What are single gene disorders?

What are single gene disorders?

Single-gene disorders , or monogenic disorders, are those originating in a single gene . In fact, they are also called Mendelian disorders. These are diseases that can be predicted if they are diagnosed in advance.

A monogenic disorder isn't very common, although many exist, and they are inherited . They consist of alterations of various types, located in a specific gene. Sometimes, the genes must be modified in both parents, while in other cases, it only needs to occur in one parent. Likewise, boys and girls don't always inherit the disease in the same way, nor do they always manifest at the same age.

However, there are different typologies that should be known, as well as inheritance patterns : autosomal dominant, autosomal recessive, Y-linked inheritance, mitochondrial maternal inheritance, X-linked dominant and X-linked recessive . This implies different probabilities of developing a disease, depending on the parent.

That said, the number of disorders that exist is diverse, and the consequences are also of varying severity. We recommend performing various tests before conception to prevent and minimize problems.

What are the most common single gene disorders?

The most common single-gene disorders are the following, along with the different cases we may encounter. Take note, this will interest you:

1. Autosomal dominant disorders

In autosomal dominant disorders, having only one defective gene from one parent is enough to develop the disease. Examples include Huntington's disease, neurofibromatosis type 1 , Marfan syndrome , and Steinert myotonic dystrophy .

We're talking about a 50% chance of contracting the disease. Furthermore, it should be noted that there are no significant differences in the risk of contracting the disease between men and women.

2. Autosomal recessive disorders

Autosomal recessive disorders require both parents to have the genetic alteration for it to be passed on to their offspring; therefore, the chances are substantially reduced. Some examples are cystic fibrosis , spinal muscular atrophy, thalassemia , and Fanconi anemia . Although their frequency and incidence are lower, this does not mean they are not equally serious.

What we can say is that, most of the time, we're dealing with diseases that manifest early. Therefore, it's very important to perform genetic testing at the slightest suspicion to confirm or rule out the possibility.

3. Y-linked inherited disorders

Y-linked inherited disorders are extremely rare. First, because only males have them, and second, because this means they will only be passed on to sons. However, some cases do exist, and they can lead to Jacobs syndrome and problems with infertility or male development .

On the other hand, we must note that, due to their characteristics, many of these disorders can only be detected in adulthood. This makes early detection or treatment more difficult if it is not done specifically.

4. Maternally inherited mitochondrial disorders

Maternally inherited mitochondrial disorders are inherited because the genetic modifications are transmitted through the oocyte . It should be noted that, unlike other types of diseases, which manifest in infants, mitochondrial diseases can appear during adulthood . Some of these diseases are Leigh syndrome, Kearns-Sayre syndrome, MELAS syndrome , and MERRF syndrome .

In this case, genetic testing is essential. But even more so, if you're planning to undergo in vitro fertilization, checking the condition of your eggs is equally important.

5. X-linked dominant disorders

X-linked dominant disorders can occur in both men (mutation) and women (duplication), and only one parent needs to have the condition. The likelihood of children suffering from the disease is 50% , although men only transmit it to girls, and when it is transmitted by mothers, the symptoms tend to be milder in girls than in boys. Rickets is the most common disorder, although we could also talk about Bloch-Sulzberger syndrome .

Remember that, when we talk about a dominant gene , a smaller number of people are needed to develop a disease. Precisely for this reason, it would be a good idea for both parents to get tested before conceiving.

6. X-linked recessive single-gene disorders

X-linked recessive single-gene disorders affect boys , very rarely girls, even if their mother has a genetic disorder. The best-known recessive disorder of this nature is hemophilia , which is also associated with inbreeding. Although some disorders won't prevent you from living a relatively comfortable life, they should still be known.

How to avoid single-gene disorders?

Every person should know their genetic background, whether they want to have a child with their partner or are considering it in the future. To achieve this, there are two types of tests: one individual and one joint:

1. Genetic testing: This is an individual test designed to detect genetic modifications or hereditary disorders . Even if you don't have a disease or it hasn't yet manifested, it's very useful because you know whether or not your children could develop certain diseases in the future.
2. Genetic compatibility test: The genetic compatibility test is a joint test that examines the DNA of both members of a couple and determines whether there is a high probability that the offspring will suffer from a genetic disease. Remember that, in some cases, the relevant factor is whether both parents have the gene, or whether the father or mother has it.

Ultimately, you may have a certain genetic background, but you can minimize the chances of your children having it. Therefore, having this information in advance is especially useful.

In summary…

Single-gene disorders can be very harmful to those who suffer from them, which is why prevention is essential. At Genotica, you'll find all types of genetic tests and exams at the best price and with guaranteed confidentiality. Contact us and we'll give you more information!