The nasty, ugly fact of off-target effects

Once upon a time, it was imagined that siRNAs specifically knock down the intended target gene.

Unfortunately, this turned out to be wrong.

The disappointing results from siRNA screening following the initial high hopes brings to mind T.H. Huxley‘s famous quote about a beautiful theory being killed by an ugly, nasty little fact.

As pointed out by S.J. Gould in Eight Little Pigs, the origin of the quote is given in the autobiography of Sir Francis Galton.

Galton’s autobiography is inspirational.  As one reviewer put it, “there is a feeling of calmness and awe that comes from knowing that a person of his genius, wisdom and versatility actually existed.”  He was 70, and had already made significant contributions to genetics, statistics, meteorology, and geography, when he published his first major work on fingerprints, which would become the basis for modern forensic fingerprint analysis.

His work on fingerprints also provides the context for the famous Huxley quote:

Much has been written, but the last word has not 
been said, on the rationale of these curious papillary 
ridges ; why in one man and in one finger they form 
whorls and in another loops. I may mention a 
characteristic anecdote of Herbert Spencer in con- 
nection with this. He asked me to show him my 
Laboratory and to take his prints, which I did. Then 
I spoke of the failure to discover the origin of these 
patterns, and how the fingers of unborn children had 
been dissected to ascertain their earliest stages, and so 
forth. Spencer remarked that this was beginning in 
the wrong way ; that I ought to consider the purpose 
the ridges had to fulfil, and to work backwards. 
Here, he said, it was obvious that the delicate mouths 
of the sudorific glands required the protection given 
to them by the ridges on either side of them, and 
therefrom he elaborated a consistent and ingenious 
hypothesis at great length. 

I replied that his arguments were beautiful and 
deserved to be true, but it happened that the mouths 
of the ducts did not run in the valleys between the crests, 
but along the crests of the ridges themselves. He 
burst into a good-humoured and uproarious laugh, and 
told me the famous story which I have heard from 
each of the other two who were present on the 
occurrence. Huxley was one of them. Spencer, 
during a pause in conversation at dinner at the 
Athenaeum, said, "You would little think it, but I 
once wrote a tragedy." Huxley answered promptly, 
" I know the catastrophe." Spencer declared it was 
impossible, for he had never spoken about it before 
then. Huxley insisted. Spencer asked what it was. 
Huxley replied, "A beautiful theory, killed by a 
nasty, ugly little fact."  

Memories of My Life, pp 257-258