Enzalutamide and olaparib synergistically suppress castration-resistant prostate cancer progression by promoting apoptosis through inhibiting nonhomologous end joining pathway / 亚洲男科学杂志(英文版)

Recent studies revealed the relationship among homologous recombination repair (HRR), androgen receptor (AR), and poly(adenosine diphosphate-ribose) polymerase (PARP); however, the synergy between anti-androgen enzalutamide (ENZ) and PARP inhibitor olaparib (OLA) remains unclear. Here, we showed that the synergistic effect of ENZ and OLA significantly reduced proliferation and induced apoptosis in AR-positive prostate cancer cell lines. Next-generation sequencing followed by Gene Ontology and Kyoto Encyclopedia of Genes and Genomes enrichment analyses revealed the significant effects of ENZ plus OLA on nonhomologous end joining (NHEJ) and apoptosis pathways. ENZ combined with OLA synergistically inhibited the NHEJ pathway by repressing DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and X-ray repair cross complementing 4 (XRCC4). Moreover, our data showed that ENZ could enhance the response of prostate cancer cells to the combination therapy by reversing the anti-apoptotic effect of OLA through the downregulation of anti-apoptotic gene insulin-like growth factor 1 receptor ( IGF1R ) and the upregulation of pro-apoptotic gene death-associated protein kinase 1 ( DAPK1 ). Collectively, our results suggested that ENZ combined with OLA can promote prostate cancer cell apoptosis by multiple pathways other than inducing HRR defects, providing evidence for the combined use of ENZ and OLA in prostate cancer regardless of HRR gene mutation status.

Scaffold protein MAPK8IP2 expression is a robust prognostic factor in prostate cancer associated with AR signaling activity / 亚洲男科学杂志(英文版)

Mitogen-activated protein kinase-8-interacting protein 2 (MAPK8IP2) is a scaffold protein that modulates MAPK signal cascades. Although MAPK pathways were heavily implicated in prostate cancer progression, the regulation of MAPK8IP2 expression in prostate cancer is not yet reported. We assessed MAPK8IP2 gene expression in prostate cancer related to disease progression and patient survival outcomes. MAPK8IP2 expression was analyzed using multiple genome-wide gene expression datasets derived from The Cancer Genome Atlas (TCGA) RNA-sequence project and complementary DNA (cDNA) microarrays. Multivariable Cox regressions and log-rank tests were used to analyze the overall survival outcome and progression-free interval. MAPK8IP2 protein expression was evaluated using the immunohistochemistry approach. The quantitative PCR and Western blot methods analyzed androgen-stimulated MAPK8IP2 expression in LNCaP cells. In primary prostate cancer tissues, MAPK8IP2 mRNA expression levels were significantly higher than those in the case-matched benign prostatic tissues. Increased MAPK8IP2 expression was strongly correlated with late tumor stages, lymph node invasion, residual tumors after surgery, higher Gleason scores, and preoperational serum prostate-specific antigen (PSA) levels. MAPK8IP2 upregulation was significantly associated with worse overall survival outcomes and progression-free intervals. In castration-resistant prostate cancers, MAPK8IP2 expression strongly correlated with androgen receptor (AR) signaling activity. In cell culture-based experiments, MAPK8IP2 expression was stimulated by androgens in AR-positive prostate cancer cells. However, MAPK8IP2 expression was blocked by AR antagonists only in androgen-sensitive LNCaP but not castration-resistant C4-2B and 22RV1 cells. These results indicate that MAPK8IP2 is a robust prognostic factor and therapeutic biomarker for prostate cancer. The potential role of MAPK8IP2 in the castration-resistant progression is under further investigation.

Integrative molecular characterization of Chinese prostate cancer specimens / 亚洲男科学杂志(英文版)

Prostate cancer (PCa) exhibits epidemiological and molecular heterogeneity. Despite extensive studies of its phenotypic and genetic properties in Western populations, its molecular basis is not clear in Chinese patients. To determine critical molecular characteristics and explore correlations between genomic markers and clinical parameters in Chinese populations, we applied an integrative genetic/transcriptomic assay that combines targeted next-generation sequencing and quantitative real-time PCR (qRT-PCR) on samples from 46 Chinese patients with PCa. Lysine (K)-specific methyltransferase 2D (KMT2D), zinc finger homeobox 3 (ZFHX3), A-kinase anchoring protein 9 (AKAP9), and GLI family zinc finger 1 (GLI1) were frequently mutated in our cohort. Moreover, a clinicopathological analysis showed that RB transcriptional corepressor 1 (RB1) deletion was common in patients with a high risk of disease progression. Remarkably, four genomic events, MYC proto-oncogene (MYC) amplification, RB1 deletion, APC regulator of WNT signaling pathway (APC) mutation or deletion, and cyclin-dependent kinase 12 (CDK12) mutation, were correlated with poor disease-free survival. In addition, a close link between KMT2D expression and the androgen receptor (AR) signaling pathway was observed both in our cohort and in The Cancer Genome Atlas Prostate Adenocarcinoma (TCGA-PRAD) data. In summary, our results demonstrate the feasibility and benefits of integrative molecular characterization of PCa samples in disease pathology research and personalized medicine.

Transcriptional repression by androgen receptor: roles in castration-resistant prostate cancer / 亚洲男科学杂志(英文版)

Androgen receptor (AR), a hormonal transcription factor, plays important roles during prostate cancer progression and is a key target for therapeutic interventions. While androgen-deprivation therapies are initially successful in regressing prostate tumors, the disease ultimately comes back as castration-resistant prostate cancer (CRPC) or at the late stage as neuroendocrine prostate cancer (NEPC). CRPC remains largely dependent on hyperactive AR signaling in the milieu of low androgen, while NEPC is negative of AR expression but positive of many AR-repressed genes. Recent technological advances in genome-wide analysis of transcription factor binding sites have revealed an unprecedented set of AR target genes. In addition to its well-known function in activating gene expression, AR is increasingly known to also act as a transcriptional repressor. Here, we review the molecular mechanisms by which AR represses gene expression. We also summarize AR-repressed genes that are aberrantly upregulated in CRPC and NEPC and represent promising targets for therapeutic intervention.

Phenotypic and molecular characteristics of androgen insensitivity syndrome patients / 亚洲男科学杂志(英文版)

Androgen insensitivity syndrome (AIS), an X-linked recessive genetic disorder of sex development, is caused by mutations in the androgen receptor (AR) gene, and is characterized by partial or complete inability of specific tissues to respond to androgens in individuals with the 46,XY karyotype. This study aimed to investigate AR gene mutations and to characterize genotype-phenotype correlations. Ten patients from unrelated families, aged 2-31 years, were recruited in the study. Based on karyotype, altered hormone profile, and clinical manifestations, nine patients were preliminarily diagnosed with complete AIS and one with partial AIS. Genetic analysis of AR gene revealed the existence of 10 different mutations, of which five were novel (c.2112 C>G[p.S704R], c.2290T>A[p.Y764N], c.2626C>T[p.Q876X], c.933dupC[p.K313Qfs*28], and c.1067delC[p.A356Efs*123]); the other five were previously reported (c.1789G>A[p.A597T], c.2566C>T[p.R856C], c.2668G>A[p.V890M], c.2679C>T[p.P893L], and c.1605C>G[p.Y535X]). Regarding the distribution of these mutations, 60.0% were clustered in the ligand-binding domain of AR gene. Exons 1 and 8 of AR gene each accounted for 30.0% (3/10) of all mutations. Most of the truncation mutations were in exon 1 and missense mutations were mainly located in exons 4-8. Our study expands the spectrum of AR gene mutations and confirms the usefulness of AR gene sequencing to support a diagnosis of AIS and to enable prenatal or antenatal screening.

Implicancias del polimorfismo de repeticiones de glutamina del receptor de andrógenos en la presentación de eventos peripuberales / Implications of androgen receptor gene glutamine repeat polymorphism in the presentation of peripubertal events

Puberty is a period of transition during which girls and boys acquire secondary sexual characteristics and reproductive capacity. The order of appearance of the pubertal traits accounts for a correct or otherwise incorrect activation of the hypothalamic-pituitary-gonadal axis. The growth of the pubic hair before 8 years in girls and 9 years in boys (precocious pubarche, PP) without any other apparent cause has been largely attributed to the early increase of adrenal androgen levels. Also, premature adrenarche (PA) was traditionally considered an extreme within the normal range, however emerging evidence links early androgen excess with the metabolic syndrome. In this context, it has been suggested that an exacerbated clinical manifestation of androgens may be related to greater sensitivity of the androgen receptor (AR). The purpose of this review is to summarize the current knowledge of the contribution of the CAG repeats polymorphisms of AR in the peripubertal manifestations of androgens with special emphasis on precocious pubarche and body composition

Analyzing gene expression profiles in dilated cardiomyopathy via bioinformatics methods

Dilated cardiomyopathy (DCM) is characterized by ventricular dilatation, and it is a common cause of heart failure and cardiac transplantation. This study aimed to explore potential DCM-related genes and their underlying regulatory mechanism using methods of bioinformatics. The gene expression profiles of GSE3586 were downloaded from Gene Expression Omnibus database, including 15 normal samples and 13 DCM samples. The differentially expressed genes (DEGs) were identified between normal and DCM samples using Limma package in R language. Pathway enrichment analysis of DEGs was then performed. Meanwhile, the potential transcription factors (TFs) and microRNAs (miRNAs) of these DEGs were predicted based on their binding sequences. In addition, DEGs were mapped to the cMap database to find the potential small molecule drugs. A total of 4777 genes were identified as DEGs by comparing gene expression profiles between DCM and control samples. DEGs were significantly enriched in 26 pathways, such as lymphocyte TarBase pathway and androgen receptor signaling pathway. Furthermore, potential TFs (SP1, LEF1, and NFAT) were identified, as well as potential miRNAs (miR-9, miR-200 family, and miR-30 family). Additionally, small molecules like isoflupredone and trihexyphenidyl were found to be potential therapeutic drugs for DCM. The identified DEGs (PRSS12 and FOXG1), potential TFs, as well as potential miRNAs, might be involved in DCM.

Clinical Characteristics and Genotype-Phenotype Correlation of Korean Patients with Spinal and Bulbar Muscular Atrophy

PURPOSE: Spinal and bulbar muscular atrophy (SBMA) is an X-linked motor neuron disease characterized by proximal muscle weakness, muscle atrophy, and fasciculation. Although SBMA is not uncommon in Korea, there is only one study reporting clinical characteristics and genotype-phenotype correlation in Korean patients. MATERIALS AND METHODS: In this study, age at the onset of symptoms, the score of severity assessed by impairment of activities of daily living milestones, and rate of disease progression, and their correlations with the number of CAG repeats in the androgen receptor (AR) gene, as well as possible correlations among clinical characteristics, were analyzed in 40 SBMA patients. RESULTS: The median ages at onset and at diagnosis were 44.5 and 52.5 years, respectively, and median interval between onset and diagnosis and median rate of disease progression were 5.0 years and 0.23 score/year, respectively. The median number of CAG repeats in the AR gene was 44 and the number of CAG repeats showed a significant inverse correlation with the age at onset of symptoms (r=-0.407, p=0.009). In addition, patients with early symptom onset had slower rate of disease progression. CONCLUSION: As a report with the largest and recent Korean cohort, this study demonstrates clinical features of Korean patients with SBMA and reaffirms the inverse correlation between the age at disease onset and the number of CAG repeats. Interestingly, this study shows a possibility that the rate of disease progression may be influenced by the age at onset of symptoms.

Effect of curcumin on the interaction between androgen receptor and Wnt/beta-catenin in LNCaP xenografts

PURPOSE: Curcumin is a nontoxic, chemopreventive agent possessing multifaceted functions. Our previous study showed that curcumin inhibits androgen receptor (AR) through modulation of Wnt/beta-catenin signaling in LNCaP cells. Therefore, we investigated the in vivo effects of curcumin by using LNCaP xenografts. MATERIALS AND METHODS: LNCaP cells were subcutaneously inoculated in Balb/c nude mice. When the tumor volume reached greater than 100 mm3, either curcumin (500 mg/kg body weight) or vehicle was administered through oral gavage three times weekly for 4 weeks. The expression of AR and intermediate products of Wnt/beta-catenin were assessed. RESULTS: Curcumin had an inhibitory effect on tumor growth during the early period, which was followed by a slow increase in growth over time. Tumor growth was delayed about 27% in the curcumin group. The mean prostate-specific antigen (PSA) doubling time in the curcumin group was approximately twice that in the untreated group. Curcumin significantly decreased AR expression at both the mRNA and protein level. The PSA levels tended to be reduced in the curcumin group. However, there were no significant changes in expression of Wnt/beta-catenin pathway intermediates. CONCLUSIONS: This study revealed that curcumin initially interferes with prostate cancer growth by inhibiting AR activity and possibly by reducing PSA expression. Further research is needed to investigate the plausible mechanism of the antiandrogenic action of curcumin.

Genetic analysis of a family with complete androgen insensitivity syndrome.

Androgen insensitivity causes impaired embryonic sex differentiation leading to developmental failure of normal male external genitalia in 46 XY genetic men. It results from diminished or absent biological actions of androgens, which is mediated by the androgen receptor (AR) in both the embryo and secondary sexual development. Mutations in the AR located on the X chromosome are responsible for the disease. Almost 70% of affected individuals inherit the mutation from their carrier mother. We hereby report a 10‑year‑old girl with all the characteristics of complete androgen insensitivity syndrome (CAIS). Similar scenario was observed in 3 maternal aunts, Sequencing of the AR gene in all the family members revealed C 2754 to T transition in exon 6. It was concluded that the C 2754 to T transition rendered the AR incapable of both ligand‑binding and activating the transcription and was the cause of CAIS in the patient.

Androgen receptor CAG polymorphism and the risk of benign prostatic hyperplasia in a Brazilian population

Benign prostatic hyperplasia (BPH) is a very frequent age-related proliferative abnormality in men. Polymorphic CAG repeat in the androgen receptor (AR) can alter transactivation of androgen-responsive genes and potentially influence BPH risk. We investigated the association between CAG repeat length and risk of BPH in a case-control study of a Brazilian population. We evaluated 214 patients; 126 with BPH and 88 healthy controls. DNA was extracted from peripheral leucocytes and the AR gene was analyzed using fragment analysis. Hazard ratio (HR) and 95% confidence interval were estimated using logistic regression models. Mean CAG length was not different between patients with BPH and controls. The CAG repeat length was examined as a categorical variable (CAG < 21 vs. CAG > 21 and CAG < 22 vs. CAG > 22) and did not differ between the control vs. the BPH group. We found no evidence for an association between AR CAG repeat length in BPH risk in a population-based sample of Brazilians.

Cáncer de próstata y apoptosis / Prostate Cancer and Apoptosis

El cáncer de próstata presenta una progresión andrógeno-dependiente mediada por el receptor de andrógeno (AR), por lo que el bloqueo androgénico es la terapia estándar para su tratamiento en estado avanzado. Sin embargo, a pesar de una sensibilidad inicial, estos cánceres usualmente evolucionan hacia un estado hormono-resistente. Esta resistencia puede ser debida a una amplificación del gen AR, a sus mutaciones y al aumento en la expresión de proteínas co-activadoras. Igualmente, el receptor AR puede permanecer activo, independientemente de la fijación del ligando por fosforilación de factores de crecimiento y de citosinas. Adicionalmente, hay otras posibles vías independientes del receptor AR, como lo ejemplifica la adquisición del fenotipo neuroendocrino. En esta revisión se examinan tanto los mecanismos moleculares involucrados en la progresión del cáncer de próstata así como la forma en que sus células evaden la apoptosis.

Prostate cancer presents an androgen-dependent growth mediated by the androgen receptor (AR). Androgen pathway blockage is the standard therapy for the treatment of prostate cancer at an advanced stage. In spite of an initial sensitivity, prostate cancer usually becomes refractory to hormone treatment. This resistance can be due to the amplification of the AR gene, AR mutations and the increase in co-activator protein expression. Likewise, growth factors and cytokines can induce AR phosphorylation, independently of ligand fixation. Moreover, there are other AR-independent pathways, such as the acquisition of the neuroendocrine phenotype. In this review, we examine the molecular mechanisms that are involved in the progression of prostate cancer, as well as the ways its cells evade apoptosis.

Absolute measurement of androgen receptor mRNA in peripheral blood mononuclear, preputial skin and urethral mucosa cells of control individuals with phimosis using qRT-PCR / Valor absoluto do mRNA do receptor androgênico em células mononucleares do sangue periférico e células da pele do prepúcio e mucosa uretral em indivíduos controle com fimose, determinado por meio de qRT-PCR

INTRODUCTION: Androgen actions are exerted upon the androgen receptor (AR), and complete genital virilization of normal 46,XY individuals depends on adequate function and expression of the AR gene in a tissue-specific manner. OBJECTIVE: Standardization of normal ARmRNA in androgen-sensitive tissues. MATERIALS AND METHODS: In this study, we determined the quantitative amounts of ARmRNA in peripheral blood mononuclear, urethral mucosa and preputial skin cells of control subjects with phimosis by using RT-PCR. RESULTS: The mean (SD) values of AR expression in blood, urethra and prepuce were: 0.01 (0.01); 0.43 (0.32); 0.31 (0.36), respectively. CONCLUSION: The AR expression is low in blood and equivalent in urethral mucosa and preputial skin, which may be useful in the diagnosis of individuals with abnormal external genitalia.

INTRODUÇÃO: As ações androgênicas são exercidas por meio do receptor androgênico (AR), e a completa virilização genital de indivíduos 46,XY normais depende de adequada expressão do gene AR de forma tecido específica. OBJETIVO: Padronizar valores normais de ARmRNA em tecidos sensíveis aos andrógenos. MATERIAIS E MÉTODOS: Neste estudo, determinamos as quantidades de ARmRNA em células mononucleares do sangue periférico e em células da mucosa uretral e pele do prepúcio de indivíduos controles com fimose, utilizando RT-PCR. RESULTADOS: A média (dp) dos valores de expressão do AR em sangue, uretra e prepúcio foram: 0,01 (0,01); 0,43 (0,32); 0,31 (0,36), respectivamente. CONCLUSÃO: A expressão do AR é baixa em sangue periférico e equivalente em mucosa uretral e pele prepucial, sendo sua quantificação útil no diagnóstico de indivíduos com alterações da genitália externa.

Clonality analysis of giant cell lesions of the jaws

Despite the importance of clonality to understand the pathogenesis and progression of tumors, it has not been investigated yet in giant cell lesions of the jaws. The aim of this study was to analyze the clonality of peripheral giant cell lesions (PGCL) and central giant cell lesions (CGCL) of the jaws. Six samples of PGCL and 5 samples of CGCL were analyzed in this study using the polymorphic human androgen receptor locus (HUMARA) assay. Three out of the 5 samples of the CGCL and 3 out of 6 samples of PGCL exhibited a monoclonal pattern. Our findings demonstrate that some giant cell lesions of the jaws are clonal, which indicate that these lesions may have a common genetic mechanism of development. Further studies are necessary to better elucidate the molecular mechanisms involved in the pathogenesis of such lesions.

Apesar da importância que a clonalidade das lesões tem para o entendimento da patogênese e progressão dos tumores, ainda não foi feita essa investigação em lesões de células gigantes dos maxilares. O objetivo desse trabalho foi analisar a natureza clonal de lesões periféricas de células gigantes (LPCG) e de lesões centrais de células gigantes (LCCG). Foram analisadas nesse estudo 6 amostras de LPCG e 5 amostras de LCCG, sendo todas elas provenientes de pacientes do sexo feminino. Para essa investigação foi utilizado o método baseado na região polimórfica do exon um do gene humano para oreceptor de andrógeno (HUMARA). Três das 5 amostras de LCCG e 3 das 6 amostras de LPCG exibiram um padrão monoclonal. Nossos resultados demonstram que algumas lesões de células gigantes dos maxilares apresentam uma natureza monoclonal indicando que essas lesões podem ter um mecanismo genético comum de desenvolvimento. Outros estudos são necessários para uma maior compreensão dos mecanismos moleculares envolvidos na patogênese dessas lesões.

Androgens and the male reproductive tract: an overview of classical roles and current perspectives: [review] / Androgênios e o trato reprodutor masculino: ações clássicas e perspectivas atuais: [revisão]

Androgens are steroid hormones that play key roles in the development and maintenance of male phenotype and reproductive function. These hormones also affect the function of several non-reproductive organs, such as bone and skeletal muscle. Endogenous androgens exert most of their effects by genomic mechanisms, which involve hormone binding to the androgen receptor (AR), a ligand-activated transcription factor, resulting in the modulation of gene expression. AR-induced non-genomic mechanisms have also been reported. A large number of steroidal and non-steroidal AR-ligands have been developed for therapeutic use, including the treatment of male hypogonadism (AR agonists) and prostate diseases (AR antagonists), among other pathological conditions. Here, the AR gene and protein structure, mechanism of action and AR gene homologous regulation were reviewed. The AR expression pattern, its in vivo regulation and physiological relevance in the developing and adult testis and epididymis, which are sites of sperm production and maturation, respectively, were also presented.

Os androgênios são hormônios esteroides com papel fundamental no desenvolvimento e na manutenção do fenótipo masculino e da função reprodutiva. Esses hormônios também afetam a função de diversos tecidos não reprodutivos, como, por exemplo, o ósseo e musculoesquelético. Os androgênios endógenos exercem a maioria de suas funções por mecanismo genômico, que envolve a ligação do hormônio ao receptor de androgênio (RA), um fator de transcrição ativado por ligante, o que resulta no controle da expressão gênica. Mecanismos não genômicos também têm sido associados aos efeitos induzidos pelo RA. Um grande número de ligantes do RA, esteroidais e não esteroidais, tem sido desenvolvido para o uso terapêutico, incluindo o tratamento do hipogonadismo masculino (agonistas do RA) e de doenças da próstata (antagonistas do RA), entre outras condições patológicas. Neste trabalho, foram discutidas as características estruturais básicas do RA (gene e proteína), os mecanismos de ação desse receptor, bem como aspectos relacionados à sua regulação homóloga. O padrão de expressão do RA, sua regulação in vivo e relevância fisiológica durante o desenvolvimento e a vida adulta na função do testículo e epidídimo, tecidos responsáveis pela produção e maturação de espermatozoides, respectivamente, também foram discutidos.

Cryptic mosaicism involving a second chromosome X in patients with Turner syndrome

The high abortion rate of 45,X embryos indicates that patients with Turner syndrome and 45,X karyotype could be mosaics, in at least one phase of embryo development or cellular lineage, due to the need for the other sex chromosome presence for conceptus to be compatible with life. In cases of structural chromosomal aberrations or hidden mosaicism, conventional cytogenetic techniques can be ineffective and molecular investigation is indicated. Two hundred and fifty patients with Turner syndrome stigmata were studied and 36 who had female genitalia and had been cytogenetically diagnosed as having "pure" 45,X karyotype were selected after 100 metaphases were analyzed in order to exclude mosaicism and the presence of genomic Y-specific sequences (SRY, TSPY, and DAZ) was excluded by PCR. Genomic DNA was extracted from peripheral blood and screened by the human androgen receptor (HUMARA) assay. The HUMARA gene has a polymorphic CAG repeat and, in the presence of a second chromosome with a different HUMARA allele, a second band will be amplified by PCR. Additionally, the CAG repeats contain two methylation-sensitive HpaII enzyme restriction sites, which can be used to verify skewed inactivation. Twenty-five percent (9/36) of the cases showed a cryptic mosaicism involving a second X and approximately 14 percent (5/36), or 55 percent (5/9) of the patients with cryptic mosaicism, also presented skewed inactivation. The laboratory identification of the second X chromosome and its inactivation pattern are important for the clinical management (hormone replacement therapy, and inclusion in an oocyte donation program) and prognostic counseling of patients with Turner syndrome.

Evaluación del patrón de inactivación del cromosoma X en portadoras sintomáticas y mujeres con hemofilia / Assessing the inactivation pattern in chromosome X among symptomatic carriers and women with haemophilia

La inactivación del cromosoma X es un fenómeno estocástico que ocurre en la embriogénesis temprana femenina para lograr una compensación de dosis génica respecto a los varones. Ciertos mecanismos genéticos afectan el proceso normal, propiciando una inactivación sesgada con efectos clínicos relevantes en portadoras de trastornos recesivos ligados al cromosoma X, como la hemofilia. La herramienta molecular mayormente utilizada para la evaluación del patrón de inactivación del cromosoma X es la amplificación por PCR del gen del receptor de andrógenos humano (HUMARA). El empleo de esta técnica en portadoras sintomáticas y mujeres con hemofilia permite esclarecer si las manifestaciones de la enfermedad se deben a una lyonización desfavorable. Estos estudios, además, son importantes para la comprensión del proceso de inactivación del cromosoma X en humanos.

X chromosome inactivation is a stochastic event that occurs early in female embryo development to achieve dosage compensation with males. Certain genetic mechanisms affect the normal process causing a skewed X inactivation pattern which has clinical relevance in female carriers of X-linked recessive disorders, like haemophilia. The most commonly used assay to evaluate the X inactivation pattern is the PCR amplification of the human androgen receptor gene (HUMARA). The use of this technique in bleeding carriers and women with haemophilia allows identifying if their hemorrhagic symptoms are due to an unfavourable lyonization. Furthermore, these studies are important for understanding the X chromosome inactivation process in humans.