Biallelic loss‐of‐function variants in TBC1D2B cause a neurodevelopmental disorder with seizures and gingival overgrowth

Abstract

The family of Tre2‐Bub2‐Cdc16 (TBC)‐domain containing GTPase activating proteins (RABGAPs) is not only known as key regulatorof RAB GTPase activity but also has GAP‐independent functions. Rab GTPases are implicated in membrane trafficking pathways, such as vesicular trafficking. We report biallelic loss‐of‐function variants in TBC1D2B, encoding a member of the TBC/RABGAP family with yet unknown function, as the underlying cause of cognitive impairment, seizures, and/or gingival overgrowth in three individuals from unrelated families. TBC1D2B messenger RNA amount was drastically reduced, and the protein was absent in fibroblasts of two patients. In immunofluorescence analysis, ectopically expressed TBC1D2B colocalized with vesicles positive for RAB5, a small GTPase orchestrating early endocytic vesicle trafficking. In two independent TBC1D2B CRISPR/Cas9 knockout HeLa cell lines that serve as cellular model of TBC1D2B deficiency, epidermal growth factor internalization was significantly reduced compared with the parental HeLa cell line suggesting a role of TBC1D2B in early endocytosis. Serum deprivation of TBC1D2B‐deficient HeLa cell lines caused a decrease in cell viability and an increase in apoptosis. Our data reveal that loss of TBC1D2B causes a neurodevelopmental disorder with gingival overgrowth, possibly by deficits in vesicle trafficking and/or cell survival.

Development and Clinical Validation of Novel 8-Gene Prognostic Signature Associated With the Proportion of Regulatory T Cells by Weighted Gene Co-Expression Network Analysis in Uterine Corpus Endometrial Carcinoma

“…Eight genes were selected for further analysis and had been used as prognostic markers in other diseases. CDC16 has a connection with multiple neurodevelopmental disorders ( 50 , 51 ). It has been found that CDC16 has potential therapeutic function in melanoma ( 52 ).…”

Bi-allelic Pathogenic Variants in HS2ST1 Cause a Syndrome Characterized by Developmental Delay and Corpus Callosum, Skeletal, and Renal Abnormalities

“…RNA isolation, complementary DNA (cDNA) synthesis, and quantitative reverse transcription PCR (RT-qPCR) to determine the relative HS2ST1 mRNA amount in fibroblasts of affected and healthy individuals were performed as previously described. 23 Qualitative RT-PCR to analyze HS2ST1 transcripts was performed on fibroblast-derived cDNA according to standard PCR protocols with the OneTaq Quick-Load 2X Master Mix (New England Biolabs). PCR products were directly Sanger-sequenced.…”

“…Cell lysates from affected individuals' and control fibroblasts were prepared, and immunoblotting was performed as previously described. 23 Briefly, cells were harvested in ice-cold RIPA buffer and protein extracts were separated on SDS-PAGE and transferred to polyvinylidene fluoride membranes. The membrane was incubated with the indicated primary antibody at 4 C overnight and fluorescent dye-linked secondary antibodies at room temperature for 1 h.…”

“…Quantification of inner and outer FAs, the total number of FAs, and FA length was performed in at least six fibroblasts per cell line and experiment (control 1 [experiment #1: 6 cells; experiment #2: 9 cells; experiment #3: 7 cells], control 2 [8; 7; 7], individual 1 [6; 10; 8], individual 2 [6; 10; 7], individual 3 [7; 6; 8]) and a minimum of 21 cells in total per cell line from three independent experiments. The number of analyzed FAs from [number of cells] were for control 1 cell line 1,387 [22], control 2 1,627 [24], individual 1 1,108 [24], individual 2 1,128 [23], and individual 3 1,009 [21]. We investigated family 1 with one affected girl (individual 1), first seen at age 3 years and 6 months (Figure 1 and Table 1).…”

The Rab GTPase activating protein TBC-2 regulates endosomal localization of DAF-16 FOXO and lifespan

“…TBC1D2 has in vitro GAP activity toward Rab7 and regulates endosome trafficking and autophagy (Frasa et al ., 2010; Serva et al ., 2012; Carroll et al ., 2013; Toyofuku et al ., 2015; Jaber et al ., 2016). TBC1D2B interacts with Rab22 and Rab31, Rab5 related GTPases, and colocalizes with Rab5 and Rab7, but a specific Rab GTPase target of GAP activity has not been demonstrated (Kanno et al ., 2010; Manshouri et al ., 2019; Harms et al ., 2020; Wei et al ., 2021).…”