Human CalDAG-GEFI gene (RASGRP2) mutation affects platelet function and causes severe bleeding

Area of Science:

• Hematology
• Genetics
• Molecular Biology

Background:

• Inherited platelet disorders can cause severe bleeding.
• The RAS guanyl-releasing protein-2 (RASGRP2) gene encodes CalDAG-GEFI, crucial for platelet signaling.
• Understanding the genetic basis of these disorders is vital for developing treatments.

Purpose of the Study:

• To investigate the genetic cause of a severe inherited bleeding disorder in three siblings.
• To elucidate the functional consequences of the identified mutation in RASGRP2/CalDAG-GEFI.
• To explore the therapeutic potential of targeting CalDAG-GEFI.

Main Methods:

• Whole-exome sequencing to identify mutations.
• Functional assays in patient platelets and HEK293T cells to assess Rap1 activation and signaling.
• Analysis of platelet adhesion, spreading, and thrombus formation under flow conditions.
• Rescue experiments using gene transfection.

Main Results:

• A c.G742T mutation in the RASGRP2 gene was identified as the cause of the disorder.
• The mutation abolished CalDAG-GEFI's ability to activate Rap1, impairing αIIbβ3 integrin signaling.
• Patient platelets showed reduced thrombus formation and spreading due to impaired Rac1 activation.
• Heterozygous carriers were asymptomatic, but their platelets exhibited impaired adhesion and spreading.

Conclusions:

• The identified RASGRP2 mutation leads to a novel inherited platelet disorder characterized by impaired Rap1 activation and bleeding.
• CalDAG-GEFI plays a critical role in platelet function, particularly in adhesion and spreading under flow.
• Targeting CalDAG-GEFI represents a promising therapeutic strategy for preventing thrombosis, as a single functional allele prevents bleeding.