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Microcephaly UPSC NOTE

 Why in news

  • The SASS6 gene and its variants have been implicated in a developmental process that leads to microcephaly

  • A new study has found that if one copy of this gene is non-functional, the other retains some function

  • So if both copies are non-functional, a human embryo dies before it becomes a foetus


  • Microcephaly is a condition in which a baby’s head is much smaller than normal. 

  • Most children with microcephaly also have a small brain, poor motor function, poor speech, and abnormal facial features, and are intellectually disabled.

  • Researchers believe the roots of the condition lie in the peak phase of brain development in the embryo — when the cells that eventually become neurons fail to divide normally. 

  • Clinicians can diagnose microcephaly before the baby is born using foetal ultrasound and magnetic resonance imaging.


  • 70% or more of cases of congenital microcephaly seen in the clinic come from consanguineous marriages

    • These are marriages between closely related individuals, such as between uncle and niece or between first cousins.

  • Consanguinity increases the risk of an individual inheriting a mutated copy of a gene from both parents

  • The risk is greater if the mutated gene is rarer in the general population.

  • Microcephaly is caused by mutations in 30 genes

  • Cells use 10 of these genes to encode proteins that are required to assemble the centrioles and for their subsequent function

  • When a cell divides, its centrioles help form another structure called the spindle.

  • During cell division, the old and new cells need to take a series of careful steps

  • The spindle is like the handrail along this staircase, helping the cells form and maintain their structure. 

  • For example, once the old cell makes two copies of its chromosomes, each copy sticks to the centre of the spindle, which is an elongated structure. 

  • From there, the spindle moves each copy to its two ends. 

  • Each of these ends then becomes the nucleus of a new cell.

  • If a cell creates centriole proteins from mutated genes, however, cell division is affected as well

SASS6 gene

  • In 2004, researchers discovered the SASS6 gene in the roundworm Caenorhabditis elegans

  • They also found that the protein that cells made using this gene was conserved across animals, meaning natural selection allowed this protein to exist in all members of the animal kingdom.

  • When the researchers suppressed the SASS6 gene in C. elegans embryos, they found that the cells failed to assemble new centrioles, resulting in arrested development.

  • All the microcephaly affected individuals were found to carry a mutated version of the human SASS6 gene on both their copies of chromosome 1: one inherited from the father and the other from the mother.

  • The SASS6 gene encodes a protein that has 657 amino acids. 

  • This protein assembles new centrioles during the cell division process.



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Learnerz IAS | Concept oriented UPSC Classes in Malayalam: Microcephaly UPSC NOTE
Microcephaly UPSC NOTE
Learnerz IAS | Concept oriented UPSC Classes in Malayalam
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