The recent description of biallelic DNAJC30 variants in Leber hereditary optic neuropathy (LHON) and Leigh syndrome (LS) challenged the longstanding assumption for LHON to be exclusively maternally inherited and broadened the genetic spectrum of LS, the most frequent paediatric mitochondrial disease. Herein, we characterise 28 so far unreported individuals from 26 families carrying a homozygous DNAJC30 p.Tyr51Cys founder variant, 24 manifesting with LHON, two manifesting with LS, and two remaining asymptomatic. This collection of unreported variant carriers confirms sex-dependent incomplete penetrance of the homozygous variant given a significant male predominance of disease and the report of asymptomatic homozygous variant carriers. The autosomal recessive LHON (arLHON) patients demonstrate an earlier age of disease onset and a higher rate of idebenone-treated and spontaneous recovery of vision in comparison to reported figures for maternally inherited disease (mtLHON). Moreover, the report of two additional patients with childhood- or adult-onset LS further evidences the association of DNAJC30 with LS, previously only reported in a single childhood-onset case.