[Pedigree Analysis of ACTN1-Related Thrombocytopenia Attributed to A Novel Mutation]

AbstractObjective: To investigate the clinical phenotype and genotype of an ACTN1-associated thrombocytopenic family and explore its molecular pathogenesis.

All the family members' peripheral blood was collected for routine blood tests, blood smear, coagulation function, and platelet aggregation test. Flow cytometry was used to detect the expression of platelet CD41 and CD61. The proband and her father were tested bone marrow cytomorphology. Whole-exome sequencing techniques were performed to detect and uncover mutant loci of suspected pathogenic genes. Bioinformatics was used to assess the conserved nature of the mutated loci and to analyze the effect of the mutated genes leading to the function of the corresponding amino acid sequences.

The platelet count of the proband was 88×10⁹/L, and the blood smear showed dumbbell-shaped platelets, snake-shaped platelets and platelets of various sizes. Her bone marrow cytomorphology revealed normal megakaryocyte morphology with a count of 270. The platelet count of the proband's father was 74×10⁹/L, with large platelets and platelets of various sizes observed in the blood smear, and the morphology of megakaryocytes was normal in bone marrow with a megakaryocyte count of 239. Her grandfather had a platelet count of 83×10⁹/L, with snake-shaped platelets and platelets of various sizes on blood smears. Other family members were normal in all tests. The missense mutation c.2396G > A in exon 20 of the ACTN1 gene in the proband resulted in the mutation of 799 amino acids of the encoded protein, i.e., Arg, to His. The sequencing results of her father and grandfather at this locus were found to be consistent with her. Furthermore, bioinformatics analysis indicated that the locus was highly conserved across species and that variation in this locus might lead to functional impairment of the protein. The protein model analysis demonstrated that α-actin-1 at position 799 Arg and Glu at position 811 could form a critical salt bridge which stabilizes the conformation of the Ca2⁺ binding loop within the calmodulin-like motif. the mutation of R799H lost this critical salt bridge and destabilized this structural domain.

In the present study, the newly uncovered missense mutation c.2396G＞A in exon 20 of the ACTN1 gene is potentially the molecular mechanism for the thrombocytopenia.