ACTN1 mutations cause congenital macrothrombocytopenia

Area of Science:

• Genetics
• Hematology
• Molecular Biology

Background:

• Congenital macrothrombocytopenia (CMTP) is a rare bleeding disorder with reduced platelet counts and large platelets.
• Genetic causes for CMTP are identified in only about half of affected individuals.
• A dominant inheritance pattern is suspected in some CMTP cases without known genetic links.

Purpose of the Study:

• To identify novel mutations causing CMTP, particularly in families with suspected dominant transmission.
• To investigate the role of ACTN1 gene variants in the pathogenesis of CMTP.

Main Methods:

• Whole-exome sequencing and targeted Sanger sequencing were performed on Japanese CMTP pedigrees.
• In vitro transfection experiments in Chinese hamster ovary cells were used to assess the functional impact of ACTN1 variants.
• Mouse fetal liver-derived megakaryocytes were transduced to study cytoskeletal organization and proplatelet formation.

Main Results:

• ACTN1 variants were identified in 46% of the studied Japanese CMTP pedigrees, representing 5.5% of dominant CMTP cases.
• ACTN1 variants were the fourth most common cause of dominant CMTP in the Japanese cohort.
• Altered alpha-actinin-1 disrupted cytoskeletal structure in vitro and in megakaryocytes, leading to abnormal proplatelet formation.

Conclusions:

• ACTN1 variants are a significant cause of dominant congenital macrothrombocytopenia, particularly in Japanese individuals.
• Disruption of the actin cytoskeleton by abnormal alpha-actinin-1 underlies the pathogenesis of this CMTP subtype.
• These findings expand the understanding of genetic factors contributing to rare platelet disorders.