Clinical Features of Female Taiwanese Carriers with X-linked Chronic Granulomatous Disease from 2004 to 2019

PURPOSE

Female carriers with X-linked chronic granulomatous disease (XL-CGD) who have < 10% reactive oxygen species (ROS) production due to profound X-chromosome inactivation (XCI or lyonization) are more susceptible to infections. We assessed ROS production in Taiwanese female carriers with XL-CGD to investigate whether the level of ROS correlated to their clinical features of infection, autoimmunity, and autoinflammation.

METHODS

Clinical course, ROS production, flavocytochrome b558 (Cyto b558) expression, and genetic analysis in carriers were investigated after identifying their index cases between 2004 and 2019.

RESULTS

A total of 19 mothers (median 27 years; range 25-60 years) and three of four girls (range 4-6 years) relative to 22 male index XL-CGD cases from 19 unrelated families were enrolled. Approximately half (8/19, 42%) of the mothers had novel one-allele mutations. Twenty-two of the 23 females were carriers. One carrier with de novo [Arg290X]CYBB who suffered from refractory salmonella sepsis and chorioretinitis as an XL-CGD phenotype had extreme XCI, absent Cyto b558 expression, and only 8% ROS production. The remaining carriers had bimodal patterns of Cyto b558 expressions (median 40.2%, 26.8-52.4%) and ROS production (38.3%, range 28.2-54.2%) sufficient to prevent significant infections, although neck lymphadenitis recurred in one mother and sister who had ROS expressions of 28.2% and 38.0%, respectively. However, none of the carriers had manifestations of autoimmunity or autoinflammation (e.g., photosensitivity, aphthous stomatitis, or joint disorders), of which each was seen in approximately one-third of XL-CGD carriers from the Western world.

CONCLUSION

One carrier had undetectable Cyto b558 expression and an extremely low ROS production, and consequently presented with an XL-CGD phenotype. One mother and her daughter experienced recurrent neck lymphadenitis despite having sufficient ROS production. Significant autoimmunity/autoinflammation did not develop in any of the carriers. Studies with a longer follow-up period are needed to validate our findings.

Glucose-6-phosphate dehydrogenase deficiency in the Han Chinese population: molecular characterization and genotype-phenotype association throughout an activity distribution

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is a common hereditary disorder in China. The existing prevalence and molecular epidemiology of G6PD deficiency in China were geographically limited. In this study, the spectrum of G6PD gene mutations was well characterized in a large and diverse population all over the country; and the correlation of genotype and enzyme activity phenotype was explored for the first time. The results showed that the overall prevalence of G6PD deficiency in China was 2.10% at the national level. The top six common mutations were c.1388 G>A, c.1376 G>T, c.95 A>G, c.392 G>T, c.871 G>A and c.1024 C>T, accounting for more than 90% of G6PD deficient alleles. Compound mutation patterns were frequently observed in females with severe deficiency. The distribution of G6PD activities depended on the type of mutation patterns and genders. Hemizygote, homozygote, and compound heterozygote were predominantly associated with severe G6PD deficiency, whereas heterozygotes with single mutation mainly presented moderate enzyme deficiency. A significant gap between G6PD activities in hemizygous and normal males was observed, and yet, the overall distribution of that in females carrying missense mutations was a continuum from G6PD severely deficient to normal. This is the first report of discussing the association between G6PD genetic variants in the Chinese and enzyme activity phenotypes.

60 Years of clonal hematopoiesis research: From X-chromosome inactivation studies to the identification of driver mutations

The history of clonal hematopoiesis (CH) research is punctuated by several seminal discoveries that have forged our understanding of cancer development. The clever application of the principle of random X-chromosome inactivation (XCI) in females led to the development of the first test to identify clonal derivation of cells. Initially limited by a low level of informativeness, the applicability of these assays expanded with differential methylation-based assays at highly polymorphic genes such as the human androgen receptor (HUMARA). Twenty years ago, the observation that skewing of XCI ratios increases as women age was the first clue that led to the identification of mutations in the TET2 gene in hematologically normal aging individuals. In 2014, large-scale genomic approaches of three cohorts allowed definition of CH, which was reported to increase the risk of developing hematologic cancers and cardiovascular diseases. These observations created a fertile field of investigation aimed at investigating the etiology and consequences of CH. The most frequently mutated genes in CH are DNMT3A, TET2, and ASXL1, which have a role in hematopoietic stem cell (HSC) development and self-renewal. These mutations confer a competitive advantage to the CH clones. However, the penetrance of CH is age dependent but incomplete, suggesting the influence of extrinsic factors. Recent data attribute a modest role to genetic predisposition, but several observations point to the impact of a pro-inflammatory milieu that advantages the mutated clones. CH may be a barometer of nonhealthy aging, and interventions devised at curbing its initiation or progression should be a research priority.

X-Linked Emery-Dreifuss Muscular Dystrophy: Study Of X-Chromosome Inactivation and Its Relation with Clinical Phenotypes in Female Carriers

X-linked Emery–Dreifuss muscular dystrophy (EDMD1) affects approximately 1:100,000 male births. Female carriers are usually asymptomatic but, in some cases, they may present clinical symptoms after age 50 at cardiac level, especially in the form of conduction tissue anomalies. The aim of this study was to evaluate the relation between heart involvement in symptomatic EDMD1 carriers and the X-chromosome inactivation (XCI) pattern. The XCI pattern was determined on the lymphocytes of 30 symptomatic and asymptomatic EDMD1 female carriers—25 familial and 5 sporadic cases—seeking genetic advice using the androgen receptor (AR) methylation-based assay. Carriers were subdivided according to whether they were above or below 50 years of age. A variance analysis was performed to compare the XCI pattern between symptomatic and asymptomatic carriers. The results show that 20% of EDMD1 carriers had cardiac symptoms, and that 50% of these were ≥50 years of age. The XCI pattern was similar in both symptomatic and asymptomatic carriers. Conclusions: Arrhythmias in EDMD1 carriers poorly correlate on lymphocytes to a skewed XCI, probably due to (a) the different embryological origin of cardiac conduction tissue compared to lymphocytes or (b) the preferential loss of atrial cells replaced by fibrous tissue.

Development of canine X-chromosome inactivation pattern analysis for the detection of cell clonality by incorporating the examination of the SLIT and NTRK-like family member 4 (SLITRK4) gene

X-chromosome inactivation pattern (XCIP) analysis can be used to assess the clonality of cell populations of various origin by distinguishing the methylated X chromosome from the unmethylated X chromosome. In this study, the utility of XCIP analysis was improved by incorporating the examination of AC dinucleotide repeats in SLIT and NTRK-like family member 4 (SLITRK4) gene into the previously reported CAG repeat examination of androgen receptor (AR) gene in dogs. The rate of heterozygosity when both genes were analysed (125/150, 83.3%) was higher than AR gene examination alone (86/150, 57.3%). Blood samples from heterozygous dogs in either AC-1 or AC-2 of SLITRK4 gene were examined for the corrected inactivation allele ratio (CIAR), resulting in the determination of a reference range of CIAR <3.8 in non-neoplastic cell/tissue samples. Using this analytical method, 49% (21/43) of neoplastic tissue samples from dogs showed a CIAR >3.8, indicating the presence of a clonal population. Through the present study, the availability of canine XCIP analysis was improved by incorporating the examination of the SLITRK4 gene, providing a highly useful laboratory examination system for the detection of the clonality of various cell/tissue samples in dogs.

Investigation of the clonal origin of multifocal papillary thyroid carcinoma according to the X-chromosome inactivation pattern

Patients with papillary thyroid carcinoma (PTC) usually have multiple tumors, or foci. It remains unclear if these foci originate from independent tumors or a single tumor mass. The present study included 89 female patients with bilateral PTC who had been treated with a total thyroidectomy. An X-chromosome inactivation assay was used to examine the clonal origin of the tumors according to the status of the X-linked human androgen receptor gene. Of the 89 patients, 5 were informative. The X-chromosome inactivation pattern was the same in multiple foci in 3 cases, indicating a monoclonal origin of the tumors. In 1 case, the X chromosome inactivation pattern was different between the tumors. Mixed patterns were observed in 1 case. The results of the present study suggest that in certain cases of multifocal PTC, tumors arise independently, whereas in other cases, separate foci are the outcome of intra-thyroid spread by a single tumor mass.

Sex Chromosome Effects on Male-Female Differences in Mammals

Fundamental differences exist between males and females, encompassing anatomy, physiology, behaviour, and genetics. Such differences undoubtedly play a part in the well documented, yet poorly understood, disparity in disease susceptibility between the sexes. Although traditionally attributed to gonadal sex hormone effects, recent work has begun to shed more light on the contribution of genetics - and in particular the sex chromosomes - to these sexual dimorphisms. Here, we explore the accumulating evidence for a significant genetic component to mammalian sexual dimorphism through the paradigm of sex chromosome evolution. The differences between the extant X and Y chromosomes, at both a sequence and regulatory level, arose across 166 million years. A functional result of these differences is cell autonomous sexual dimorphism. By understanding the process that changed a pair of homologous ancestral autosomes into the extant mammalian X and Y, we believe it easier to consider the mechanisms that may contribute to hormone-independent male-female differences. We highlight key roles for genes with homologues present on both sex chromosomes, where the X-linked copy escapes X chromosome inactivation. Finally, we summarise current experimental paradigms and suggest areas for developments to further increase our understanding of cell autonomous sexual dimorphism in the context of health and disease.

A vicious interplay between genetic and environmental insults in the etiology of blood cancers

Over the years, the etiology of cancer has been attributed alternatively to genetic and environmental insults. According to the genetic hypothesis, cancer cells arise from the acquisition of mutations that dysregulate the intrinsic mechanisms controlling normal cell growth and survival. In contrast, the environmental hypothesis holds that cancer can be caused by multiple extrinsic challenges that alter normal tissue homeostasis, but may not necessarily involve mutations. It is, however, quite possible that these two mechanisms are not mutually exclusive. According to this third hypothesis, environmental challenges, by mechanisms still poorly understood, may act by imposing a selection pressure that confers a proliferative advantage on cells carrying specific driver mutations, leading to disease initiation. The authors of a brief report published in this journal (Exp Hematol. 2017;56:1-6) tested this third hypothesis experimentally and provide new evidence that chronic inflammation, by increasing tumor necrosis factor (TNF)-α, may positively select malignant hematopoietic stem cells (HSCs) carrying loss-of-function TET2 mutations that switch the TNF-α signaling responses to activate proliferation rather than inducing quiescence. Furthermore, these mutations skew hematopoietic differentiation toward the myelomonocytic lineage and the output of macrophages producing TNF-α constitutively, promoting further environment-independent expansion of the malignant HSCs. These findings support a model in which the formation of a malignant population is triggered by a vicious interplay between genetic (TET2 mutations) and environmental (inflammation) insults, suggesting the need for strategies that target both the malignant cells and their environment.

Age-associated changes in human hematopoietic stem cells

Aging has a broad impact on the function of the human hematopoietic system. This review will focus primarily on the effect of aging on the human hematopoietic stem cell (HSC) population. With age, even though human HSCs increase in number, they have decreased self-renewal capacity and reconstitution potential upon transplantation. As a population, human HSCs become more myeloid-biased in their differentiation potential. This is likely due to the human HSC population becoming more clonal with age, selecting for myeloid-biased HSC clones. The HSC clones that come to predominate with age may also contain disease-causing genetic and epigenetic changes that confer an increased risk of developing into an age-associated clonal hematopoietic disease, such as myelodysplastic syndrome, myeloproliferative disorders, or leukemia. The selection of these aged human HSC clones may be in part due to changes in the aging bone marrow microenvironment. While there have been significant advances in the understanding of the effect of aging on mouse hematopoiesis and mouse HSCs, we have comparatively less detailed analyses of the effect of aging on human HSCs. Continued evaluation of human HSCs in the context of aging will be important to determine how applicable the findings in mice and other model organisms are to the human clinical setting.

Aging, clonal hematopoiesis and preleukemia: not just bad luck?

Chronological human aging is associated with a number of changes in the hematopoietic system, occurring at many levels from stem to mature cells, and the marrow microenvironment as well. This review will focus mainly on the aging of hematopoietic stem and progenitor cells (HSPCs), and on the associated increases in the incidence of hematological malignancies. HSPCs manifest reduced function and acquire molecular changes with chronological aging. Furthermore, while for many years it has been known that the human hematopoietic system becomes increasingly clonal with chronological aging (clonal hematopoiesis), only in the last few years has it become clear that clonal hematopoiesis may result from the accumulation of preleukemic mutations in HSPCs. Such mutations confer a selective advantage that leads to clonal hematopoiesis, and that may occasionally result in the development of leukemia, and define the existence of both preleukemic stem cells, and of 'preleukemia' as a clinical entity. While it is well appreciated that clonal hematopoiesis is very common in the elderly, several questions remain unanswered: why and how does clonal hematopoiesis develop? How is clonal hematopoiesis related to the age-related changes observed in the hematopoietic system? And why do only some individuals with clonal hematopoiesis develop leukemia?

Buccal swab as a reliable predictor for X inactivation ratio in inaccessible tissues

Background

As a result of the epigenetic phenomenon of X chromosome inactivation (XCI) every woman is a mosaic of cells with either an inactive paternal X chromosome or an inactive maternal X chromosome. The ratio between inactive paternal and maternal X chromosomes is different for every female individual, and can influence an X-encoded trait or disease. A multitude of X linked conditions is known, and for many of them it is recognised that the phenotype in affected female carriers of the causative mutation is modulated by the XCI ratio. To predict disease severity an XCI ratio is usually determined in peripheral blood samples. However, the correlation between XCI ratios in peripheral blood and disease affected tissues, that are often inaccessible, is poorly understood. Here, we tested several tissues obtained from autopsies of 12 female individuals for patch size and XCI ratio.

Methods

XCI ratios were analysed using methyl-sensitive PCR-based assays for the AR, PCSK1N and SLITRK4 loci. XCI patch size was analysed by testing the XCI ratio of tissue samples with decreasing size.

Results

XCI patch size was analysed for liver, muscle, ovary and brain samples and was found too small to confound testing for XCI ratio in these tissues. XCI ratios were determined in the easily accessible tissues, blood, buccal epithelium and hair follicle, and compared with ratios in several inaccessible tissues.

Conclusions

Buccal epithelium is preferable over peripheral blood for predicting XCI ratios of inaccessible tissues. Ovary is the only inaccessible tissue showing a poor correlation to blood and buccal epithelium, but has a good correlation to hair follicle instead.

Chronic granulomatous disease presenting as refractory pneumonia in late adulthood

We present a case of refractory pneumonia in an adult patient with underlying chronic granulomatous disease (CGD). Her lobectomy tissue grew B urkholderia cepacia and histopathology revealed diffuse severe pneumonic consolidation with suppurative/necrotizing granulomata. An initial attempt to find an underlying immune deficiency was unsuccessful. Following recurrent invasive infections, repeat immunological assessment revealed reduced neutrophil function, demonstrating skewed carrier status (lyonization) for X-linked CGD (only 3% normal cells). A pathogenic mutation in the CYBB gene was found on sequencing. CYBB gene encodes the gp91phox, a catalytic subunit of nicotinamide adenine dinucleotide phosphate-oxidase that produces reactive oxygen species in phagocytes. Lyonization increases with age, explaining the delayed clinical CGD. CGD is a rare neutrophil disorder that usually presents in early life with recurrent infections due to bacteria and fungi primarily involving lungs and skin. It is secondary to a defective NADPH oxidase system needed to kill intracellular organisms and activate the formation of neutrophil extracellular traps.

Lower reference limits of quantitative cord glucose-6-phosphate dehydrogenase estimated from healthy term neonates according to the Clinical and Laboratory Standards Institute guidelines: a cross sectional retrospective study

BACKGROUND

Previous studies have reported the lower reference limit (LRL) of quantitative cord glucose-6-phosphate dehydrogenase (G6PD), but they have not used approved international statistical methodology. Using common standards is expecting to yield more true findings. Therefore, we aimed to estimate LRL of quantitative G6PD detection in healthy term neonates by using statistical analyses endorsed by the International Federation of Clinical Chemistry (IFCC) and the Clinical and Laboratory Standards Institute (CLSI) for reference interval estimation.

METHODS

This cross sectional retrospective study was performed at King Abdulaziz Hospital, Saudi Arabia, between March 2010 and June 2012. The study monitored consecutive neonates born to mothers from one Arab Muslim tribe that was assumed to have a low prevalence of G6PD-deficiency. Neonates that satisfied the following criteria were included: full-term birth (37 weeks); no admission to the special care nursery; no phototherapy treatment; negative direct antiglobulin test; and fathers of female neonates were from the same mothers' tribe. The G6PD activity (Units/gram Hemoglobin) was measured spectrophotometrically by an automated kit. This study used statistical analyses endorsed by IFCC and CLSI for reference interval estimation. The 2.5th percentiles and the corresponding 95% confidence intervals (CI) were estimated as LRLs, both in presence and absence of outliers.

RESULTS

207 males and 188 females term neonates who had cord blood quantitative G6PD testing met the inclusion criteria. Method of Horn detected 20 G6PD values as outliers (8 males and 12 females). Distributions of quantitative cord G6PD values exhibited a normal distribution in absence of the outliers only. The Harris-Boyd method and proportion criteria revealed that combined gender LRLs were reliable. The combined bootstrap LRL in presence of the outliers was 10.0 (95% CI: 7.5-10.7) and the combined parametric LRL in absence of the outliers was 11.0 (95% CI: 10.5-11.3).

CONCLUSION

These results contribute to the LRL of quantitative cord G6PD detection in full-term neonates. They are transferable to another laboratory when pre-analytical factors and testing methods are comparable and the IFCC-CLSI requirements of transference are satisfied. We are suggesting using estimated LRL in absence of the outliers as mislabeling G6PD-deficient neonates as normal is intolerable whereas mislabeling G6PD-normal neonates as deficient is tolerable.

Heterozygous genetic variations of FOXP3 in Xp11.23 elevate breast cancer risk in Chinese population via skewed X-chromosome inactivation

FOXP3 (forkhead box P3: also known as IPEX, XPID) is not only a hallmark of immunosuppressive regulatory T cells (Tregs), but also an X-linked breast cancer suppressor gene expressed in tumor cells. A two-stage investigation was conducted in individuals from northern, southern and eastern China. Individuals carrying a FOXP3 rs2294021CT genotype showed about 1.5-fold increased risk of breast cancer compared with TT carriers. In a related biochemical assay, the rs2294021C allele was found to significantly enhance transcription activity, leading to higher mRNA levels of FOXP3 compared with T allele. Moreover, the number of Tregs and its corresponding interleukin-10 (IL-10) secretion were elevated whereas the proliferation of antitumor T cells was decreased in the C-allele carriers. The breast cancer oncogenes Her-2/ErbB2 and Skp2 were also found to be significantly inhibited in C-allele carriers. Moreover, skewed X-chromosome inactivation (SXCI) analysis showed that rs2294021CT carriers with SXCI showed higher risk than the homozygous carriers and CT carriers without SXCI, suggesting a possible interaction between the rs2294021CT genotype and SXCI. Taken together, these findings indicate that the rs2294021CT genotype may increase an individual's susceptibility to breast cancer by breaking the balance between Treg-mediated immune tolerance and FOXP3-controlled tumor-suppressive effect.

Evaluation of X-Chromosome Inactivation Patterns in Patients with Acute Myeloid Leukemia during Remission

The aim of this study was to evaluate the patterns of X-chromosome inactivation during the remission in acute myeloid leukemia (AML) at the RNA level. Two hundred normal females and 45 female patients with AML entered the study. The frequency of heterozygosity was 48.5% (119/245) for P55, 40% (93/245) for IDS, and only 28.9% (71/245) for G6PD. Some individuals were heterozygous for more than one gene polymorphism. Overall, one hundred normal individuals proved showed to be heterozygous for at least one of the above polymorphisms. 92/100 (92%) normal females showed a polyclonal pattern. Clonal patterns were observed in 44/45 (98%) AML patients at presentation. Of 27 patients who were followed after remission, 23 (85.2%) patients showed a clonal pattern. Ten patients were available for a longer followup (up to 12 months) and the clonal pattern was observed in seven patients. It can be concluded that clonality at remission is a frequent event in AML and does not necessarily mean relapse of the disease. There is also a possibility of conversion of clonality to polyclonality over time.

Cell cloning-based transcriptome analysis in Rett patients: relevance to the pathogenesis of Rett syndrome of new human MeCP2 target genes

More than 90% of Rett syndrome (RTT) patients have heterozygous mutations in the X-linked methyl-CpG binding protein 2 (MECP2) gene that encodes the methyl-CpG-binding protein 2, a transcriptional modulator. Because MECP2 is subjected to X chromosome inactivation (XCI), girls with RTT either express the wild-type or mutant allele in each individual cell. To test the consequences of MECP2 mutations resulting from a genome-wide transcriptional dysregulation and to identify its target genes in a system that circumvents the functional mosaicism resulting from XCI, we carried out gene expression profiling of clonal populations derived from fibroblast primary cultures expressing exclusively either the wild-type or the mutant MECP2 allele. Clonal cultures were obtained from skin biopsy of three RTT patients carrying either a non-sense or a frameshift MECP2 mutation. For each patient, gene expression profiles of wild-type and mutant clones were compared by oligonucleotide expression microarray analysis. Firstly, clustering analysis classified the RTT patients according to their genetic background and MECP2 mutation. Secondly, expression profiling by microarray analysis and quantitative RT-PCR indicated four up-regulated genes and five down-regulated genes significantly dysregulated in all our statistical analysis, including excellent potential candidate genes for the understanding of the pathophysiology of this neurodevelopmental disease. Thirdly, chromatin immunoprecipitation analysis confirmed MeCP2 binding to respective CpG islands in three out of four up-regulated candidate genes and sequencing of bisulphite-converted DNA indicated that MeCP2 preferentially binds to methylated-DNA sequences. Most importantly, the finding that at least two of these genes (BMCC1 and RNF182) were shown to be involved in cell survival and/or apoptosis may suggest that impaired MeCP2 function could alter the survival of neurons thus compromising brain function without inducing cell death.

The human androgen receptor X-chromosome inactivation assay for clonality diagnostics of natural killer cell proliferations

Clonality is a frequently exploited characteristic of lymphoid malignancies. However, in the natural killer (NK) cell subset of large granular lymphocyte proliferations, clonality is difficult to prove because of the lack of specific genetic markers, such as immunoglobulin or T-cell receptor gene rearrangements. The human androgen receptor (HUMARA) assay, a polymerase chain reaction-based X-chromosome inactivation assay, is a potential diagnostic tool in these disorders. Although there is much experience with X-chromosome inactivation assays in myeloid proliferations, these assays have found only very limited application in clonality assessment of NK cell proliferations. We applied the HUMARA assay in laboratory diagnostics for detection of clonality in NK cell proliferations. We describe its test performance and report three cases in which clonality of NK cell populations was investigated by use of this assay. Our results demonstrate the usefulness of the HUMARA assay in the diagnostic workup of NK cell proliferations.

G6PD deficiency from lyonization after hematopoietic stem cell transplantation from female heterozygous donors

To determine whether during hematopoietic stem cell transplantation (HSCT), X-chromosome inactivation (lyonization) of donor HSC might change after engraftment in recipients, the glucose-6-phosphate dehydrogenase (G6PD) gene of 180 female donors was genotyped by PCR/allele-specific primer extension, and MALDI-TOF mass spectrometry/Sequenom MassARRAY analysis. X-inactivation was determined by semiquantitative PCR for the HUMARA gene before/after HpaII digestion. X-inactivation was preserved in most cases post-HSCT, although altered skewing of lyonization might occur to either of the X-chromosomes. Among pre-HSCT clinicopathologic parameters analyzed, only recipient gender significantly affected skewing. Seven donors with normal G6PD biochemically but heterozygous for G6PD mutants were identified. Owing to lyonization changes, some donor-recipient pairs showed significantly different G6PD levels. In one donor-recipient pair, extreme lyonization affecting the wild-type G6PD allele occurred, causing biochemical G6PD deficiency in the recipient. In HSCT from asymptomatic female donors heterozygous for X-linked recessive disorders, altered lyonization might cause clinical diseases in the recipients.

Severe X-linked chronic granulomatous disease in two unrelated females

Chronic granulomatous disease (CGD) is a rare primary immunodeficiency caused by mutations of one of the subunits of phagocyte reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase leading to decreased or complete absence of neutrophil oxidative burst. We report the clinical and laboratory findings in two young unrelated females 14 and 9 years of age and natives of Tahiti and Reunion Islands, respectively, with severe X-linked granulomatous disease. In both cases, the infectious pattern was unusual, with convergent symptoms suggesting underlying mycobacterial infection. Functional analysis revealed low residual NADPH oxidase activity with about 5-10% of normal neutrophil population. De novo null mutations affecting the CYBB gene that encodes the gp91 protein were found in both cases in the heterozygous state (in patient 1, p.Arg130X in exon 5, and in patient 2, a novel insertion in exon 6, c.632_633insCATC). Methylation analysis confirmed that phenotype expression was linked to skewed X inactivation and showed that the de novo mutation arose on the maternally inherited chromosome in one case and on the paternally inherited chromosome in the other case. In conclusion, X-linked CGD carriers could therefore be at risk for severe infectious diseases depending on the skewed X inactivation pattern and the infectious context.

Acquisition of the V617F mutation of JAK2 is a late genetic event in a subset of patients with myeloproliferative disorders

An acquired gain-of-function mutation in the Janus kinase 2 (JAK2-V617F) is frequently found in patients with myeloproliferative disorders (MPDs). To test the hypothesis that JAK2-V617F is the disease-initiating mutation, we examined whether all cells of clonal origin carry the JAK2-V617F mutation. Using allele-specific polymerase chain reaction (PCR) assays for the JAK2 mutation and for the X-chromosomal clonality markers IDS and MPP1, we found that the percentage of granulocytes and platelets with JAK2-V617F was often markedly lower than the percentage of clonal granulocytes determined by IDS or MPP1 clonality assays in female patients. Using deletions of chromosome 20q (del20q) as an autosomal, X-chromosome–independent clonality marker, we found a similar discrepancy between the percentage of cells carrying JAK2-V617F and del20q. Our results suggest that in a proportion of patients with MPDs, JAK2-V617F occurs on the background of clonal hematopoiesis caused by a somatic mutation in an as-yet-unknown gene.

Chromosomal Abnormalities and Molecular Markers in Myeloproliferative Disorders

The first possibly causative molecular aberration in patients with myeloproliferative disorders has recently been described. A point mutation in the Janus kinase 2 exchanging a valine for a phenylalanine at position 617 (JAK2 V617F) was found in 65% to 97% of polycythemia vera (PV) patients, as well as in approximately 50% of essential thrombocythemia (ET) and idiopathic myelofibrosis (IMF) patients. In addition, a growing set of molecular and genetic markers, some possibly contributing to disease development, some more likely epiphenomena, has been characterized in these patients over the last few years. Compiling and synthesizing the increasing knowledge on the genetic changes observed in myeloproliferative disorder (MPD) patients will allow us to generate testable hypotheses on the molecular etiology of disease development. Therefore, this review will summarize the current knowledge on chromosomal aberrations, molecular markers, and gene expression studies in MPD patients. From these data, a model depicting our current understanding of the interplay between these markers is presented.

Reduced proportion of Purkinje cells expressing paternally derived mutant Mecp2308 allele in female mouse cerebellum is not due to a skewed primary pattern of X-chromosome inactivation

Rett syndrome (RTT) is an X-linked disorder caused by mutations in the methyl CpG binding protein 2 (MECP2) gene. The pattern of X-chromosome inactivation (XCI) is thought to play a role in phenotypic severity. In the present study, patterns of XCI were assessed by lacZ staining of embryos and adult brains of mice heterozygous for a X-linked Hmgcr-nls-lacZ transgene on a mutant mouse model of RTT. We found that there was no difference between the lacZ staining patterns in the brain of wild-type and heterozygous mutant embryos at embryonic day 9.5 (E9.5) suggesting that Mecp2 has no effect on the primary pattern of XCI. At 20 weeks of age, there was no significant difference between XCI patterns in the Purkinje cells in the cerebellum of heterozygous mutant and wild-type mice when the mutant allele was inherited from the mother. However, when the mutant allele was paternally inherited, a significant difference was detected. Thus, parental origin of the mutation may have a bearing on phenotype through XCI patterns. An estimation of the Purkinje cell precursor number based on XCI mosaicism revealed that, when the mutation was paternally inherited, the precursor number was less than that in the wild-type mice. Therefore, it is likely that the number of precursor cells allocated to the Purkinje cell lineage is affected by a paternally inherited mutation in Mecp2. We also observed that the pattern of XCI in cultured fibroblasts was significantly correlated with patterns in the Purkinje cells in mutant animals but not in wild-type mice.

The presence of clonal cell subpopulations in peripheral blood and bone marrow of patients with refractory cytopenia with multilineage dysplasia but not in patients with refractory anemia may reflect a multistep pathogenesis of myelodysplasia

A clonal origin of hematopoiesis was studied by investigation of X-chromosome inactivation patterns (XCIP) in isolated granulocyte, CD14(+) and CD3(+) subpopulations obtained from bone marrow and peripheral blood of 36 female patients with primary myelodysplastic syndrome (MDS). Clonality was assessed by PCR amplification of polymorphic short tandem repeats of the human androgen receptor (HUMARA) gene and by investigation of silent polymorphism of iduronate sulphatase (IDS) or p55 genes. On the basis of results in a control group of 20 healthy age related females, a ratio of at least 9:1 between the two alleles was considered a significant marker of monoclonal hematopoiesis. Ten of the 11 patients with advanced forms of MDS (RAEB, RAEB-T, CMML) had clonal granulocytes and CD14(+) cells in peripheral blood. In patients with early disease, only 2 out of 11 patients (18%) with RA or RARS, according to WHO classification, had clonal granulocytes and CD14(+) cells in peripheral blood and bone marrow and 2 other patients with 5q-syndrome exhibited extremely oligoclonal granulocyte subpopulation in bone marrow. In contrast, we found clonal granulocytes in 12 out of 14 patients (86%) with refractory cytopenia with multilineage dysplasia (RCMD) and 8 of them simultanously exhibited clonal CD14(+) cells. Estimated 3 years survival of patients with early disease and clonal cell subpopulations was 61% as compared with 88% in patients without clonal hematopoiesis. Karyotype abnormalities were detected in 11 of the 25 females with early disease. Clonal patterns were present in 7 out of 8 patients with abberations diagnosed by routine cytogenetics, nevertheless, FISH revealed 5q deletion in 3 patients without signs of clonality in XCIP assay. No correlation was found between the presence of clonal subpopulations and the degree of telomere shortening in early MDS. Despite some limitations, the measurement of XCIP remains a sensitive tool for diagnosis of the first transforming mutation in the clonal development of MDS especially when combined with FISH and when an age related group is used to establish an appropriate allele ratio to exclude constitutional or acquired skewing. The occurrence of clonal cell subpopulations in most of the RCMD patients in contrast to RA may reflect a proposed multistep pathogenesis of MDS with dysplastic changes limited to erythropoiesis in early step and with subsequent development of multilineage dysplasia. The results also support the usefulness of separation of RCMD from 'pure' RA; however, a more complex insight combining different molecular techniques performed in a large number of patients is needed for refined classification of MDS on the basis of new molecular prognostic factors and for indication of more effective targeted therapy.

The dynamics of X-inactivation skewing as women age

Non-random X-chromosome inactivation (XCI) has been associated with X-linked diseases, neoplastic diseases, recurrent pregnancy loss, and trisomy risk. It also occurs more commonly in older female populations. To understand the etiology of non-random XCI and utilize this assay appropriately in clinical research and practice, the age-related alteration in XCI patterns in normal females needs to be clearly defined. In the present study, we evaluated the XCI status in 350 unselected women aged 0-88 years with unknown history of genetic disorders or abnormal pregnancies. DNA samples were extracted from peripheral blood and analyzed by a methylation-based assay at the androgen receptor locus. A weak but significant positive correlation was observed between age and degree of skewing in XCI over the whole age range (r = 0.23, p < 0.0001), and skewing values become non-normally distributed at older ages. However, the increase in skewed XCI appears to be more pronounced after age 30 than at younger ages. This trend supports the model of increased skewing with age as a consequence of hematopoietic stem cell senescence. An alternative possibility is that there is allele-specific loss of methylation with time that results in the appearance of increased XCI skewing using a methylation-based assay.

Monitoring treatment efficiency in MDS at the molecular level; possibilities now and in the future

Myelodysplastic syndromes (MDS) are a heterogeneous group of bone marrow (BM) diseases. MDS patients suffer from bone marrow failure because of the expansion of a malignant clone, resulting in abnormal differentiation of blood cells and severe pancytopenias. MDS patients have a high propensity for the development of acute myeloid leukemia (AML). During the last few years it has become increasingly clear that MDS is a stem cell disease. Two methods have generally been used to study the clonal origin of MDS bone marrow cells. First, the combination of fluorescent in situ hybridization (FISH) in combination with cell sorting has been used to study MDS specific numerical chromosomal aberrations in various cell types. Secondly, the determination of the X-chromosome inactivation patterns (XCIP) in different cell types of female MDS patients has been used to study clonality irrespective of the presence of a disease-specific marker. Both techniques have also been used to monitor treatment efficiency. Both methods showed that a molecular remission occurred in approximately half of the patients who achieved complete clinical remission after intensive antileukemic treatment, depending on the study and the type of treatment. In case of cytogenetic analysis this proved to be of prognostic significance. This review discusses the advantages and disadvantages of both techniques for the determination of clonality at diagnosis as well as for the assessment of treatment efficiency in past and in ongoing clinical trials. Future directions and possibilities for further research are also discussed.

Discrimination of polycythemias and thrombocytoses by novel, simple, accurate clonality assays and comparison with PRV-1 expression and BFU-E response to erythropoietin

Essential thrombocythemia (ET) and polycythemia vera (PV) are clonal myeloproliferative disorders that are often difficult to distinguish from other causes of elevated blood cell counts. Assays that could reliably detect clonal hematopoiesis would therefore be extremely valuable for diagnosis. We previously reported 3 X-chromosome transcription-based clonality assays (TCAs) involving the G6PD, IDS, and MPP1 genes, which together were informative in about 65% of female subjects. To increase our ability to detect clonality, we developed simple TCA for detecting the transcripts of 2 additional X-chromosome genes: Bruton tyrosine kinase (BTK) and 4-and-a-half LIM domain 1 (FHL1). The combination of TCA established the presence or absence of clonal hematopoiesis in about 90% of female subjects. We show that both genes are subject to X-chromosome inactivation and are polymorphic in all major US ethnic groups. The 5 TCAs were used to examine clonality in 46 female patients along with assays for erythropoietin-independent erythroid colonies (EECs) and granulocyte PRV-1 mRNA levels to discriminate polycythemias and thrombocytoses. Of these, all 19 patients with familial polycythemia or thrombocytosis had polyclonal hematopoiesis, whereas 22 of 26 patients with clinical evidence of myeloproliferative disorder and 1 patient with clinically obscure polycythemia were clonal. Interestingly, interferon alpha therapy in 2 patients with PV was associated with reversion of clonal to polyclonal hematopoiesis. EECs were observed in 14 of 14 patients with PV and 4 of 12 with ET, and increased granulocyte PRV-1 mRNA levels were found in 9 of 13 patients with PV and 2 of 12 with ET. Thus, these novel clonality assays are useful in the diagnosis and follow-up of polycythemic conditions and disorders with increased platelet levels.

X-chromosome inactivation (XCI) patterns in placental tissues of a paternally derived bal t(X;20) case

Non-random X-chromosome inactivation (XCI) is often seen in female carriers of balanced X-autosome translocations and is generally attributed to a selective growth of cells that inactivate the normal X chromosome. However, little is known concerning when in development the selection acts, and thus whether skewed XCI would also be seen in placental tissues. Furthermore, as males with X-autosome translocations are normally infertile, all translocations studied to date for XCI-skewing have been either maternal or de novo in origin. We now present an analysis of XCI status in cord blood, umbilical cord and four different extraembryonic tissues from a female carrier of a paternally derived balanced (X;20) translocation. Using methylation based assays to determine XCI status, we found preferential inactivation of the non-translocated X in cord blood, umbilical cord and amnion samples of the propositus. Remarkably, random XCI was evident in several placental tissues analyzed (chorion, and chorionic villi trophoblast and mesenchyme). While these findings support the hypothesis of strong selection against cells with an inactive translocated X-chromosome in most embryonic/fetal tissues, they also suggest weaker selective forces taking place during placental development. Additionally, the finding of normal placental development in the present case, rules out the possibility of a parental bias to XCI in human extraembryonic tissues as a requisite for normal development. The finding of hypomethylation in extraembryonic tissues for two out of three markers used in the study is consistent with previous findings demonstrating low levels of methylation in these tissues.

X-inactivation patterns in human embryonic and extra-embryonic tissues

Mice have skewed X chromosome inactivation (XCI) in extraembryonic tissue while examination of human placentae have yielded conflicting results. We investigated XCI patterns in human embryonic and extra-embryonic tissues. First and early second trimester placental and foetal tissues were collected. Cytotrophoblasts were isolated from the placentae. Female samples were identified and X-inactivation patterns were determined by analysis of androgen receptor (HAR) methylation patterns. Among 55 females heterozygous at the HAR, 37 had random and 18 skewed XCI. In foetal tissues a skewed XCI pattern was only observed in one liver and one intestine sample. A greater incidence of skewed XCI pattern was present in extra-embryonic compared to embryonic tissues (P=0.022). A markedly skewed XCI pattern was only found in one cytotrophoblast sample. Random and skewed XCI patterns were detected in human embryonic and extra-embryonic tissues. The extra-embryonic tissue had a higher proportion of skewed XCI, but marked skewed XCI was uncommon in both tissues. Skewed XCI may not play a role in normal human placentation.

Monoclonal constitution of neutrophils detected by PCR-based human androgen receptor gene assay in a subset of idiopathic thrombocytopenic purpura patients

It is well known that some patients with monopathic thrombocytopenia in myelodysplastic syndrome (MDS) show clinico-hematologic features resembling chronic idiopathic thrombocytopenic purpura (ITP). This study examined the monoclonal nature of ITP to obtain a further insight into patients with borderline ITP and monopathic thrombocytopenia in MDS, using polymorphic trinucleotide CAG repeats in the X-linked human androgen receptor (HUMARA) gene. In this study, we separated peripheral neutrophils and mononuclear cells (MNCs) from 18 patients with chronic ITP, and analyzed them in comparison with those from normal or MDS female subjects by PCR-based HUMARA assay. All normal controls showed a polyclonal pattern of the HUMARA gene, whereas some MDS patients had monoclonality in MNC and/or neutrophils. Among ITP patients, two had a nonrandom inactivation pattern of the HUMARA gene in neutrophils, which was considered to be derived from hematopoietic cells of clonal origin, whereas no ITP patient had MNC of clonal nature. Two ITP patients with a monoclonal pattern in the neutrophil fraction were refractory to ordinary treatment. This approach may provide further information in patients with borderline hematologic disorders between chronic ITP and refractory thrombocytopenia of MDS.

Familial-skewed X-chromosome inactivation as a predisposing factor for late-onset X-linked sideroblastic anemia in carrier females

X-linked sideroblastic anemia (XLSA) is caused by mutations in the erythroid-specific 5-aminolevulinic acid synthase (ALAS2) gene. An elderly woman who presented with an acquired sideroblastic anemia is studied. Molecular analysis revealed that she was heterozygous for a missense mutation in the ALAS2 gene, but she expressed only the mutated gene in reticulocytes. Her 2 daughters and a granddaughter were heterozygous for this mutation, had normal hemoglobin levels, and expressed the normal ALAS2 gene in reticulocytes. A grandson with a previous diagnosis of thalassemia intermedia was found to be hemizygous for the ALAS2 mutation. Treatment with pyridoxine completely corrected the anemia both in the proband and her grandson. All women who were analyzed in this family showed skewed X-chromosome inactivation in leukocytes, which indicated a hereditary condition associated with unbalanced lyonization. Because the preferentially active X chromosome carried the mutant ALAS2 allele, acquired skewing in the elderly likely worsened the genetic condition and abolished the normal ALAS2 allele expression in the proband.

Familial-skewed X-chromosome inactivation as a predisposing factor for late-onset X-linked sideroblastic anemia in carrier females

X-linked sideroblastic anemia (XLSA) is caused by mutations in the erythroid-specific 5-aminolevulinic acid synthase (ALAS2) gene. An elderly woman who presented with an acquired sideroblastic anemia is studied. Molecular analysis revealed that she was heterozygous for a missense mutation in the ALAS2 gene, but she expressed only the mutated gene in reticulocytes. Her 2 daughters and a granddaughter were heterozygous for this mutation, had normal hemoglobin levels, and expressed the normal ALAS2 gene in reticulocytes. A grandson with a previous diagnosis of thalassemia intermedia was found to be hemizygous for the ALAS2 mutation. Treatment with pyridoxine completely corrected the anemia both in the proband and her grandson. All women who were analyzed in this family showed skewed X-chromosome inactivation in leukocytes, which indicated a hereditary condition associated with unbalanced lyonization. Because the preferentially active X chromosome carried the mutant ALAS2 allele, acquired skewing in the elderly likely worsened the genetic condition and abolished the normal ALAS2 allele expression in the proband.

Clonality analysis of defined cell populations in paraffin-embedded tissue sections by RT-PCR amplification of X-linked G6PD gene

This paper establishes a method of clonality analysis using the reverse transcription-polymerase chain reaction (RT-PCR) to amplify X-linked G6PD transcripts on defined cell populations microdissected from archival, paraffin-embedded tissue sections. Four known monoclonal low-grade B-cell lymphomas from females who were heterozygous (informative) at the 1131 exonic polymorphic locus of the G6PD gene were used to validate the method. Lymphoma and reactive lesions in each case were separated by microdissection. In order to preserve the intact RNA species in the lesion, sections were digested on the slides before microdissection. A one-step RT-PCR was performed with a single pair of primers, one of which contained a mismatched base adjacent to the polymorphic site, to generate a PvuI cutting site. Successful amplification and allele identification by PvuI digestion were achieved from all RNA samples studied. Three of four samples from non-neoplastic reactive lesions showed two bands with equal intensity, representing transcription of the two alleles of the G6PD gene, while the corresponding tumour samples demonstrated a biased intensity in one allele, indicating monoclonality. To assess the method further, the clonal nature of in situ and invasive breast cancers was examined, along with adjacent normal breast tissue and hyperplastic lesions from three informative females from our archives. Apart from the clusters of normal terminal duct-lobular units, all lesions were monoclonal. This result is in agreement with data derived from other X-linked gene studies and loss of heterozygosity (LOH) analyses of pre-invasive breast disease. The results suggest that the clonality analysis method presented here is simple and reliable, and is therefore potentially applicable in a wide range of pathological conditions.

Clonality markers in polycythaemia and primary thrombocythaemia

Our current understanding of the pathogenesis of the myeloproliferative disorders is based on the assumption that they represent a clonal disorder resulting from transformation of a haematopoietic stem cell. Clonality assays exploit the fact that female cells have only one active X-chromosome. Methods for determining X chromosome inactivation have been devised at the protein (G6PD isoenzymes); DNA (HUMARA; phosphoglycerate kinase (PGK); hypoxanthine-phosphoribosyl transferase (HPRT) and RNA (G6PD; P55; IDS) levels. In this type of RNA assay the product of the active X chromosome is quantified by studying polymorphisms present in mRNA. The presence of skewed lyonization in normal females is a potential limitation to the method, although the use of T cells as a control makes it possible to distinguish clonal haematopoiesis from skewed lyonization. However, the phenomenon of acquired skewing in normal elderly women means that X-inactivation patterns in elderly patients must be interpreted with caution. Clonality studies have been conducted in polycythaemia vera (PV) and essential thrombocythaemia (ET) patients. They usually demonstrate a clonal X-inactivation pattern in granulocytes and/or platelets but a polyclonal pattern in T cells. However, in both ET and PV a significant minority of patients exhibit polyclonal haematopoiesis with polyclonal patterns in granulocytes/platelets. Female patients with polyclonal haematopoiesis differ from those with clonal haematopoiesis in terms of age and platelet count and possibly in their requirements for treatment. This new technology for the investigation of the MPD seems promising for understanding certain clinical aspects of these diseases and may be introduced for evaluation of new modalities of treatment.