X Linked Dominant

X-linked dominant disorders usually affect females more than males. It is a hereditary disease, and an abnormal gene on the X-chromosome can lead to a dominant sex-linked disease. In some conditions, the absence of a functional gene results in the death of affected males.

Chromosomes and genes

Genes are found on chromosomes in every cell in our bodies. The genes send information to the cell and make essential chemical products such as proteins. Thousands of genes provide information for the human body to develop, grow and remain healthy.

The human cell contains 46 chromosomes that are arranged into 23 pairs. One of every pair is passed to the offspring from each parent. 22 of the chromosome pairs are numbered, and the 23rd pair is made up of the sex chromosomes known as X and Y. Since chromosomes come in pairs, there are two copies of every one of the genes. The anomaly to this rule applies to the genes carried on the X and Y sex chromosomes. A change in a gene that produces a fault is what's known as a mutation. If a DNA change happens in only one of the pair genes, it leads to a health condition known as dominant mutation.

What is X-linked dominant inheritance?

Dominant traits are those that need only one copy of the gene for them to express the disorder. X-linked characteristics mean that they are represented on the X chromosome. Remember that females possess two X chromosomes (XX), while males possess a single X chromosome (XY). Such a difference shows how they are affected by X-linked genes. In women, despite having two X chromosomes, only one is used for making the gene product, and the other X is switched off.

The switching off is known to occur randomly. This means that in some of the cells of a woman, one particular X chromosome will be switched off and in another cell, it will be active.

X-dominant inheritance happens when a gene that is responsible for the disorder or trait is found on the X-chromosome. The abnormal gene is usually from one parent that causes the disease. Both males and females can inherit the disorder or display the trait when they have a copy of the gene inherited from the parent.

How X-linked dominant gene mutations are passed down through the family

a) A father affected by a dominant gene combines with unaffected mother

A father usually passes the X-linked dominant gene mutation to all the daughters and all the Y chromosomes to all the sons. The unaffected mother gives the working gene to her children. There are two possibilities in the combination of the genes.

If the father carries the abnormal gene, all the daughters will inherit the disease. The main reason is that daughters always inherit the X chromosome from their father.

All his sons will be disease-free since sons only inherit the Y chromosome from the father. They will also inherit the working gene copy from their mother.

b) Affected mother

When a mother is affected by the condition, there are different combinations of genetic information that a child can get from their parents.

If the mother carries the abnormal X chromosome, half of all her children, both sons and daughters, will likely inherit the disease.

What it means if you have an X-linked dominant gene mutation:

Mutations on the X chromosomes are usually recessive. This indicates that if there is a copy of the same gene working normally in each cell of an individual, they will not show symptoms of the condition. However, when a gene mutation is dominant, the body cannot work normally with less than the usual amount of working gene product. The X-linked dominant mutation will then override the unchanged information in the working copy of the gene. A woman having both of her X chromosomes contain a dominant gene mutation is exceptionally uncommon.

Causes of X-linked dominant disorders

X-linked dominant disorders are generated by mutations in the genes on the X chromosome. A variation in one of the two copies is enough to cause the disease. In many of the cases, males usually experience more severe symptoms of the disorder than females.

Symptoms and conditions caused by X-linked dominant

Symptoms usually vary depending on the particular condition involved. Some conditions are linked to X-linked dominant inheritance. They include:

  • Rett syndrome - A condition that leads to intellectual and physical disability.
  • Vitamin D-resistant rickets - This condition differs from most cases of rickets since the ingestion of vitamin D or use of ultraviolet radiation during treatment is usually ineffective.
  • Goltz syndrome - This is a rare multi-system disorder that generally involves the development of the hands, feet, skin and eyes. It causes the teeth, nails, glands and hair to develop and function abnormally.
  • Incontinentia pigmenti (IP) - It usually affects hair, teeth, the central nervous system and particularly the skin. It is characterized by skin abnormalities that evolved from childhood to young adulthood.
  • Coffin-Lowry syndrome is a disorder marked by abnormalities of the facial and head area, mental retardation, soft hands with short, thin fingers as well as other cardiac, auditory and visual defects.
  • Hereditary nephritis - This disorder is usually identified by nephritic syndromes such as proteinuria, hematuria, hypertension and finally renal insufficiency. Sensorineural deafness may also accompany this.
  • An oral-facial-digital syndrome - this syndrome is characterized by flaws and defects in the growth of the structure of the oral cavity including the tongue, teeth, mouth and jaw. It also affects the development of facial features such as the head, nose and eyes, and the toes and fingers accompanied by varying degrees of mental retardation.
  • The fragile syndrome - this condition leads to a wide range of developmental problems including cognitive impairment and learning disabilities. People affected usually have delayed development of language and speech by age 2.

Treatment

While there's no known treatment for the disorder, treatment depends on individual defects or anomalies presented.