Three of the following four letter-clusters are alike in a certain way and one is different. Pick the odd one out.

XYZ LNM ABC IJK

LNM

XYZ ⇒ X →(+1)→ Y →(+1) → Z LNM ⇒ L →(+2)→ N→(-1) → M (ODD) ABC ⇒ A →(+1)→ B →(+1) → C IJK ⇒ I →(+1)→ J →(+1) → K