Large Purine Repeat Sequences – Genetic Research

Published on: 2018/08/16

Himanshu Singh


Purine Repeats (PRs) can preferentially adopt non-B DNA structures such as triple helical DNA and are randomly distributed in the human genome. A range of stable DNA-triplex forming pathogenic PR was reported to be 198-5400, in an autosomal recessive neurological disorder Friedreich’s ataxia (FRDA). Triplexes were reported to have a disease-causing effect on various physiological processes, including recombination, replication, transcriptional control etc. Therefore, we focused on Purine Repeats, n ≥ 200

Interest Category

Purine repeats, genetic research, lifescience research

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Purine repeats

Purine repeat sequences present in a gene have a high tendency form unusual DNA-triple helix structures. Purine repeats are unique. DNA- triplexes are associated with the only human disease Friedreich’s ataxia. It is the only human disease and it is an autosomal neurodegenerative disorder.

In this study, the hidden purine repeats in the human genome are studied to find out if they are associated with neurological disorders. Genes carrying purine repeats of n ≥200 are down-regulated. They are found to be linked with several neurological, brain-related diseases. Studying the purine repeats can help in the application of developing therapeutics for these diseases.

Friedreich’s ataxia (FRDA) and Purine repeats

As mentioned earlier, it is an autosomal recessive inherited disease which causes progressive damage to the nervous system. The incidence of this disease is 1 in 50000. (1) The degeneration of nervous tissue in the spinal cord in a person results to Friedreich’s ataxia. The spinal cord gets thin causing nerve cells to lose their myelin sheath.

Symptoms of this disease are:

  1. A weakness of muscles in arms and legs
  2. Poor coordination
  3. Vision and hearing impairment
  4. Scoliosis (curvature of the spine)
  5. Slurred speech
  6. Heart disorders
  7. Diabetes


Diseases associated with large purine repeats

  1. FRDA is reported to have a range of stable DNA-triplex forming pathogenic purine repeats. Other diseases associated with purine repeats are,
  2. Autosomal Dominant Polycystic Kidney Disease (ADPKD) – Growth of cysts in kidneys.
  3. Lymphangioleiomyomatosis (LAM) – a progressive and indolent growth of smooth muscle cells throughout the lungs.
  4. Tuberous sclerosis (TSC) – a rare genetic disorder that causes benign tumors in the brain and other vital organs
  5. Follicular Lymphoma
  6. Hereditary Persistence of fetal hemoglobin.

Read more – Large purine repeat sequences and their effect on neurological disorders, a research paper by Himanshu Singh

Other genetic neurological disorders

Gene mutation may cause some neurological conditions that can be inherited. The neurological diseases that are inherited are, (2)

  1. Parkinson’s disease – Caused by deletion of dopamine (neurotransmitter)
  2. Alzheimer’s disease – Mutations in genes PSEN1 (Presenilin), PSEN2 and amyloid precursor protein (APP) and variations in APOE (Apolipoprotein) are identified in families with early onset of Alzheimer’s disease.
  3. Epilepsy – Mutations in the GABRA1 gene causes epilepsy.
  4. Huntington’s disease – caused by a single defective inherited gene.
  5. Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL) – NOTCH3 is the gene involved in CADASIL