X­chromosome loss rescues Sertoli cell maturation and spermatogenesis in Klinefelter syndrome.

Klinefelter syndrome (47,XXY) causes infertility with a testicular histology comprising two types of Sertoli cell-only tubules, representing mature and immature-like Sertoli cells, and occasionally focal spermatogenesis. Here, we show that the immature-like Sertoli cells highly expressed XIST and had two X-chromosomes, while the mature Sertoli cells lacked XIST expression and had only one X-chromosome. Sertoli cells supporting focal spermatogenesis also lacked XIST expression and the additional X-chromosome, while the spermatogonia expressed XIST despite having only one X-chromosome. XIST was expressed in Sertoli cells until puberty, where a gradual loss was observed. Our results suggest that a micro-mosaic loss of the additional X-chromosome is needed for Sertoli cells to mature and to allow focal spermatogenesis.

Age, Sperm Retrieval, and Testicular Histology in Klinefelter Syndrome.

PURPOSE: We sought to examine sperm retrieval and testicular histology in males of different ages with Klinefelter syndrome. MATERIALS AND METHODS: We identified all males with Klinefelter syndrome who underwent microdissection testicular sperm extraction at our institution from 1995 to 2020. Patients were divided into adolescent (<20 years) and adult (≥20 years) cohorts. Histology and sperm retrieval were compared using chi-square statistics. Multivariable logistic regression models were used to examine factors associated with successful sperm retrieval. RESULTS: We identified 217 males with Klinefelter syndrome, of whom 59 were adolescents and 158 were adults. Adults were stratified into 10-year groupings (20-29 years, n = 62; 30-39 years, n = 88; ≥40 years, n = 8). Approximately 17% of adolescents had testis histology containing germ cells compared with 15% of the 20 to 29-year cohort, 14% of the 30 to 39-year cohort, and 0% over 40 years. In comparison to adolescents (53%), the sperm retrieval rate was significantly higher in the 20 to 29-year cohort (71%, P = .04) and lower in the ≥40-year cohort (13%, P = .03). In multivariable analysis, the presence of hypospermatogenesis on testis biopsy (OR 5.8, P = .03) was associated with higher odds of successful sperm retrieval. CONCLUSIONS: Younger males more frequently had germ cell-containing testis histology, however this finding was not associated with a higher odds of sperm retrieval. Reproductive urologists should counsel azoospermic males with Klinefelter syndrome that sperm retrieval during adolescence for fertility preservation is not required and can be performed in young adulthood.

The Klinefelter Syndrome and Testicular Sperm Retrieval Outcomes.

Klinefelter syndrome (KS), caused by the presence of an extra X chromosome, is the most prevalent chromosomal sexual anomaly, with an estimated incidence of 1:500/1000 per male live birth (karyotype 47,XXY). High stature, tiny testicles, small penis, gynecomastia, feminine body proportions and hair, visceral obesity, and testicular failure are all symptoms of KS. Endocrine (osteoporosis, obesity, diabetes), musculoskeletal, cardiovascular, autoimmune disorders, cancer, neurocognitive disabilities, and infertility are also outcomes of KS. Causal theories are discussed in addition to hormonal characteristics and testicular histology. The retrieval of spermatozoa from the testicles for subsequent use in assisted reproduction treatments is discussed in the final sections. Despite testicular atrophy, reproductive treatments allow excellent results, with rates of 40-60% of spermatozoa recovery, 60% of clinical pregnancy, and 50% of newborns. This is followed by a review on the predictive factors for successful sperm retrieval. The risks of passing on the genetic defect to children are also discussed. Although the risk is low (0.63%) when compared to the general population (0.5-1%), patients should be informed about embryo selection through pre-implantation genetic testing (avoids clinical termination of pregnancy). Finally, readers are directed to a number of reviews where they can enhance their understanding of comprehensive diagnosis, clinical care, and fertility preservation.

[Clinicopathological characteristics of Klinefelter syndrome: a testicular biopsy analysis of 87 cases].

Objective: To investigate the clinicopathological characteristics of testicular biopsies from Klinefelter syndrome (KS) patients. Methods: The testicular biopsy specimens of 87 patients with KS (a total of 107 biopsy specimens) were collected from the Department of Pathology, Peking University Third Hospital, Beijing, China from January 2017 to July 2022. All patients were diagnosed as KS by peripheral blood karyotyping analysis. The testicular histopathologic features, testicular volume and hormone levels were evaluated retrospectively. The histopathologic analysis was used to assess the quantity and morphology of Leydig cells, the spermatogenic state of seminiferous tubules, the thickening of the basement membrane of seminiferous tubules and the changes of stroma. Results: Leydig cell proliferative nodules were seen in 95.3% (102/107) of KS testicular biopsy tissues. The eosinophilic inclusion bodies and lipofuscin in Leydig cells were found in 52.3% (56/107) and 57.9% (62/107) of specimens, respectively. The Sertoli cell only seminiferous tubules and the hyalinized tubules were found in 66.4% (71/107) and 76.6% (82/107) of the examined tissues, respectively. The tubules with complete spermatogenic arrest were found in 15.9% (17/107) of specimens, and 5.6% (6/107) of the specimens showed low spermatogenesis or incomplete spermatogenic arrest. In 85.0% (91/107) of the specimens, increased thick-walled small vessels with hyaline degeneration were identified. Conclusions: The most common features of KS testicular specimens are Leydig cell proliferative nodules, hyaline degeneration of seminiferous tubules and proliferation of thick-walled blood vessels. Testicular biopsy specimens of KS are rare. The pathologists can make a tentative diagnosis of KS based on the histological findings, combined with the ultrasound and laboratory results, which is helpful for further diagnosis and treatment of KS.

Testicular Architecture of Men with 46,XX Testicular Disorders of Sex Development.

BACKGROUND: A subtype of disorders of sex development (DSD) in individuals with a 46,XX karyotype who are phenotypically male is classified as testicular DSD (46,XX TDSD). These individuals develop testes but are infertile due to germ cell loss. However, little is known about their testicular architecture. METHODS: We analyzed biopsies of four SRY positive 46,XX TDSD men for testicular architecture, Sertoli (SCs) and Leydig cells (LCs). These were compared with biopsies of men with normal spermatogenesis (NS, n = 4), men with Klinefelter syndrome, 47 XXY (KS, n = 4), and men with AZF deletions (AZF, n = 5). Testicular architecture was evaluated and SCs and LCs were analyzed for specific markers (SC: SOX9, DMRT1; LC: INSL3). RESULTS: A smaller number of tubules, more SOX9-negative but similar proportions of DMRT1-negative SCs were found in 46,XX TDSD compared to NS. The lower number of tubules and severe LC hyperplasia observed in 46,XX TDSD were similar to KS. CONCLUSION: Testicular architecture and marker expression of SCs and LCs in 46,XX TDSD men display unique patterns, which are discernable from chromosomal aneuploidies. Given the reduced Y-chromosomal gene content in 46,XX TDSD, the supernumerary X chromosome effects may be decisive regarding the damage on testicular composition and endocrine function.

A dual-center study of predictive factors for sperm retrieval through microdissection testicular sperm extraction and intracytoplasmic sperm injection outcomes in men with non-mosaic Klinefelter syndrome.

PURPOSE: This study evaluated the predictors of sperm retrieval (SR) in non-mosaic Klinefelter syndrome (KS) patients undergoing microsurgical testicular sperm extraction (mTESE). The cutoff values of the predictors of SR and overall pregnancy rates after intracytoplasmic sperm injection (ICSI) were analyzed for the positive SR (PSR) cases. MATERIALS AND METHODS: The study was a dual-center retrospective study. Overall 118 patients with KS underwent mTESE between January 2011 and July 2021. Clinicopathological factors including comorbidities, endocrine profiles, and testicular volumes were analyzed. RESULTS: A total of 58 patients showed PSR (49.2%) and 60 patients (50.8%) had negative SR (NSR). The mean overall age of the patients was 32.5 years. The NSR patients had a significantly greater prevalence of obesity, diabetes mellitus, and cerebrovascular disease. The PSR group had a significantly higher left testis mean volume (p=0.039). The differences between the two study groups regarding follicular-stimulating hormone, luteinizing hormone, and testosterone variations at 1 and 3 months after mTESE were insignificant. Preoperative mean neutrophil-to-lymphocyte ratio was significantly greater in the NSR group (p=0.011), but the platelet-to-lymphocyte ratio showed no significant difference between the two study groups. A live child birth was achieved in 53.4% of the PSR patients. Multivariate logistic analysis showed that total testicular volume >3.93 mL, left testis volume >1.79 mL, and neutrophil-to-lymphocyte ratio ≤1.82 were significantly associated with PSR. CONCLUSIONS: mTESE-ICSI is a feasible method for KS patients to have a child, and total testicular volume, left testis volume, and neutrophil-to-lymphocyte ratio might be predictors of successful SR.

Transcriptomic differences between fibrotic and non-fibrotic testicular tissue reveal possible key players in Klinefelter syndrome-related testicular fibrosis.

Klinefelter syndrome (KS; 47,XXY) affects 1-2 in 1000 males. Most men with KS suffer from an early germ cell loss and testicular fibrosis from puberty onwards. Mechanisms responsible for these processes remain unknown. Previous genomics studies on testis tissue from men with KS focused on germ cell loss, while a transcriptomic analysis focused on testicular fibrosis has not yet been performed. This study aimed to identify factors involved in the fibrotic remodelling of KS testes by analysing the transcriptome of fibrotic and non-fibrotic testicular tissue. RNA sequencing was performed to compare the genes expressed in testicular samples with (KS and testis atrophy) and without (Sertoli cell-only syndrome and fertile controls) fibrosis (n = 5, each). Additionally, differentially expressed genes (DEGs) between KS and testis atrophy samples were studied to reveal KS-specific fibrotic genes. DEGs were considered significant when p < 0.01 and log2FC > 2. Next, downstream analyses (GO and KEGG) were performed. Lastly, RNA in situ hybridization was performed to validate the results. The first analysis (fibrotic vs non-fibrotic) resulted in 734 significant DEGs (167 up- and 567 down-regulated). Genes involved in the extracellular structure organization (e.g. VCAM1) were found up-regulated. KEGG analysis showed an up-regulation of genes involved in the TGF-ß pathway. The KS vs testis atrophy analysis resulted in 539 significant DEGs (59 up- and 480 down-regulated). Chronic inflammatory response genes were found up-regulated. The overlap of X-linked DEGs from the two analyses revealed three genes: matrix-remodelling associated 5 (MXRA5), doublecortin (DCX) and variable charge X-Linked 3B (VCX3B). RNA in situ hybridization showed an overexpression of VCAM1, MXRA5 and DCX within the fibrotic group compared with the non-fibrotic group. To summarize, this study revealed DEGs between fibrotic and non-fibrotic testis tissue, including VCAM1. In addition, X-linked fibrotic genes were revealed, e.g. MXRA5, DCX and VCX3B. Their potential role in KS-related testicular fibrosis needs further study.

Testicular biopsy for fertility preservation in early-diagnosed Klinefelter patients: patient characteristics and long-term follow-up.

RESEARCH QUESTION: Which early-diagnosed Klinefelter syndrome patients have been offered cryopreservation of testicular tissue as part of fertility preservation before spermatogonial stem cell (SSC) loss? Do these Klinefelter syndrome patients present with behavioural, cognitive and/or psychological problems? Does a testicular biopsy procedure have long-term effects on the gonadal development of Klinefelter syndrome patients? DESIGN: Early-diagnosed Klinefelter syndrome patients followed between 2009 and 2020 and offered testicular tissue banking in an experimental context at the Universitair Ziekenhuis Brussel were included. The prevalence of behavioural, cognitive and/or psychological problems was determined. Changes in testicular volume and in gonadal function (LH, FSH, testosterone and inhibin B [INHB]) were studied. RESULTS: Of the 48 Klinefelter syndrome patients included, 22 had testicular tissue removed (biopsy group) and 26 had no surgical intervention (control group). The need for specialized education was significantly higher in prenatally (P = 0.0159) and prepubertally (P = 0.0002) diagnosed Klinefelter syndrome patients. Psychological problems were significantly more prevalent in Klinefelter syndrome patients who did not opt for fertility preservation (P = 0.0447). In the first 4.2 (1.9-9.1) years after testicular biopsy, no difference in testicular volume was observed between the biopsied and the contralateral non-biopsied testes (P > 0.9999). After pubertal onset, no differences in LH, FSH, testosterone and INHB were found between the biopsy and the control groups (P = 0.1324 for LH, P > 0.9999 for FSH, P = 0.5433 for testosterone, P > 0.9999 for INHB). CONCLUSION: Early-diagnosed Klinefelter syndrome patients presented with behavioural, cognitive and/or psychological problems. Only psychological problems seemed to influence the decision towards fertility preservation. Follow-up data confirm that harvesting testicular tissue does not have a long-term impact on the gonadal development of Klinefelter syndrome patients.

Intratesticular xenografting of Klinefelter pre-pubertal testis tissue as potential model to study testicular fibrosis.

RESEARCH QUESTION: Is intratesticular xenotransplantation a potential ex-vivo model for studying testicular fibrosis related to Klinefelter syndrome? STUDY DESIGN: First, a feasibility study of an ex-vivo model to study testicular fibrosis in patients with Klinefelter syndrome was performed. Testis tissue from boys with pre-pubertal Klinefelter syndrome (n = 3) and controls (n = 2) (<18 years) was grafted to the mouse testis (n = 12) and recovered after 2, 4, 6 and 8 weeks. Part two of this study consisted of a validation of this model, evaluating the effects of the mast cell blocker ketotifen on the histology of the grafts of Klinefelter syndrome (n = 5) and controls (n = 3), transplanted to mice (n = 10), after 4 weeks of ketotifen or saline treatment. Immunohistochemistry determined the histology of the grafts and the presence of mast cells and spermatogonia. RESULTS: The feasibility study showed that 4 weeks after transplantation, all Klinefelter syndrome grafts could be recovered. Later, degeneration was observed. Most recovered grafts showed an intact histology, with 67 ± 12% intact tubules for the Klinefelter syndrome grafts and 65 ± 15% of intact tubules for the control grafts. In the few remaining Klinefelter syndrome grafts, treatment with ketotifen improved testicular histology compared with non-treated grafts. Graft survival was patient dependent. No germ cell loss was observed after transplantation. CONCLUSION: Xenografting could become a model for the longitudinal study of the fibrotic process related to Klinefelter syndrome; however, the current model has a limited survival period and patient-specific differences in histology.

Z-scores for comparative analyses of spermatogonial numbers throughout human development.

OBJECTIVE: To normalize age-dependent effects on standardized measures of spermatogonial quantity such as the number of spermatogonia per tubular cross-section (S/T) or fertility index. DESIGN: Published quantitative histologic data on human spermatogonial numbers were used to create Z-scores for reference means and tested on archived testicular tissue samples. SETTING: Retrospective cohort study. PATIENT(S): The sample cohort comprised testicular samples from 24 boys with cancer diagnosis and 10 with Klinefelter syndrome, as part of the fertility preservation programs NORDFERTIL and Androprotect, as well as archived histologic samples from 35 prepubertal boys with acute lymphoblastic leukemia and 20 testicular biobank samples. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Z-score values for S/T and fertility index on the basis of morphology and germ cell-specific markers (MAGEA4 and/or DDX4) were calculated, and the impact of cancer therapy exposure and genetic disorders on Z-score values was evaluated. RESULT(S): The Z-scores for S/T values in the nontreated samples (-2.08 ± 2.20, n = 28) and samples treated with nonalkylating agents (-1.90 ± 2.60, n = 25) were comparable within ±3 standard deviations of the reference mean value but differed significantly from samples exposed to alkylating agents (-12.14 ± 9.20, n = 22) and from patients with Klinefelter syndrome (-11.56 ± 4.89, n = 8). The Z-scores for S/T were correlated with increasing cumulative exposure to alkylating agents (r = -0.7020). CONCLUSION(S): The Z-score values for S/T allow for the quantification of genetic and cancer treatment-related effects on testicular tissue stored for fertility preservation, facilitating their use for patient counseling.

The contribution of Xp22.31 gene dosage to Turner and Klinefelter syndromes and sex-biased phenotypes.

Turner syndrome (TS) is a rare developmental condition in females caused by complete, or partial, loss of the second sex chromosome; it is associated with a number of phenotypes including short stature, ovarian failure and infertility, as well as neurobehavioural and cognitive manifestations. In contrast, Klinefelter syndrome (KS) arises from an excess of X chromosome material in males (typical karyotype is 47,XXY); like TS, KS is associated with infertility and hormonal imbalance, and behavioural/neurocognitive differences from gonadal sex-matched counterparts. Lower dosage of genes that escape X-inactivation may partially explain TS phenotypes, whilst overdosage of these genes may contribute towards KS-related symptoms. Here, I discuss new findings from individuals with deletions or duplications limited to Xp22.31 (a region escaping X-inactivation), and consider the extent to which altered gene dosage within this small interval (and of the steroid sulfatase (STS) gene in particular) may influence the phenotypic profiles of TS and KS. The expression of X-escapees can be higher in female than male tissues; I conclude by considering how lower Xp22.31 gene dosage in males may increase their likelihood of exhibiting particular phenotypes relative to females. Understanding the genetic contribution to specific phenotypes in rare disorders such as TS and KS, and to more common sex-biased phenotypes, will be important for developing more effective, and more personalised, therapeutic approaches.

Central hypogonadism in Klinefelter syndrome: report of two cases and review of the literature.

PURPOSE: Klinefelter syndrome (KS) is characterized by late adolescence/young adulthood onset of primary hypogonadism. Hypogonadotropic hypogonadism (HH), when congenital, is usually associated with absent/incomplete puberty and low/normal gonadotropins. We report the clinical and genetic features of two subjects with KS and an unexpected HH hormone profile. METHODS: Magnetic resonance imaging (MRI) of hypothalamus-pituitary region and next generation sequencing (NGS) of congenital HH-associated genes were obtained. A narrative review of the literature was conducted. RESULTS: Patients were diagnosed with Klinefelter syndrome following karyotype analysis. Nevertheless, they showed unusual features: both had incomplete puberty, low gonadotropins and testosterone levels, and the first one was anosmic. Sellar lesions were excluded by MRI, and NGS was negative in both subjects. Our data add to those of the only 14 similar cases reported so far. Unexplained HH rarely occurs in KS and is variably associated with anosmia, other pituitary hormones deficiencies and heterogeneous karyotypes. However, most cases show an early, pre-pubertal onset of hypogonadism. If the causes behind this gonadotropins defect are largely unknown, hereby we provide the first review of the literature on this topic and propose some pathogenetic hypotheses, including the coexistence of KS and congenital HH as suggested by overlapping clinical features in some of these patients. CONCLUSION: HH is an exceptional occurrence in Klinefelter syndrome and is associated with heterogeneous phenotypes and, probably, aetiologies. Moreover, KS could underlie HH nonresponsive to gonadotropins. An exhaustive diagnostic workup and a tailored clinical management are advisable in these rare forms.

Genital malformation: Trigger of the diagnosis of severe variants of Klinefelter syndrome. / Malformación genital: Disparador del diagnóstico de variantes severas de síndrome de Klinefelter.

INTRODUCTION: Among the disorders of sexual development, Klinefelter syndrome and its variants are classified as an alteration in the number of sex chromosomes. These patients show signs of hypergonadotropic hypogonadism at puberty, however cases of severe variants also present neurocognitive and language problems from an early age. OBJECTIVE: To describe two patients with genital malformation with genetic diagnosis of severe variants of Klinefelter syndrome, and to review clinical and therapeutic aspects. CLINICAL CASES: Case 1: Diagnosis of atypical genitalia at birth: Small and curved phallus with the urethral meatus at scrotal level, and bifid scrotum. No other somatic abnormality was observed, except for subtle clinodactyly of the fifth finger. Karyotype: 49, XXXXY. At one year of life, genitalia were reconstructed. The patient presented a global developmental delay, mainly in language, which was managed with early stimulation and speech and language therapy since he was two months old. Finally, he was able to attend kindergarten. Case 2: At one month of life, a small and severe curved phallus (more than 70°) was observed, and testicles were in the scrotum. Karyotype: 48, XXYY. At one year of life, the penile malformation was corrected. The patient presented global developmental delay, mainly in expressive language which was managed with early stimulation since the age of four months, achieving kindergarten attendance. CONCLUSION: Genital malformations led to the diagno sis of severe variants of Klinefelter syndrome, and were corrected around the year of life. The early identification of these variants allowed the intervention of the neurostimulation team, favoring the neurocognitive development and social integration of these children.

Expression profile of microRNAs in the testes of patients with Klinefelter syndrome.

Klinefelter syndrome (KS) is the most common sex chromosome aneuploidy. A distinctive characteristic of KS is oligozoospermia. Despite multiple studies that have described the natural history of the degenerative process of germ cells in patients with KS, the molecular mechanisms that initiate this process are not well characterized. MicroRNA (miRNA)-mediated post-transcriptional control mechanisms have been increasingly recognized as important regulators of spermatogenesis; however, only a few studies have evaluated the role of miRNAs in the gonadal failure of these patients. Here, we describe a differential expression profile for the miRNAs in testicular tissue samples taken from KS patients. We analysed testicular tissue samples from 4 KS patients and 5 control patients (obstructive azoospermia) through next-generation sequencing, which can provide information about the mechanisms involved in the degeneration of germ cells. A distinctive differential expression profile was identified for 166 miRNAs in the KS patients: 66 were upregulated, and 100 were downregulated. An interactome analysis was performed for 7 of the upregulated and the 20 downregulated miRNAs. The results showed that the target genes are involved in the development, proliferation, and differentiation processes of spermatogenesis, which may explain their role in the development of infertility. This is the first report of a miRNA expression profile generated from testicular tissue samples of KS patients.

Epigenetics and genomics in Klinefelter syndrome.

Since the first description of Klinefelter syndrome (KS) was published in 1942 in The Journal of Clinical Endocrinology, large inter-individual variability in the phenotypic presentation has been demonstrated. However, our understanding of the global impact of the additional X chromosome on the genome remains an enigma. Evidence from the existing literature of KS indicates that not just one single genetic mechanism can explain the phenotype and the variable expressivity, but several mechanisms may be at play concurrently. In this review, we describe different genetic mechanisms and recent advances in the understanding of the genome, epigenome, and transcriptome of KS and the link to the phenotype and clinical heterogeneity. Future studies are needed to unite clinical data, genomic data, and basic research attempting to understand the genetics behind KS. Unraveling the genetics of KS will be of clinical relevance as it may enable the use of polygenic risk scores to predict future disease susceptibility and enable clinical risk stratification of KS patients in the future.

Minipuberty in Klinefelter syndrome: Current status and future directions.

Klinefelter syndrome is highly underdiagnosed and diagnosis is often delayed. With the introduction of non-invasive prenatal screening, the diagnostic pattern will require an updated description of the clinical and biochemical presentation of infants with Klinefelter syndrome. In the first months of life, the hypothalamic-pituitary-gonadal (HPG)-axis is transiently activated in healthy males during the so-called minipuberty. This period represents a "window of opportunity" for evaluation of the HPG-axis before puberty and without stimulation tests. Infants with Klinefelter syndrome present with a hormonal surge during the minipuberty. However, only a limited number of studies exist, and the results are contradictory. Further studies are needed to clarify whether infants with Klinefelter syndrome present with impaired testosterone production during the minipuberty. The aim of this review is to describe the clinical and biochemical characteristics of the neonate and infant with Klinefelter syndrome with special focus on the minipuberty and to update the clinical recommendations for Klinefelter syndrome during infancy.

The epidemiology of sex chromosome abnormalities.

Sex chromosome abnormalities (SCAs) are characterized by gain or loss of entire sex chromosomes or parts of sex chromosomes with the best-known syndromes being Turner syndrome, Klinefelter syndrome, 47,XXX syndrome, and 47,XYY syndrome. Since these syndromes were first described more than 60 years ago, several papers have reported on diseases and health related problems, neurocognitive deficits, and social challenges among affected persons. However, the generally increased comorbidity burden with specific comorbidity patterns within and across syndromes as well as early death of affected persons was not recognized until the last couple of decades, where population-based epidemiological studies were undertaken. Moreover, these epidemiological studies provided knowledge of an association between SCAs and a negatively reduced socioeconomic status in terms of education, income, retirement, cohabitation with a partner and parenthood. This review is on the aspects of epidemiology in Turner, Klinefelter, 47,XXX and 47,XYY syndrome.

Rare sex chromosome variation 48,XXYY: An integrative review.

While the most common Sex Chromosome Aneuploidy (SCA) is 47,XXY, other variations, such as 48,XXYY, are less studied, perhaps due to its rarity. 48,XXYY occurs with an estimated prevalence of 1:18,000-40,000 male births. This SCA is associated with a variety of complex physical, psychological, and neuroanatomical findings. The purpose of this integrative review is to summarize the available evidence related to 48,XXYY and identify gaps in the literature. This study utilized integrative review and PRISMA-guided methodology to search six databases for information pertaining to 48,XXYY. There were no exclusion criteria related to design methodology, given the paucity of available research. Among 397 articles reviewed for potential inclusion, 30 articles remained after inclusion and exclusion criteria were applied. Seven of these articles concentrated solely on participants with 48,XXYY. Literature was summarized into categories of physical phenotype, psychosocial, behavioral, neurocognitive, and brain function. Clinical description of 48,XXYY has evolved over time to develop a deeper understanding of this complex disorder. Large gaps remain, especially a lack of experimental studies, clinical guidelines, and treatments. Additionally, few studies explore methodologies such as interviews or self-report surveys in this population. 48,XXYY presents with a wide spectrum of physical, psychological, and neurocognitive symptoms, and frequently requires complex interdisciplinary care. In order to better understand this disorder and to appropriately treat the individuals affected by it, future research should focus on experimental studies and research that utilizes a variety of methods, including participant interviews and patient-report surveys.