1 Mb Deletion in 10q26.3 and the Likely Pathogenic Variant in the TRIO Gene: A Twin Case Study Challenging Their Role in Autism Diagnosis

Here, we present a case study of twin boys aged 2 and 7 years who both met the diagnostic criteria for autism spectrum disorders (ASDs) based on the standard diagnostic instruments ADOS-2 and ADI-R. The clinical indication for genetic diagnostics in the first boy was autism with high severity of symptoms, delayed speech development, and mild facial dysmorphia. The second boy's indication was autism with moderate severity of symptoms, delayed speech development, mild facial features, slowed psychomotor development, and microcephaly. The microarray-based analysis of chromosome aberrations revealed a heterozygous 977,456 bp deletion of region 10q26.3 in both boys. The region includes 28 genes, some of these genes are important in the development of the central nervous and urogenital systems, and heterozygous deletions in this region have been associated with mental retardation, growth and development disorders, and craniofacial anomalies. The whole exome sequencing confirmed the presence of this deletion in both boys and, at the same time, led to the identification of a pathogenic SNV variant in the TRIO gene in the boy with microcephaly and delayed psychomotor development, which may explain the different phenotype of both boys. However, the segregation analysis of these variants in the family revealed that the microdeletion was inherited from the asymptomatic father, and the c.2149C > T variant in the TRIO gene was inherited from the asymptomatic mother, making the diagnostic finding uncertain. This case highlights that when pathogenic or likely pathogenic variants are inherited from unaffected parents, the clinical phenotype may result from a combined burden of multiple rare variants and polygenic risk, underscoring the importance of a comprehensive genomic analysis in complex cases. Thus, we emphasize the importance of utilizing available methods, such as whole exome sequencing besides microarray-based comparative genomic hybridization, in the genetic diagnosis of autism patients in Slovakia.