In Greek sources he is also surnamed "longhanded" (Ancient Greek: μακρόχειρ Makrókheir; Latin: Longimanus), allegedly because his right hand was longer than his left....
According to a paper published in 2011, the discrepancy in Artaxerxes’ limb lengths may have arisen as a result of the inherited disease neurofibromatosis.
Artaxerxes I. (2024 Jan 2). In Wikipedia. https://en.wikipedia.org/wiki/Artaxerxes_I
The first Artaxerxes, preëminent among the kings of Persia for gentleness and magnanimity, was surnamed Longimanus, because his right hand was longer than his left, and was the son of Xerxes; the second Artaxerxes
Plutarch. The Parallel Lives. Published in Vol. XI of the Loeb Classical Library edition, 1926 https://penelope.uchicago.edu/Thayer/E/Roman/Texts/Plutarch/Lives/Artaxerxes*.html