Connexin 30 (Cx30), a member of the large gap junction protein family, plays a role in the homeostasis of the epidermis and inner ear through gap junctional intercellular communication (GJIC). Here, we investigated the underlying mechanisms of four autosomal dominant Cx30 gene mutations linked to hearing loss and/or various skin diseases. First, the T5M mutant linked to non-syndromic hearing loss formed functional gap junction channels and hemichannels, similar to wild type Cx30. The loss-of-function V37E mutant associated with Clouston syndrome or keratitis-ichthyosis-deafness syndrome was retained in the endoplasmic reticulum and significantly induced apoptosis. The G59R mutant linked to Vohwinkel and Bart-Pumphrey syndromes was retained primarily in the Golgi apparatus and exhibited loss of gap junction channel and hemichannel function, but did not cause cell death. Lastly, the A88V mutant related to Clouston syndrome also significantly induced apoptosis, although through an endoplasmic reticulum-independent mechanism. Collectively, we discovered that four unique Cx30 mutants may cause disease through different mechanisms that also likely include their selective transdominant effects on co-expressed connexins, highlighting the overall complexity of connexin-linked diseases and the importance of GJIC in disease prevention.