Autosomal Dominant

Autosomal dominant or dominance is a pattern of genetic inheritance that occurs within autosomes (non-sex chromosomes). Their appearance and function are mostly the results of the dominance of one parental gene over the other. From a medical point of view, autosomal dominant disorders represent disorders caused by a single copy of a mutated gene.  Scientists refer to a mutated gene as an allele.  Alleles are carried by both parents and affect both male and female offspring. One copy of the mutation from one parent can cause an autosomal dominant inherited disorder.

Autosomal Dominant vs. Recessive

For a geneticist, the concept of autosomal dominant vs autosomal recessive gene inheritance can easily be understood. The likelihood that a gene will be expressed defines whether a gene is recessive or dominant. A gene is only located on the non-sex chromosomes when it is autosomal. The millions of alleles that make up human DNA’s twenty-two autosomal chromosomal pairs can mutate everywhere. Our chromosomes come paired and we inherit one set from our biological father and one set from our biological mother.

This combination, in which some portions of the genetic code from one parent take priority over the identical genetic information from the other determines how we appear and how we behave. Our genotype, or genetic make-up, appears incredibly intricate. For instance, there are many distinct alleles involved in determining eye color rather than just one. Our dominant genes, which are typically the outcome of smaller dominant alleles, determine whether the genetic information from our mother or father is expressed. Even if they don’t have a direct impact while dominant alleles exist, recessive alleles can impact subsequent generations.

The Definitions to Fully Understand

Let’s quickly examine the distinctions between a gene, an allele, and a chromosome to make autosomal dominance more understandable. Chromosomes contain an organism’s entire genetic blueprint, made up of information shared by parents. We have exact copies of our parents’ DNA and our DNA contains a mixture of them.

A gene is a length of DNA that determines a genetic trait, such as a propensity to develop a particular type of cancer. We were born with these traits, or damage to our DNA can cause certain traits to form over time. Our genotype is responsible for the characteristics of our DNA. Dominant and recessive genes determine whether these traits are pronounced. The expressed genes (usually dominant genes) give rise to phenotypes (functional or visual traits).

Allele

An extremely particular portion of a gene or chromosome that is located at the same position is known as an allele. Every gene has 2 alleles, one from each parent. While an eye color gene may exist, different alleles will determine the precise color. The alleles determine the blood type you have if one of your genes has the blood type characteristic. Given that several alleles make up a single gene in the case of autosomal dominance, we should really speak of dominant alleles. It has the ability to impact the entire gene, even if just one of tens of thousands of alleles appears damaged.

The afflicted gene is frequently the name of an autosomal dominant (or recessive) ailment. As such, the gene’s related alleles cause the condition. One allele has prevailed over another, according to the definition of the word dominant. A phenotype can occur by a gene with only one copy from one biological parent. But a recessive mutation must pass by both parents. When up against a dominant allele, a recessive allele cannot prevail. The dominant gene in your dark hair originates from your father if both of your parents have brown hair. The brown hair allele is also dominant over a blonde allele in your DNA.

If the male does not have a dominant gene for brown hair, and the female is blond then the children will have blonde hair. When both parents carry the recessive gene, the child will also have blonde hair. This child will have brown hair if it receives a dominant and recessive gene or a group of alleles. Since so many distinct alleles may impact hair color, scientists can rarely anticipate the precise shade of brown.

Carriers

An adult can carry a recessive gene, but it will not result in an identifiable trait (phenotype). Two recessive exact genes will result in the related phenotype when combined with a recessive gene from the other parent. The recessive gene is suppressed when a dominant gene is present. Blonde hair is recessive and dominant in the autosomal dominance scenario from above. Blonde hair gene expression is prevented by the presence of a dominant dark hair gene.

Temporary concealment of an autosomal dominant disease is possible in some circumstances. This means that before we learned about genetic fingerprinting, we believed that some diseases were not genetically caused but rather brought on by the environment. For instance, Huntington’s disease is a progressive autosomal dominant brain condition that impairs cognition, emotion, and movement.  However, only when the gene undergoes a certain stage of mutation. Because Huntington’s gene has not reached the threshold that triggered the symptoms, a parent can pass on the gene without ever having been officially diagnosed with the condition.

Although it is now feasible to detect the presence of a gene long before symptoms show, it is still impossible to forecast whether a person would experience the symptoms or the ailment. We now understand that Huntington’s is a unique form of autosomal dominant illness. One diseased parent will pass on a faulty gene to the affected child, although this parent may not have manifested any symptoms of the illness. Parents cannot carry an autosomal dominant gene.

Symptoms don’t begin to manifest until a specific number of mutations occur. A condition can occur by our surroundings just as much as by the existence of a dominant gene. 

Autosomal Dominant Examples

Examples of autosomal dominance can relate to genetic behaviors. For example, it relates to skin, hair, and eye color, risk of developing certain diseases, and even neurological traits. It shows the odds or odds of inheriting brown, blue, or green eyes from either parent.  However, eye color results because of a myriad of alleles and does not always become predictable. As an example, we recommend focusing on individual mutant alleles. This aids in the ability to eliminate the influence of other genetic factors.

Huntingtin Disease

The huntingtin protein gene (HTT gene), which appears on chromosome 4, has between 10 and 35 instances of a particular section of code called the CAG trinucleotide repeat. These repeats take place 40 or more times in people with Huntington’s disease. Although it has recently been revealed that repeat expansions can fluctuate in size over the course of one or more generations, this may be inherited. Huntington’s disease does not automatically occur in those who carry the HTT gene.

It has previously been noted that this condition appears as an autosomal dominant disorder with a twist; if the cause of greater repeat expansions is identified, researchers will treat or even eradicate the diseases linked to it. Multiple genetic abnormalities are brought on by repeat expansions. Being an autosomal dominant condition, all it takes for a characteristic to pass along on to the next generation is for one parent to have it.

An uppercase letter H in the above figure stands in for the mother’s huntingtin gene. The unshaded squares show that there is no HTT gene (hh) mutation, whereas the gray-shaded boxes signify HTT gene mutation (Hh). The parent with the mutant HTT may not exhibit Huntington’s symptoms and have fewer CAG trinucleotide repeats. This gene is dynamic, so greater repetitions might develop later in life or over the lifetime of any children this parent has.

Polycystic Kidney Disease

The figure makes it obvious that half of a Hh and hh parent’s kids are susceptible to the mutant characteristic (Hh). Punnet squares and pedigree charts are terms used to describe diagrams that display hereditary qualities. Another common example of autosomal dominance is polycystic kidney disease. In this disorder, multiple cysts develop in the kidneys and reduce their ability to filter waste products from the blood.

Similar to Huntington’s disease, autosomal dominant polycystic kidney disease (ADPKD) is the product of transmission of the disease from one parent. In this case, a single mutated copy of the PKD1 or PKD2 gene causes disease. PKD1 appears on chromosome 16. PDK2 on chromosome 4. A relatively newly discovered gene on chromosome 11 can cause combined polycystic kidney disease and liver disease. Similar to HD, some cases of ADPKD result in new mutations. Contrary to Huntington’s disease, polycystic kidney disease can also classify as autosomal recessive (ARPKD).

Additional Autosomal Dominant Conditions:

Spondylocostal Dysostosis 
Spondyloepiphyseal Dysplasia 
Spondylothoracic Dysostosis
Goldenhar Syndrome 
Cleidocranial Dysplasia 
Charcot-Marie-Tooth Disease 
Neurofibromatosis Tumors
Marfan Syndrome 

Medical City Children’s Orthopedics and Spine Specialists are experts in the management of Autosomal Dominant conditions. We can help  patients with Autosomal Dominant conditions because we have the greatest medical professionals and cutting-edge facilities. Get in touch with Medical City Children’s Orthopedics and Spine Specialists as soon as you can and make an appointment for your child.