Y chromosome specific probes identify breakpoint in a 45,X/46,X,del(Y)(pter----q11.1:) karyotype of an infertile male

45,X/46,XY mosaicism: report of 27 cases

OBJECTIVES

There exist substantial differences between prenatally and postnatally diagnosed cases of 45,X/46,XY mosaicism. Ninety percent of prenatally diagnosed cases show a normal male phenotype, whereas the postnatally diagnosed cases show a wide spectrum of phenotypes. This 10% risk of an abnormal outcome in prenatally diagnosed cases requires further attention. The purpose of the present study is to provide more information on the postnatally diagnosed 45,X/46,XY mosaicism cases. To date, only a few series have been reported. An accurate diagnosis in these patients is essential not only to their follow-up, but also to providing appropriate genetic counselling and subsequent prenatal diagnosis to their parents.

METHODS

The clinical, cytogenetic, endocrinologic, histologic and molecular biological findings of 27 patients with 45, X/46,XY mosaicism are analyzed.

RESULTS

The reported cases showed a wide spectrum of phenotypes as Turner syndrome, mixed gonadal dysgenesis (MGD), male pseudohermaphroditism (MPH) and apparently normal male. However, Ulrich-Turner stigmata were the most common features found in this series. Patients with MGD or MPH presented with various degrees of sex reversal such as hypospadias and/or abnormal internal genitalia. No correlation between the proportion of the 45,X/46,XY cell lines in the blood or the fibroblasts and the phenotype was found. Mild mental retardation was present in 4 of the patients and 2 patients showed signs of autism.

CONCLUSIONS

Two major points are emphasized in this series: 1) the presence in 7 histologically analyzed streak gonads of a homogeneous 45,X chromosomal complement suggests that the invasion of the primitive genital ridge by a such a cell line may induce abnormal gonadal development; 2) 3 males, apparently normal at birth, developed late onset abnormalities such as dysgenetic testes leading to infertility, Ulrich-Turner stigmata, dysmorphic features, and mild mental retardation. These data indicate the importance of an accurate clinical and histologic evaluation of any patient presenting with 45, X/46,XY mosaicism.

Genetic abnormalities and male infertility. A comprehensive review

The development of assisted reproductive technologies, such as intracytoplasmic sperm injection (ICSI) substantially improved the outlook for patients with severe male fertility problems. However this implies that for the first time genetic defects associated with male in- or subfertility might be transmitted to offspring and result in genetic disease [de Kretser DM, The potential of intracytoplasmic sperm injection (ICSI) to transmit genetic defects causing male infertility. Reprod. Fertil. Dev. 1995;7:137-142]. The knowledge of male specific fertility genes on the Y chromosome increased enormously in the last decade. The SRY gene plays a critical role in gonadal differentiation. DAZ, SPGY and related genes on the Y chromosome are very important for spermatogenesis. Interstitial Y-chromosomal microdeletions encompassing the AZFa, b or c region have become an additional class of genetic abnormalities causing male infertility. A review is given of the different genetic aspects of male infertility.

Short stature and azoospermia in a patient with Y chromosome long arm deletion

We report on a 42-year old male with short stature, azoospermia and a wide deletion of long arm of Y chromosome. On physical examination, the patient showed height of 149 cm (< 1 degree centile) and reduced volume (3 ml) and consistency of the testes. On hormonal evaluation, he showed increased serum gonadotropins and normal serum testosterone levels though its HCG stimulated levels were limited. Serum thyroid hormones were normal. Serum GH levels in baseline evaluation as well as after GHRH and GHRH + pyridostigmine administration were normal. Serum IGF I levels were lower than normal in baseline evaluation whereas its response to the GH administration was in the normal range. The bilateral testicular biopsy showed tubular atrophy, hyalinosis, interstitial sclerosis and a histological picture of a Sertoli cell only syndrome. Moreover the patient showed arthropathy, otopathy, small chin, small mouth and truncal obesity. On genetic evaluation, the patient showed a 46,X,delY (pter--q11.1:) karyotype and loss of several DNA loci on Yq. In fact he preserved short arm SRY, centromeric DYZ3 and more proximal euchromatic region Yq loci, including DYS270, DYS271, DYS272, DYS11, DYS273, DYS274, DYS148, DYS275, and missed more distal DNA loci from DYS246 to DYZ2. These results disclosed a wide Y long arm deletion, including all hypothized Yq azoospermia loci (except for AZFa and probably for one of the RBM genes, which lie proximally to the deletion) and possibly the Y-specific growth control region (GCY), mapped between DYS11 and DYS246 loci. This deletion is responsible for the complete azoospermia of the patient and probably also for his short stature, even if other factors could be implicated in the statural impairment. It further possibly allowed to relate the GCY gene(s) to the control of GH or IGF-I receptor or post-receptor pathway, being the alteration of this gene(s) consistent with the hormonal pattern of the patient.

Mixed gonadal dysgenesis and cell line differentiation. Case presentation and literature review

A male patient with mixed gonadal dysgenesis, involving a streak gonad on the right and a histologically normal testis in the left, was found to have a 45,X/46,X,dic(Yp) chromosome constitution on peripheral blood cultures. Fibroblasts grown from both gonads showed the "normal" testicular tissue to have e 45,X/46,X,dic(Yp), whereas the cells from the streak gonad were all 45,X. The structure of the dic(Yp) chromosome was confirmed using non-isotopic in situ hybridization with Y centromere and Yp specific probes. On hormonal stimulation, testosterone levels rose by 50%. The "normal" testis was left in situ, but close follow up will be required in view of the malignant potential.

Mental retardation and Ullrich-Turner syndrome in cases with 45,X/46X,+mar: additional support for the loss of the X-inactivation center hypothesis

Four cases having mosaicism for a small marker or ring [45,X/46,X,+mar or 45,X/46,X,+r] chromosome were ascertained following cytogenetic studies requested because of minor anomalies (cases 1, 3, and 4) and/or short stature (cases 2 and 4). While all 4 cases had traits typical of Ullrich-Turner syndrome (UTS), cases 1, 3, and 4 had manifestations not usually present in UTS, including unusual facial appearance, mental retardation/developmental delay (MR/DD) (cases 3 and 4), and syndactylies (case 1). The facial appearances of cases 1 and 3 were similar yet distinct from that of case 4. Using fluorescence in situ hybridization (FISH), each of the markers in these 4 cases was identified as having been derived from an X chromosome. The level of mosaicism for the mar/r(X) cell line in these cases varied from 70% (case 1) to 16% (case 4) but was not apparently correlated with the presence of MR/DD. Replication studies demonstrated a probable early replication pattern for the mar/r(X) in cases 1, 3, and 4, while the marker in case 2 was apparently late replicating. To date, 41 individuals having mosaicism for a small mar/r(X) chromosome have been described. Interestingly, most of the 14 individuals having a presumedly active mar/r(X) demonstrated clinical findings atypical of UTS, including abnormal facial changes (11) and MR/DD (13). MR was noted most frequently in those cases having at least 50% mosaicism for the marker or ring. In contrast, atypical UTS facial appearance or MR/DD was not noted in 14 of the 16 cases with UTS who carried a probable late replicating marker or ring. In conclusion, although the phenotype of 45,X/46,X,mar/r(X) individuals appears to be influenced by the genetic content and degree of mosaicism for the mar/r(X), the most significant factor associated with MR/DD appears to be the activity status of the mar/r(X) chromosome. Thus, our 4 cases provide further support for the hypothesis that a lack of inactivation of a small mar/r(X) chromosome may be a factor leading to the MR and other phenotypic abnormalities seen in this subset of individuals having atypical UTS.

Characterization of a deleted Y chromosome in a male with Turner stigmata

A 46,X,+mar karyotype was detected in an 11-year-old male with a clinical picture characterized by obesity, short stature, bilateral cryptorchidism and coarctation of the aorta. The presence of ZFY and SRY genes was demonstrated by PCR amplification, and the origin of the marker chromosome from a deleted Y chromosome was analyzed by in situ hybridization. The proximal limits of a deletion in Yq were defined by the absence of Southern blot hybridization signals upon probing with Yq11 markers. Cytogenetics and molecular methods taken together indicate a deletion in q11.21. In addition, the loss of Yp subtelomeric sequences was suggested by the analysis of Southern blots hybridized with a 29A24 (DXYS14) probe and by the presence of coarctation of the aorta tentatively localized in Yp. The karyotype of the patient was suggested to be: 46,X,del (Y) (p11.3-q11.21).

Multiple minute marker chromosomes derived from Y identified by FISH in an intersexual infant

Chromosomal analysis in a child with ambiguous sex showed mosaicism of at least two cell lines with one or more marker chromosomes or none at all. They were shown to be derived from the Y chromosome by fluorescent in situ hybridisation (FISH) using different DNA probes that cover parts of the long and the short arm.

Molecular detection of a translocation (Y;11) (q11.2;q24) in a 45,X male with signs of Jacobsen syndrome

A 45,X karyotype was found in a boy with dysmorphic features, hypoglycaemia and pancytopenia. DNA analysis showed the presence of the Y-chromosomal DNA sequences SRY, ZFY, DYZ4, DYZ3 and DYS1. Using fluorescent in situ hybridization, we located DYZ4 and DYZ3 on chromosome 11qter and concluded that a de novo translocation (Y;11) (q11.2;q24) with a deletion of 11q24----qter and a deletion of Yq11.2----Yqter were present; Jacobsen syndrome and azoospermia are associated with these deletions. Signs of Jacobsen syndrome were observed in the patient.

Sex chromosome marker: clinical significance and DNA characterization

Two patients are described with a virtually identical marker sex chromosome that was so small as to defy classification by conventional cytogenetic studies. DNA hybridization with Y probes allows classification into Y or non-Y, and in situ hybridization with X centromere specific sequences, into X or non-X. One patient was proven to have a Y fragment, and the second, an X fragment. DNA characterization is important since prognosis and clinical management depends on proper identification of the small marker sex chromosome.

Determining the origins and the structural aberrations of small marker chromosomes in two cases of 45,X/46,X, + mar by use of chromosome-specific DNA probes

A 17-year-old girl (S.M.) and a 13-year-old girl (C.L.) both with Ullrich-Turner syndrome (UTS) were found to have 45,X/46,X, + mar mosaicism. The marker chromosomes in both patients were very small in size. In S.M. the marker chromosome was present in 80% of phytohemagglutinin-stimulated lymphocytes, 28% of skin fibroblasts, and 11-20% of gonadal fibroblasts. In C.L., the small marker chromosome was found in 50% of stimulated lymphocytes. S.M. is of normal height, but C.L. is short. Molecular hybridization with a number of Y-specific DNA probes demonstrated their presence in S.M. but absence in C.L. In situ hybridization with Y-specific and X-centromere-specific DNA probes confirmed the Y origin of the marker chromosome in S.M. and the X origin of the minute chromosome in C.L. Biotinylated centromere and telomere probes were also used for in situ hybridization to show the presence of centromeric and telomeric sequences in the Y-marker chromosome, suggesting that the deletion of this marker chromosome is interstitial.