A Novel Approach Using Microarray Testing as a Screening Method with Clinical Validation Using Whole-Genome Sequencing and Karyotyping for Identifying 46,XX Testicular Differences of Sex Development

<b>Background:</b> Microarray testing is commonly used as a screening method for phenotypic traits and common diseases and for genome-wide association studies (GWASs). Despite the known limitations, microarray services can potentially be used as a prescreening tool for chromosomal disorders, which affect approximately 0.4-0.6% of the world population, followed by further clinical diagnostic methods when appropriate. <b>Case Presentation</b>: Here we present a case study of a male subject in his 40s who underwent direct-to-consumer (DTC) genetic testing that utilized microarray, which revealed the absence of Y chromosome haplogroup data despite possessing a typical male phenotype. Subsequent medical consultation, whole-genome sequencing (WGS), and chromosomal analysis confirmed a diagnosis of 46,XX testicular differences of sex development (DSD, formerly XX male syndrome) characterized by the presence of Y chromosome-derived genomic material, including the <i>SRY</i> gene. An initial microarray test gave an indeterminate result for the Y chromosome call rate and an X chromosome heterozygosity result that aligned with the female average. These indeterminate results, coupled with the subject's male phenotype, led to further testing-WGS, karyotyping, fluorescence in situ hybridization using an <i>SRY</i> Probe, and endocrine testing. From these results, the subject was diagnosed with 46,XX testicular DSD. <b>Conclusions</b>: To our knowledge, this represents the first reported case where 46,XX testicular DSD was diagnosed starting from a DTC test which led to medical consultation and comprehensive genomic and cytogenetic analysis. This case underscores the potential diagnostic value of consumer-initiated DTC microarray screening in the era of genomic medicine and for supporting social needs such as gender confirmation for sports.