Novel Mutation in SACS Gene in a Patient with Autosomal Recessive Spastic Ataxia Charlevoix-Saguenay

Documenting manifestations and impacts of autosomal recessive spastic ataxia of Charlevoix-Saguenay to develop patient-reported outcome

BACKGROUND

Autosomal recessive cerebellar ataxias (ARCA) are a group of rare inherited disorders characterized by degeneration or abnormal development of the cerebellum. Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is one of the most prevalent in Europe.

OBJECTIVES

The aim of this study is to provide a better understanding of the manifestations and impacts of ARSACS.

METHODS

A systematic review of the literature was conducted, followed by a qualitative study using semistructured interviews and discussion groups to obtain the experience of people affected.

RESULTS

According to the PROMIS framework, the results show manifestations and impacts in three components of health: physical, mental, and social. Fatigue and struggles with balance and dexterity are the physical manifestations of the disease most often cited by participants. Negative affects such as frustration and depression are among the mental health impacts with some loss in cognitive abilities. Social health is the least documented component; nonetheless, people with the disease report significant impacts in terms of social relationships, activities and work.

CONCLUSIONS

These findings shed new light on the experience of people with recessive ataxia and identify key aspects to assess to improve their overall health.

Hereditary spastic paraplegia: Genetic heterogeneity and common pathways

Hereditary Spastic Paraplegias (HSPs) are a heterogeneous group of disease, mainly characterized by progressive spasticity and weakness of the lower limbs resulting from distal degeneration of corticospinal tract axons. Although HSPs represent rare or ultra-rare conditions, with reported cases of mutated genes found in single families, overall, with 87 forms described, they are an important health and economic problem for society and patients. In fact, they are chronic and life-hindering conditions, still lacking a specific therapy. Notwithstanding the number of forms described, and 73 causative genes identified, overall, the molecular diagnostic rate varies among 29% to 61.8%, based on recent published analysis, suggesting that more genes are involved in HSP and/or that different molecular diagnostic approaches are necessary. The accumulating data in this field highlight several peculiar features of HSPs, such as genetic heterogeneity, the discovery that different mutations in a single gene can be transmitted in dominant and recessive trait in families and allelic heterogeneity, resulting in the involvement of HSP-genes in other conditions. Based on the observation of protein functions, the activity of many different proteins encoded by HSP-related genes converges into some distinct pathophysiological mechanisms. This suggests that common pathways could be a potential target for a therapy, possibly addressing several forms at once. Furthermore, the overlap of HSP genes with other neurological conditions can further expand this concept.

Genetics of Autosomal Recessive Spastic Ataxia of Charlevoix-Saguenay (ARSACS) and Role of Sacsin in Neurodegeneration

Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset neurodegenerative disease that was originally discovered in the population from the Charlevoix-Saguenay-Lac-Saint-Jean (CSLSJ) region in Quebec. Although the disease progression of ARSACS may start in early childhood, cases with later onset have also been observed. Spasticity and ataxia could be common phenotypes, and retinal optic nerve hypermyelination is detected in the majority of patients. Other symptoms, such as pes cavus, ataxia and limb deformities, are also frequently observed in affected individuals. More than 200 mutations have been discovered in the SACS gene around the world. Besides French Canadians, SACS genetics have been extensively studied in Tunisia or Japan. Recently, emerging studies discovered SACS mutations in several other countries. SACS mutations could be associated with pathogenicity either in the homozygous or compound heterozygous stages. Sacsin has been confirmed to be involved in chaperon activities, controlling the microtubule balance or cell migration. Additionally, sacsin may also play a crucial role in regulating the mitochondrial functions. Through these mechanisms, it may share common mechanisms with other neurodegenerative diseases. Further studies are needed to define the exact functions of sacsin. This review introduces the genetic mutations discovered in the SACS gene and discusses its pathomechanisms and its possible involvement in other neurodegenerative diseases.