Differences in genetic background might contribute to the discrepant phenotypes, which could be either allelic differences (for example, relative expressivity of mutant and wild-type PRRX1 allele, as observed in the case of RBM8A pathogenic variants in thrombocytopenia-absent radius syndrome)41 or nonallelic differences; although beyond the scope of this work, it would be interesting to explore possible allelic modifiers in further studies. The gene discussed is RBM8A; the disease is Thrombocytopenia - absent radius.