The dominant limb preferentially stabilizes posture in a bimanual task with physical coupling.

Humans are endowed with an ability to skillfully handle objects, like when holding a jar with the nondominant hand while opening the lid with the dominant hand. Dynamic dominance, a prevailing theory in handedness research, proposes that the nondominant hand is specialized for postural stability, which would explain why right-handed people hold the jar steady using the left hand. However, the underlying specialization of the nondominant hand has only been tested unimanually, or in a bimanual task where the two hands had different functions. Using a dedicated dual-wrist robotic interface, we tested the dynamic dominance hypothesis in a bimanual task where both hands carry out the same function. We examined how left- and right-handed subjects held onto a vibrating virtual object using their wrists, which were physically coupled by the object. Muscular activity of the wrist flexors and extensors revealed a preference for cocontracting the dominant hand during both holding and transport of the object, which suggests proficiency in the dominant hand for stabilization, contradicting the dynamic dominance hypothesis. While the reliance on the dominant hand was partially explained by its greater strength, the Edinburgh inventory was a better predictor of the difference in the cocontraction between the dominant and nondominant hands. When provided with redundancy to stabilize the task, the dominant hand preferentially cocontracts to absorb perturbing forces.NEW & NOTEWORTHY We found that subjects prefer to stabilize a bimanually held object by cocontracting their dominant limb, contradicting the established view that the nondominant limb is specialized toward stabilization.

Pharmacological considerations in antipsychotic drug selection for prevention of drug-induced dysphagia.

Antipsychotic drugs have the ability to induce dysphagia. The aim of this study was to determine the association between the receptor affinity of antipsychotic drugs and the time-to-onset of dysphagia, and to identify factors that prevent antipsychotic drug-induced dysphagia. We used the receptor affinity of 13 antipsychotic drugs for which data were reported in an in vitro test using human receptors, extracted time-to-onset dysphagia from the Japan Adverse Drug Event Report database, and used data from 46 patients to evaluate the correlation between receptor affinity and time-to-onset of dysphagia. We found a negative correlation between D2 receptor affinity and time-to-onset of dysphagia (r = -0.4572, p = 0.0016), and a positive correlation between H1, M1, and M3 receptor affinity and time-to-onset of dysphagia (r = 0.5006, p = 0.0006; r = 0.4130, p = 0.0059; and r = 0.4149, p = 0.0057, respectively). Antipsychotic drugs with a strong D2 receptor-blocking action may accelerate the onset of dysphagia, whereas a strong H1, M1, and M3 receptor-blocking action may delay the onset of dysphagia. The current study revealed the relationship between the receptor affinity of antipsychotic drugs and the time-to-onset of dysphagia, which should aid in the selection of antipsychotic drugs, while preventing dysphagia.

Assessment of "look-alike" packaging designs related to medication errors using information technology.

This study aimed to assess the similarity among press-through pack (PTP) sheets of pharmaceutical products in Japan. The appearance of PTPs was assessed using a pharmaceutical design database (PDD) of 2,750 pharmaceutical tablets comprising approximately 40 % of the 6,840 products marketed in Japan. Package sheet color (Sc), tablet color (Tc), character color (Cc), sheet line color (SLc), and upper color (Uc) were used to evaluate the uniformity of PTP sheet design. To assess the risk of misidentification, 1,000 prescriptions for 82,273 cancer patients were retrieved from 21,026,742 records in the claims database of the Japan Medical Data Center Co. Ltd., Tokyo, Japan. The most frequent PTP sheet colors for 143 drugs were Sc (silver), Tc (white), Cc (blue), SLc (none), and Uc (silver). The prescribing pattern of 1000 randomly chosen prescriptions was analyzed. Database records of prescriptions without tablets (n = 69), including only one PTP tablet (n = 292), and those with lack of PDD prescription data (n = 388) were excluded. Eventually, 236 prescriptions were evaluated. Fourteen prescriptions (5.9%) had PTP sheets with five matching elements and 29 had with four matching elements (12.3%). This novel PDD database for information technology concept easily identified similar PTP sheets involved in prescriptions dispensed in 18 % of evaluated cancer patients. The concept seems to be applicable for preventing look-alike dispensing errors.

Distinct X chromosomal rearrangements in four haemophilia B patients with entire F9 deletion.

INTRODUCTION: Haemophilia B is an X-linked bleeding disorder caused by a coagulation factor IX gene (F9) abnormality. Numerous F9 defects have been identified to date; however, only a few with an entire F9 deletion have been reported in detail. AIM: To elucidate the cause of severe haemophilia B, we investigated the precise X chromosome abnormalities in four Japanese patients who did not show all amplifications in F9-specific PCR. METHODS: We analysed the patient's genomic DNA using Multiplex ligation-dependent probe amplification (MLPA). To assess the extent of any deletions, we further performed mapping PCRs, inverse PCRs or long-range PCRs and direct sequencing analyses of the X chromosome. RESULTS: We detected entire F9 deletions in four haemophilia B patients and identified the precise deleted regions of the X chromosome including F9. Patient 1 had a 149-kb deletion with breakpoints 90-kb upstream and 30-kb downstream from F9. Patients 2 and 3 showed 273-kb and 1.19-Mb deletions respectively. Patient 4 had two deleted regions: a 1663-bp deletion 1.34-Mb upstream from F9 and a 7.2-Mb deletion including F9. These distinct breakpoints found in four different patients suggest that the mechanism of X chromosome deletion may be different between individuals. Non-allelic homologous recombination (NAHR), microhomology-mediated break-induced replication (MMBIR) or fork stalling and template switching (FoSTeS) may occur in respective X chromosomes of the four haemophilia B patients analysed. CONCLUSIONS: We identified diverse X chromosomal rearrangements in four haemophilia B patients, which might be caused by distinct mechanisms of genomic rearrangement.

Sphingosine kinase 1 expression is downregulated during differentiation of Friend cells due to decreased c-MYB.

Sphingosine kinase 1 (SPHK1) overexpression in malignant cells has been reported. Mouse Friend cells showed higher SPHK1 but not SPHK2 expression compared with other mouse cell lines. A Sphk1 promoter analysis demonstrated the region between -53bp and the first exon as the minimal promoter. Further promoter truncation revealed the importance of a MYB-binding site. EMSA using this region as the probe demonstrated one band containing c-MYB protein, and its intensity decreased during erythroid differentiation with hexamethylane bisacetamide (HMBA), a potent inducer of erythroid differentiation of Friend cells. ChIP assay also revealed in vivo binding of c-MYB. c-MYB overexpression and siRNA for c-Myb affected SPHK1 expression, confirming the important regulatory role of c-MYB in SPHK1 expression. HMBA reduced c-MYB expression rapidly. Induced differentiation by HMBA caused a marked and rapid reduction of SPHK1 mRNA, protein and enzyme activity leading to the rapid decrease of cellular sphingosine 1-phosphate level. Moreover, terminally differentiated cells did not resume SPHK1 expression. Compared with original Friend cells, stable overexpression of wild-type SPHK1 showed higher cell proliferation, resistance to cell death by serum depletion. Interestingly, HMBA-induced differentiation of these cells was delayed but not completely suppressed. In contrast, SPHK inhibitor and its siRNA inhibited cell growth and enhanced HMBA-induced differentiation significantly, suggesting that SPHK1 delayed HMBA-induced differentiation by its cell proliferation-promoting activity. Effects of pertussis toxin, a G-protein-coupled receptor inhibitor, and S1P receptor antagonist on Friend cell growth and differentiation were negligible, suggesting the importance of the intracellular SPHK1/S1P signaling in Friend cells.

Effects of fermented soymilk with Lacticaseibacillus paracasei YIT 9029 on gut microbiota and defecation habits: a randomised, double-blind, placebo-controlled study.

Previous studies have demonstrated that soymilk and Lacticaseibacillus paracasei YIT 9029 (strain Shirota: LcS) each beneficially affect the gut microbiota and defecation habits. To investigate the effects of daily consumption of fermented soymilk containing LcS (FSM), we conducted a randomised, double-blind, placebo-controlled study of 112 healthy Japanese adults with a low faecal Bifidobacterium count. They consumed 100 ml FSM or placebo (unfermented soymilk base) once daily for 4 weeks. Their gut microbiota was analysed by 16S rRNA gene amplicon sequencing and quantitative reverse transcription-polymerase chain reaction (PCR), and faecal short-chain fatty acids (SCFAs) and urinary putrefactive products were assessed during the pre- and post-consumption periods. Defecation habits were examined weekly using a subjective questionnaire. In the post-consumption period, living LcS were not detected in two subjects in the FSM group (n = 57) but were detected in one subject in the SM group (n = 55). The FSM group had a significantly higher number and relative abundance of faecal lactobacilli compared with the placebo group. The relative abundance of Bifidobacterium, alpha-diversity of microbiota, and concentrations of acetate and total SCFAs in faeces were significantly increased in the FSM group, although no significant differences were detected between the groups. The number of defecations and defecation days per week significantly increased in both groups. Subgroup analysis of 109 subjects, excluding 3 with inconsistent LcS detection (2 and 1 subjects in the FSM and SM groups, respectively), revealed that the FSM group (n = 55) had significantly greater increases in faecal acetate concentration compared with the SM group (n = 54) and significant upregulation of pathways related to energy production or glucose metabolism in the gut microbiota. These findings suggest that daily FSM consumption improves the gut microbiota and intestinal environment in healthy adults and may help to maintain health and prevent diseases. Registered at the University Hospital Medical Information Network (UMIN) clinical trials registry under: UMIN 000035612.

Multidirectional lip-closing force in adults with mandibular deviation.

The purpose of this study was to investigate the relationship between multidi-rectional lip-closing force and facial soft tissue morphology in adults with mandibular deviation. Fifteen Japanese adults with mandibular deviation participated in this study. The deviation value was defined as the horizontal distance between soft tissue menton and the facial midline. The side of the soft tissue menton relative to the facial midline was defined as the deviated side and the opposite side as the non-deviated side. The signals of directional lip-closing force (DLCF) were investigated in 8 directions. Total lip-closing force (TLCF) was calculated by adding DLCFs in 8 directions. Correlations and differences between the variables were analysed statistically. Significant positive correlations between TLCF and DLCFs were determined in six directions with the exception of the horizontal direction. Significant positive correlations for seven pairs of opposing DLCFs were found. The lower non-deviated DLCF was smaller than the three pairs of opposing lip-closing forces. Negative significant correlation was found between the deviation value and the upper deviated DLCF (P < 0·05). In individuals with mandibular deviation, lip-closing force in the lower non-deviated direction was found to be smaller than the opposing lip-closing forces. When mandibular deviation was greater, the upper deviated lip-closing force was smaller.

Mesp2 initiates somite segmentation through the Notch signalling pathway.

The Notch-signalling pathway is important in establishing metameric pattern during somitogenesis. In mice, the lack of either of two molecules involved in the Notch-signalling pathway, Mesp2 or presenilin-1 (Ps1), results in contrasting phenotypes: caudalized versus rostralized vertebra. Here we adopt a genetic approach to analyse the molecular mechanism underlying the establishment of rostro-caudal polarity in somites. By focusing on the fact that expression of a Notch ligand, Dll1, is important for prefiguring somite identity, we found that Mesp2 initiates establishment of rostro-caudal polarity by controlling two Notch-signalling pathways. Initially, Mesp2 activates a Ps1-independent Notch-signalling cascade to suppress Dll1 expression and specify the rostral half of the somite. Ps1-mediated Notch-signalling is required to induce Dll1 expression in the caudal half of the somite. Therefore, Mesp2- and Ps1-dependent activation of Notch-signalling pathways might differentially regulate Dll1 expression, resulting in the establishment of the rostro-caudal polarity of somites.

The psychiatric disease risk factors DISC1 and TNIK interact to regulate synapse composition and function.

Disrupted in schizophrenia 1 (DISC1), a genetic risk factor for multiple serious psychiatric diseases including schizophrenia, bipolar disorder and autism, is a key regulator of multiple neuronal functions linked to both normal development and disease processes. As these diseases are thought to share a common deficit in synaptic function and architecture, we have analyzed the role of DISC1 using an approach that focuses on understanding the protein-protein interactions of DISC1 specifically at synapses. We identify the Traf2 and Nck-interacting kinase (TNIK), an emerging risk factor itself for disease, as a key synaptic partner for DISC1, and provide evidence that the DISC1-TNIK interaction regulates synaptic composition and activity by stabilizing the levels of key postsynaptic density proteins. Understanding the novel DISC1-TNIK interaction is likely to provide insights into the etiology and underlying synaptic deficits found in major psychiatric diseases.

Cyclooxygenase-2 inhibition restores ultraviolet B-induced downregulation of ATP2A2/SERCA2 in keratinocytes: possible therapeutic approach of cyclooxygenase-2 inhibition for treatment of Darier disease.

BACKGROUND: ATP2A2 encoding the sarcoplasmic/endoplasmic reticulum Ca(2+) -ATPase2 (SERCA2) is a Darier disease (DD)-related gene. Ultraviolet (UV) B irradiation downregulates ATP2A2/SERCA2 expression in keratinocytes, whereas cyclooxygenase-2 (COX-2) expression is dramatically upregulated by UVB. OBJECTIVES: To analyse the involvement of COX-2 in ATP2A2/SERCA2 expression. METHODS: Keratinocytes were transfected with COX-2 siRNA or treated with COX-2 inhibitor, celecoxib, to evaluate the effect of COX-2 on ATP2A2/SERCA2 expression. Quantitative real-time polymerase chain reaction, Western blotting analysis and reporter assay were used to determine the amount of mRNA, protein level and transcription activity, respectively. RESULTS: COX-2 knockdown by siRNA resulted in upregulation of ATP2A2 transcription. Treatment by celecoxib rescued UVB-mediated suppression of the ATP2A2 transcription and SERCA2 protein expression. Simple addition of prostaglandin (PG) E(2) , which is a product of COX-2 enzyme, reduced the amounts of ATP2A2 mRNA and SERCA2 protein in keratinocytes. CONCLUSIONS: UVB downregulates ATP2A2/SERCA2 expression via induction of COX-2 expression and subsequent increase of PGE(2) production in keratinocytes. Considering that DD is caused by the decreased function of SERCA2 due to the reduced expression of the ATP2A2 gene, this finding shows the possibility that COX-2 inhibition may be useful to prevent and/or treat DD.

Double-balloon endoscopy versus magnet-imaging enhanced colonoscopy for difficult colonoscopies, a randomized study.

BACKGROUND AND STUDY AIMS: Studies have estimated that failure of cecal intubation occurs with conventional colonoscopy in up to 10 % of cases. Double-balloon endoscopy (DBE) systems, magnetic endoscope imaging (MEI), and transparent cap have been shown to improve success rates for colonoscopy. This study evaluated the utility of DBE for complete examination of the colon compared with MEI plus cap (MEI-Cap) after incomplete or technically difficult colonoscopy in a randomized comparative manner. PATIENTS AND METHODS: A total of 94 patients with incomplete or technically difficult colonoscopy were randomly assigned to receive either DBE (n = 47) or colonoscopy with MEI-Cap (n = 47). The primary end point was cecal intubation rate within 30 minutes. Secondary end points included intubation time, pain score using a visual analog scale, abdominal pressure attempts, doses of sedative medication, and changes in patient position during colonoscopy. RESULTS: Patient characteristics were comparable in both groups. Cecal intubation rate within 30 minutes was significantly higher for DBE (45 /47, 95.7 %) than for MEI-Cap (34 /47, 72.3 %) (P = 0.0049). Mean time to reach the cecum was significantly lower in the DBE group (13.0 ±â€Š5.3 minutes) than in the MEI-Cap group (16.4 ±â€Š4.8 minutes; P = 0.0003). No complications were encountered in either group.   CONCLUSION: DBE is more useful for complete examination of the colon than MEI-Cap in patients with incomplete or technically difficult colonoscopy.

FcepsilonRIalpha gene (FCER1A) promoter polymorphisms and total serum IgE levels in Japanese atopic dermatitis patients.

Two promoter polymorphisms of the high-affinity IgE receptor alpha-subunit (FcepsilonRIalpha) gene (FCER1A), -66T>C (rs2251746) and -315C>T (rs2427827), were analysed in Japanese atopic dermatitis subjects. Patients with the -315CT/TT genotype tended to have higher total serum IgE levels, while the proportion of -315CT/TT genotype or the -315T allele was significantly higher in those with highly elevated total serum IgE concentrations.

A novel microsatellite polymorphism of sodium channel beta1-subunit gene (SCN1B) may underlie abnormal cardiac excitation manifested by coved-type ST-elevation compatible with Brugada syndrome in Japanese.

OBJECTIVE: Brugada syndrome (BrS) is a rare sodium channelopathy typically seen in middle-aged, Southeast Asian males conferring high risks of cardiac sudden death. Loss-of-function mutations in SCN5A encoding the alpha-subunit of cardiac sodium channels may account partially for its etiology. We aimed to study whether mutations in the beta-subunits of sodium channel (SCN1B and SCN2B) would also be associated with abnormal cardiac excitation in BrS. METHODS: 85 Japanese patients suspected to have BrS undertook a diagnostic challenge test with a sodium channel blocker, pilsicainide. Genetic screenings were performed for SCN5A, SCN1B and SCN2B by PCR-SSCP and direct sequence of amplicons in the patients and 50 healthy controls. RESULTS: 30 patients exhibited BrS-like ECG pattern (i.e., a coved-type ST-segment elevation) either at baseline or after the drug challenge. Genetic screenings revealed a sequence variation (p.R190Q) and 3 polymorphisms (p.H558R, p.R1193Q, IVS24+53T > C) in SCN5A, a sequence variation (g.-26G > T) and 2 polymorphisms (IVS1+53G > T and IVS3 +2996(TTA)8-15) in SCN1B and 2 polymorphisms (IVS2+27A > G, IVS2+76G > A) in SCN2B. A logistic analysis revealed that male, middle age (40 - 59 years of age) and IVS3+2996(TTA)8 of SCN1B were significantly (p < 0.05) associated with the development of BrS-like ECG pattern with odds ratios (95% confidence intervals) of 5.9 (1.8 - 19.6), 2.9 (1.4 - 6.1) and 2.3 (1.1 - 4.9), respectively. While the IVS3+2996(TTA)8 allele has not been reported in Caucasians previously, its allelic frequency in the patients exhibiting the BrS-like ECG pattern (0.250) was comparable to that in the healthy controls (0.260). CONCLUSION: The IVS3+ 2996(TTA)8 allele commonly seen in Japanese would not be pathogenic itself but may render male, middle-aged Japanese more susceptible to BrS.

Endpoint stiffness magnitude increases linearly with a stronger power grasp.

Humans can increase the endpoint stiffness of their arm to reduce self-generated movement variability and to reject unpredictable perturbations from the environment, like during handheld drilling, thereby increasing movement precision. Existing methods to estimate changes in the endpoint stiffness use robotic interfaces to apply position or force perturbations to measure the arm's dynamic response. We propose an alternative method of measuring changes in the power grasp force to estimate adaptations in the magnitude of the arm's endpoint stiffness. To validate our method, we examined how the strength of the power grasp, when holding onto a robotic manipulandum, affected the arm's endpoint stiffness in three different locations of the workspace. The endpoint stiffness magnitude increased linearly with the grasp force, and this linear relationship did not depend on the arm's posture or position in the workspace. The endpoint stiffness may have increased as a combination of greater grasp stiffness and greater arm stiffness, since larger co-contraction was observed in the elbow and shoulder with a stronger grasp. Changes in the grasp force could serve as a metric in assessing how humans adapt their endpoint stiffness magnitude.

p27 deregulation by Skp2 overexpression induced by the JAK2V617 mutation.

Janus kinase 2 (JAK2) V617F mutation has been regarded as the major cause of myeloproliferative disorders (MPD). However, the mechanisms of abnormal cell growth by JAK2V617F have not been elucidated. In this study, cell cycle regulatory protein expression was analyzed using JAK2V617F-Ba/F3 and mock-Ba/F3. JAK2V617F-Ba/F3, but not mock-Ba/F3, showed IL-3 independent cell growth and constitutive STATs activation. Deregulation of p27(Kip1), the cell cycle regulator at the G1 to S transition, was observed in JAK2V617F-Ba/F3 but not in mock-control. p27(Kip1) deregulation was not due to p27(Kip1) mRNA level but due to high Skp2 expression, a subunit of ubiquitin E3 ligase, through the STAT binding in the Skp2 promoter. Like JAK2V617F overexpression, constitutively active STAT5 or STAT3 induced aberrant p27(Kip1) expression of Ba/F3 cells. Similar findings were observed in BCR/ABL-transfected Ba/F3. Our results elucidate the regulatory mechanism by which JAK2V617F modulates Skp2 gene expression through the STAT transcription factors.

Increase in Grasp Force Reflects a Desire to Improve Movement Precision.

Grasping is an action engraved in the human genome, enabling newborn infants to hang from a monkey-bar immediately after birth. The grasp force provides rich information about the brain's control of arm movements. In this study, we tested the hypothesis that the grasp force increases to improve the hand's movement precision during reaching. In two reaching experiments, subjects increased grasp force to suppress movement imprecision that arose from both self-generated motor noise and from an unpredictable environment. Furthermore, the grasp force did not increase constantly, but increased specifically along the movement where the hand's deviation was greatest. The increased grasp was premeditated and was not a reaction to environmental forces, suggesting that the central nervous system has a predictive, state-dependent model of movement precision during reaching. The grasp force provides a high temporal resolution and calibration-less estimate of movement precision adaptation.

Ewing's sarcoma fusion protein, EWS/Fli-1 and Fli-1 protein induce PLD2 but not PLD1 gene expression by binding to an ETS domain of 5' promoter.

It was reported that short interfering RNA (siRNA) of EWS/Fli-1 downregulated phospholipase D (PLD)2 in Ewing's sarcoma (EWS) cell line, suggesting that PLD2 is the target of aberrant transcription factor, EWS/Fli-1. Here, we further investigated the regulation of PLD2 gene expression by EWS/Fli-1 and Fli-1 in another EWS cell line, and also in EWS/Fli-1- or Fli-1-transfected cell line. EWS/Fli-1- or Fli-1-overexpressed cells showed higher PLD2 but not PLD1 protein expression and enhanced cell proliferation as compared to mock transfectant. The treatment of these cells with 1-butanol or siRNA of PLD2 inhibited cell growth, suggesting the pivotal role of PLD in cell growth promotion. PLD2 but not PLD1 mRNA level was also increased in EWS/Fli-1 or Fli-1-transfectants. After determining the transcription initiation points, we cloned the 5' promoter of both PLD1 and PLD2 and analysed promoter activities. Results showed that EWS/Fli-1 and Fli-1 increase PLD2 gene expression by binding to an erythroblast transformation-specific domain (-126 to -120 bp from the transcription initiation site) of PLD2 promoter, which is the minimal and most powerful region. Electrophoresis mobility shift assay using truncated proteins showed that both DNA-binding domain and trans-activating domain were necessary for the enhanced gene expression of PLD2.

L1503R is a member of group I mutation and has dominant-negative effect on secretion of full-length VWF multimers: an analysis of two patients with type 2A von Willebrand disease.

Type 2A von Willebrand disease (VWD) is characterized by decreased platelet-dependent function of von Willebrand factor (VWF); this in turn is associated with an absence of high-molecular-weight multimers. Sequence analysis of the VWF gene from two unrelated type 2A VWD patients showed an identical, novel, heterozygous T-->G transversion at nucleotide 4508, resulting in the substitution of L1503R in the VWF A2 domain. This substitution, which was not found in 60 unrelated normal individuals, was introduced into a full-length VWF cDNA and subsequently expressed in 293T cells. Only trace amount of the mutant VWF protein was secreted but most of the same was retained in 293T cells. Co-transfection experiment of both wild-type and mutant plasmids indicated the dominant-negative mechanism of disease development; as more of mutant DNA was transfected, VWF secretion was impaired in the media, whereas more of VWF was stored in the cell lysates. Molecular dynamic simulations of structural changes induced by L1503R indicated that the mean value of all-atom root-mean-squared-deviation was shifted from those with wild type or another mutation L1503Q that has been reported to be a group II mutation, which is susceptible to ADAMTS13 proteolysis. Protein instability of L1503R may be responsible for its intracellular retention and perhaps the larger VWF multimers, containing more mutant VWF subunits, are likely to be mal-processed and retained within the cell.

Skewed X chromosome inactivation in fraternal female twins results in moderately severe and mild haemophilia B.

Female carriers of haemophilia B are usually asymptomatic; however, the disease resulting from different pathophysiological mechanisms has rarely been documented in females. In this study, we investigated the mechanisms responsible for haemophilia B in fraternal female twins. We sequenced the factor IX gene (F9) of the propositus, her father, a severe haemophilia B patient and the other family members. X chromosome inactivation was assessed by the methylation-sensitive HpaII-PCR assay using X-linked polymorphisms in human phosphoglycerate kinase 1 gene (PGK1) and glutamate receptor ionotropic AMPA 3 gene (GRIA3). The twins were found to be heterozygotes with a nonsense mutation (p.Arg384X) inherited from their father. The propositus, more severely affected twin, exhibited a significantly higher percentage of inactivation in the maternally derived X chromosome carrying a normal F9. The other twin also showed a skewed maternal X inactivation, resulting in a patient with mild haemophilia B. Thus, the degree of skewing of maternal X inactivation is closely correlated with the coagulation parameters and the clinical phenotypes of the twins. Furthermore, we identified a crossing-over in the Xq25-26 region of the maternal X chromosome of the more severely affected twin. This crossing-over was absent in the other twin, consistent with their fraternal state. Differently skewed X inactivation in the fraternal female twins might cause moderately severe and mild haemophilia B phenotypes, respectively.