Pna is a hyponym of xna.

In biochemistry|lang=en terms the difference between pna and xna

is that pna is (biochemistry) peptide nucleic acid while xna is (biochemistry) nucleic acid analogue (nucleic acid analog) ; (backformation) ; x nucleic acid, where "x" is a stand-in for multitude of various nucleic acid acronyms, which are not dna or rna.

As initialisms the difference between pna and xna

is that pna is polish national alliance while xna is (internet).

As a noun xna is

(biochemistry) nucleic acid analogue (nucleic acid analog) ; (backformation) ; x nucleic acid, where "x" is a stand-in for multitude of various nucleic acid acronyms, which are not dna or rna.