SMALED2 with BICD2 gene mutations: Report of two cases and portrayal of a classical phenotype

Cargo specificity, regulation, and therapeutic potential of cytoplasmic dynein

Intracellular retrograde transport in eukaryotic cells relies exclusively on the molecular motor cytoplasmic dynein 1. Unlike its counterpart, kinesin, dynein has a single isoform, which raises questions about its cargo specificity and regulatory mechanisms. The precision of dynein-mediated cargo transport is governed by a multitude of factors, including temperature, phosphorylation, the microtubule track, and interactions with a family of activating adaptor proteins. Activating adaptors are of particular importance because they not only activate the unidirectional motility of the motor but also connect a diverse array of cargoes with the dynein motor. Therefore, it is unsurprising that dysregulation of the dynein-activating adaptor transport machinery can lead to diseases such as spinal muscular atrophy, lower extremity, and dominant. Here, we discuss dynein motor motility within cells and in in vitro, and we present several methodologies employed to track the motion of the motor. We highlight several newly identified activating adaptors and their roles in regulating dynein. Finally, we explore the potential therapeutic applications of manipulating dynein transport to address diseases linked to dynein malfunction.

JNK-interacting protein 4 is a central molecule for lysosomal retrograde trafficking

Lysosomal positioning is an important factor in regulating cellular responses, including autophagy. Because proteins encoded by disease-responsible genes are involved in lysosomal trafficking, proper intracellular lysosomal trafficking is thought to be essential for cellular homeostasis. In the past few years, the mechanisms of lysosomal trafficking have been elucidated with a focus on adapter proteins linking motor proteins to lysosomes. Here, we outline recent findings on the mechanisms of lysosomal trafficking by focusing on adapter protein c-Jun NH2 -terminal kinase-interacting protein (JIP) 4, which plays a central role in this process, and other JIP4 functions and JIP family proteins. Additionally, we discuss neuronal diseases associated with aberrance in the JIP family protein. Accumulating evidence suggests that chemical manipulation of lysosomal positioning may be a therapeutic approach for these neuronal diseases.

Late adult-onset spinal muscular atrophy with lower extremity predominance (SMALED)

An elderly man in his early 80s presented with a 6-month history of worsening lower limb weakness on a background of a longer-standing waddling gait. Examination revealed bilateral scapular winging, and weakness in his proximal and distal lower limbs. Electromyography showed widespread chronic partial denervation changes, while sensory and motor nerve conduction parameters were preserved. After little progression over the course of 18 months, motor neuron disease was deemed less likely. Genetic testing revealed BICD2-related spinal muscular atrophy with lower extremity dominance (SMALED2), a disease that is usually of earlier onset. He is the oldest patient in the literature to be diagnosed with SMALED2 while maintaining ambulation, suggesting the milder spectrum of BICD2-related disease.