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In the beginning of a sentence, should I capitalize abbreviations such as the following:

  • hPSC (human pluripotent stem cell)
  • mESC (mouse embryonic stem cell)
  • rDNA (recombinant deoxyribonucleic acid)

I have seen both lower and upper case for the two first, while rDNA always seems to be in lower case. I'm curious which is the linguistically correct form.

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Wikipedia, at least, seems to use the lowercase letter at the beginning of a sentence, for example see the article on mRNA: en.wikipedia.org/wiki/MRNA –  jbeldock Apr 8 '13 at 23:46
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Apparently, the Chicago Manual of Style's 16th edition includes a new provision permitting sentences beginning with a brand name (e.g. iPad, iPod) which starts with a lowercase letter to retain the lowercase letter: chicagomanualofstyle.org/about16_rules.html. This might be analogous. –  jbeldock Apr 8 '13 at 23:51
    
Yeah, I use the same approach as Wikipedia on this one. I am, however, curious if there exist a correct and incorrect approach. I don't think the iPad rule applies since these are abbreviations rather than names, but it's an interesting one nonetheless. –  cheflo Apr 8 '13 at 23:58
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2 Answers

up vote 1 down vote accepted

Whenever you encounter a situation where a "rule" (such as begin a sentence with an upper case letter) will reduce the readability of your test (Is MESC the same as mESC?) then rewrite. Do not try to find a loophole or a special rule that will need to be explained or justified. The meaning of your text is paramount.

There is a reason why chemistry texts do not begin a sentence about acids and bases with pH.

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I side with your advice more than my own accepted answer, i.e. do away with the ambiguity altogether! –  Andrew Cheong Apr 19 '13 at 20:32
    
Revisiting my question, I also prefer this advice as it explains the reasoning behind the rules of acheong87's answer. –  cheflo Jun 19 '13 at 3:21
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According to Scientific Style and Format: The CBE Manual for Authors, Editors, and Publishers (C B E Style Manual),

Even if the editor chooses a style that calls for initial capitalization of every term, some terms should retain an initial lowercase letter. [...] 3 A standard symbol or abbreviation that begins with a lowercase letter (pH, pK', mRNA).

Also, according to apsstylemanual.org,

An abbreviation that begins with a lowercase letter, or a term that must remain lowercase should not be changed to all caps when it begins a sentence; it should not be expanded. The word following should be is lowercase unless it is a proper noun or another acronym. If possible, reword the sentence so that it does not begin with the lowercase term

I don't see anything (other than the one regarding brand names) in the Chicago Manual of Style.

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