There are four entries that refer the four classic elements.
EARTH3AFIRST ELEMENT; dug up
[-----] ;
WATER76ASECOND ELEMENT; at this present time, according to Chaucer
[-----] ;
AIR37DTHIRD ELEMENT; hinderance
[---] ; and
FIRE27DFOURTH ELEMENT; Nov. 5 in Britain
[----] . Each such entry has as secondary clue that refers to a word of phrase that is formed by the three entries in that line: unEARTHed; noW
AT ERst; impAIRment; and bonFIRE night.
5D5DIn this meta, what the clue "Disease prevention by DNA modification" has been
[-------] refers to a "removed clue". And quintessence and quintessential derive from and literally mean, the concept of a "Fifth Element".
So..... The removed clue that is not included in this grid would be: FIFTH ELEMENT; Disease prevention by DNA modification. And there'd be a row of entries that along with the name of the fifth element would answer the clue "Disease prevention by DNA modification".
In the center row we have entries
GEN38AFlowers involved in a sex scandal that actually helped the political candidate. (Now that's a clue taylored for the ---- Xer's)
[---] and
APY40AReal rate of return (taking compound interest into account) abbr.
[---] with a row of five blank spaces. If we insert the name of the Fifth Element into it we get:
genE THERapy.
ETHER (or Aether) is the fifth element in classical Greek philosophy and therefore the answer to the meta.