A Novel WT1 Mutation Identified in a 46,XX Testicular/Ovotesticular DSD Patient Results in the Retention of Intron 9

Simple Summary Disorders/differences of sexual development are very diverse. Among them is a condition characterized by the presence of testicular tissue in people with female chromosomes, which is typically manifested by male or ambiguous genitalia. While genetic counseling is beneficial for these people and their families, the genetic causes of these cases are only partially understood. We describe a new mutation in the WT1 gene that results in the presence of testicular tissue in a child with a female karyotype. We propose molecular mechanisms disrupted by this mutation. This finding widened our understanding of processes that govern sexual development and can be used to develop diagnostic tests for disorders/differences of sexual development. The 46,XX testicular DSD (disorder/difference of sexual development) and 46,XX ovotesticular DSD (46,XX TDSD and 46,XX OTDSD) phenotypes are caused by genetic rearrangements or point mutations resulting in imbalance between components of the two antagonistic, pro-testicular and pro-ovarian pathways; however, the genetic causes of 46,XX TDSD/OTDSD are not fully understood, and molecular diagnosis for many patients with the conditions is unavailable. Only recently few mutations in the WT1 (WT1 transcription factor; 11p13) gene were described in a group of 46,XX TDSD and 46,XX OTDSD individuals. The WT1 protein contains a DNA/RNA binding domain consisting of four zinc fingers (ZnF) and a three-amino acid (KTS) motif that is present or absent, as a result of alternative splicing, between ZnF3 and ZnF4 (+/- KTS isoforms). Here, we present a patient with 46,XX TDSD/OTDSD in whom whole exome sequencing revealed a heterozygous de novo WT1 c.1437A>G mutation within an alternative donor splice site which is used for -KTS WT1 isoform formation. So far, no mutation in this splice site has been identified in any patient group. We demonstrated that the mutation results in the retention of intron 9 in the mature mRNA of the 46,XX TDSD/OTDSD patient. In cases when the erroneous mRNA is translated, exclusively the expression of a truncated WT1 +KTS protein lacking ZnF4 and no -KTS protein occurs from the mutated allele of the patient. We discuss potential mechanisms and pathways which can be disturbed upon two conditions: Absence of Zn4F and altered +KTS/-KTS ratio.