The definite e-form is historically identical to the so-called weak declension of the Germanic adjective, cf.
2nd declension two-syllable male names never undergo consonant shift (Uldis, Artis, Gatis, and so forth.) Besides body parts (acs, auss) there is a number of other words that historically do not undergo consonant shift, e.g., the name of the town of Cēsis.
From a grammatical or typological point of view, they share agglutinative, ergative-absolutive languages, with the same system of declension.