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Mahesh

28/12/23 07:04 AM IST

Huntington’s disease

In News
  • Every month, the medical genetics clinic in the Nizam’s Institute of Medical Sciences, Hyderabad, sees about three to four people with Huntington’s disease.
Huntington disease
  • At first, Huntington’s disease patients have mild symptoms: forgetfulness, loss of balance, and clumsiness in performing simple tasks.
  • The symptoms begin in the ages 30-50, by when the patient might also have had children.
  • The condition progressively worsens.
  • The patient suffers mood swings, has difficulty in reasoning, shows abnormal and uncontrollable jerky movements, and experiences difficulty in speaking, swallowing, and walking.
  • The patient eventually dies, but not before raising the spectre that one or more of their children will suffer the same fate. There is no cure.
HTT- gene
  • The patient’s misfortune is that they carry a mutated version of a gene called HTT. The HTT gene codes for a protein called huntingtin, or Htt.
  • Nerve cells in the human body require the Htt protein for their normal functioning and survival.
  • The mutated gene, however, encodes an abnormal Htt protein that instead destroys the neurons that regulate movement, thinking, and memory.
  • The normal HTT gene contains a stretch of DNA that specifies the number of times the amino acid glutamine is repeated in the Htt protein.
  • This number varies from 11 to 31. In the mutant versions of the HTT gene, this stretch is expanded to encode 35 or more repeats.  Researchers have even found variants with more than 150 repeats.
  • As the number of repetitions increase, the severity of Huntington’s disease increases and its debilitation begins at an earlier age.
  • Each one of us has two copies of the HTT gene: one we inherited from the father and one from the mother. The disease is triggered even if only one copy of the gene is mutated while the other is normal.
About research
  • Researchers used a gene called Gal4 from baker’s yeast (Saccharomyces cerevisiae).
  • Gal4 contains information with which cells manufacture a protein called Gal4p. This protein binds specifically to a short DNA sequence called the upstream activating sequence (UAS).
  • In baker’s yeast, when Gal4p binds to UAS, it activates the expression of all the genes that come after (i.e. downstream), allowing the yeast to utilise the sugar galactose.
  • The Gal4/UAS system also works in the fruit fly genome. When the DNA sequence for the Gal4p protein is placed downstream of a fly gene called elav, something curious happens: the Gal4p protein is expressed in all of the fly’s neurons – and only in the neurons.
  • If the fly also carries the mutated HTT gene downstream of UAS, then the fly’s neuronal cells make the bad Htt protein, with its polyglutamine tract. Again, these proteins are made only in the neurons.
Source- The Hindu

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