What is Huntington's disease ?

1. HUNTINGTON’S DISEASE
A DEADLY LEGACY

2. Every human body is made of billions of cells.
Cells are the very small units that make up all living things.

3. In every cell there’s a Nucleus.
The Nucleus contains 23 pair of identical chromosomes
(exept for nr. 45 and 46, they are the human sex chromosomes)

4. A chromosome is made up
of proteins and DNA
The chromosomes serve as
the structure that holds the
DNA.
The DNA acts as a complete
set of instructions that tells
our bodies how to develop.

5. A gene is a short section of DNA.
DNA is made up of millions of small chemicals called bases.
The chemicals come in four types A, C, T and G.
three nucleotides—called a triplet or codon—codes for
one particular amino acid in the protein.

6. Chromosome 4 likely contains 1,000 to 1,100 genes
that provide instructions for making proteins. These
proteins perform a variety of different roles in the body.
Huntington's disease is caused by changes (mutations) of a
gene that is located on the short arm (p) of chromosome 4

7. Everybody has the Huntingtin gene (HTT), the protein is necessary in the
brain.
But when this gene has a particular mutation in the middle of it, the result
is Huntington’s disease.
The defect in the HTT gene responsible for Huntington’s disease is known
as a CAG trinucleotide repeat expansion.
This is a small section of the HTT gene in which the bases “CAG” are
repeated multiple times in a row.

8. Normally, the HTT gene CAG trinucleotide repeat contains
10 to 35 repeats of this sequence.
In people with Huntington’s disease, however, it may be
repeated from 36 to more than 120 times.
People with 40 or more repeats almost always develop
Huntington’s, whereas for people with 36 to 39 repeats, the
disease is incompletely penetrant — meaning an individual
may or may not develop the disease. The reasons for this are
still not completely understood.
The number of repeats inversely correlates with the age of
onset of the disease. That means that the more repeats there
are, the earlier in life a person is likely to develop symptoms.
In juvenile Huntington’s disease, which affects children and
young adults, the CAG trinucleotide is generally repeated
more than 60 times.

11. Huntington’s is an autosomal dominant disorder.
The mutated gene is a dominant gene located on one of the
nonsex chromosomes (autosomes). You need only one
mutated gene to be affected by this type of disorder.
A person with an autosomal dominant disorder — in this
case, the father — has a 50% chance of having an affected
child with one mutated gene (dominant gene) and a 50%
chance of having an unaffected child with two normal genes
(recessive genes).

12. What does Huntington's disease do to brain cells?
Huntington's disease is a relatively rare fatal inherited
condition that gradually kills off healthy nerve cells in
the brain, leading to loss of language, thinking and
reasoning abilities, memory, coordination and movement.