This study primarily aimed to comprehensively characterize the neurological, neuroradiological and neurocognitive profiles, as well psychiatric features of individuals with Spinocerebellar Ataxia Type 34 (SCA34) associated with pathogenic variants in the ELOVL4 gene. Secondarily, we investigated the relationship between neurocognitive functions and cerebellar morphology in individuals with SCA34 by correlating structural changes to cognitive performance. Given involvement of the cerebellum in SCA34, our findings will contribute to a broader understanding of the role of the cerebellum in cognition. Four individuals (52 f, 72 m, 76 m, 76 f) underwent DNA testing using Next-Generation Sequencing and detailed assessment of neurocognitive functions. The test battery evaluated all six cognitive domains: verbal functions, executive functions, attention and processing speed, learning and memory, visuospatial perception and abilities, and social cognition. In addition, cerebellar and motor functions were evaluated using Finger Tapping, Prism Adaptation, and the Motor Speed subtest of the Delis-Kaplan executive function system (D-KEFS). Test results were compared with each individual's estimated premorbid cognitive level, determined from their highest educational attainment or occupational status prior to disease onset. Psychiatric symptoms related to anxiety, depression, and sleep were reported using clinical scales. The Scale for the Assessment and Rating of Ataxia (SARA) was used to assess ataxia severity. Two individuals and one matched control underwent high-resolution 7T MRI to characterize cerebellar morphology. Neurocognitive assessments identified cognitive and motor dysfunction across all individuals, including distinct neurocognitive impairments consistent with cerebellar cognitive-affective syndrome (CCAS), along with additional deficits in learning, visual and verbal episodic memory, emotion recognition-a component of social cognition. Anxiety and sleep disturbance, but not depression, were observed in both female participants. High-resolution 7 T MRI revealed structural cerebellar alterations, with moderate to severe bilateral cerebellar atrophy, including the vermis and multiple lobules (Crus II, VIIb, VIIIa, VIIIb, IX), as well as atrophy of the middle and superior cerebellar peduncles, accompanied by mild pontine atrophy. Genetic analyses confirmed the involvement of ELOVL4-related disruptions in long-chain fatty acid biosynthesis, offering insight into the molecular underpinnings of cerebellar degeneration in SCA34. Individuals with SCA34 show cerebellar degeneration accompanied by cognitive, motor, and social-affective impairments consistent with CCAS. Atrophy of the vermis, multiple lobules, and cerebellar peduncles align with these deficits, highlighting the cerebellum's key role in cognition. ELOVL4-related disruptions in fatty acid biosynthesis provides insight into the molecular basis of SCA34. Together, these findings advance our understanding of how cerebellar pathology contributes to complex neurocognitive and psychiatric symptoms in genetic ataxias.

Spinocerebellar ataxia type 34 (SCA34) is a dominantly inherited disease that causes late-onset ataxia, in association with skin lesions in the form of erythrokeratodermia variabilis. It is caused by mutations in the ELOVL4 gene, which encodes for the ELOVL4 protein and has the function of lengthening very long chain (VLC) fatty acids (FA), which are important components of central myelin. The aim of this work was to review the medical literature on the biochemical abnormalities of SCA34, and based on the obtained information, to propose supplementation of deficient FAs. A review of the ad hoc medical literature was performed. Plasma levels of the ELOVL4 products C32, C34 and C36 FA have not been reported in SCA34 yet. However, pathogenic variants of ELOVL4 revealed deficient biosynthesis of C28, C30, C32, C34 and C36 FA compared to WT in cell cultures, and the levels of ceramides and phosphatidylcholines containing ≥ 34 C FA were decreased compared to WT in HeLa cells expressing mutant SCA34 proteins. Besides, a pathological study of SCA34 revealed myelin destruction and loss of oligodendrocytes in cerebral and cerebellar white matter. Levels of VLC-FA should be determined, to identify specifically deficient FAs in SCA34. Cerebellar ataxia could possibly be improved by administration of the deficient FAs, as found in SCA38 with supplementation of docosahexaenoic acid. The authors suggest investigators with access to SCA34, to take into consideration this therapeutic hypothesis, and try to verify the potential efficacy of administration of VLCFA in this disease.

Autosomal dominant variants in ELOVL4 cause spinocerebellar ataxia type 34 (SCA34; ATX-ELOVL4), classically associated with a skin condition known as erythrokeratoderma. Here, we report a large Italian-Maltese-Australian family with spinocerebellar ataxia. Notably, while there were dermatological manifestations (eczema), erythrokeratoderma was not present. Using a next-generation sequencing panel, we identified a previously reported ELOVL4 variant, NM_022726.4: c.698C > T p.(Thr233Met). The variant was initially classified as a variant of uncertain significance; however, through segregation studies, we reclassified the variant as likely pathogenic. We next identified an individual from another family (Algerian-Maltese-Australian) with the same ELOVL4 variant with spinocerebellar ataxia but without dermatological manifestations. We subsequently performed the first dedicated literature review of ELOVL4-associated ataxia to gain further insights into genotype-phenotype relationships. We identified a total of 60 reported cases of SCA34 to date. The majority had gait ataxia (88.3%), limb ataxia (76.7%), dysarthria (63.3%), and nystagmus (58.3%). Of note, skin lesions related to erythrokeratoderma were seen in a minority of cases (33.3%). Other extracerebellar manifestations included pyramidal tract signs, autonomic disturbances, retinitis pigmentosa, and cognitive impairment. For brain MRI data, cerebellar atrophy was seen in all cases (100%), whereas the hot cross bun sign (typically associated with multiple system atrophy type C) was seen in 32.4% of cases. Our family study and literature review highlight the variable phenotypic spectrum of SCA34. Importantly, it shows that erythrokeratoderma is not found in most cases and that, while a dermatological assessment may be helpful in these patients, SCA34 diagnosis should be considered irrespective of dermatological manifestations.

Spinocerebellar ataxias (SCAs) are autosomal dominant diseases characterized by cerebellar atrophy and ataxia. The SCA subtype SCA34 is caused by specific mutations in the gene ELOVL4, which encodes a fatty acid (FA) elongase that synthesizes ultra-long-chain (ULC; ≥C26) FAs. However, the pathogenesis and molecular mechanism that confers dominant inheritance remains unknown. Here, a cell-based assay demonstrated that each of the five known SCA34 mutants produced shorter ULC polyunsaturated FA-containing phosphatidylcholines (ULC-PCs) than wild-type protein, in the following order of severity: Q180P and T233M > W246G > I171T and L168F. Next, we generated knock-in mouse embryonic stem cells that contained heterozygous Q180P, heterozygous W246G, or homozygous W246G mutations. Neuronal differentiation-dependent production of ULC-PCs was reduced in heterozygous Q180P and homozygous W246G cells relative to control cells, and we observed shortening of the FA moiety in all mutant cells. This FA shortening was consistent with our prediction that amino acid residues substituted by SCA34 mutations are located in the transmembrane helices that interact with the ω-end region of the FA moiety of the substrate acyl-CoA. Hence, reduced levels and shortening of ULC-PCs in neurons may cause SCA34, and incomplete elongation of ULC polyunsaturated acyl-CoAs by mutated ELOVL4 may induce dominant inheritance.