A Novel Mutation in the Stalk Domain of KIF5A Causes a Slowly Progressive Atypical Motor Syndrome

KIF5A encodes the heavy chain A of kinesin; A motor protein involved in motility functions within neuron. Mutations in the KIF5A N-terminal motor domain are known to cause SPG10; An autosomal dominant hereditary spastic paraplegia (HSP), as well as rare Charcot-Marie-Tooth disease 2 (CMT2) cases. Recently C-terminal cargo-binding tail domain mutations have been associated with an amyotrophic lateral sclerosis (ALS) phenotype. Here we describe a subject presenting with an atypical slowly progressive motor syndrome evolving over a period of 4 years; Characterized by walking difficulties; Muscle hypotrophy mainly involving upper limbs and pyramidal signs confined to the lower limbs. Electromyography demonstrated chronic neurogenic damage and active denervation while electroneurography showed slowly worsening axonal damage. We identified the novel heterozygote variant c.2341A>G in the exon 21 of the KIF5A gene resulting in the amino acid change p.Lys781Glu. The residue Lys781 is located within the terminal region of the stalk domain and is highly evolutionary conserved. Our findings confirm that mutations in KIF5A cause ALS-like phenotypes. However, the stalk domain mutation described here appears to result in an “intermediate” slowly progressive phenotype having aspects resembling ALS as well as HSP and axonal neuropathy. We suggest that KIF5A gene should be considered as a candidate gene in all atypical progressive motor syndromes.

Kinesins in neurological inherited diseases: a novel motor-domain mutation in KIF5A gene in a patient from Southern Italy affected by hereditary spastic paraplegia

Kinesins are a family of proteins for anterograde transport of the molecules from the neuronal cell body and their impairment has been widely associated with neurodegeneration of the motor neurons. KIF5A gene causes autosomal dominant spastic paraplegia 10, a neurological disorder characterized by spasticity and weakness of the lower limbs (SPG10). We carried out a screening of KIF5A gene in 50 subjects affected by HSP negative to diagnostic test for SPG4, ATL1 and REEP1. We identified a novel variation p.Ile255Met in a 58-year-old man who developed progressive gait disturbance due to spastic paraparesis complicated by axonal neuropathy.

JASPAC: Japan Spastic Paraplegia Research Consortium

Hereditary spastic paraplegias (HSPs) are a group of neurodegenerative disorders characterized by weakness and spasticity of the lower extremities. HSPs are heterogeneous disorders that involve over 80 causative genes. The frequency of HSPs is estimated to be 10–100/1,000,000. With this background, the Japanese research group “Japan Spastic Paraplegia Research Consortium: JASPAC” was organized in 2006 to elucidate the molecular epidemiologies of HSPs in Japan and the molecular pathologies of HSPs. To date, the JASPAC has collected 714 HSP families and analyzed 488 index patients. We found 279 pathogenic variants or probable pathogenic variants of causative genes in the 488 HSP patients. According to our results, we found 178 families with autosomal dominant patients (65%), and 101 with autosomal recessive and sporadic patients (48%). We found 119 patients with SPG4, 17 with SPG3A, 15 with SPG31, 13 with SPG11, and 11 with SPG10. Other HSP genes were the cause in less than five patients. On the other hand, we could not find causative genes in 35% of the autosomal dominant patients, or 52% of the autosomal recessive and sporadic patients. We are now trying to find new causative genes and elucidate the molecular mechanisms underlying HSPs.

Late-onset spastic paraplegia type 10 (SPG10) family presenting with bulbar symptoms and fasciculations mimicking amyotrophic lateral sclerosis

Pathogenic mutations in the KIF5A-SPG10 gene, encoding the kinesin HC5A, can be associated with autosomal dominant hereditary spastic paraplegia (ADHSP). It accounts for about 10% of the complicated forms of ADHSP. Peripheral neuropathy, distal upper limb amyotrophy, and cognitive decline are the most common additional clinical features. We examined a 66-year-old Japanese woman manifesting gait disturbance and spastic dysarthria for 6years with positive family history. She showed evidence of upper and lower motor neuron involvement and fasciculations, thus mimicking amyotrophic lateral sclerosis (ALS). Genetic analysis revealed a heterozygous variant in KIF5A (c.484C>T, p.Arg162Trp) in 2 symptomatic members. The mutation was also identified in 4 asymptomatic members, including 2 elderly members aged over 78years. Electromyography in the 2 symptomatic members revealed evidence of lower motor neuron involvement and fasciculation potentials in distal muscles. This report describes the first known Asian family with a KIF5A mutation and broadens the clinical and electrophysiological spectrum associated with KIF5A-SPG10 mutations. Given that our cases showed pseudobulbar palsy, fasciculation and altered penetrance, KIF5A-SPG10 might well be considered as a differential diagnosis of sporadic ALS.

A novel KIF5A mutation in an Italian family marked by spastic paraparesis and congenital deafness

Hereditary spastic paraplegia (HSP) includes a group of diseases characterized by progressive spastic weakness of the lower limbs (pure forms) with possible additional signs (complicated forms). The SPG10 form is due to alteration in the kinesin1A gene (KIF5A) that encodes the neuronal kinesin heavy chain, a protein required for the anterograde axonal transport. We performed clinical, neurophysiological and molecular studies in two siblings affected by AD-HSP complicated by deafness. The screening of the KIF5A gene revealed the novel mutation p.Leu259Gln in two affected siblings and in their father with a pure form of HSP.

Role of kinesin-1 in the pathogenesis of SPG10, a rare form of hereditary spastic paraplegia

Molecular protein motors play key roles in processes such as intracellular cargo transport and brain wiring, and failure of function can give rise to serious diseases. Kinesin-1, a member of the kinesin superfamily (also known as KIFs) is a two-headed motor protein that uses energy derived from ATP hydrolysis to transport diverse types of intracellular cargo toward the plus-ends of microtubules within axons. Recent studies at the level of a single molecule have provided extensive knowledge on how kinesin-1 moves along microtubules. Further elucidation of kinesin-1 movement may shed light on its influence on axon generation, thereby leading to therapies for diseases such as spastic paraplegia type 10 (SPG10), the subject of this review. SPG10 is an autosomal dominant form of hereditary spastic paraplegia caused by mutations in KIF5A, which encodes one of the isoforms of kinesin-1 (KIF5A, KIF5B, and KIF5C). Although little is known about the cargo of KIF5A, a recent study revealed an axonal transport defect of mitochondria in a KIF5A (-/-) mouse model. This review discusses the consensus moving model of kinesin-1 and the pathogenicity of SPG10 caused by defective KIF5A function.