6th June Huntington's Diseases
By uday chakma - June 01, 2018
6th June
Huntington’s Disease(HD), which
is an inherited disorder, that result’s
in the death of brain cells.
Symptoms are often subtle with mental
abilities. When the disease advances, uncoordinated,
jerky body movements become more apparent, which lead to the worsening of the physical abilities which makes
the persons unable to talk. Mental
abilities generally decline into dementia and
the symptoms vary from person to person. Most peoples suffer under the age
group of 30 and 50 years of age gap. The disease can start at early before 30
years also. About eight percent of cases start before the age of 20
years and typically present with symptoms
more similar to Parkinson's disease.
HD is mainly inherited from
parents, however,10% of the cases are due to a new
mutation, which is caused by autosomal dominant
mutation of two gene called Huntingtin, which means a child of an affected
person has 50% of inheriting the disease. Diagnosis is given generally by genetic
testing, which can be carried out at any time,
regardless of whether or not symptoms are present.
There is no
cure for HD, and full-time care is required at later stages of the disease. HD
affects about 4 to 15 in 100,000 people of European descent. The disease
is very rare among Japanese while for occurrence
rate is unknown for the Africans. This disease affects men and women equally
and 9% of the death occurs due to suicide.
Charles Oscar
Waters, in 1841 discovered the disease and in 1872 by physician George
Huntington, after whom it was named, and the genetic basis was discovered in 1933 with
the collaboration Hereditary Disease Foundation, and later on, research was carried out for public awareness.
Genetic Mutation
Humans have two copies of Huntingtin gene(HTT), coding for the protein
huntingtin. The gene is a repeated section known as trinucleotide repeat, varying
in length between humans. If the repeat is present in a healthy gene, a
dynamic mutation may increase the repeat count and result in a defective gene. When it’s length reaches a certain threshold, it produces an altered form
of the protein, called mutant Huntingtin protein. It is not inherited according
to sex, but the length of the repeated section of the gene and hence its
severity can be influenced by the sex of the affected parent.
Inheritance
It has autosomal dominant inheritance, which means, an
affected individual typically inherits one copy of the gene from the
affected parent. Due to highness of the penetrance,
people with a mutated copy will have the
disease. In this type of inheritance pattern, each offspring of an affected
individual has a 50% risk of inheriting the mutant allele and therefore being
affected with the disorder. Trinucleotide
CAG repeats over 28 are unstable during replication and this
instability increases with the number of repeats present, leading to
generation pass instead of reproducing an exact copy of the trinucleotide repeat.
In the rare
situations where both parents have an expanded HD gene, the risk increases to
75%, and when either parent has two expanded copies, the risk is 100%.
Diagnosis
The disease can be diagnosed in two separate testing. 1. Clinical & 2. Predictive
genetic testing. In clinical testing, physical examination can tell the onset of the disease has begun, with unintentional movements of the body
parts seeking medical consultation. How
far the disease has progressed can be measured using the unidentified Huntington disease rating scale, which provides an
overall rating system based on motor, behavioral, cognitive, and functional
assessment. While in Predictive genetic testing, the autosomal dominant pattern of inheritance
shows individuals more risk in inheriting
the disease.
Testing before the onset of symptoms is a
life-changing event and a very personal decision, which aim to give career and family decision aid. Before 1993
there was not an available test for individuals to learn if they carried the
Huntington's gene. At that time surveys indicated that 50–70% of at-risk
individuals would have been interested in receiving testing, but since
predictive testing has been offered far fewer choose to be tested. Over
95% of individuals at risk of inheriting HD do not proceed with testing, mostly
because there is no treatment.
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