A Locus for Autosomal Recessive Pseudoxanthoma Elasticum, with Penetrance of Vascular Symptoms in Carriers, Maps to Chromosome 16p13.1

Pseudoxanthoma elasticum (PXE) is a heritable systemic disorder characterized by calcification of the elastic fibers of the connective tissue. Symptoms are predominantly noted in the eye, the skin, and the cardiovascular system, resulting in visual loss, skin lesions, and life-threatening vascular disease. In this study we combined homozygosity mapping and genome scanning with 374 markers in affected individuals from a PXE family from a genetically isolated population in The Netherlands. Initial homozygosity in two or three patients was found with up to 20 markers, among which D16S292 located in 16p13.1. Upon refined and more extensive family screening of the latter region, close linkage without recombination was found with the marker D16S764 (Z_max=6.27). Despite clear autosomal recessive inheritance of the ocular symptoms in PXE, vascular symptoms appear in 40%–50% of the heterozygotes.     

Summaries from the XVIII World Congress of Psychiatric Genetics, Athens, Greece, 3-7 October 2010

The XVIIIth World Congress of Psychiatric Genetics, sponsored by The International Society of Psychiatric Genetics took place in Athens, Greece on October 3-7, 2010. Approximately 950 participants gathered to discuss the latest findings in this rapidly advancing field. The following report was written by junior travel awardees, as well as others who were volunteers from student meeting attendees. Each was assigned sessions as rapporteurs. This report represents some of the areas covered in oral presentation during the conference, and reports on some of the notable major new findings described at this 2010 World Congress of Psychiatric Genetics.     

Dppa2 and Dppa4 are closely linked SAP motif genes restricted to pluripotent cells and the germ line

Despite the enormous medical potential of ESCs, the molecular mechanisms conferring the ability to differentiate into all cell types of the embryo remain elusive. We used an in silico approach to identify genes expressed exclusively in mouse preimplantation embryos and pluripotent cell lines. Two of these genes were developmental pluripotency-associated gene 2 (Dppa2) and Dppa4, which we show are closely linked genes encoding putative nuclear SAP domain proteins expressed in human and mouse pluripotent stem cells and germ cell tumor-derived embryonal carcinoma cells. In the mouse, these genes are transcribed in germinal vesicle-stage oocytes and throughout the cleavage stages of embryogenesis. They then become restricted to the pluripotent inner cell mass of blastocysts and are subsequently downregulated. After gastrulation, Dppa2 and Dppa4 are expressed only in the developing germ line, showing that these genes mark cells of the pluripotent cycle. In the germ line, both genes are downregulated as the germ cells commit to the oogenic pathway or soon after commitment to the spermatogenic pathway. We have observed similar germ line expression profiles for other pluripotent markers, and these results are consistent with the hypothesis that pluripotent markers must be downregulated during fetal germ line development, a process that may be required to facilitate appropriate germ line differentiation. The study of expression and function of pluripotent markers such as Dppa2 and Dppa4 is likely to unveil new aspects of the regulation of pluripotency and germ line development in mammals.     

Genetic Relationships among Reptilian and Mammalian Campylobacter fetus Strains Determined by Multilocus Sequence Typing

Reptile Campylobacter fetus isolates and closely related strains causing human disease were characterized by multilocus sequence typing. They shared ∼90% nucleotide sequence identity with classical mammalian C. fetus, and there was evidence of recombination among members of these two groups. The reptile group represents a possible separate genomospecies capable of infecting humans.Campylobacter fetus is a human and animal pathogen which can be divided into two subspecies: subsp. fetus and subsp. venerealis (16). C. fetus subsp. fetus has a wide host range and causes abortions in sheep and cattle; C. fetus subsp. venerealis is host restricted, being isolated specifically from the bovine genital tract, and it causes fertility problems in cattle (5). C. fetus is an opportunistic pathogen in humans, particularly affecting severely immunocompromised patients. Initially, the bacterium can cause gastroenteritis; then, bacteremia can lead to septicemia and disseminated infections (1, 8). These two subspecies of mammalian C. fetus are referred to subsequently as “classical C. fetus.”A multilocus sequence typing (MLST) scheme has been developed for classical C. fetus (http://pubmlst.org/cfetus/) and used to genotype 140 isolates from humans and animals (14). The data showed that classical C. fetus is genetically homogeneous and clonal. C. fetus has also been isolated from reptiles (7), and DNA hybridization and nucleotide sequence data indicate that these reptile C. fetus isolates are genetically distinct from classical C. fetus (12). Reptile-like C. fetus strains have also been isolated from cases of human disease (11). In the present study, both the reptile and the human reptile-like strains are referred to collectively as “reptile C. fetus strains.”The MLST scheme for classical C. fetus was modified in this study to allow typing of reptile C. fetus (Table ​(Table1)1) and comparisons within and among Campylobacter species. The MLST method for classical C. fetus (15) was modified as follows. First, the annealing temperature of the PCR amplification was reduced to 47°C. Second, one of the oligonucleotide primers used to amplify the glyA locus (glyA2) was replaced with glyS4, 5′-AGGTGATTATCCGTTCCATCGC-3′, derived from the C. jejuni sequence. New allele and ST numbers were assigned, and the data were deposited at http://pubmlst.org/cfetus/. Data analysis was performed using the programs MEGA (http://www.megasoftware.net/) (9) and ClonalFrame (3). ClonalFrame is a model-based method for using multilocus sequence data to infer the clonal relationships of bacteria and the chromosomal position of homologous recombination events that disrupt a clonal pattern of inheritance.

TABLE 1.

MLST data for C. fetus reptile isolates recovered from humans and reptiles

Linkage analysis of anorexia and bulimia nervosa cohorts using selected behavioral phenotypes as quantitative traits or covariates.

To increase the likelihood of finding genetic variation conferring liability to eating disorders, we measured over 100 attributes thought to be related to liability to eating disorders on affected individuals from multiplex families and two cohorts: one recruited through a proband with anorexia nervosa (AN; AN cohort); the other recruited through a proband with bulimia nervosa (BN; BN cohort). By a multilayer decision process based on expert evaluation and statistical analysis, six traits were selected for linkage analysis (1): obsessionality (OBS), age at menarche (MENAR), and anxiety (ANX) for quantitative trait locus (QTL) linkage analysis; and lifetime minimum body mass index (BMI), concern over mistakes (CM), and food-related obsessions (OBF) for covariate-based linkage analysis. The BN cohort produced the largest linkage signals: for QTL linkage analysis, four suggestive signals: (for MENAR, at 10p13; for ANX, at 1q31.1, 4q35.2, and 8q13.1); for covariate-based linkage analyses, both significant and suggestive linkages (for BMI, one significant [4q21.1] and three suggestive [3p23, 10p13, 5p15.3]; for CM, two significant [16p13.3, 14q21.1] and three suggestive [4p15.33, 8q11.23, 10p11.21]; and for OBF, one significant [14q21.1] and five suggestive [4p16.1, 10p13.1, 8q11.23, 16p13.3, 18p11.31]). Results from the AN cohort were far less compelling: for QTL linkage analysis, two suggestive signals (for OBS at 6q21 and for ANX at 9p21.3); for covariate-based linkage analysis, five suggestive signals (for BMI at 4q13.1, for CM at 11p11.2 and 17q25.1, and for OBF at 17q25.1 and 15q26.2). Overlap between the two cohorts was minimal for substantial linkage signals.     

Positional cloning of the gene for X-linked retinitis pigmentosa 3: homology with the guanine-nucleotide-exchange factor RCC1

The gene for retinitis pigmentosa 3 (RP3), the most frequent form of X- linked RP (XLRP), has been mapped previously to a chromosome interval of less than 1000 kbp between the DXS1110 marker and the OTC locus at Xp21.1-p11.4. Employing a novel technique, YAC Representation Hybridization (YRH)', we have recently identified a small XLRP associated microdeletion in this interval, as well as several putative exons including the 3' end of a gene that was truncated by the deletion. cDNA library screening and sequencing of a cosmid centromeric to the deletion has now enabled us to identify numerous additional exons and to detect several point mutations in patients with XLRP. The predicted gene product shows homology to RCC1, the guanine-nucleotide- exchange factor (GEF) of the Ras-like GTPase Ran. Our findings suggest that we have cloned the long-sought RP3 gene, and that it may encode the GEF of a retina-specific GTP-binding protein.      

Localization of a novel X-linked congenital stationary night blindness locus: close linkage to the RP3 type retinitis pigmentosa gene region

X-linked congenital stationary night blindness (CSNBX) is anon-progressive retinal disorder characterized by decreasedvisual acuity and loss of night vision. CSNBX Is clinicallyheterogeneous with respect to the involvement of retinal rodsand/or cones in the disease. in this study, we localize a newlocus for CSNBX to Xp21.1, thus providing evidence that CSNBXis also genetically heterogeneous. A clear correlation betweendifferent genotypes and phenotypes cannot be found yet. Thenew CSNBX gene described here is closely linked to the X-linkedretinitis pigmentosa type 3 gene region, which supports thehypothesis that there may be a functional relationship betweencongenital stationary night blindness and retinitis pigmentosa.     

Generation and characterization of CD1d‐specific single‐domain antibodies with distinct functional features

Ligation of the CD1d antigen‐presenting molecule by monoclonal antibodies (mAbs) can trigger important biological functions. For therapeutic purposes camelid‐derived variable domain of heavy‐chain‐only antibodies (VHH) have multiple advantages over mAbs because they are small, stable and have low immunogenicity. Here, we generated 21 human CD1d‐specific VHH by immunizing Lama glama and subsequent phage display. Two clones induced maturation of dendritic cells, one clone induced early apoptosis in CD1d‐expressing B lymphoblasts and multiple myeloma cells, and another clone blocked recognition of glycolipid‐loaded CD1d by CD1d‐restricted invariant natural killer T (iNKT) cells. In contrast to reported CD1d‐specific mAbs, these CD1d‐specific VHH have the unique characteristic that they induce specific and well‐defined biological effects. This feature, combined with the above‐indicated general advantages of VHH, make the CD1d‐specific VHH generated here unique and useful tools to exploit both CD1d ligation as well as disruption of CD1d–iNKT interactions in the treatment of cancer or inflammatory disorders.     

Therapeutic problems in cyanide poisoning

In three patients with severe acute cyanide poisoning, a cyanosis was observed instead of the bright pink skin coloration often mentioned as a sign in textbooks. Treatment of cardiopulmonary insufficiency is as essential as antidotal therapy and the use of sodium nitrite and 4-DMAP is not without risk as, in practice, the methemoglobin-level induced is difficult to control.