SRY is the founding member of the SRY-like HMG box (SOX) family of transcription factors, characterized by a HMG domain . It is involved in the binding and bending of DNA and contains two nuclear localization signals. Mutations in SRY are present in 10-15% of 46,XY DSD patients , and these patients have an increased risk of developing GCC, related to the presence of the GBY region (with TSPY as the most likely candidate gene), and the prolonged expression of OCT3/4 (POU5F1) in the germ cells [8, 19, 20]. Several authors have described mutations in SRY in rare cases with a mosaic sex chromosome constitution [11–13, 21–23], indicating a potential involvement of SRY in abnormal gonadal development of 45,X/46,X,der(Y) patients.
However, in this study no confirmed mutations in SRY were identified in any of the fourteen cases analyzed. In case no. 14 with a 45,X/46,XX/46,XY karyotype, a deletion of T on position 197 of SRY (ref. seq. NM_003140.1) was found by deep sequencing in 21% of the sequence reads. However, subsequent analysis by sequencing subcloned PCR products only produced wild type SRY sequences, indicating that the original deep sequencing result was most likely a false positive. The results presented here are in agreement with, and extend the data reported by (and others summarized in) Nishi et al. , who found only one SRY polymorphism (c.561C → T) in a group of 27 patients (fourteen TS and thirteen mixed gonadal dysgenesis patients. In Table 1, next to the cases analyzed here, an overview of SRY mutations that have been reported in chromosomal DSD cases is shown. The results published until now, showing a SRY mutation in approximately 8% of cases, have all been obtained using conventional Sanger sequencing; the findings presented here show that, although analyzed with a highly sensitive sequencing technique, variations in SRY are not common in patients with a mosaic sex chromosomal constitution.
Shahid et al. describes a mosaic TS patient, with gonadoblastoma, having a frameshift mutation (L94fsX180) in SRY which was inherited from the father. He was found to be mosaic for the SRY mutation and had oligoasthenozoospermia and a testicular GCC (seminoma), which are signs of mild Testicular Dysgenesis Syndrome (TDS), the underlying entity proposed by Skakkebæk et. al.. They suggest that the presence of the mutated SRY gene might play a role in the development of gonadoblastoma and seminoma, being the precursor lesion and the invasive component of GCC respectively. However, in the series of samples analyzed here and published by others, no clear link between presence of SRY mutations and development of a gonadoblastoma in these patients can be made (Table 1 and references therein). Domenice et al.  describe a patient with partial gonadal dysgenesis and a SRY missense (S18N) mutation whose unaffected male relatives also harbored the mutation, showing no link between SRY mutation and TDS. However, a family with two sisters with 46,XY DSD, pure gonadal dysgenesis and a phenotypically normal brother has been described, in which a SRY frameshift mutation was found in the two sisters and in a mosaic constitution in their father. He showed signs associated with TDS; hypospadias, cryptorchidism, a testicular GCC (seminoma) and oligoasthenozoospermia, suggesting that mutations in SRY may be associated with TDS . If variations in SRY play a significant role in TDS and the development of a testicular GCC remains unresolved, and may warrant further investigation.
It has been found in chimeric XX-XY mouse models that if the gonad contains less than 30% Y-positive cells, the gonad will develop as an ovary, suggesting a correlation between percentage of Y-containing cells and the gonadal differentiation pattern . This seemed at first to be confirmed in humans [27, 28], however two subsequent case reports and analysis of a larger series of samples show no correlation between the degree of gonadal mosaicism and differentiation pattern [6, 29, 30]. The study by Cools et al. revealed no clear correlation between peripheral blood karyotype and gonadal karyotype, or between the gonadal karyotype and differentiation pattern found in the gonads. The inconsistency between gonadal karyotype and gonadal differentiation pattern cannot be explained by the presence of SRY mutations, as they are found only in rare cases, and do not seem to correlate with the differentiation pattern reported [11, 12, 14, 21, 23], even when ascertained by a highly sensitive next generation sequencing approach, as shown in this study.