Genetic Disorders

Genetic Disorders

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Genetic disorders happen when mutations or changes in our genes cause problems. While some changes can make us stronger or better suited to our environment, others can lead to diseases. These changes can also make us look different from one another, like having unique eye or hair color. But when they cause genetic disorders, they can lead to negative outcomes. So, while genetic variation can be fascinating, it's important to understand the potential risks as well.

Genetic Disorder Definition

Genetic disorders are diseases that happen when there are changes to an organism's DNA sequence. This often means that the DNA is different from what is considered normal. Some genetic disorders are called syndromes, like Down's Syndrome or Turner Syndrome, because they involve a set of symptoms that occur together. Other genetic disorders are called diseases, like maple syrup urine disease or sickle cell disease. Regardless of the name, the key thing to remember is that there are many of these disorders, and they can have negative effects on our health.

Tools for Determining Genetic Disorders and Genetic Disorder Testing

To determine if an individual has a genetic disorder, we use a process called genetic testing. There are different types of genetic testing available at different stages of life, and with varying levels of technology. One type of genetic testing is called pedigree analysis, which looks like a family tree. It helps determine the health status of family members, such as whether they are carriers of a disorder or have the disorder itself. Pedigree analysis is best used for existing families where everyone's traits are already known. It can also help determine the inheritance patterns of existing disorders. For example, if two healthy individuals give birth to a child with a disorder, as shown in Figure 1, we can tell that the disorder is recessively inherited. It would be impossible for a dominantly inherited allele to cause this pattern.

Recessively Inherited Genetic Disease Pedigree

There are different types of genetic testing available, including amniocentesis, chorionic villus sampling (CVS), and karyotyping. Amniocentesis involves taking a small amount of amniotic fluid from a pregnant woman's uterus and analyzing the genetic material of her baby. This method is used to check for genetic abnormalities in fetuses, such as Down Syndrome and other trisomies. CVS involves taking a sample of the placenta and testing it for genetic abnormalities. It is also used to check for genetic abnormalities in fetuses, and it can be done a few weeks earlier in pregnancy than amniocentesis. Karyotyping involves visualizing the full set of chromosomes under a microscope to analyze their size, shape, and number, as well as any abnormalities like breakage. This type of testing can be done at any age and only requires a DNA sample.

Human Karyotype
Human Karyotype

Sometimes karyotypes add on FISH (fluorescent in-situ hybridization), allowing different chromosomes to fluoresce different colors. This can help scientists see if chromosomes have broken off and rejoined in the wrong place if there's a color where it should not be!

Genetic Disorders List

Genetic disorders can be categorized based on their inheritance pattern. Autosomal recessive genetic disorders include sickle cell anemia, cystic fibrosis, Tay Sachs disease, alpha and beta thalassemia, Wilson's disease, Neimann-Pick disease, hemochromatosis H syndrome, phenketonuria. Autosomal dominant genetic disorders include achondroplasia (dwarfism), familial hypercholesterolemia, Marfan syndrome, Huntington's disease, hypertrophic cardiomyopathy, Romano-Ward syndrome, Diamond-Blackfan anemia, aniridia, Ehler's Danlos syndrome (some forms), and osteogenesis imperfecta (some forms). X-linked dominant genetic disorders include Aicardi syndrome, Goltz syndrome, Alport syndrome, hypophosphatemic rickets, and Rett syndrome. X-linked recessive genetic disorders include hemophilia A and B, Duchenne and Becker's muscular dystrophy, ocular albinism, Fabry's disease, Lesch-Nyhan syndrome, G6PD deficiency, sideroblastic anemia, and Bruton agammaglobulinemia.

Chromosomal disorders

Another example of a genetic disorder is Turner's Syndrome, which is an example of a sex chromosome disorder. It occurs when a female is born with only one X chromosome instead of the usual two. This can result in various physical and developmental issues, such as short stature, infertility, and heart problems.

Cri du chat syndrome is an example of a chromosomal disorder, specifically a deletion disorder. It occurs when a portion of chromosome 5 is missing, which can cause developmental delays, intellectual disability, and distinct facial features.

Down syndrome (Trisomy 21) is another example of a chromosomal disorder, specifically a trisomy disorder. It occurs when there is an extra copy of chromosome 21, resulting in developmental delays, intellectual disability, and various physical features such as a flattened facial profile and upward slanting eyes.

MELAS syndrome is an example of a mitochondrial inheritance disorder, which is passed down from the mother. It can cause a variety of symptoms, including seizures, muscle weakness, and vision and hearing problems.

These are just a few examples of the vast array of genetic disorders that can occur, each with their own unique causes, symptoms, and inheritance patterns.

Genetic Disorders: Sickle Cell Disease (SCD)

In Turner's Syndrome, the absence of one X chromosome can lead to a variety of physical and developmental issues. For example, these individuals may have a webbed neck, a broad chest, and a lack of breast development. They may also experience developmental delays, particularly in spatial reasoning and math skills, and may have difficulty with social interactions.

Cri du chat syndrome, caused by a deletion on chromosome 5, can result in a range of symptoms depending on the size and location of the deletion. Common symptoms include intellectual disability, delayed development, and a distinctive high-pitched cry in infancy. Individuals with this disorder may also have facial features such as a small head size and widely spaced eyes.

Down syndrome, caused by an extra copy of chromosome 21, can lead to intellectual disability, developmental delays, and a range of physical features including a flat facial profile, short stature, and low muscle tone. This disorder also increases the risk of certain health issues such as heart defects and respiratory infections.

MELAS syndrome and other mitochondrial inheritance disorders can cause a variety of symptoms depending on the specific genetic mutation involved. Common symptoms include muscle weakness, seizures, hearing and vision problems, and developmental delays.

Overall, these genetic disorders highlight the complex interplay between genetics and disease, and the importance of understanding the underlying molecular mechanisms to develop effective treatments and therapies.

Sickle cell vs. Normal RBC
Sickle cell vs. Normal RBC

Genetic Disorders: Marfan Syndrome

Another example of an autosomal dominant disorder is Huntington's disease, which is caused by a mutation on chromosome 4. This disorder typically manifests in midlife, with symptoms including involuntary movements, cognitive decline, and psychiatric disturbances.

Cystic fibrosis is an example of an autosomal recessive disorder, caused by mutations in the CFTR gene on chromosome 7. This disorder affects the function of certain glands, leading to thick, sticky mucus in the lungs, pancreas, and other organs. This can cause respiratory infections, digestive problems, and other complications.

Tay-Sachs disease is another example of an autosomal recessive disorder, caused by mutations in the HEXA gene on chromosome 15. This disorder affects the breakdown of certain fats in the brain and nervous system, leading to severe neurological symptoms and early death.

These genetic disorders, along with the ones mentioned previously, demonstrate the wide range of effects that genetic can have on the human body. While some may be relatively mild or manageable, others can be life-threatening and require ongoing medical care. Early diagnosis and treatment can be crucial in managing symptoms and improving outcomes for individuals with genetic disorders.

Genetic Disorders: Rett Syndrome

Rett syndrome is an X-linked dominant disorder that causes severe developmental regression and premature death. A highly lethal mutation causes this disorder, and because of its lethality, boys (XY) who have this gene don't survive till birth. Girls (XX) who have one normal X chromosome can survive until their 20s. The symptoms of this disorder usually start in girls around ages 2 - 5, with hand flapping, seizures, and loss of ability to walk and talk.

Genetic Disorders: Hemophilia A

Hemophilia is the classic X-linked recessive disorder. Famously, Alexander Romanov had this, and his symptoms of severe bleeding from minor wounds or painful hemarthroses (bleeding between the joints) are tell-tale of this disease. Because Hemophilia A is X-linked recessive, it occurs most often in boys, while girls tend only to be carriers. For a female to actually have Hemophilia A disease, the mutation would need to be on both of their X chromosomes.

Genetic Disorders: Down Syndrome

Another example of a chromosomal disorder is Turner Syndrome, which affects females and is caused by the absence all or part of. This lead a symptoms, including short stature, infertility, and heart and kidney problems.

Klinefelter Syndrome is another chromosomal disorder, affecting males and characterized by the presence of an extra X chromosome. This can lead to a range of symptoms, including infertility, reduced muscle mass, and breast development.

Chromosomal disorders can occur due to errors in cell division during meiosis, which can result in an incorrect number of chromosomes in the resulting gamete. They can also occur due to errors during fertilization, where the resulting zygote ends up with an abnormal number of chromosomes.

While many chromosomal disorders can have significant impacts on health and development, advances in diagnosis and treatment have improved outcomes for individuals with these conditions. Genetic counseling and testing can also help individuals and families better understand their risks and options.

Down Syndrome features. Arizona Department of Health Services
Down Syndrome features. Arizona Department of Health Services

Genetic Disorders: MELAS Syndrome

MELAS stands for Myopathy, Encephalopathy, Lactic Acidosis, and Strokes. These four features are the classic features of MELAS syndrome. This disorder is unique in that it is mitochondrially inherited, and the genes and mutations for this disorder occur on the circular mitochondrial chromosome (not one of the 46 nuclear chromosomes). Mitochondrial DNA is only maternally inherited, so a mother passes down this disorder to her children. Typically, MELAS presents with muscular symptoms, like weakness, temporary paralysis, loss of coordination, and neurological symptoms like seizures, vision loss, and headaches.

Common Genetic Disorders

Which genetic disorders are considered common? In genetics, common is relative. Cystic Fibrosis occurs commonly in people of North European ancestry, so it is common to this group. But to people with solely West African ancestry, cystic fibrosis incidence is extremely rare. The reverse could be said about sickle cell disease, which is rather common in people with West African ancestry, but very rare in people with solely North European ancestry. Remember that common genetic diseases are usually common to a particular population or ethnicity. Nevertheless, genetic disorders typically classified as common include cystic fibrosis, sickle cell anemia, Tay-Sachs (in Ashkenazi Jewish people), alpha and beta-thalassemia (in people of Mediterranean and Asian ancestry), Down Syndrome, and Huntington's disease.

Rare Genetic Disorders

Thankfully, the vast majority of genetic disorders are uncommon. But which are considered especially rare?

Heritable mitochondrial disorders, like DAD syndrome or LHON, are very rare. Disorders that lead to dangerously decreased immunity to viruses and bacteria, like SCID and Agammaglobulinemia, are quite rare. Heritable polydactyly, a genetic condition that leads an individual to have more than the normal number of fingers or toes, is an example of a spectrum of phenotype and rareness. An extra digit on the pinky finger, for example, is relatively common, while polydactyly of the thumb is rare, and polydactyly of the middle finger is extremely rare!

Genetic Disorders - Key takeaways Genetic disorders are diseases or syndromes that arise because of mutations in the DNA of the affected individual. To test or analyze a genetic disorder, we can do pedigrees, karyotyping, CVS, or amniocentesis (for fetuses).Broadly, genetic disorders include autosomal recessive, autosomal dominant, X-linked, chromosomal, and mitochondrially inherited. Common genetic disorders include sickle cell anemia and cystic fibrosis. Rare genetic disorders include mitochondrially inherited disorders like Leber's Hereditary Optic Neuropathy.

Genetic Disorders

Is autism a genetic disorder?

Autism is a disorder with multifactorial causes; both genetic and environmental

Is bipolar disorder genetic?

Bipolar disorder is known to have a genetic component (more likely in related family members) but it also has idiopathic or environmental causes.

What is a genetic disorder?

Genetic disorders are diseases or syndromes that arise because of mutations in the DNA of the affected individual

Is borderline personality disorder genetic?

Borderline personality disorder is a psychiatric disorder that has a genetic component, but also an environmental component. 

Are eating disorders genetic?

Research has shown significant genetic component to eating disorders, however they have a multifactorial etiology.

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