Female monozygotic twins discordant for hemophilia A due to nonrandom X-chromosome inactivation

Insights into the Molecular Genetic of Hemophilia A and Hemophilia B: The Relevance of Genetic Testing in Routine Clinical Practice

Hemophilia A and hemophilia B are rare congenital, recessive X-linked disorders caused by lack or deficiency of clotting factor VIII (FVIII) or IX (FIX), respectively. The severity of the disease depends on the reduction of coagulation FVIII or FIX activity levels, which is determined by the type of the pathogenic variants in the genes encoding the two factors (F8 and F9, respectively). Molecular genetic analysis is widely applied in inherited bleeding disorders. The outcome of genetic analysis allows genetic counseling of affected families and helps find a link between the genotype and the phenotype. Genetic analysis in hemophilia has tremendously improved in the last decades. Many new techniques and modifications as well as analysis softwares became available, which made the genetic analysis and interpretation of the data faster and more accurate. Advances in genetic variant detection strategies facilitate identification of the causal variants in up to 97% of patients. In this review, we discuss the milestones in genetic analysis of hemophilia and highlight the importance of identification of the causative genetic variants for genetic counseling and particularly for the interpretation of the clinical presentation of hemophilia patients.

Sex differences in number of X chromosomes and X-chromosome inactivation in females promote greater variability in hearing among males

BACKGROUND

For more than 150 years, research studies have documented greater variability across males than across females ("greater male variability"-GMV) over a broad range of behavioral and morphological measures. In placental mammals, an ancient difference between males and females that may make an important contribution to GMV is the different pattern of activation of X chromosomes across cells in females (mosaic inactivation of one the two X chromosomes across cells) vs males (consistent activation of a single X chromosome in all cells). In the current study, variability in hearing thresholds was examined for human listeners with thresholds within the normal range. Initial analyses compared variability in thresholds across males vs. across females. If greater across-male than across-female variability was present, and if these differences in variability related to the different patterns X-chromosome activation in males vs. females, it was expected that correlations between related measures within a given subject (e.g., hearing thresholds at given frequency in the two ears) would be greater in males than females.

METHODS

Hearing thresholds at audiometric test frequencies (500-6000 or 500-8000 Hz) were extracted from two datasets representing more than 8500 listeners with normal hearing (4590 males, 4376 females). Separate data analyses were carried out on each dataset to compare: (1) relative variability in hearing thresholds across males vs. across females at each test frequency; (2) correlations between both across-ear and within-ear hearing thresholds within  males vs. within  females, and (3) mean thresholds for females vs. males at each frequency.

RESULTS

A consistent pattern of GMV in hearing thresholds was seen across frequencies in both datasets. In addition, both across-ear and within-ear correlations between thresholds were consistently greater in males than females. Previous studies have frequently reported lower mean thresholds for females than males for listeners with normal hearing. One of the datasets replicated this result, showing a clear and consistent pattern of lower mean thresholds for females. The second data set did not show clear evidence of this female advantage.

CONCLUSIONS

Hearing thresholds showed clear evidence of greater variability across males than across females and higher correlations across related threshold measures within males than within females. The results support a link between the observed GMV and the mosaic pattern of X-activation for females that is not present in males.

Hemophilia A and C in a female: The first case report in literature

INTRODUCTION

One of the relatively rare hemostatic disorders is coagulation factors' deficiency, where a single factor or multiple factors can be deficient. All hereditary coagulation factors' deficiencies are autosomal recessive, so they can manifest in both genders, but Hemophilia A and B are X-linked disorders. Therefore, females can rarely be affected. This paper reports the first case of simultaneous coagulation factors' deficiencies of FVIII and FXI in a female.

CASE PRESENTATION

A 17-year-old female came to the office due to prolonged epistaxis, with a history of severe menstrual bleeding and frequent episodes of epistaxis. In her familial history, a brother complained of epistaxis episodes. Bleeding time and prothrombin time were normal but activated partial thromboplastin time was increased. Von Willebrand disease was excluded, and she was diagnosed with hemophilia A and C.

DISCUSSION

Females can be affected with X-linked disorders such as hemophilia A and B in some rare cases: a carrier mother and affected father, skewed X chromosome inactivation, Turner syndrome, inhibiting antibodies (acquired hemophilia), or a sporadic mutation on the most activated X chromosome. On the other hand, Hemophilia C is an autosomal recessive disease. Treatment of such cases is a challenge, and the recombinant coagulation factors are the treat-of-choice.

CONCLUSION

Although Von Willebrand disease is the most common hereditary bleeding disorder in females, other rare diseases could be suspected such as Hemophilia. X-linked Hemophilia should be kept in mind as a differential diagnosis in any female patient suffering from hemorrhage.

Genetic causes of haemophilia in women and girls

Women and girls reported as "haemophilic females" may have complex genetic causes for their haemophilia phenotype. In addition, women and girls may have excessive bleeding requiring treatment simply because they are heterozygous for haemophilia alleles. While severe and moderate haemophilia are rare in females, 16% of patients with mild haemophilia A and almost one-quarter of those with mild haemophilia B seen in U.S. haemophilia treatment centres are women and girls. A phenotypic female with a low level of factor VIII or factor IX may be classified into one of the following categories of causality: homozygosity (two identical haemophilia alleles), compound heterozygosity (two different haemophilia alleles), hemizygosity (one haemophilia allele and no normal allele), heterozygosity (one haemophilia allele and one normal allele), genetic causes other than haemophilia and non-genetic causes. Studies required for classification may include coagulation parameters, F8 or F9 sequencing, F8 inversion testing, multiplex ligation-dependent probe amplification, karyotyping and X chromosome inactivation studies performed on the patient and parents. Women and girls who are homozygous, compound heterozygous or hemizygous clearly have haemophilia, as they do not have a normal allele. Heterozygous women and girls with factor levels below the haemostatic range also meet the definitions used for haemophilia treatment.

Differential phenotypic expression of a novel PDHA1 mutation in a female monozygotic twin pair

Pyruvate dehydrogenase complex (PDC) deficiency caused by mutations in the X-linked PDHA1 gene has a broad clinical presentation, and the pattern of X-chromosome inactivation has been proposed as a major factor contributing to its variable expressivity in heterozygous females. Here, we report the first set of monozygotic twin females with PDC deficiency, caused by a novel, de novo heterozygous missense mutation in exon 11 of PDHA1 (NM_000284.3: c.1100A>T). Both twins presented in infancy with a similar clinical phenotype including developmental delay, episodes of hypotonia or encephalopathy, epilepsy, and slowly progressive motor impairment due to pyramidal, extrapyramidal, and cerebellar involvement. However, they exhibited clear differences in disease severity that correlated well with residual PDC activities (approximately 60% and 20% of mean control values, respectively) and levels of immunoreactive E1α subunit in cultured skin fibroblasts. To address whether the observed clinical and biochemical differences could be explained by the pattern of X-chromosome inactivation, we undertook an androgen receptor assay in peripheral blood. In the less severely affected twin, a significant bias in the relative activity of the two X chromosomes with a ratio of approximately 75:25 was detected, while the ratio was close to 50:50 in the other twin. Although it may be difficult to extrapolate these results to other tissues, our observation provides further support to the hypothesis that the pattern of X-chromosome inactivation may influence the phenotypic expression of the same mutation in heterozygous females and broadens the clinical and genetic spectrum of PDC deficiency.

Pervasive Inter-Individual Variation in Allele-Specific Expression in Monozygotic Twins

Despite being developed from one zygote, heterokaryotypic monozygotic (MZ) co-twins exhibit discordant karyotypes. Epigenomic studies in biological samples from heterokaryotypic MZ co-twins are of the most significant value for assessing the effects on gene- and allele-specific expression of an extranumerary chromosomal copy or structural chromosomal disparities in otherwise nearly identical germline genetic contributions. Here, we use RNA-Seq data from existing repositories to establish within-pair correlations for the breadth and magnitude of allele-specific expression (ASE) in heterokaryotypic MZ co-twins discordant for trisomy 21 and maternal 21q inheritance, as well as homokaryotypic co-twins. We show that there is a genome-wide disparity at ASE sites between the heterokaryotypic MZ co-twins. Although most of the disparity corresponds to changes in the magnitude of biallelic imbalance, ASE sites switching from either strictly monoallelic to biallelic imbalance or the reverse occur in few genes that are known or predicted to be imprinted, subject to X-chromosome inactivation or A-to-I(G) RNA edited. We also uncovered comparable ASE differences between homokaryotypic MZ twins. The extent of ASE discordance in MZ twins (2.7%) was about 10-fold lower than the expected between pairs of unrelated, non-twin males or females. The results indicate that the observed within-pair dissimilarities in breadth and magnitude of ASE sites in the heterokaryotypic MZ co-twins could not solely be attributable to the aneuploidy and the missing allelic heritability at 21q.

Management of Thrombosis Risk in a Carrier of Hemophilia A with Low Factor VIII Levels with Atrial Fibrillation: A Clinical Case and Literature Review

Nonvalvular atrial fibrillation (AF) is a common age-related arrthymia and a leading cause of stroke in the elderly; with an aging hemophilia population, the number of patients developing AF is increasing. There are no controlled trials on thromboprophylaxis in this group of patients, only consensus opinion was based on small case reports. We present a female patient, carrier for hemophilia and with clinically moderately severe hemophilia who developed FA. We discuss the literature with respect to this group of patients and current recommendations for thromboprophylaxis.

Lifetime physical inactivity is associated with increased risk for Hodgkin and non-Hodgkin lymphoma: A case-control study

BACKGROUND

Although physical activity is a well-established risk factor for several cancer types, studies evaluating its association with lymphoma have yielded inconclusive results. In such cases where physical activity is not clearly associated with cancer risk in a dose-dependent manner, investigators have begun examining physical inactivity as an independent exposure of interest.

METHODS

Associations of self-reported, lifetime physical inactivity with risk of developing Hodgkin lymphoma (HL) and non-Hodgkin lymphoma (NHL) were evaluated in a hospital-based case control study using data from the Patient Epidemiology Data System at Roswell Park Comprehensive Cancer Center. Participants included 87 patients with HL and 236 patients with NHL as well as 348 and 952 cancer-free controls, respectively. Multivariable-adjusted logistic regression models were fit to calculate odds ratios (OR) and 95% confidence intervals (CI) estimating the association between physical inactivity and lymphoma risk.

RESULTS

We observed significant, positive associations between lifetime recreational physical inactivity and risk of both HL (OR = 1.90, 95% CI: 1.15-3.15) and NHL (OR = 1.35, 95% CI: 1.01-1.82).

CONCLUSIONS

The current analysis provides evidence for a positive association between physical inactivity and risk of both HL and NHL. These results add to a growing body of research suggesting that lifetime physical inactivity may be an important independent, modifiable behavioral risk factor for cancer.

Identification of novel informative loci for DNA-based X-inactivation analysis

The HUMARA assay, the most common method for evaluation of X-inactivation skewing in blood cells, has been reported to be usable in only about 80% of females, emphasizing the need for alternative methods for testing of HUMARA-uninformative individuals. We conducted an in silico search for potentially polymorphic tri-to-hexanucleotide repeats in the proximity of CpG islands located in 5' regions of X-chromosome genes to design five candidate assays (numbered I, II, III, IV, and V) combining methylation-specific restriction digest with PCR amplification in a manner similar to the HUMARA assay. The results obtained by these assays in 100 healthy females were compared to X-inactivation skewing measured by the AR-MSP method which is based on methylation-specific PCR amplification of the first exon of the AR gene. On the basis of statistical evidence, three of the novel assays (II, IV, and V), which were informative in 18%, 61%, and 55% of females in the cohort, respectively, may be used as alternatives or conjointly with the HUMARA assay to improve its reliability. The three new assays were combined with the HUMARA assay into a novel X-inactivation test leading to the increase of informative females in the cohort from 67% to 96%.

Severe and moderate haemophilia A and B in US females

Haemophilia A and B are rare X-lined hemorrhagic disorders that typically affect men. Women are usually asymptomatic carriers, but may be symptomatic and, rarely, also express severe (factor VIII (FVIII) or factor IX (FIX) <0.01 U mL(-1)) or moderately severe (FVIII/FIX 0.01-0.05 U mL(-1)) phenotypes. However, data on clinical manifestations, genotype and the psychosocial ramifications of illness in severely affected females remain anecdotal. A national multi-centre retrospective study was conducted to collect a comprehensive data set on affected US girls and women, and to compare clinical observations to previously published information on haemophilic males of comparable severity and mildly affected haemophilic females. Twenty-two severe/moderate haemophilia A/B subjects were characterized with respect to clinical manifestations and disease complications; genetic determinants of phenotypic severity; and health-related quality of life (HR-QoL). Clinical data were compared as previously indicated. Female patients were older than male patients at diagnosis, but similarly experienced joint haemorrhage, disease- and treatment-related complications and access to treatment. Gynaecological and obstetrical bleeding was unexpectedly infrequent. F8 or F9 mutations, accompanied by extremely skewed X-chromosome inactivation pattern (XIP), were primary determinants of severity. HR-QoL was diminished by arthropathy and viral infection. Using systematic case verification of participants in a national surveillance registry, this study elucidated the genetics, clinical phenotype and quality of life issues in female patients with severe/moderate haemophilia. An ongoing international case-controlled study will further evaluate these observations. Novel mechanistic questions are raised about the relationship between XIP and both age and tissue-specific FVIII and FIX expression.

Where genotype is not predictive of phenotype: towards an understanding of the molecular basis of reduced penetrance in human inherited disease

Some individuals with a particular disease-causing mutation or genotype fail to express most if not all features of the disease in question, a phenomenon that is known as 'reduced (or incomplete) penetrance'. Reduced penetrance is not uncommon; indeed, there are many known examples of 'disease-causing mutations' that fail to cause disease in at least a proportion of the individuals who carry them. Reduced penetrance may therefore explain not only why genetic diseases are occasionally transmitted through unaffected parents, but also why healthy individuals can harbour quite large numbers of potentially disadvantageous variants in their genomes without suffering any obvious ill effects. Reduced penetrance can be a function of the specific mutation(s) involved or of allele dosage. It may also result from differential allelic expression, copy number variation or the modulating influence of additional genetic variants in cis or in trans. The penetrance of some pathogenic genotypes is known to be age- and/or sex-dependent. Variable penetrance may also reflect the action of unlinked modifier genes, epigenetic changes or environmental factors. At least in some cases, complete penetrance appears to require the presence of one or more genetic variants at other loci. In this review, we summarize the evidence for reduced penetrance being a widespread phenomenon in human genetics and explore some of the molecular mechanisms that may help to explain this enigmatic characteristic of human inherited disease.

F8 gene dosage defects in atypical patients with severe haemophilia A

We performed molecular analysis of the factor 8 gene (F8) in 272 unrelated Spanish patients with haemophilia A (HA) and detected a mutation by routine analysis in 267 of them (98.1%). No mutation was detected in the remaining five patients despite clinical and laboratory confirmation of HA. The aim is to describe the molecular alterations in F8 discovered by gene dosage methodologies in three of these patients. For methodology, F8 sequencing, intragenic marker analysis, multiplex ligation-dependent probe amplification and quantitative real time-PCR were followed. One patient had Klinefelter syndrome (47,XXY) and a large deletion spanning exons 1-12 masked by the other F8 allele; the second patient showed a large duplication spanning exons 2-10 and the third patient revealed a non-contiguous double duplication of exons 14 and 23-25. The remaining two patients had mild HA and dosage results were normal. The application of gene dosage methods is useful to define haemophilic patients in whom mutations are not detected using other routine methods. Nevertheless, in a small percentage of patients (<1%), no molecular pathology can be identified after testing several genetic methodologies.

Twins Reared Apart: A Forgotten Case / Twin Research Reviews: X-Inactivation and Female Co-Twin Discordance for Hemophilia; Transplantation for Breast Reconstruction; Chimerism and Telomere Attrition in Dizygotic Twins; Divergent Life Histories in Twins Reared Apart / Current Concerns: High ACT-Scoring Twins; Dating a Twin; When Gender Identities Diverge / The Holland Twins

A forgotten story of monozygotic twins reared apart is described. The pair, born in 1941 in Fribourg, Switzerland, were separated due to switch-baby incident in the hospital. This caused one twin to be raised as a singleton by an unrelated family, and the other twin to be raised as a ‘dizygotic’ twin with an unrelated child. This is followed by reviews of recent twin research and case studies of X-inactivation and hemophilia, breast reconstruction, chimerism and life histories. The final section of the article includes human interest pieces on academic twins, dating twins, transsexual twins and athletic twins.

An Investigation Into Etiological Pathways of DCD and ADHD Using a Monozygotic Twin Design

We previously described a co-twin control design using questionnaire data on monozygotic twins discordant and concordant for developmental coordination disorder (DCD) and attention deficit hyperactivity disorder (ADHD). Our results suggested that DCD and developmental ADHD had different causal pathways, and that second-born twins were at higher risk for oxygen perfusion problems than first-born twins. In the current study we further explored our findings using DNA confirmed zygosity and assessments of 4 female and 10 male sets of monozygotic twins, aged 8 to 17 years, from the first study. Using the McCarron Assessment of Neuromuscular Development (MAND), twice as many second- as first-born twins met criteria for DCD. Second-born twins attained significantly lower scores on 1-minute Apgar, MAND Gross Motor, Bimanual Dexterity and Neuromuscular Development Index. Seven of the nine twins who met criteria for DCD experienced perinatal oxygen perfusion problems. This supported findings in the first study of an association between perinatal oxygen perfusion problems and DCD, and our hypothesis that DCD and cerebral palsy have similar causal pathways. We found similar numbers of males and females discordant for DCD. On telephone interview using the Diagnostic Interview Schedule for Children Parent Interview, the only first-, and all five second-born twins who met criteria for ADHD had an inattentive component — three Inattentive; three Combined. All twins positive for ADHD were male. This adds support to our hypothesis that ADHD symptoms found in some participants may reflect secondary ADHD associated with environmental factors, rather than developmental ADHD.

The value of twins in epigenetic epidemiology

During past decades, twin studies have played an important role in genetic epidemiology studies of complex traits. The strength of twin studies lies in the ability to disentangle genetic and environmental factors that contribute to a phenotype, by comparing genetically identical monozygotic twins to dizygotic twins, who share on average 50% of genetic variants. Twin studies now offer the opportunity to study epigenetic variation across the genome with two aims. First, twin studies can improve our understanding of the factors regulating epigenetic variability by assessing the heritability of epigenetic variants. Secondly, the use of twins in epigenetic research is increasingly recognized as an important approach to help unravel the complexities associated with human development and disease. The strategic use of identical twins discordant for complex disease has revealed the importance of linking epigenetic disruption to the disease-associated risk in humans. Lastly, we also discuss the possibility that epigenetic effects on disease may in part explain some of the missing heritability in genome-wide association studies. The study of human epigenetic factors in twins can inform the role of genetics, as well as in utero and postnatal environments to the establishment, maintenance and functional consequences of human epigenome variation.

Noninvasive prenatal diagnosis of hemophilia by microfluidics digital PCR analysis of maternal plasma DNA

Hemophilia is a bleeding disorder with X-linked inheritance. Current prenatal diagnostic methods for hemophilia are invasive and pose a risk to the fetus. Cell-free fetal DNA analysis in maternal plasma provides a noninvasive mean of assessing fetal sex in such pregnancies. However, the disease status of male fetuses remains unknown if mutation-specific confirmatory analysis is not performed. Here we have developed a noninvasive test to diagnose whether the fetus has inherited a causative mutation for hemophilia from its mother. The strategy is based on a relative mutation dosage approach, which we have previously established for determining the mutational status of fetuses for autosomal disease mutations. In this study, the relative mutation dosage method is used to deduce whether a fetus has inherited a hemophilia mutation on chromosome X by detecting whether the concentration of the mutant or wild-type allele is overrepresented in the plasma of heterozygous women carrying male fetuses. We correctly detected fetal genotypes for hemophilia mutations in all of the 12 studied maternal plasma samples obtained from at-risk pregnancies from as early as the 11th week of gestation. This development would make the decision to undertake prenatal testing less traumatic and safer for at-risk families.

The first case described: monozygotic twin sisters with the fragile X premutation but with a different phenotype for premature ovarian failure

OBJECTIVE

To describe the first case of monozygotic twin sisters with fragile X premutation and discordance for premature ovarian failure (POF).

DESIGN

A descriptive case study.

SETTING

Academic center.

PATIENT(S)

Monozygotic twin sisters with fragile X premutation and discordance for POF.

INTERVENTION(S)

Serum laboratory testing, fragile X premutation screening, zygosity testing, X-inactivation ratio and Southern blot studies.

MAIN OUTCOME MEASURE(S)

Incidence of POF in this twin cohort.

RESULT(S)

Zygosity analysis using polymerase chain reaction of 15 polymorphic markers via capillary gel electrophoresis in these patients confirmed their monozygosity. X-inactivation studies were performed using the human androgen receptor (HUMARA) gene and revealed similar X-inactivation ratios for both the patient and her sister (11:89 and 12:88, respectively) from peripheral serum samples. Southern blot evaluation of the proband and her sister revealed a similar methylation pattern in which the premutation allele was unmethylated much more than the normal allele. The contribution of the premutation on the active allele as determined by Southern blot analysis was consistent between sisters.

CONCLUSION(S)

The inactivation ratio studies and subsequent Southern blot analysis do not show differences between the patients; therefore, we are unable to identify a causative mechanism for the identical sisters' discordant phenotypes. It is possible that the inactivation ratios observed from the peripheral blood specimens obtained from the sisters do not represent the allele expression and skewing present at the level of the ovary.

Molecular pathology of haemophilia A in Indian patients: identification of 11 novel mutations

BACKGROUND

The identification of pathogenic mutations in haemophilia A (HA) patients is important as a basis for genetic diagnosis and also for the assessment of clinical manifestations.

METHOD

We analyzed 36 inversion negative congenital HA cases (28 unrelated and 8 familial) by multiplex PCR and the conformation sensitive gel electrophoresis (CSGE) technique, followed by DNA sequencing. The pathogenicity of each of these mutations was assessed using various prediction software.

RESULTS

We found 17 missense, 5 deletions, 3 insertions, and 2 nonsense mutations, out of which 16 were recurrent and 11 novel. All novel substitution mutations were found to be deleterious using the prediction softwares. We also encountered a double mutation (1 novel and 1 hot-spot mutation) in a family with a strong family history. A missense mutation in heterozygous state was also detected in a female bleeder with very low factor VIII levels, probably due to extreme lyonization.

CONCLUSION

High heterogeneity in mutational profile has been observed in the present study. The outcome of this study would enable us to give an accurate diagnosis in all affected families by direct mutation analysis.

Identical but not the same: the value of discordant monozygotic twins in genetic research

Monozygotic (MZ) twins show remarkable resemblance in many aspects of behavior, health, and disease. Until recently, MZ twins were usually called "genetically identical"; however, evidence for genetic and epigenetic differences within rare MZ twin pairs has accumulated. Here, we summarize the literature on MZ twins discordant for Mendelian inherited disorders and chromosomal abnormalities. A systematic literature search for English articles on discordant MZ twin pairs was performed in Web of Science and PubMed. A total number of 2,016 publications were retrieved and reviewed and 439 reports were retained. Discordant MZ twin pairs are informative in respect to variability of phenotypic expression, pathogenetic mechanisms, epigenetics, and post-zygotic mutagenesis and may serve as a model for research on genetic defects. The analysis of single discordant MZ twin pairs may represent an elegant approach to identify genes in inherited disorders.

X chromosome inactivation in clinical practice

X chromosome inactivation (XCI) is the transcriptional silencing of the majority of genes on one of the two X chromosomes in mammalian females. Females are, therefore, mosaics for two cell lines, one with the maternal X and one with the paternal X as the active chromosome. The relative proportion of the two cell lines, the X inactivation pattern, may be analyzed by simple assays in DNA from available tissues. This review focuses on medical issues related to XCI in X-linked disorders, and on the value of X inactivation analysis in clinical practice.