Chromosomal Variants in Klinefelter Syndrome

Klinefelter syndrome (KS) was first described by Harry F. Klinefelter in 1942 [Klinefelter et al., 1942]. He reported 9 men with testicular abnormalities who failed to produce sperm and had gynecomastia. In 1959, this was found to be the result of an additional X chromosome [Jacobs and Strong, 1959]. About 80% of KS patients show a 47,XXY karyotype, 20% have other numeric sex chromosome abnormalities (48,XXXY, 48,XXYY, 49,XXXXY), 46,XY/47,XXY mosaicism, or structurally abnormal sex chromosomes [Lanfranco et al., 2004].

In approximately half of the Klinefelter cases the aberrant X chromosome is thought to be paternally derived, and recent evidence suggests that it may be related to advancing paternal age, although this is controversial [Jacobs et al., 1988; Lowe et al., 2001]. With a frequency of 1 out of 600 newborn males KS is described to be the most common sex chromosome abnormality [Bojesen and Gravholt, 2007]. Affected patients are characterized by an increase of the body height of about 6.5 cm, narrow shoulders, broad hips, sparse body hair, gynecomastia, small testes, absent spermatogenesis, normal to moderately reduced Leydig cell function, increased secretion of follicle-stimulating hormone (FSH), androgen deficiency, and normal to slightly decreased verbal intelligence [Bojesen and Gravholt, 2007; Wikstrom and Dunkel, 2008]. Apart from that, amongst others, osteoporosis [van den Bergh et al., 2001], varicose veins, thromboembolic disease [Igawa and Nishioka, 2003], or diabetes mellitus [Ota et al., 2002] are observed. KS is the most frequent genetic cause of male infertility, and is found in 11% of azoospermic men and 4% of infertile men [Wikstrom and Dunkel, 2008]. In most of the cases KS is not diagnosed before puberty and even in adulthood it was estimated that only a fourth of affected males receive diagnosis, mostly by their infertility [Bojesen and Gravholt, 2007], because in many cases the phenotype is not as distinct as described above.

If somebody has an additional X chromosome, there is an excess of X-chromosomal genes. Normally 1 of the 2 X chromosomes in a female is inactivated, but it has been shown that in total, about 15% of X-linked genes escape inactivation [Carrel and Willard, 2005]. The same applies for KS patients and, therefore, it is very likely that these genes are responsible for most of the KS features.

Over the last almost 50 years there have been reported many cases of KS patients with a different karyotype than 47,XXY. These variants show, amongst others, a 47,X,der(X),Y karyotype, a 47,XX,der(Y) karyotype, an additional isochromosome Xq, as well as translocations or deletions involving one of the sex chromosomes. Apart from that there have been reported a lot of male cases with a 46,XX karyotype as well as women with a 47,XXY chromosome complement. In addition to all these patients with variations on the sex chromosomes, male KS patients with 2 X and 1 Y chromosomes and an additional rearrangement on one or more autosomal chromosomes have been described.

In this review we focused on the different genetic variants of the sex chromosomes in KS patients. Therefore, we attended to male patients with 2 or more X chromosomes and women with a 47,XXY karyotype. The aim of the review is to summarize the diverse phenotypes of these different variants of KS and to compare them to that of the classical 47,XXY KS patients. For our search we used 2 different databases: First PubMed using the following search terms: ‘Klinefelter’ AND ‘Syndrome’; ‘Klinefelter’ AND ‘Isochromosome X’; ‘46 XX’ AND ‘Male’; ‘47 XXY’ AND ‘Female’; ‘48 XXYY’; ‘48 XXXY’ and ‘49 XXXXY’ and second for the KS cases with derivative X or Y chromosomes the online database of the Jena University Hospital, Institute of Human Genetics, Jena (Germany). All searches were restricted to articles in English and German. We were looking exclusively for studies in which additional aberrations on the sex chromosomes were described. Articles on additional autosomal chromosomes or 47,XXY/46,XY karyotypes were excluded. For 46,XX males and 47,X,der(X),Y patients we included only SRY (sex-determining region Y) and XIST- (X (inactive)-specific transcript) positive patients or those where the breakpoints were obviously distal to the XIST location.

In the end we found more than 300 articles of KS variant patients at which most of the studies describe KS patients with other numeric sex chromosome abnormalities and XX males. Much of the literature was published between the 60s and 80s of the last century. In these cases the used ISCN nomenclature differs from the current version. To prevent misinterpretation or even adulteration of the original karyotypes, we always took over the karyotypes as indicated in the original literature.

The prevalence of the Klinefelter variant with an additional isochromosome Xq is calculated to be between 0.3–0.9% in males with a KS phenotype [Arps et al., 1996]. The first study of a 47,X,i(Xq),Y male was reported in 1969 [Zang et al., 1969]. Apart from that, to our knowledge, 24 further cases of isochromosome Xq have been reported so far [Demirhan et al., 2009]. Most of them described a monocentric isochromosome. The clinical and laboratory data on these cases are summarized in table 1. The patients show a nearly similar phenotype with characteristic features such as infertility, elevated plasma luteinizing hormone (LH) and FSH levels, low or normal testosterone levels, sometimes gynecomastia, normal to reduced body height, and a normal to slightly reduced intelligence level [Demirhan et al., 2009]. Most of the literature indicated that the normal height is due to the presence of only one Xp carrying the growth gene SHOX (short stature homeobox-containing gene) [Richer et al., 1989; Stemkens et al., 2007] and other putative Xp-specific growth genes [Rao et al., 1997]. The observation of increased body height in a KS patient with an isodicentric X (pter→q22::q22→pter), with 3 copies of Xp and one distal part of Xq, is in agreement with this theory [Zelante et al., 1991].

Zang et al. [1969] described the origin of an additional isochromosome Xq as an unusual event, because it would require a double error during meiosis. Arps et al. [1996] proposed that the most probable origin of an additional isochromosome Xq is a misdivision of the centromere or a sister-chromatid exchange of one X chromosome. Höckner et al. [2008] investigated a male patient with a 47,X,idic(X)(p11.1),Y karyotype and found loss of heterozygosity for all informative Xq markers on the isochromosome and the presence of the other maternal allele on the normal homolog in each case of maternal heterozygosity. These results are in line with a maternal origin of a true dicentric isochromosome and not a maternal Xq/Xq translocation, and most likely postzygotic formation subsequent to a nondisjunction in maternal meiosis II [Höckner et al., 2008].

In the literature, only 5 cases with a 47,X,der(X),Y karyotype have been described. All of the cases were reported before 1981. Therefore, there is only little information about these rearrangements. The clinical and laboratory data on these cases are summarized in table 2. The first case showing such a karyotype was reported by Nielsen who described a male KS patient with terminal deleted X chromosome mosaic (10% normal 46,XY cells) [Nielsen, 1966]. At the age of 54 years, the man was just 160 cm tall and his whole body hair was scanty. He did not show gynecomastia, his penis was of normal size, and his testes were soft and measured 10 mm from pole to pole. His personality was described as childish and primitive and in comparison with ‘normal’ Klinefelter patients he showed more marked personality defects and his sexual activity was more pronounced. The sex chromatin percentage in buccal smear was 14% which is less than usually found in patients with KS. The decreased body height in the man, stands, because of his 2 Xp arms, in contrast to the hypothesis about the relevance of the number of SHOX gene copies, but it should be mentioned that Nielsen et al. published the case in 1966 and it is not possible to control the correctness of the karyotype.

Chandra et al. [1971] also reported a male patient with a 47,XXq-Y karyotype. A little less than half of the long arm appears to have been deleted from one of the X chromosomes. One sex chromatin body could be seen in 40–60% of the examined cells from hair roots and buccal mucosa. The patient was described as a dull-looking boy with rather a large build for his age and bilateral gynecomastia. His body hair had a feminine distribution and the testes were small and soft. All these symptoms resemble to those of normal KS patients and are partly identical to those of Nielsen’s case. The differences between these 2 cases are the gynecomastia and the body height, which supports the assertion of the SHOX gene hypothesis. However, it should be mentioned that Chandra et al. [1971] described a boy of unknown age and Nielsen [1966] a 54-year-old man.

Patil et al. [1981] reported a case of a 19-year-old KS patient with gynecomastia, small testes, and azoospermia. The analysis of the chromosomes showed a deletion of parts of the long arm of the X chromosome with the breakpoint in q22. The authors interpreted the karyotype as 47,X,del(X)(pter→q22:),Y. Growth, weight and intellectual development were normal. Just the FSH and LH levels were increased. These symptoms were consistent with those reported in the case by Chandra et al. [1971]. Patil et al. [1981] suggested that the region q11→22 might be associated with the phenotype of the KS, but this was revised in the same year by Fryns. He described a case of a 30-year-old male with completely normal phenotype without gynecomastia and normal sexual development [Fryns, 1981]. Both testes were small and sperm analysis revealed azoospermia. According to the study, his testosterone and LH levels were normal but FSH levels were elevated. The karyotype was 47,XY,+del(Xp11). Buccal smear analysis showed a small Barr body in 20% of the cells.

In comparison, we can say that a terminal deletion of the X chromosome shows a nearly similar phenotype to ‘normal’ KS. Just the body height differs from the typical KS phenotype and is normal to slightly reduced in the patients. The only reported case of a del(Xp) differs from all the other cases and did not even show affinity to the cases with an additional isochromosome Xq.

Eleven cases of KS patients with a 47,XX,der(Y) karyotype were found, but only 7 of them were described in detail (table 3). As the individual cases differ greatly from each other, we must consider them separately.

The most recent case we found was reported in 2009. The group presented a case of an unborn boy with a 47,XX,mar(Y) karyotype [Sheth et al., 2009]. Using different FISH clones for the SRY gene and for the centromeric and the subtelomeric region of the Y chromosome they found the presence of a neocentric inv dup (Y)(pter→Yp11.2::Yp11.2→pter). Spinner et al. [2008] presented a case of a newborn infant with ovotesticular disorder of sex development and sex chromosome mosaicism. The karyotype was defined as 46,XXr(Y)[10]/46,XX[40]. The patient showed ambiguous genitalia and a micropenis. After an exploratory laparotomy the right gonad could be identified as an ovotestis and the left gonad as an undescended dysgenetic testis and a uterus lacking endothelial uterine glands. The r(Y) chromosome was transmitted via ICSI from the oligospermic but otherwise unremarkable father to the child. Apart from this article we found another one which described a case of an additional r(Y) chromosome [Weimer et al., 2006]. The patient showed signs of KS including gynecomastia, decreased body hair, hypergonadotropic hypogonadism, learning difficulties, an increased value of FSH, and a decreased value of testosterone. His sex development was male, consistent with the presence of the SRY locus on the r(Y) chromosome. At the age of 15 years, the boy presented with a mild overgrowth (182 cm), obesity (121 kg), and a slight outsized head circumference (59 cm). The karyotype was described as 48,XX,r(Y),+r(8)[68]/ 47,XX,+r(Y)[19]/47,XX,r(8)[6]/46,XX[8]. In 2006, a case of a 24-year-old man with a KS karyotype and an additional microdeletion on the Y chromosome was presented [Samli et al., 2006]. The man was infertile and showed abnormally high LH and FSH levels but a lower testosterone level than usual. The group found a deletion in the AZFa region on the Y chromosome. The phenotype of the patient did not differ from those of KS patients without microdeletions in this region. Microdeletions in AZFa are often associated with Sertoli-cell-only syndrome and azoospermia and with a frequency of 1–2% they are one of the most frequent reasons of spermatogenetic failure and infertility [Poongothai et al., 2009].

An interesting case about a 31-year-old male patient with an in part Klinefelter phenotype and an isodicentric Y-chromosome was reported by Heinritz et al. [2005]. The karyotype was indicated as 47,XX,+idic(Y)(q12). The man showed a tall stature, unproportionally long slender legs, a normal male body hair patterning, but slightly reduced growth of his facial hair, gynecomastia, genitalia with hypoplastic, soft testes, and a small penis. The behavior of the man was described as aggressive with rapid alterations of the mood and a naive and inappropriate social performance. The LH and FSH levels were increased, but testosterone levels were lower than normal [Heinritz et al., 2005]. Normally, psychological and behavioral problems like violence, aggressiveness, and a low IQ are the main features of males with 48,XXYY and are very untypical for KS patients [Heinritz et al., 2005]. In earlier studies, the presence of an additional Y chromosome, as in men with 47,XYY, was discussed to be related to personality problems and mainly a quick-tempered behavior, but the molecular basis for the behavioral anomalies in patients with structural rearrangements of the sex chromosomes is not fully understood [Heinritz et al., 2005].

Arnedo et al. [2005] reported a case of a transmitted SRY-positive ring Y chromosome from the father to his KS son. The frequency of ring chromosomes in clinically detected conceptions is 1:25,000 and has been reported for all human chromosomes [Arnedo et al., 2005]. In most of the cases a mosaic is presented and only ≤1% of all the ring chromosomes are inherited. In the study of Arnedo et al. [2005], the boy had a 47,XX,r(Y)/46,XX karyotype and his father a 46,X,r(Y)/45,X karyotype. All men with a r(Y) studied so far were infertile and also the father showed a moderate oligozoospermia (4.5 × 10⁶ sperm/ml) which could be explained by the arrest of the spermatocytes during meiosis [Arnedo et al., 2005]. However, his wife became pregnant by natural conception. Both the father and his son showed no phenotype abnormalities and their intelligence level was reported as normal. Because of the normal body height of the father the group suggested that the loss of genetic material implicated in ring Y formation may not have included the SHOX locus on Yp. Via microsatellite DNA markers the paternal origin of the additional X chromosome could also be detected. Further information like the hormonal status was not provided in the study.

In conclusion, most of the patients show some typical phenotype features of KS like small testes or increased FSH and LH levels. In one of the patients an increased aggressive and primitive behavior could be determined, whereas all other patients presented with normal behavior and intelligence levels despite from their aberration on the Y chromosome. A comparison of the cases is not possible because the rearrangements are located on diverse parts of the Y chromosome.

Sex reversal syndrome (SRS) is a human genetic disease, which is characterized by inconsistency between gonadal sexuality and chromosome sexuality and includes 46,XY females and 46,XX males [Wang et al., 2009]. The XX male SRS, also called de la Chapelle syndrome, was first characterized in 1972 [de la Chapelle, 1972]. With an incidence of 1:20,000–25,000 the syndrome is rare [Rajender et al., 2006]. Most XX men result from an abnormal X-Y interchange while spermatogenesis. During meiosis the human X and Y chromosomes pair in homologous regions named pseudoautosomal region 1 (PAR1) on Xp22.3 and Yp11.3 and pseudoautosomal region 2 (PAR2) on Xq28 and Yq12. PAR1 spans about 2.7 Mb and PAR2 about 0.33 Mb on each chromosome. A translocation of Y material, which includes the key sex-determining region (SRY) that is located centromeric to PAR1, to the X chromosome during paternal meiosis results in 46,XX males, with normal male sexual development [Ferguson-Smith, 1966; Rigola et al., 2002].

Individuals with 46,XX maleness can be classified as Y-positive or Y-negative according to the presence or absence of the SRY gene [Valetto et al., 2005]. Approximately 90% of the patients without ambiguous genitalia carry Y-derived material, particularly the SRY gene caused by an X/Y or Y/autosome rearrangement [Ramos et al., 1996]. In agreement most XX males with ambiguous genitalia are SRY negative [Ramos et al., 1996]. In XX individuals 1 of the 2 X chromosomes is inactivated in early embryonic development as a mechanism of dosage compensation for sex-linked genes [Sharp et al., 2005]. A skewed X inactivation was found in XX males with complete masculinization. Also, XX sex-reversed individuals with incomplete masculinization commonly show non-random inactivation, preferentially of the SRY-carrying X chromosome [Bouayed Abdelmoula et al., 2003]. Sharp et al. [2005] suggested that incomplete masculinization in cases of X/Y translocations is a result of abnormal SRY gene expression by a positional effect, rather than X chromosome inactivation.

While the clinical symptoms of XX male patients often show some degree of heterogeneity [Ergun-Longmire et al., 2005], usually, the development of genitalia is normal and masculinity signs are obvious in SRY gene-positive patients [Wang et al., 2009]. Development of the genitals and sex psychology was described to be normal as well as erection and ejaculation, and there are almost no significant signs except cryptorchidism before puberty in most of the patients [Wang et al., 2009]. In most of the cases the patients are found by chromosome analysis for the reason of infertility. The clinical and laboratory data on XX male patients are summarized in table 4.

Only 3 cases have been described in the literature about 46,XX men with SRY located on an autosomal chromosome [Dauwerse et al., 2006; Queralt et al., 2008; Chien et al., 2009]. It was postulated that the translocation between the SRY carrying Y chromosome and an autosomal chromosome was due to nonhomologous recombination between the autosomal chromosome and Ypter (containing SRY locus) during paternal meiosis [Queralt et al., 2008; Chien et al., 2009]. Regarding the phenotype there are no differences between the patients with the SRY gene on the X chromosome and the patients carrying the SRY gene on an autosomal chromosome.

On the contrary, SRY gene-negative patients can often be easily discriminated due to abnormality of genitalia shortly after birth. Some patients even show genital ambiguity [Ergun-Longmire et al., 2005] and belong to the group of true hermaphrodites and in some cases the patients have normal male genitalia in face of SRY-negative 46,XX karyotype [Rajender et al., 2006; Mustafa and Mehmet, 2010]. In many cases masculinity signs are not clear in SRY-negative patients. Mainly in adult patients, breast development and female secondary sex characteristics were found. Domenice et al. [2004] proposed that 90% of 46,XX males carried Y chromosome material including the SRY gene. There have been postulated 2 different theories for the remaining 10%: The first indicates that a structural gene that determines human gender could be located on an autosomal chromosome which is regulated by X chromosome inactivation and the activation of Y chromosome [Wang et al., 2009]. Due to defects in the X inactivation, which result in spontaneous activation of a downstream gene in the absence of SRY, 46,XX males could develop [Wang et al., 2009]. In previous studies, other genes in mouse and goat have been identified that lead, in the case of a mutation, to SRS. The corresponding homologs in human, FOXL2 (forkhead box L2) and WNT4 (wingless-type MMTV integration site family, member 4) were also mostly analyzed since these findings [Temel et al., 2007]. In different studies it was postulated that NR0B1 (nuclear receptor subfamily 0, group B, member 1), also known as DAX1 (dosage-sensitive sex reversal, adrenal hypoplasia congenital critical region on the X chromosome, gene 1) acts as an anti-testis gene by antagonizing SRY function and that this genemay be necessary for testis development and its effect seems to be dosage sensitive [Ergun-Longmire et al., 2005]. Domenice et al. [2004] analyzed mutations in the DAX1 and the WNT4 genes in sex-reversed patients and found out that the dosage of these genes was normal in their patients. With the help of these data, they proposed that the DAX1 and WNT4 are rarely involved in the etiology of male gonadal development in sex-reversed patients. This fact suggests the presence of other genes in the sex determination cascade.

The second hypothesis is about a SOX9 gene (SRY box-related gene 9) overexpression. It was suggested that this gene might function downstream to the SRY gene in the sex-determination pathway. Therefore, an upregulation of SOX9 expression caused by chromosomal abnormalities or mediated by other bypass activation mutations could lead to female-to-male sex reversal in 46,XX SRY-negative males [Dorsey et al., 2009; Wang et al., 2009].

Maciel-Guerra et al. [2008] identified in 2008 a case of XX maleness and XX true hermaphroditism in SRY-negative monozygotic twins, suggesting that these entities might represent pleomorphic manifestations of the same disorder of gonadal development. Rajender et al. [2006] also described an SRY-negative man with 46,XX karyotype who presented with normal genitalia. The group did not find a mutation in the coding region of the SOX9 and the DAX1 gene and no copy number variant in the SOX9 gene. In general, the reported patients with SRY-negative 46,XX karyotype have small or undescended testes [Valetto et al., 2005; Rajender et al., 2006; Temel et al., 2007; Dorsey et al., 2009] and in part additional ovarian tissue [Maciel-Guerra et al., 2008; Dorsey et al., 2009]. Most of the men have normal body hair and no gynecomastia. In that part they differ from the ‘normal’ KS patients. However, the hormone status shows the typically increased FSH and LH values and normal to decreased testosterone levels.

Searching in PubMed we found only 13 cases describing a female phenotype with a 47,XXY karyotype and one patient with a 47,XX+der(Y) karyotype. Seven of these cases have been diagnosed as suffering from androgen insensitivity (testicular feminization) syndrome resulting from mutations in the androgen receptor (AR) gene [German and Vesell, 1966; Bartsch-Sandhoff et al., 1976; Gerli et al., 1979; Müller et al., 1990; Uehara et al., 1999; Saavedra-Castillo et al., 2005; Girardin et al., 2009]. Only 3 cases are reported about women with an additional or at least parts of the Y chromosome. One report describes a mother and her daughter with a 47,XXY SRY-negative karyotype [Röttger et al., 2000] and the other a woman with a 47,XX+mar karyotype where the extra chromosome contained centromeric DNA derived from the Y chromosome [Causio et al., 2002]. In the other two 47,XXY female cases, the cause for their femaleness could not be clarified [Schmid et al., 1992; Thangaraj et al., 1998]. The clinical and laboratory data of the reported 47,XXY women are summarized in table 5.

The complete androgen insensitivity syndrome (CAIS) describes an X-linked disorder in which affected people have normal female external genitalia, female breast development, absence of the müllerian structures and abdominal or inguinal testes, despite a normal male karyotype. At puberty, female secondary sex characteristics like breasts develop, but menstruation and fertility do not. The prevalence of CAIS is estimated between 1 in 20,000–60,000 births [Girardin et al., 2009]. It is due to mutations in the AR gene, which is located on the X chromosome on Xq12 and may occur de novo or be inherited.

Normally, a defect resulting from a mutant AR allele on one X chromosome is masked by the effect of the normal allele on the other X chromosome [Uehara et al., 1999]. In 2009, two different hypotheses were suggested that could explain a CAIS phenotype in a 47,XXY individual. The first is that the homozygosity for the mutated AR gene implies either complete or partial maternal molecular identical material. The second hypothesis involves 2 different X chromosomes with 2 different AR alleles but with skewed X inactivation of the nonmutated X chromosome [Girardin et al., 2009].

The external genitalia like breast development or formation of the vagina differ in the reported cases. German and Vesell [1966] described monozygotic female twins with a 47,XXY karyotype and normal female external genitalia. However, Saavedra-Castillo et al. [2005] reported a woman with the same karyotype but hypoplasia of labial folds, clitoris, and vagina. Apart from that, the internal genitalia are nearly similar. All patients are characterized by the absence of the uterus and ovaries. Most of them have no wolffian and müllerian ducts but testes. Interestingly, in most of the described cases the testosterone levels were lower than expected in androgene insensitivity. This could be explained by testicular dysgenesis due to the 47,XXY karyotype. Just in one case the testosterone and LH levels were increased as expected in CAIS [Girardin et al., 2009]. The high FSH level likely reflects testicular dysgenesis in the context of the 47,XXY karyotype. Girardin et al. [2009] found a point mutation in the AR gene on both X chromosomes and Uehara et al. [1999] found 2 mutations in the AR gene in a 30-year-old woman with severely increased hormone levels. This can explain why CAIS occurred in this XXY patient. In the other cases the AR gene was not sequenced.

Röttger et al. [2000] reported the only 2 cases of women with an SRY-negative 47,XXY karyotype. They described these 47,XXY females resulting from an aberrant X-Y interchange with transfer of Xp material onto Yp, with concomitant loss of the SRY gene. The 2 patients are mother and daughter, which is very uncommon because normally XXY women are sterile. The data of Röttger et al. [2000] indicated that the Y chromosome in the mother and, by inference, in the daughter show a replacement of the Yp material that includes SRY and PRKY(protein kinase, Y-linked) by Xp material up to and including PRKX (protein kinase, X-linked). The absence of SRY explains the sex reversal in these two 47,XXY females. One X and the Y chromosome in the daughter were inherited from the mother. Her phenotype was not described. At her birth the daughter showed a female phenotype with normal external genitalia and bilateral clubbed feet. Two years later a patient was reported with a normal female karyotype but an additional marker chromosome, resembling an Y chromosome in size and QFQ-staining pattern [Causio et al., 2002]. The woman presented an apparently normal female habitus, with normal secondary sexual development. The extra chromosome contained centromeric regions of the Y. By means of sequence-tagged-sites PCR the absence of the SRY gene and the presence of the AZF genes could be defined. In none of 2 further reports the reason of the femaleness could be determined [Schmid et al., 1992; Thangaraj et al., 1998].

A comparison between the symptoms of a Klinefelter patient and a 47,XXY female is hardly possible because most of the KS symptoms also relate to a more feminine expression of certain body parts (e.g. gynecomastia). Symptoms like a tall stature, sparse body and pubic hair development, and elevated FSH and LH levels occur in most but not all of the described women. These characteristics are similar to those of KS.

Besides the 47,XXY karyotype, a less frequent group of KS patients have additional X and/or Y chromosomes and show karyotypes like 48,XXYY, 48,XXXY, or 49,XXXXY [Visootsak and Graham, 2009].

48,XXYY syndrome occurs in approximately 1:17,000–1:45,000 males [Borja-Santos et al., 2010]. The physical features have been described to be similar to 47,XXY but with some more pronounced phenotypic abnormalities. These are mild craniofacial dysmorphism, skeletal anomalies such as radioulnar synostosis and clinodactyly, lower IQ (typically between 70 and 80), significant developmental delays, and medical problems like neurological symptoms such as intention tremor, poor dentition, or reactive airway disease [Lenroot et al., 2009; Visootsak and Graham, 2009]. The behavior of the patients is described to be shy and reserved. It can include hyperactivity, attention problems, impulsivity, aggression, mood instability, ‘autistic-like’ behaviors, and poor social function [Lenroot et al., 2009; Visootsak and Graham, 2009]. In comparison to 47,XXY patients, men with 48,XXYY karyotype show a greater impairment in cognitive, verbal, and social functioning [Visootsak and Graham, 2009] and also the physical height is increased [Lenroot et al., 2009]. Tartaglia et al. [2008] reported a cohort of 95 subjects ranging from 1 to 55 years of age and having a 48,XXYY karyotype. 92% of the men showed speech/language delays and 100% received special education for learning disabilities. The group found common medical problems including allergies and asthma, congenital heart defects, radioulnar synostosis, inguinal hernia and/or cryptorchidism, and seizures in the patients [Tartaglia et al., 2008]. In the adulthood, medical features like hypogonadism, deep vein thrombosis, intention tremor, and type II diabetes were found [Tartaglia et al., 2008, 2009]. In the same year, Zhang and Li [2009] reported a case with 48,XXYY karyotype. They proposed the origin of this karyotype in a successive nondisjunction during paternal meiosis I and II. As the father of the patient was 56 years old, this case adds to the evidence that an age-related increase in sex chromosomal aneuploidies occurs in sperm.

The 48,XXXY karyotype is considered a variant of KS with features generally more pronounced than 47,XXY but less severe than 49,XXXXY and with an incidence of 1:17,000 to 1:50,000 in male births it is uncommon [Linden et al., 1995; Venkateshwari et al., 2010]. Affected males show a normal to tall stature with a decreased upper segment to lower segment ratio, hypertelorism and epicanthic folds, simplified ears and mild prognathism, skeletal anomalies including clinodactyly, abnormalities of the elbows and radioulnar synostosis, hypergonadotropic hypogonadism and testicular histology similar to 47,XXY and 48,XXYY, gynecomastia, and an abnormal glucose tolerance [Linden et al., 1995]. One fourth of these patients has a hypoplastic penis and is infertile [Linden et al., 1995]. In accordance with Zhang and Li [2009], the IQs of the patients range between 40 and 60, and a greater deficit in daily living skills, communication, and socialization in comparison to 48,XXYY cases could be detected [Visootsak et al., 2007]. Behavioral characteristics are immaturity, passivity, and irritability with temper tantrums [Visootsak and Graham, 2009]. Similarities to the 48,XXYY males are the activity level, the helpfulness, the pain tolerance, the morality, and the rejection based on the Reiss Personality Profile [Visootsak et al., 2007].

The rarest of the described variants in this review is the 49,XXXXY that shows an incidence of 1:85,000 to 1:100,000, and is in addition described to be the most severe variant of KS [Linden et al., 1995]. The extra X chromosomes in this variant accrue during maternal meiosis I and II and are the product of a double nondisjunction event [Simsek et al., 2009]. A correlation between maternal age and 49,XXXXY syndrome could not be detected in previous studies [Celik et al., 1997]. Clinical features of the syndrome are a coarse face with microcephaly, ocular hypertelorism, flat nasal bridge, upslanting palpebral fissures, bifid uvula and/or cleft palate, skeletal abnormalities including radioulnar synostosis, genu valgum, pes cavus, or clinodactyly, short stature with hypotonia, hyperextensible joints, and underdeveloped genitalia with hypergonadotropic hypogonadism [Visootsak et al., 2007]. The behavior of affected people is described as timid and shy to friendly, but the patients show a low frustration tolerance and so irritability and bout of temper can occur sometimes [Linden et al., 1995]. The IQs of the patients range between 20 to 60 points [Linden et al., 1995]. Therefore, mental retardation was long described to be a characteristic feature for the syndrome. However, recent studies have reported that cognitive delays were not as significant as described in the past and personalities and learning styles are similar to 47,XXY cases [Samango-Sprouse, 2001; Visootsak et al., 2001, 2007; Visootsak and Graham, 2006; Gropman et al., 2010]. Variability in clinical and cognitive functioning may reflect skewed X inactivation, mosaicism, or other factors that warrant further investigation [Gropman et al., 2010]. Recently, Ottesen et al. [2010] reported a study about the increased height in patients with additional sex chromosomes. In line with other reports [Bojesen and Gravholt, 2007; Tartaglia et al., 2008], they found an increased stature in subjects with 47,XXY, 47,XYY, or 48,XXYY karyotypes. In patients with a 49,XXXXY karyotype the stature was reduced and for that the group suggests a nonlinear effect of the number of sex chromosomes on height [Ottesen et al., 2010]. Altogether, the phenotypic features of 49,XXXXY patients share some characteristics with 47,XXY, but there are also other unique and distinctive traits.

In conclusion, the effects on physical and mental development increase with the number of extra X chromosomes, and each X reduces the overall IQ by 15–16 points, with language most affected [Polani, 1969]. In addition, it was found that height decreases and radioulnar synostosis becomes more frequent as the number of X chromosomes increases [Visootsak et al., 2007].