of 46 chromosomes.
How are Gene Disorders Inherited?
A gene disorder can be inherited if a gene mutation occurs in egg or sperm cells during conception, or you have a dominant disease gene in your DNA. Genes can be dominant or recessive. You can develop a gene disorder if you have one copy of a dominant disease gene in a chromosome pair or if you have two recessive disease genes in a chromosome pair.
Most people carry 5 to 10 disease genes in their cells, but they do not have the genetic disorder because they do not have the right combination of genes. Certain disorders, like hemophilia, are considered sex-linked or X-linked because the recessive disease gene is carried only on the X chromosome. Because girls have two X chromosomes they have an extra healthy copy of the gene so they do not develop the disease. But boys only have one X chromosome, so they are more likely to develop the disease.
Gene Disorders Influenced by the Environment
Sometimes altered genes can interact with environmental factors to produce a problem. For example, people who already have a genetic mutation that increases their risk of cancer may make themselves even more vulnerable to developing cancer by smoking. Some people may have an increased susceptibility to developing a certain genetic disorder, which their lifestyle habits may put them at increased risk of developing, such as asthma, diabetes or cancer.
Genetic Testing for Gene Disorders
If you are pregnant or thinking about getting pregnant, you may be considering genetic testing. Your doctor can use genetic testing to predict or diagnose some genetic disorders. These tests can usually be done with little discomfort to you and involve taking a blood, hair, skin or saliva sample to test. You may have genetic testing done for several reasons:
- to determine if you are susceptible to developing a certain genetic disease
- to confirm a diagnosis of a disease
- to determine if you or your partner carry diseased genes
- to determine if your unborn baby will have a gene disorder
- to discover if your newborn baby has a genetic disease
Who Has Genetic Testing Done?
Certain people are at risk of developing a genetic disorder or passing one down to their children. Your doctor will advise you to have genetic testing conducted if:
- You have a family history of genetic disorders,birth defects or cancer
- You have had two or more miscarriages or stillbirths
- You have a child with a genetic disorder, birth defect or developmental delay
- You plan to become pregnant after the age of 35
- You receive abnormal test results indicating a genetic disorder or chromosome abnormality
- Your ethnic background puts you at higher risk of carrying a genetic disorder. For instance, Tay Sachs disease is more likely to be carried by Jewish people or those from Eastern Europe while sickle-cell anemia is more frequently carried in African-Americans.
- You plan to become pregnant with a partner with whom you are blood- related.
Should You Have Genetic Testing Done?
Deciding whether or not to have genetic testing done is an extremely personal decision. You will want to discuss your options with a genetic counselor. Although you may want to know what your chances of developing a certain disease are, having testing done may lead to unnecessary anxiety. Genetic testing also has several limitations that you should be aware of:
- Test results are not always accurate
- A positive result does not mean you or your child will develop a disease
- A negative result does not mean you will not develop a disease
- Tests do not indicate disease severity
- Tests do not take into consideration environmental factors
- Tests are expensive, ranging from $100 to a couple thousand dollars