How Common Are Genetic Disorders in the United States?

Scientists have long understood that there is a link between certain diseases and abnormalities within the genome. These abnormalities are known as “gene mutations.”

Gene mutations are actually quite common. The impact they have on a person’s health can vary greatly. Some gene mutations confer beneficial traits and others may cause serious medical conditions.

In this article we take a look at the most common hereditary genetic disorders, their frequency, and the integral role of preconception carrier screening in family planning.

How are hereditary genetic disorders passed on?

Hereditary genetic disorders fall into six distinct categories in terms of inheritance patterns: autosomal recessive, autosomal dominant, X-linked recessive, X-linked dominant, Y-linked, and mitochondrial.

Most genetic disorders are autosomal recessive in nature. Recessive genetic diseases only manifest if both an individual’s parents are carriers of the same genetic disorder and that individual inherits the genetic mutation from both parents.

Dominant genetic disorders can arise if just one parent has the genetic mutation.

X and Y chromosomes are sex-determining chromosomes. X-linked genetic diseases, therefore, affect males and females differently. Females inherit two X chromosomes, with males inheriting just one. Males have no “spare” X chromosome to revert to if they inherit a faulty one. As a result, they are generally more severely affected by X-linked genetic disorders.

Only males transmit Y chromosomes. This means that only males can pass on or inherit a Y-linked genetic disorder. Y-linked genetic disorders are very rare, with many causing fertility problems.

Mitochondria are present in egg cells but not sperm. Only the mother can pass on a mitochondrial genetic disease to her offspring. Again, this type of genetic disorder is rare.

How common are genetic mutations?

A gene mutation is a difference in a gene’s DNA sequence that renders it different from that found in most people. To some extent, we all carry gene mutations.

The human genome is a set of detailed instructions on how to make a human being. Only identical twins carry the same DNA. This is because they originate from a single fertilized egg. Genetic anomalies dictate our physical traits, how our bodies function, and our predisposition to certain diseases.

Gene mutations are often an evolutionary response to external factors, adapting the body to suit its environment. Most gene mutations are neutral or beneficial. However, some are harmful, predisposing the carrier and his or her offspring to disease.

Some disease-associated gene mutations are more prevalent in certain populations. Nevertheless, most genetic disorders can affect people of all ethnic origins, occurring in families with no known history of genetic disease. The American College of Obstetricians and Gynecologists therefore advocates genetic carrier screening for all women planning a family, irrespective of family history or ethnicity.

What are the most common genetic disorders in the United States?

One of the most common genetic disorders in the United States is sickle cell anemia. This disease affects the formation of hemoglobin. This substance is instrumental in the circulation of oxygen throughout the body and keeps vital organs functioning properly. People with sickle cell anemia have misshaped hemoglobin cells, which can get stuck in vessels, causing painful blockages and starving tissue and organs of vital oxygen.

Experts estimate that over 100 million people worldwide carry the sickle cell anemia-causing gene mutation. Sickle cell anemia is autosomal recessive in nature. Approximately 100,000 United States citizens have sickle cell anemia.

Cystic fibrosis is more prevalent in Caucasians of North European origin, but is found in all ethnic groups. Around 30,000 people have cystic fibrosis in the United States, with approximately 100,000 people affected worldwide. Experts estimate that some 10 million Americans (equating to 1 in 31 US citizens) carry the associated gene mutation.

Symptoms of the disorder include breathing difficulties and digestive problems due to the body’s production of a characteristic, thick sticky mucus. This mucus can build up, causing blockages in the lungs as well as infection. Secondary complications include liver problems, arthritis, and osteoporosis.

Cystic fibrosis follows an autosomal recessive inheritance pattern, meaning that only a child of two carriers can inherit the disorder. If both parents are carriers, the chance that their child will inherit the disorder is 1 in 4, with a 1 in 2 chance that the child will be a carrier. There is also a 1 in 4 chance that their child will be born neither a carrier nor with the associated disorder.

Preconception carrier screening plays a key role in family planning

Carrier screening provides prospective parents with insight into their potential pregnancy. If a person is found to be a carrier of a genetic disorder, genetic counsellors can provide guidance, helping them make decisions ahead of time and take proactive steps, drastically improving individual outcomes.

An estimated 80 percent of people affected by genetic disorders are born to families with no known history. This is why health practitioners worldwide advocate preconception genetic screening as an integral step in planning a pregnancy.