Evaluation of von Willebrand factor phenotypes and genotypes in Hemophilia A patients with and without identified F8 mutations.

BACKGROUND: Hemophilia A (HA) is an X-linked bleeding disorder caused by a deficiency in factor VIII (FVIII). von Willebrand disease (VWD) is characterized by a quantitative or qualitative defect in von Willebrand factor (VWF). Patients with VWD with severely low VWF or VWD Type 2N (VWD2N), a VWD subtype distinguished by defective VWF binding to FVIII, may have reduced FVIII levels secondary to their VWD. These patients superficially resemble patients with HA and pose a potential for misdiagnosis. OBJECTIVES: To investigate the unexplained cause of bleeding in HA patients without known FVIII mutations by assessing plasma VWF antigen (VWF:Ag), FVIII binding capacities and VWF genotypes. PATIENTS/METHODS: Thirty-seven of 1027 patients with HA studied as part of the Hemophilia Inhibitor Research Study lacked identifiable F8 mutations. These patients (cases) and 73 patients with identified F8 mutations (controls) were evaluated for VWF:Ag, a patient's VWF capacity to bind FVIII (VWF:FVIIIB) and VWF sequence. RESULTS: Four cases had VWF:Ag < 3 IU dL(-1) and VWF mutations consistent with Type 3 VWD. Six cases and one control were heterozygous for mutations previously reported to cause Type 1 VWD (VWD1) (n = five cases and one control) or predicted to be deleterious by Polyphen2 and SIFT prediction tools (n = 1 case). One control had VWF:Ag < 30 IU dL(-1) and seven patients (four cases and three controls), including two cases who were heterozygous for a known VWD2N mutation, had reduced VWF:FVIIIB. CONCLUSIONS: These data emphasize that some patients diagnosed with HA require VWF assessments in order to achieve a comprehensive diagnosis and an optimal treatment strategy.

Analysis of a malsegregating mouse Y chromosome: evidence that the earliest cleavage divisions of the mammalian embryo are non-disjunction-prone.

Despite the clinical importance of human aneuploidy, we know little of the causes of mammalian non-disjunction. In part, this reflects the fact that, unlike lower organisms, segregation 'impaired' chromosomes are virtually non-existent in mammals. To address this issue, we have studied the mouse Y chromosome on the BALB/cWt ('Wt') inbred background, a system in which loss of the Y chromosome in gonadal tissue has been linked to hermaphroditism. Our results indicate that the Wt Y chromosome is stably transmitted during meiotic cell divisions, but non-disjoins at an extremely high frequency in mitosis. Surprisingly, the non-disjunction events are largely restricted to the earliest cleavage divisions, indicating that there is a temporal 'window' during which the Wt Y chromosome is susceptible to non-disjunction. The non-disjunction phenotype has both cis and trans components: the Wt Y chromosome malsegregates on a variety of genetic backgrounds, demonstrating an intrinsic defect; however, the incidence of non-disjunction is significantly influenced by strain background, indicating the existence of modifying loci and thus providing evidence for a genetic effect on mammalian non-disjunction. These studies suggest that the earliest cell divisions in mammals are non-disjunction-prone, an interpretation which provides an explanation for the high rate of chromosome mosaicism observed in studies of in vitro fertilization (IVF)-derived human preimplantation embryos. Further, our observations raise the possibility that the IVF setting adversely affects chromosome segregation and suggest that genetic quality be an important consideration in any attempt to improve or modify in vitro procedures for use on human eggs and embryos.

Alphoid variant-specific FISH probes can distinguish autosomal meiosis I from meiosis II non-disjunction in human sperm.

Over the past few years, several groups have used fluorescence in situ hybridization (FISH) to study aneuploidy in human sperm. Several important observations have derived from these studies, including the demonstration of chromosome-specific variation in non-disjunction frequencies, and the possible association of aneuploidy with environmental agents and with increasing paternal age. However, an important technical limitation of these studies has been the inability to distinguish between autosomal non-disjunction occurring at meiosis I and meiosis II. In the present report, we describe a simple FISH-based approach designed to overcome this limitation. Using oligonucleotide probes capable of distinguishing subtle differences in the alpha satellite sequences of chromosome 17, we demonstrate that (in appropriate heterozygotes) it is possible to simultaneously identify disomic sperm and to determine the meiotic stage of origin of the additional chromosome. This novel approach has important implications for future FISH sperm studies, since the ability to distinguish between meiosis I and meiosis II non-disjunction will make it possible to determine whether putative etiological agents affect chromosome segregation at both, or only one, of the two meiotic stages.

Temporally unstable recurrence of earthquakes due to breaks in fractal scaling.

Observed sequences of large earthquakes are not consistent in either recurrence time or energy release; long-term prediction has been impossible even in areas, such as Parkfield, with well-defined recurrence intervals. The seismic gap hypothesis, which predicts characteristic earthquakes in areas of the circum-Pacific belt that have not produced recent great earthquakes, has also failed to predict the observed clustering of high-energy events. Models in which fractal scaling is broken at high magnitude predict that characteristic events and recurrence behavior will be unstable in time. The central predictions of these models are supported by recent observations at Landers and Big Bear in California.