Free Essay: What is Trinucleotide Repeat Disorder?
Trinucleotide repeat disorder is a genetic condition caused when triplet nucleotides in the DNA repeat themselves in certain genes exceeding the normal and stable threshold. This repetition causes excess copies of certain nucleotide triplet and abnormality in the genes.
Trinucleotide repeat disorder is also referred to as:
- trinucleotide repeat expansion disorders
- codon reiteration disorders
- triplet repeat expansion disorders
The Trinucleotide Repeat Disorder is responsible for 14 genetic disorders which are currently documented and being researched on.
What are the causes and symptoms of this disorder?
The trinucleotide repeat disorder is usually caused when there is an abnormal expansion of triplet nucleotides. Scientists state that trinucleotide repeat expansion is the main cause of these disorders. This is usually a genetic condition and is therefore hereditary. When the DNA triplets abnormally repeat themselves within the genes they cause chromosomal instability.
The discovery of the link between trinucleotide repeat disorders as a basis for varied hereditary neurological disorders has helped scientists and doctors to have a better understanding of the problems they are dealing with.
The following are some of the symptoms that come about as a result of the trinucleotide repeat disorders:
- Varying levels of intellectual disabilities
- Varying levels of learning disabilities
- Longer faces in the patients
- Larger ears
- Susceptibility to connective tissue problems
- Larger testicles in male patients who reach puberty
- Behavioral disorders such as ADHD, ADD, autism, social anxiety etc.
- Slowed developmental abilities
While these are the main symptoms exhibited by the patients suffering from trinucleotide repeat disorders, each disease caused by trinucleotide repeat expansion is different and may hence exhibit different patients. Male and female patients also have different symptoms. For instance, only the male patients may show signs of enlarged testicles as opposed to females. In some patients, there may be no symptoms at all despite the presence of the disorder. In such cases, the patient must be tested before proper diagnosis of the disease is done.
What are the types of Trinucleotide Repeat Disorders?
Trinucleotide repeat disorders vary. From 1990 to date only 14 documented diseases exist. These diseases are caused by different replications and are generally categorized into three:
- Polyglutamine diseases. These are the most common of all trinucleotide repeat disorders. They are caused by the repetition of the codon CAG. This stands for the gene codes for amino acid glutamine. They are also called PolyQ diseases because of the glutamine in the codes. These include: Huntington Disease (HD), Spinobulbar Muscular Atrophy (SBMA), Spinocerebellar Ataxias (SCA types 1, 2, 3, 6, 7, and 17) and Dentatorubro-Pallidoluysian Atrophy (DRPLA).
- Non polyglutamine diseases. This category is for the diseases which are caused by DNA triplet expansion for gene codes that are not related to glutamine. These include: Fragile X Syndrome (FRAXA), Fragile XE Mental Retardation (FRAXE), Friedreich Ataxia (FRDA), Myotonic Dystrophy (DM, not MD) and Spinocerebellar Ataxias (SCA types 8, and 12).
- Non polyglutamine diseases caused by polyalanine tract expansion. Although this category is similar to the non polyglutamine disease category, the diseases in this case are caused by the expansion of the polyalanine tract and are mostly referred to as PA diseases. These include: Blepharophimosis, ptosis and epicanthus inversus (BPES) Cleidocranial dysplasia (CCD), Congenital central hypoventilation syndrome (CCHS), Hand–foot–genital syndrome (HFGS), Holoprosencephaly (HPE), Oculopharyngeal muscular dystrophy (OPMD), Syndromic and non-syndromic X-linked mental retardation (XLMR), Synpolydactyly type II (SPD) and X-linked hypopituitarism (XH).
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