Clinical and molecular characterization of a novel pathogenic AIFM1 E336K mutation connecting mitochondrial dysfunction and neurodegeneration.

Mutations in the AIFM1 gene, encoding the apoptosis-inducing factor (AIF), have been associated with a spectrum of neurometabolic disorders. However, the mechanistic basis underlying their pathogenicity remains poorly understood. In this work, we identified and comprehensively characterized a novel hemizygous AIFM1 mutation c.1006G > A (E336K) in a male patient presenting with a progressive hereditary axonal sensorimotor polyneuropathy with childhood onset, inherited in an X-linked recessive pattern, associated with sensorineural hearing loss and without cognitive impairment. The clinical phenotype was consistent with Charcot-Marie-Tooth disease type 4 (CMTX4). Patient-derived fibroblasts exhibited reduced AIF protein stability despite preserved mRNA expression, impaired growth in OXPHOS-dependent conditions, decreased basal respiration, and altered assembly of mitochondrial respiratory supercomplexes. These defects were accompanied by reduced CHCHD4 protein levels and mitochondrial content. The purified E336K protein exhibited compromised FAD retention, decreased thermal stability, impaired NADH affinity, destabilization of the charge-transfer complex crucial for sustaining the AIF: CHCHD4 interaction, and a shift in coenzyme preference toward NADPH. Structurally, the substitution of Glu336 with Lys remodels the electrostatic environment of the NADH-binding cleft, thereby compromising redox function and weakening CHCHD4 binding. Despite these defects, the protein with the E336K mutation retained DNA binding, nuclease activity, and binding to nuclear partners, although parthanatos induction was attenuated in patient fibroblasts. Collectively, these molecular alterations converge on defective mitochondrial bioenergetics and dynamics, providing a direct mechanistic link to the patient’s clinical evolution.These findings provide a framework for understanding AIFM1-related disorders and pave the way for the development of future personalized molecular therapies.