New phenotype of DCTN1-related spectrum: early-onset dHMN plus congenital foot deformity

Abstract

Objective To describe the clinical and genetic features of two patients with different phenotypes due to various Dynactin 1 (DCTN1) gene mutations and further explore the phenotype-genotype relationship. Methods Patient 1 is a 23-year-old man with congenital foot deformity and life-long distal muscle weakness and atrophy. Patient 2 is a 48-year-old woman with adult-onset progressive weakness, lower limbs atrophy, and pyramid bundle signs. Electrophysiology test showed normal nerve conduction velocity of both patients and neurogenic changes in needle electromyography. Open sural nerve biopsy for Patient 1 showed slight loss of myelinated nerve fibers. Both patients were performed with whole-exome sequencing followed by functional study of identified variants. Results Two mutations in DCTN1 gene were identified in Patient 1 (c.626dupC) and Patient 2 (c.3823C>T), respectively. In vitro, the wild type mostly located in cytoplasm and colocalized with alpha-tubulin. However, c.626dupC tended to be trapped into nuclear and the c.3823C>T formed cytoplasmic aggregates, both losing colocalization with alpha-tubulin. Western blotting showed a truncated mutant with less molecular weight of c.626dupC was expressed. Interpretation We identify two novel DCTN1 mutations causing different phenotypes: (1) early-onset distal hereditary motor neuropathy plus congenital foot malformation and (2) amyotrophic lateral sclerosis, respectively. We provide the initial evidence that foot developmental deficiency probably arises from subcellular localizing abnormality of Dynactin 1, revealing DCTN1-related spectrum is still expanding.