[Clinical and genetic analysis of a patient with Loeys-Dietz syndrome caused by a SMAD3 gene variant].

Objective: To explore the genetic basis of a patient suspected for Loeys-Dietz syndrome (LDS).

Methods: A adult male patient with aneurysmal dilation of the aortic root identified during the treatment for chronic myeloid leukemia at Anzhen Hospital of Capital Medical University in 2021 was selected as the study subject. Clinical data of the patient were retrospectively collected. Peripheral blood samples were collected from the patient and his family members and subjected to whole-exome sequencing (WES). Candidate variant was verified by bioinformatic analysis, with a focus on the genes associated with hereditary aortic aneurysms. Candidate variant was validated by Sanger sequencing. The online SpliceAI software was used for the prediction of protein function. The results, combined with information from public databases, were used to classify the pathogenicity of the candidate variant according to the guidelines from the American College of Medical Genetics and Genomics (ACMG). This study was approved by the Ethics Committee of Beijing Anzhen Hospital (Ethics No. 2023163X).

Results: Imaging analysis revealed that the patient had aneurysmal dilation of the aortic root. Based on his clinical features and past history, a provisional diagnosis of LDS was established. WES revealed that the patient had harbored a heterozygous splice site variant c.206+2T>G in the SMAD3 gene (NM_005902). The variant was not reported in public databases and was predicted to be pathogenic by SpliceAI. Sanger sequencing showed that the variant was also present in the proband's mother, sister, nephew, and daughter, but not in his father. Based on the guidelines from the ACMG, the variant was classified as likely pathogenic (PVS1+PM2_Supporting).

Conclusion: The heterozygous splice site variant c.206+2T>G of the SMAD3 gene probably underlay the disease in this patient. Above discovery has enriched the mutational spectrum of LDS, which may facilitate delineation of the genotype-phenotype correlation and provide a basis for further risk stratification and personalized treatment of LDS.