Accidental X-Y recombination and the aetiology of XX males and true hermaphrodites

Accidental recombination between the differential segments of the X and Y chromosomes in man occasionally allows transfer of Y-linked sequences to the X chromosome leading to testis differentiation in so-called XX males. Loss of the same sequences by X-Y interchange allows female differentiation in a small proportion of individuals with XY gonadal dysgenesis. A candidate gene responsible for primary sex determination has recently been cloned from within this part of the Y chromosome by Page and his colleagues. The observation that a homologue of this gene is present on the short arm of the X chromosome and is subject to X-inactivation, raises the intriguing possibility that sex determination in man is a quantitative trait. Males have two active doses of the gonad determining gene, and females have one dose. This hypothesis has been tested in a series of XX males, XY females and XX true hermaphrodites by using a genomic probe, CMPXY1, obtained by probing a Y-specific DNA library with synthetic oligonucleotides based on the predicted amino-acid sequence of the sex-determining protein. The findings in most cases are consistent with the hypothesis of homologous gonad-determining genes, GDX and GDY, carried by the X and Y chromosomes respectively. It is postulated that in sporadic or familial XX true hermaphrodites one of the GDX loci escapes X-inactivation because of mutation or chromosomal rearrangement, resulting in mosaicism for testis and ovary-determining cell lines in somatic cells. Y-negative XX males belong to the same clinical spectrum as XX true hermaphrodites, and gonadal dysgenesis in some XY females may be due to sporadic or familial mutations of GDX.     

A possible common origin of “Y-negative” human XX males and XX true hermaphrodites

Summary We have studied nine patients aged 1 month to 16 years with 46, XX karyotypes and testicular tissue. Some of these patients were followed through puberty. Phenotypically, two presented normal and seven abnormal external genitalia (AG). Among this latter group, four showed hypospadias and three true hermaphroditism (TH). The endocrine data were similar in all three groups: testosterone levels were within normal limits during puberty, decreasing in adulthood; gonadotrophin levels were above the control values at mid puberty. Histologies of the two sub groups of AG patients were identical up to 5 years of age and presented differences when compared with controls, regardless of the ovarian part of the ovotestis. However, in patients older than 8 years, germ cells disappeared and dysgenesis became obvious. In one patient, the ovarian zone of the gonad was detected only after complete serial sections of the removed gonad were examined. Southern blot analysis with Y-DNA probes displayed Y-specific material for the classic 46 XX males and a lack of such sequences for all patients with AG and TH. Based on these findings, we postulate that 46, XX males with AG and 46, XX TH may represent altenative manifestations of the same genetic defect. These data together with those concerning familial cases of 46, XX males with AG and 46, XX TH suggest an autosomally (or pseudoautosomally) determined mechanism.     

Genetic analysis of 38XX males with genital ambiguities and true hermaphrodites in pigs

In pig, the frequency of intersexuality ranges from 0.1 to O.6%, depending on the breed. In a closed pig herd at INRA an intersex condition was observed in 0.75% of ‘females’. The present study describes 11 animals with a 38XX karyotype and the presence of testicular tissue. Phenotypically, all presented with abnormal external or/and internal genitalia. Southern blot analysis with Y-specific probes (SRY and ZFY) revealed the absence of Y material in all animals tested. By polymerase chain reaction (PCR) amplification, 10 of 11 intersex pigs lacked the SRY gene in gonad DNA. These data are compatible with an autosomally (or pseudoautosomally) determined mechanism. Moreover, analysis of familial cases seemed to indicate that 38XX male pseudohermaprodites and 38XX true hermaphrodites may represent alternative manifestations of the same genetic defect.     

A minority of 46,XX true hermaphrodites are positive for the Y-DNA sequence including SRY

Summary A total of 30 cases of 46,XX true hermaphroditism was analysed for Y-DNA sequences including the recently cloned gene for male testis-determination SRY. In 3 cases, a portion of the Y chromosome including SRY was present and, in 2 cases, was localised, to Xp22 by in situ hybridisation. Since previous studies have shown that the majority of XX males are generated by an X-Y chromosomal interchange, the Xp22 position of the Yp material suggests that certain cases of hermaphroditism can arise by the same meiotic event. The phenotype in the 3 SRY-positive cases may be caused by X-inactivation resulting in somatic mosaicism of testis-determining factor expression giving rise to both testicular and ovarian tissues. Autosomal or X-linked mutation(s) elsewhere in the sex-determining pathway may explain the phenotype observed in the remaining 27 SRY-negative cases.     

Absence of Y-specific DNA sequences in human 46,XX true hermaphrodites and in 45,X mixed gonadal dysgenesis

Summary A search for Y-specific DNA sequences has been performed in a sample of seven 46,XX true hermaphrodites and one 45,X mixed gonadal dysgenesis case and compared with a sample of 11 XX males. Using six Y-specific DNA probes no hybridization signal was obtained in the hermaphrodite group; in contrast, all XX males gave a positive signal with at least one probe. This difference is statistically highly significant. We conclude that the aetiology of true hermaphroditism is different from that of the XX male syndrome. As all cases of the hermaphrodite group are positive for the serological sex-specific antigen (Sxs) it is concluded that this antigen can be present even in the absence of Y-specific DNA.     

Testicular development in an SRY-negative 46,XX individual harboring a distal Xp deletion

A case of a true hermaphrodite presenting with a karyotype of 46,X,del(X)(p21.1pter) is described. The testis-determining gene, SRY, was not detected in DNA prepared from either peripheral blood lymphocytes or from a gonad biopsy. The patient also presented with a series of discrete somatic abnormalities, including abnormal skin and retinal pigmentation, and mental retardation. The extent of the Xp deletion was mapped by Southern blotting. X chromosome replication studies of lymphoblast cells prepared from the patient indicated that the deleted X chromosome was inactivated in all cells examined. It is suggested that the phenotype of the patient is caused by the unmasking of a recessive allele(s) on the grossly intact X chromosome. The relationship between the Xp deletion, the intersex phenotype, and the possible role of an Xp locus involved in human sex determination is discussed.     

Escobar syndrome in three male patients of same family

We describe three male individuals from a consanguineous south Indian family affected with the multiple pterygium syndrome (Escobar syndrome). Common clinical features included short stature, multiple pterygium, skeletal anomalies, and normal intelligence. The first report of this condition was made in 1902 from this same place (Pondicherry) and the disease received its present popular name Escobar syndrome in 1982. The genetic defect for this condition was identified in 2006 as mutation in the fetal acetylcholine receptor.     

Familial XX true hermaphroditism and the H-Y antigen

Summary Two 46,XX sibs, one of female, one of male gender, and both with ambiguous external genitalia and ovotestis, were H-Y positive. The mother was H-Y negative. It is assumed that the underlying mutation was transmitted by the father, resulting in an autosomal dominant mode of inheritance. The common origin and the nature of the mutation leading to XX sex reversal are discussed.     

Ultrastructure of testicular biopsy from an XX male

Ultrastructural study of testicular biopsy specimens from an XX male showed hyalinized seminiferous tubules and tubules containing only mature Sertoli cells. These cells possessed large lipid inclusions as well as microfilament bundles which were perpendicular to the basement membrane and parallel to one another. The basal lamina was thickened and composed of several parallel layers with myofibroblast layers between them. The interstitium showed nodular to diffuse Leydig cell hyperplasia. Four types of Leydig cells were found: 1) normal Leydig cells with crystals of Reinke; 2) cells with abundant microcrystalline inclusions as well as microfilaments and concentric cisternae of smooth endoplasmic reticulum; 3) vacuolated cells containing numerous large lipid droplets; 4) immature Leydig cells. The different ultrastructural abnormalities found in the Sertoli and Leydig cells might be considered as the histological expression of a tubular-interstitial dysgenesis which is reflected in the high levels of gonadotropins and low levels of testosterone.     

Allocation of resources to male and female functions in hermaphrodites

The question of"how a self-fertile hermaphrodite will distribute the resources that it allocates to reproduction is studied by means of the ESS approach. Different models of the relations between allocation to male function, the male and female fertilities, and the selfing rate, yield different conclusions about how much resource should be allocated to male function. Values below a half are obtained with one model, while another can give values greater than a half. Even with no selfing, values other than a half are usually obtained; with both models studied, the values decrease with increasing selling. If the selfing rate is assumed to be independent of the fraction of resources allocated to male function, it can be shown that the ESS allocation to male function always decreases as selling increases. The types of relations that might be expected in species with different types of breeding biology, and some data on allocation to male function, are reviewed.
The implications for the fitness of male- and female-sterility mutations are discussed. It is argued that the concavity or convexity of the curve relating female fertility to male fertility is not a good guide to when hermaphroditism should exist when there is some selfing. Even with a concave relation, male-sterility mutants can have a higher fitness than hermaphrodites, if there is some selling and inbreeding depression. Also, when the selfing rate depends on allocation to male I unction, an hermaphrodite ESS does not always exist when the function is concave (as it does when there is no selfing), and such an ESS may exist when the relation is convex. The fitness of male- or female-sterility mutants may also depend on the existence of 'fixed costs'. It is shown that these do not ailed the ESS allocation of resources.     

Familial true hermaphroditism: paternal and maternal transmission of true hermaphroditism (46,XX) and XX maleness in the absence of Y-chromosomal sequences

We report on 46,XX true hermaphroditism and 46,XX maleness coexisting in the same pedigree, with maternal as well as paternal transmission of the disorder. Molecular genetic analysis showed that both hermaphrodites as well as the 46,XX male were negative for Y-chromosomal sequences. Thus, this pedigree is highly informative and allows the following conclusions: first, the maternal as well as paternal transmission of the disorder allows the possibility of an autosomal dominant as well as an X-chromosomal dominant mode of inheritance; second, testicular determination in the absence of Y-specific sequences in familial 46,XX true hermaphrodites as well as in 46,XX males seems to be due to the varying expression of the same genetic defect; and third, there is incomplete penetrance of the defect.     

High male reproductive success of hermaphrodites in the androdioecious Phillyrea angustifolia

Androdioecy, the coexistence of males and hermaphrodites within a population, is a rare breeding system, often considered as unlikely to evolve because of restrictive conditions for its maintenance. Phillyrea angustifolia, a wind-pollinated shrub, is one of the handful species reported to be androdioecious. Our previous studies have shown that natural populations of this species in southern France exhibit higher male frequencies (approximately 50%) than predicted on theoretical grounds. Thus, the male functionality of hermaphrodites is still debated. To assess the functional breeding system of this species in the wild, a paternity analysis was performed with two highly polymorphic microsatellite loci on 729 seeds collected on 10 maternal shrubs in a natural population of 24 mature individuals of P. angustifolia. A large proportion of seeds were found to have been sired by pollen from outside the population. Analysis of seeds sired by individuals within the study population revealed a high male fertility of hermaphrodites resulting in a low male advantage in fertility for male plants. Intermate distances were found to have a strong impact on male reproductive success, whereas sexual morph had no effect, with males and hermaphrodites performing equivalently. This study is the first to unequivocally document the occurrence of a male function of hermaphrodites in a natural population of an androdioecious species.     

Investigation of the ZFY gene in XX true hermaphroditism and Swyer syndrome

Summary Four patients with 46,XX true hermaphroditism and one patient with 46,XY pure gonadal dysgenesis (Swyer syndrome) were analyzed with a Y chromosome-derived probe that detects a specific fragment on the short arm of the Y chromosome in the putative testicle-determining region and also a fragment on the short arm of the X chromosome. Normal males and females, an individual with Turner syndrome, and patients with various causes of anomalous gonadal differentiation accompanied by cytogenetically present Y chromosome were used as controls. The Y-specific fragment was not detected in any of the persons with 46,XX true hermaphroditism. However, this fragment was positive in the 46,XY female and in all Y-bearing patients. Cytogenetic and molecular absence of the ZFY sequence in 46,XX true hermaphrodites calls for explanations other than the classic embryogenie theory. The absence of testicular differentiation in the ZFY-positive XY female evidences functionally altered sex determination or, alternatively, defective gonadal receptors.     

Y-chromatin positive cells in the smear preparations of the gonad from an XX male

Summary An ambisexual male infant showed a normal female karyotype by the leukocyteculture technique in two different occasions. Cultured fibroblasts from the right gonad had also a 46,XX complement. They were Y-chromatin negative. To our surprise, Y-chromatin was observed in 96% of the nuclei in smears from the uncultured gonad. It is emphasized that the examination of the uncultured gonad by the quinacrine technique is mandatory in the study of XX males.     

XX true hermaphroditism in southern African blacks: an enigma of primary sexual differentiation.

A high incidence of 46,XX true hermaphroditism exists among southern African blacks. The gonadal distribution and clinical presentation of 38 patients are described. The aim of our study on 11 families with histologically proven XX true hermaphroditism was to determine whether a common genetic or environmental etiology could be identified. Pedigree analysis excluded the presence of a simple inheritance pattern, and no constant environmental factors could be implicated. Hybridization studies with Y chromosome--specific probes (pDP132, pDP61, pDP105, pDP31, pDP97, and pY431-HinfA) excluded the presence of a large portion of Yp in these patients. It is possible that smaller portions of the Y chromosome or one or more X-linked or autosomal mutations, either interacting and/or with incomplete penetrance, are present.     

H-Y antigen expression in a case of XX true hermaphroditism

Summary Cells from an XX true hermaphrodite expressed a reduced amount of H-Y antigen when compared with normal XY cells and with cells from his father, who had an XY/XX chromosomal constitution. His mother had a normal karyotype and was H-Y negative. The four brothers of the patient were clinically and karyotypically normal. An X-Y interchange followed by random inactivation of the X chromosome is proposed to explain the H-Y antigen titer found in the patient.     

Polydactyly in four generations of an Algerian family with variable metacarpo-phalangeal relationship in an individual

We report an Algerian family in which four generations show polydactyly with variable numbers of metacarpals and phalanges. The extraordinary rearrangements of the metacarpals and phalanges shown in the X-rays are most unusual. The family is highly consanguineous. The mode of inheritance appears to be dominant with reduced penetrance and variable expression.