Variants in DOCK3 cause developmental delay and hypotonia

Abstract

The DOCK3 gene encodes the Dedicator of cytokinesis 3 (DOCK3) protein, which belongs to the family of guanine nucleotide exchange factors and is expressed almost exclusively in the brain and spinal cord. We used whole exome sequencing (WES) to investigate the molecular cause of developmental delay and hypotonia in three unrelated probands. WES identified truncating and splice site variants in Patient 1 and compound heterozygous and homozygous missense variants in Patients 2 and 3, respectively. We studied the effect of the three missense variants in vitro by using site-directed mutagenesis and pull-down assay and show that the induction of Rac1 activation was significantly lower in DOCK3 mutant cells compared with wild type human DOCK3 (P < 0.05). We generated a protein model to further examine the effect of the two missense variants within or adjacent to the DHR-2 domain in DOCK3 and this model supports pathogenicity. Our results support a loss of function mechanism but the data on the patients with missense variants should be cautiously interpreted because of the variability of the phenotypes and limited number of cases. Prior studies have described DOCK3 biallelic loss of function variants in two families with ataxia, hypotonia, and developmental delay. Here, we report on three patients with DOCK3-related developmental delay, wide-based or uncoordinated gait, and hypotonia, further supporting DOCK3's role in a neurodevelopmental syndrome and expanding the spectrum of phenotypic and genotypic variability.

DOCK3 is a dosage-sensitive regulator of skeletal muscle and Duchenne muscular dystrophy-associated pathologies

“…Complete loss of DOCK3 expression in both wild type and dystrophin-deficient muscle resulted in overall worse muscle health, decreased myoblast fusion, glucose intolerance, and overall defective muscle locomotive function. This is consistent with the reporting of clinical muscle hypotonia and overall muscle weakness in patients with pathogenic DOCK3 variants [10][11][12] . While the roles of other DOCK proteins in muscle are not well described, it is possible that DOCK3 may have some overlapping and non-overlapping functions with DOCK4 based on similar protein sequence structure and domains.…”

“…DOCK3 (previously called MOCA or modifier of cell adhesion) was shown to be essential for normal neuronal function and Dock3 global knockout mice develop plaques in the brain 9 . Human patients with loss-of-function DOCK3 variants develop intellectual disability, ataxia, developmental delay, and have overall low muscle tone from birth [10][11][12] . There is strong genetic evidence that the disease severity of patients with DOCK3 pathogenic variants is linked to the degree of which DOCK3 can activate RAC1 signaling as a guanine nucleotide exchange factor (GEF) protein 13 .…”

“…Human patients with loss-of-function DOCK3 variants develop intellectual disability, ataxia, developmental delay, and have overall low muscle tone from birth [10][11][12] . There is strong genetic evidence that the disease severity of patients with DOCK3 pathogenic variants is linked to the degree of which DOCK3 can activate RAC1 signaling as a guanine nucleotide exchange factor (GEF) protein 13 . Previously, we identified a muscle-enriched microRNA, miR-486, as a regulator of dystrophin-deficient skeletal muscle pathology in mice and human muscle biopsies through its negative regulation of DOCK3 mRNA expression levels 14,15 .…”

RHO to the DOCK for GDP disembarking: Structural insights into the DOCK GTPase nucleotide exchange factors

“…DOCK3 participates in axonal and neurite outgrowth processes, particularly during early developmental stages via distinct signaling cascades that involve either the brain-derived neurotrophic factor-tyrosine kinase B (BDNF-TRKB)-mediated pathway or glycogen synthase kinase-3β (GSK-3β) ( 36 , 69 , 73 , 74 ). DOCK3 gene variants leading to potentially nonfunctional protein were identified to cause developmental and motor issues in patients confirmed by a RAC1 pull-down assay and protein modeling ( 70 ). As indicated by its initial name, PBP, DOCK3 interacts with presenilin 1 (PS1), a catalytic unit of the γ-secretase proteolytic complex, which is responsible for processing amyloid precursor protein (APP) and subsequent formation and accumulation of β plaques ( 75 , 76 , 77 , 78 , 79 ).…”

“…DOCK3, a GEF for RAC1, acts as regulator of actin reorganization in neuronal tissue ( 69 , 70 , 71 , 72 ). DOCK3 participates in axonal and neurite outgrowth processes, particularly during early developmental stages via distinct signaling cascades that involve either the brain-derived neurotrophic factor-tyrosine kinase B (BDNF-TRKB)-mediated pathway or glycogen synthase kinase-3β (GSK-3β) ( 36 , 69 , 73 , 74 ).…”