Letters

Connecting the lincs
As a physician, I was absolutely astounded reading “Missing lincs” (SN: 12/17/11, p. 22) and still am. We have been waiting since DNA was discovered to find this ‘what makes us human’ aspect of our biochemistry. Even in the infancy of this research, we are discovering the chemical reasons for a type of muscular dystrophy and other conditions. What I find especially illuminating is that this may be the etiology of what we call autoimmune diseases, among other problems.

I am sure we will find it is a change in lincRNA balance or function that produces the change in regenerative ability of infants’ hearts mentioned in “Reviving a tired heart” (SN: 10/22/11, p. 26).
Linda Mendoza, Chico, Calif.

We are beginning to unravel the questions of how so few genes and also how so many genes in common across species can lead to the diversity and complexity that we see today. However, the function, if any, of microRNAs is still in question. Can it be that their reason for being is just to gum up the works?
David Shen, Reno, Nev.

Far from just gumming up the works, microRNAs help to precisely tune gene activity in cells, a job that is essential for normal cell function. The importance of RNA in general for human health is becoming more clear as scientists discover new types of noncoding RNAs and what they do. —Tina Hesman Saey

Tina Hesman Saey is really extraordinary. “Missing lincs” was very well done, just like the rest of her work. Please do not lose her to Nature, Science or Scientific American.
Peter Nicholls, Durham, N.C.

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Searching for extinction cycles
“Seeking a friendlier companion” (SN: 12/3/11, p. 32) suggests that the idea of periodic mass extinctions is dead, along with the idea of a stellar-mass companion for the sun. However, until NASA’s WISE mission, black hole or brown dwarf companions with large orbital radii had not been ruled out. In 2010, we published (Monthly Notices of the Royal Astronomical Society Letters 407, L99) new evidence that finds the same significant periodic component in extinction rate in two different fossil datasets.
Adrian L. Melott, Lawrence, Kan.

The writer is correct that, until WISE, black hole or brown dwarf companions had not been found but had not been ruled out. Attention to the periodicity of mass extinctions has waned, but perhaps the new paper will renew interest. —Elizabeth Quill