The role of the sex-determining region of the Y chromosome (SRY) in the etiology of 46,XX true hermaphroditism

Summary The syndrome of 46,XX true hermaphroditism is a clinical condition in which both ovarian and testicular tissue are found in one individual. Both Mullerian and Wolffian structures are usually present, and external genitalia are often ambiguous. Two alternative mechanisms have been proposed to explain the development of testicular tissue in these subjects: (1) translocation of chromosomal material encoding the testicular determination factor (TDF) from the Y to the X chromosome or to an autosome, or (2) an autosomal dominant mutation that permits testicular determination in the absence of TDF. We have investigated five subjects with 46,XX true hermaphroditism. Four individuals had a normal 46,XX karyotype; one subject (307) had an apparent terminal deletion of the short arm of one X chromosome. Genomic DNA was isolated from these individuals and subjected to Southern blot analysis. Only subject 307 had Y chromosomal sequences that included the pseudoautosomal boundary, SRY (sex-determining region of Y), ZFY (Y gene encoding a zinc finger protein), and DXYS5 (an anonymous locus on the distal short arm of Y) but lacked sequences for DYZ5 (proximal short arm of Y) and for the long arm probes DYZ1 and DYZ2. The genomic DNA of the other four subjects lacked detectable Y chromosomal sequences when assayed either by Southern blotting or after polymerase chain reaction amplification. Our data demonstrate that 46,XX true hermaphroditism is a genetically heterogeneous condition, some subjects having TDF sequences but most not. The 46,XX subjects without SRY may have a mutation of an autosomal gene that permits testicular determination in the absence of TDF.     

Mutations and sequence variants in the testis-determining region of the Y chromosome in individuals with a 46,XY female phenotype

The testis-determining gene SRY (sex determining region, Y) is located on the short arm of the Y chromosome and consists of a single exon, the central third of which is predicted to encode a conserved motif with DNA binding/bending properties. We describe the screening of 26 patients who presented with 46,XY partial or complete gonadal dysgenesis for mutations in both the SRY open reading frame (ORF) and in 3.8 kb of Y-specific flanking sequences. DNA samples were screened by using the fluorescence-assisted mismatch analysis (FAMA) method. In two patients, de novo mutations causing complete gonadal dysgenesis were detected in the SRY ORF. One was a nonsense mutation 5′ to the HMG box, whereas the other was a missense substitution located at the C terminus of the conserved motif and identical to one previously detected in an unrelated patient. In addition, two Y-specific polymorphisms were found 5′ to the SRY gene, and a sequence variant was identified 3′ to the SRY polyadenylation site. No duplications of the DSS region in 20 of these patients were detected. Received: 18 November 1996 / Revised: 13 December 1996     

The sex-determining region Y (SRY) gene is mapped to p12-p13 of the Y chromosome in pig (Sus scrofa domestica) by in situ hybridization

The sex-determining region Y is a gene located in the distal portion of the short arm of human (SRY) and mouse (Sry) Y chromosomes and considered to be the best candidate for the testis determining factor (TDF/Tdy). The gene is believed to be the key factor in sex differentiation in mammals and is conserved across mammalian species. We report herein that the SRY/Sry gene has been assigned to pi 2-p13 on the short arm of the Y chromosome in pig by in situ hybridization. The result confirms interspecies conservation of this chromosomal segment in the evolution of mammalian chromosomes, and suggests further use of this gene probe in genomic studies in other mammals. The assignment of the Sry gene is the second physical gene mapping data available for the Y chromosome in pigs. Such data can be used in the effort of constructing the pig gene map and for further establishment of a comparison of sex chromosome morphology in different mammalian species concerning sex-specific and pseudoautosomal regions.     

Transmission of ring chromosome 18 46,XX/46,XX,r(18) mosaicism in a mother and ring chromosome 18 syndrome in her son.

Inheritance of ring chromosomes is reported infrequently. The authors report on a phenotypically and mentally normal mother with ring chromosome 18 mosaic with a normal cell line and her polymalformed son with non-mosaic 46,XY,r(18) karyotype.     

Defective calmodulin-mediated nuclear transport of the sex-determining region of the Y chromosome (SRY) in XY sex reversal

The sex-determining region of the Y chromosome (SRY) plays a key role in human sex determination, as mutations in SRY can cause XY sex reversal. Although some SRY missense mutations affect DNA binding and bending activities, it is unclear how others contribute to disease. The high mobility group domain of SRY has two nuclear localization signals (NLS). Sex-reversing mutations in the NLSs affect nuclear import in some patients, associated with defective importin-beta binding to the C-terminal NLS (c-NLS), whereas in others, importin-beta recognition is normal, suggesting the existence of an importin-beta-independent nuclear import pathway. The SRY N-terminal NLS (n-NLS) binds calmodulin (CaM) in vitro, and here we show that this protein interaction is reduced in vivo by calmidazolium, a CaM antagonist. In calmidazolium-treated cells, the dramatic reduction in nuclear entry of SRY and an SRY-c-NLS mutant was not observed for two SRY-n-NLS mutants. Fluorescence spectroscopy studies reveal an unusual conformation of SRY.CaM complexes formed by the two n-NLS mutants. Thus, CaM may be involved directly in SRY nuclear import during gonadal development, and disruption of SRY.CaM recognition could underlie XY sex reversal. Given that the CaM-binding region of SRY is well-conserved among high mobility group box proteins, CaM-dependent nuclear import may underlie additional disease states.     

Molecular analysis of the Y chromosome in XX sex-reversed patients

Molecular genetic analysis was performed for 26 phenotypically male patients lacking the Y chromosome in the karyotype. The sex-determining region Y (SRY) gene was found in 77% of the patients. PCR analysis of Y-specific loci in the 17 SRY-positive patients revealed Yp fragments varying in size in 16 cases and cryptic mosaicism (or chimerism) for the Y chromosome in one case. The frequencies of class I, II, and III (Yp+)XX sex reversals were 18.75, 25.25, and 56%, respectively. All of the class III (Yp+)XX sex-reversed patients had a 3.5-Mb paracentric inversion flanked by inverted repeats 3 (IR3) on the short arm of the Y chromosome.     

Molecular analysis of the Y chromosome in XX sex-reversed patients

Molecular genetic analysis was performed for 26 phenotypically male patients lacking the Y chromosome in the karyotype. The sex-determining region Y (SRY) gene was found in 77% of the patients. PCR analysis of Y-specific loci in the 17 SRY-positive patients revealed Yp fragments varying in size in 16 cases and cryptic mosaicism (or chimerism) for the Y chromosome in one case. The frequencies of class I, II, and III (Yp+)XX sex reversals were 18.75, 25.25, and 56%, respectively. All of the class III (Yp+)XX sex-reversed patients had a 3.5-Mb paracentric inversion flanked by inverted repeats 3 (IR3) on the short arm of the Y chromosome.     

Deletion mapping of the testis determining locus with DNA probes in 46,XX males and in 46,XY and 46,X,dic(Y) females.

Eleven Y-specific DNA probes hybridizing with DNA from one or more 46,XX males were isolated from a recombinant phage DNA library constructed from flow sorted human Y chromosomes. Two probes hybridized with DNA from nine out of eleven, i.e. greater than 80% of these 46,XX males. The relative frequency of hybridization of the probes in the 46,XX males and in a 46,X,dic(Y) female, together with in situ hybridization data, allowed mapping of the probes on Yp in relation to a putative testis determining locus. Several of those probes were also absent in a 46,XY female, further refining a model for ordering the probes on Yp. The DNA of one XX male hybridized both with probes from Yp and probes from proximal Yq (excluding the pericentral region). This suggests that complex translocations may occur into the DNA of 46,XX males that involve not only parts of Yp but also parts of Yq.     

Rare case of mosaicism for chromosome 18, karyotype: 46, XX, del(18) (p11)/46, XX, i(18q)

Rare mosaicism of chromosome No 18 is described. The proposita is 5.5 years old and has two cell clones: 50% of cells are monosomic for 18p and 50% have isochromosome i18q. The ratio of these clones (1:1) is found to be similar at the age of the proposita 2.5 and 5.5 years. The proposita has some phenotypic characters of both 18p- (ptosis, epicanthus, deformed carious teeth, falled back sternum etc.) and trisomy 18q (contraction of external auditory meatus, femur luxatus congenitus etc.) syndromes. A possible mechanism for the origin of such a mosaicism is discussed.     

A ZFY-negative 46,XX true hermaphrodite is positive for the Y pseudoautosomal boundary

Summary Two loci on the short arm of the human Y chromosome have recently been described as candidates for the testis determining factor (TDF); namely, ZFY, and a locus distal to ZFY, near the pseudoautosomal boundary. We have previously reported on seven 46,XX true hermaphrodites and one 45,X mixed gonadal dysgenesis case all presenting with testicular tissue in their gonads in the apparent absence of Y-specific DNA sequences. A reanalysis of these cases shows them all to lack ZFY, but one 46,XX true hermaphrodite carries sequences next to the Y pseudoautosomal boundary. This case provides further evidence for assigning the TDF locus very close to the pseudoautosomal region on Yp.     

Sexual and somatic determinants of the human Y chromosome: studies in a 46,XYp- phenotypic female.

A case of a 46,XYp- phenotypic female provided an opportunity to evaluate both sexual and somatic determinants for the Y chromosome. The patient had multiple stigmata of Turner syndrome, but normal stature. Laparotomy revealed a normal uterus and tubes, with 1.5 cm undifferentiated gonads. Serological tests for H-Y antigen (ostensibly the product of Y-chromosomal testis-determining genes) indicated absence of the H-Y+ phenotype normally associated with the intact Y chromosome. We conclude that genes exist on the short arm of the human Y chromosome which both suppress some of the somatic stigmata of Turner syndrome and determine normal expression of H-Y antigen and testicular differentiation of the primitive gonad. Our data are consistent with the view that H-Y genes comprise a family of testis-determinants, and that loss of a critical moiety is inconsistent with normal development of the male gonad.     

Twin pregnancy with complete hydatidiform mole (46,XX) and fetus (46,XY): genetic origin proved by analysis of chromosome polymorphisms.

In a case of complete hydatidiform mole with fetus the genetic origins were defined by the use of chromosomal polymorphisms. The fetus had a normal 46,XY karyotype with evidence of the presence of both maternal and paternal chromosomes. The mole was 46,XX and of androgenetic origin. There was no evidence of a maternal contribution, and duplication of paternal chromosomes was shown. In such atypical molar pregnancies examining genetic polymorphisms yields much more information than do sex chromosome studies and karyotyping, particularly in confirming the diagnosis and defining the origin and aetiology of the condition.     

46,XX/46,XX,del(20)(pter-->p12.2) mosaicism limited to fibroblasts associated with MCA/MR and severe growth deficit.

In this report the authors describe an 8-year-old severely mentally retarded girl with facial features resembling the facial dysmorphism seen in patients with Alagille-Watson syndrome, severe growth retardation and a 46,XX/46,XX,del(20)(pter-->p12.2) mosaicism in fibroblasts.