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Explanation:
The genetic disorders are defined as the problems in health that are effective as a result of abnormalities in the DNA of the chromosomes or genes of a person.
Types of genetic disorders:
There are three types of genetic disorders namely, single gene disorders, multifactorial disorders and chromosomal disorders. The autosomal dominant and autosomal recessive disorders are the single gene disorders. The X-linked and Y-linked disorders come under chromosomal disorders which are inherited from the parents.
Single gene disorders:
These are disorders that are caused due to abnormality in a single gene.
Autosomal dominant:
It is a condition where a single copy of the gene is mutated enough to cause a disease. Every affected patient has at least one affected parent.
E.g. Huntington's disease
Autosomal recessive:
It is a condition where two copies of the gene are mutated to cause a disease. Every affected patient has carrier parents whose disease causing traits are transferred into the patient.
E.g. Cystic fibrosis and sickle cell anemia
Multifactorial disorders:
It occurs as the cause of environmental factors and genetic mutations.
E.g. Heart disease, diabetes and schizophrenia.
Chromosomal disorders:
It occurs as a result of abnormalities in the structure or number of chromosomes.
E.g. Down's syndrome
X-linked disorders:
These are the disorders that occur as a result of mutations in the genes on the X
chromosome. Mostly they occur in males as they have a single X chromosome and the females are known to be the carriers of the disease.
E.g. Duchenne muscular dystrophy
Y-linked disorders:
These are also known as holandric inheritance and it affects the person who has mutations in the genes on the Y chromosome. It means that only males are affected by the disease as they have one Y chromosome in them and women lack it.
E.g. Hypertrichosis
Examples of genetic disorders:
The examples of genetic disorders include cystic fibrosis, sickle cell anemia, Huntington's disease, heart disease, diabetes, schizophrenia, Down's syndrome, Duchenne muscular dystrophy and hypertrichosis.
Cystic Fibrosis (CF):
It is an autosomal recessive disorder and is caused by a mutation in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene. The two recessive alleles of the chromosome 7 (exact position is 7q31.2) in the respective person is responsible for the disease. These two recessive alleles are non-functional and do not code for any amino acids, especially phenylalanine which is the major requirement in CF patients. The symptoms include wheezing, lung infections, persistent coughing and breath shortness.
Sickle cell anemia:
It occurs due to mutation in the gene coding for the size and structure of the hemoglobin (i.e. β hemoglobin gene) which in turn carries the oxygen in the red blood cells (RBCs). It causes the abnormal shape and structure of the hemoglobin, usually sickle or rectangular size. After which, it gets blocked in the blood vessels and is unable to carry the oxygen to the nearby cells. It occurs due to mutation or presence of the two recessive alleles in the HBB gene present on chromosome 11 which codes for the β-globin gene. The symptoms involve anemia, delayed growth, jaundice, painful episodes and fatigue.
Huntington's disease:
It usually occurs due to mutation in the gene coding for the Huntington protein (Htt). An increase or decrease in the trinucleotide repeat Cytosine-Adenine-Guanine (i.e. CAG) count produces the mutant Htt and is responsible for the disease. A person with a single allele for the production of mutant Htt is affected by the disease. The symptoms include imbalancement, incoordination of limbs, impaired swallowing and speech.
Heart disease:
The fault in the structure or the function of the heart inherited through genetic mutations are the one among many causes of heart disease. The different types of heart disease that occur due to genetic mutations include cardiomyopathies, congenital heart disease, channelopathies and familial hypercholesterolemia. The symptoms involve breath shortness, discomfort, pain in legs, arms, feet and ankles, lightheadedness or dizziness.
Cardiomyopathies:
It includes heart structure abnormalities such as weakening or thickening of the heart muscles.
Congenital heart disease:
From the time of birth, there are few heart defects such as septal and valve abnormalities.
Channelopathies:
It causes faults in the electrical system of the heart such as arrhythmias or Long QT Syndrome (LQTS).
Note: Arrhythmias are abnormal heart beats. LQTS refers to the condition where the heart utilizes more time to recharge between each beat.
Familial hypercholesterolemia:
It elevates the cholesterol level which is prone to coronary artery disease.
Diabetes:
It is characterized into two main types namely, type 1 and type 2 diabetes. Both of these have its influence on genetic factors as well as environmental factors. The symptoms include elevation of the hunger levels, thirst, fatigue , urination and blurred vision.
Schizophrenia:
It is a complex genetic disorder which has its more influence on the genetic factors. It is a mental disorder which is inherited from the parents by the percentage of 50 (when both the parents are affected) or 20 (when only one of the parents is affected). The identical twins and a first degree relative with the disease are the major players for causing this disease. The symptoms involve unorganized behavior and thinking, abnormal perceptions such as delusions and hallucinations.
Down's syndrome:
It is caused by the presence of an extra chromosomal copy in the 21st chromosome of the affected individual. The affected individual is born to healthy parents. The parents who deliver their baby at the age of 30s or 40 or above have been believed to have their child with this syndrome. Mostly, the disease is caused by the advanced maternal age whereas 10 percent of the disease is caused by advanced paternal age. The symptoms include small ears, upward slanting eyes, protruding tongue, low muscle tone and a flattened face.
Note:
The advanced maternal age is defined as the age of the mother in their 30s or 40s or above.
Duchenne muscular dystrophy:
In this type of disorder, the progressive degeneration of muscles and weakness takes place. It often occurs in the boys and is characterized by the deficiency in dystrophin protein which is known to have its role in muscle fiber function and protection.
Hypertrichosis:
It is a condition where excessive growth of hair takes place in the body of a person beyond a certain limit. It is majorly divided into two types namely, congenital hypertrichosis and acquired hypertrichosis. The former one involves the presence of excess hair from the birth and the later one involves the acquiring of excess hair in the later phase of life due to stress or environmental conditions or certain medications.
Diagnosis of genetic disorders:
The genetic disorders are diagnosed through some genetic tests, family history assessments and physical examinations.
Some genetic tests:
The various genetic tests include pre-symptomatic and predictive testing, prenatal testing, diagnostic testing and carrier testing.
Pre-symptomatic and predictive testing:
It predicts the occurrence of the disease even before the appearance of the symptoms.
Prenatal testing:
It examines the fetus of the mother during their pregnancy.
Diagnostic testing:
It predicts the outcome of the symptoms in the infected person.
Carrier testing:
It examines the individuals who carry the mutated gene in them. They are known as the carriers and so is the name of this test
