Publications by authors named "Ekkehart Lausch"

49 Publications

Unsuccessful intravenous D-mannose treatment in PMM2-CDG.

Orphanet J Rare Dis 2019 10 22;14(1):231. Epub 2019 Oct 22.

Department of General Pediatrics, Adolescent Medicine and Neonatology, Faculty of Medicine, Medical Center - University of Freiburg, Mathildenstraße 1, 79106, Freiburg, Germany.

Background: PMM2-CDG (Phosphomannomutase 2 - Congenital disorder of glycosylation-Ia; CDG-Ia) is the most common glycosylation defect, often presenting as a severe multisystem disorder that can be fatal within the first years of life. While mannose treatment has been shown to correct glycosylation in vitro and in vivo in mice, no convincing effects have been observed in short-term treatment trials in single patients so far.

Results: We report on a boy with a severe PMM2-CDG who received a continuous intravenous mannose infusion over a period of 5 months during the first year of life in a dose of 0.8 g/kg/day. N-glycosylation of serum glycoproteins and mannose concentrations in serum were studied regularly. Unfortunately, no biochemical or clinical improvement was observed, and the therapy was terminated at age 9 months.

Conclusion: Postnatal intravenous D-mannose treatment seems to be ineffective in PMM2-CDG.
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http://dx.doi.org/10.1186/s13023-019-1213-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6805611PMC
October 2019

Autosomal-Recessive Mutations in MESD Cause Osteogenesis Imperfecta.

Am J Hum Genet 2019 10 26;105(4):836-843. Epub 2019 Sep 26.

Institute of Human Genetics, University Hospital of Cologne, 50931 Cologne, Germany; Faculty of Medicine, University of Cologne, 50931 Cologne, Germany.

Osteogenesis imperfecta (OI) comprises a genetically heterogeneous group of skeletal fragility diseases. Here, we report on five independent families with a progressively deforming type of OI, in whom we identified four homozygous truncation or frameshift mutations in MESD. Affected individuals had recurrent fractures and at least one had oligodontia. MESD encodes an endoplasmic reticulum (ER) chaperone protein for the canonical Wingless-related integration site (WNT) signaling receptors LRP5 and LRP6. Because complete absence of MESD causes embryonic lethality in mice, we hypothesized that the OI-associated mutations are hypomorphic alleles since these mutations occur downstream of the chaperone activity domain but upstream of ER-retention domain. This would be consistent with the clinical phenotypes of skeletal fragility and oligodontia in persons deficient for LRP5 and LRP6, respectively. When we expressed wild-type (WT) and mutant MESD in HEK293T cells, we detected WT MESD in cell lysate but not in conditioned medium, whereas the converse was true for mutant MESD. We observed that both WT and mutant MESD retained the ability to chaperone LRP5. Thus, OI-associated MESD mutations produce hypomorphic alleles whose failure to remain within the ER significantly reduces but does not completely eliminate LRP5 and LRP6 trafficking. Since these individuals have no eye abnormalities (which occur in individuals completely lacking LRP5) and have neither limb nor brain patterning defects (both of which occur in mice completely lacking LRP6), we infer that bone mass accrual and dental patterning are more sensitive to reduced canonical WNT signaling than are other developmental processes. Biologic agents that can increase LRP5 and LRP6-mediated WNT signaling could benefit individuals with MESD-associated OI.
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http://dx.doi.org/10.1016/j.ajhg.2019.08.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6817720PMC
October 2019

Hypomorphic mutations of TRIP11 cause odontochondrodysplasia.

JCI Insight 2019 Feb 7;4(3). Epub 2019 Feb 7.

Department of Pediatrics, Medical Center-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.

Odontochondrodysplasia (ODCD) is an unresolved genetic disorder of skeletal and dental development. Here, we show that ODCD is caused by hypomorphic TRIP11 mutations, and we identify ODCD as the nonlethal counterpart to achondrogenesis 1A (ACG1A), the known null phenotype in humans. TRIP11 encodes Golgi-associated microtubule-binding protein 210 (GMAP-210), an essential tether protein of the Golgi apparatus that physically interacts with intraflagellar transport 20 (IFT20), a component of the ciliary intraflagellar transport complex B. This association and extraskeletal disease manifestations in ODCD point to a cilium-dependent pathogenesis. However, our functional studies in patient-derived primary cells clearly support a Golgi-based disease mechanism. In spite of reduced abundance, residual GMAP variants maintain partial Golgi integrity, normal global protein secretion, and subcellular distribution of IFT20 in ODCD. These functions are lost when GMAP-210 is completely abrogated in ACG1A. However, a similar defect in chondrocyte maturation is observed in both disorders, which produces a cellular achondrogenesis phenotype of different severity, ensuing from aberrant glycan processing and impaired extracellular matrix proteoglycan secretion by the Golgi apparatus.
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http://dx.doi.org/10.1172/jci.insight.124701DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6413787PMC
February 2019

A common pathomechanism in GMAP-210- and LBR-related diseases.

JCI Insight 2018 12 6;3(23). Epub 2018 Dec 6.

Department of Pediatrics, Medical Centre-University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.

Biallelic loss-of-function mutations in TRIP11, encoding the golgin GMAP-210, cause the lethal human chondrodysplasia achondrogenesis 1A (ACG1A). We now find that a homozygous splice-site mutation of the lamin B receptor (LBR) gene results in the same phenotype. Intrigued by the genetic heterogeneity, we compared GMAP-210- and LBR-deficient primary cells to unravel how particular mutations in LBR cause a phenocopy of ACG1A. We could exclude a regulatory interaction between LBR and GMAP-210 in patients' cells. However, we discovered a common disruption of Golgi apparatus architecture that was accompanied by decreased secretory trafficking in both cases. Deficiency of Golgi-dependent glycan processing indicated a similar downstream effect of the disease-causing mutations upon Golgi function. Unexpectedly, our results thus point to a common pathogenic mechanism in GMAP-210- and LBR-related diseases attributable to defective secretory trafficking at the Golgi apparatus.
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http://dx.doi.org/10.1172/jci.insight.121150DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6328090PMC
December 2018

Genetic analysis of adults heterozygous for ALPL mutations.

J Bone Miner Metab 2018 Nov 13;36(6):723-733. Epub 2017 Dec 13.

Unité de Génétique Constitutionnelle, Service de Biologie, Centre Hospitalier de Versailles, 177 rue de Versailles, 78150, Le Chesnay, France.

Hypophosphatasia (HPP) is a rare inherited metabolic bone disease due to a deficiency of the tissue nonspecific alkaline phosphatase isoenzyme (TNSALP) encoded by the ALPL gene. Patients have consistently low serum alkaline phosphatase (AP), so that this parameter is a good hallmark of the disease. Adult HPP is heterogeneous, and some patients present only mild nonpathognomonic symptoms which are also common in the general population such as joint pain, osteomalacia and osteopenia, chondrocalcinosis, arthropathy and musculoskeletal pain. Adult HPP may be recessively or dominantly inherited; the latter case is assumed to be due to the dominant negative effect (DNE) of missense mutations derived from the functional homodimeric structure of TNSALP. However, there is no biological argument excluding the possibility of other causes of dominant HPP. Rheumatologists and endocrinologists are increasingly solicited for patients with low AP and nonpathognomonic symptoms of HPP. Many of these patients are heterozygous for an ALPL mutation and a challenging question is to determine if these symptoms, which are also common in the general population, are attributable to their heterozygous ALPL mutation or not. In an attempt to address this question, we reviewed a cohort of 61 adult patients heterozygous for an ALPL mutation. Mutations were distinguished according to their statistical likelihood to show a DNE. One-half of the patients carried mutations predicted with no DNE and were slightly less severely affected by the age of onset, serum AP activity and history of fractures. We hypothesized that these mutations result in another mechanism of dominance or are recessive alleles. To identify other genetic factors that could trigger the disease phenotype in heterozygotes for potential recessive mutations, we examined the next-generation sequencing results of 32 of these patients for a panel of 12 genes involved in the differential diagnosis of HPP or candidate modifier genes of HPP. The heterozygous genotype G/C of the COL1A2 coding SNP rs42524 c.1645C > G (p.Pro549Ala) was associated with the severity of the phenotype in patients carrying mutations with a DNE whereas the homozygous genotype G/G was over-represented in patients carrying mutations without a DNE, suggesting a possible role of this variant in the disease phenotype. These preliminary results support COL1A2 as a modifier gene of HPP and suggest that a significant proportion of adult heterozygotes for ALPL mutations may have unspecific symptoms not attributable to their heterozygosity.
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http://dx.doi.org/10.1007/s00774-017-0888-6DOI Listing
November 2018

Mutations in Fibronectin Cause a Subtype of Spondylometaphyseal Dysplasia with "Corner Fractures".

Am J Hum Genet 2017 Nov;101(5):815-823

Centre Hospitalier Universitaire Sainte Justine Research Centre, University of Montreal, Montreal, QC H3T 1C5, Canada. Electronic address:

Fibronectin is a master organizer of extracellular matrices (ECMs) and promotes the assembly of collagens, fibrillin-1, and other proteins. It is also known to play roles in skeletal tissues through its secretion by osteoblasts, chondrocytes, and mesenchymal cells. Spondylometaphyseal dysplasias (SMDs) comprise a diverse group of skeletal dysplasias and often manifest as short stature, growth-plate irregularities, and vertebral anomalies, such as scoliosis. By comparing the exomes of individuals with SMD with the radiographic appearance of "corner fractures" at metaphyses, we identified three individuals with fibronectin (FN1) variants affecting highly conserved residues. Furthermore, using matching tools and the SkelDys emailing list, we identified other individuals with de novo FN1 variants and a similar phenotype. The severe scoliosis in most individuals and rare developmental coxa vara distinguish individuals with FN1 mutations from those with classical Sutcliffe-type SMD. To study functional consequences of these FN1 mutations on the protein level, we introduced three disease-associated missense variants (p.Cys87Phe [c.260G>T], p.Tyr240Asp [c.718T>G], and p.Cys260Gly [c.778T>G]) into a recombinant secreted N-terminal 70 kDa fragment (rF70K) and the full-length fibronectin (rFN). The wild-type rF70K and rFN were secreted into the culture medium, whereas all mutant proteins were either not secreted or secreted at significantly lower amounts. Immunofluorescence analysis demonstrated increased intracellular retention of the mutant proteins. In summary, FN1 mutations that cause defective fibronectin secretion are found in SMD, and we thus provide additional evidence for a critical function of fibronectin in cartilage and bone.
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http://dx.doi.org/10.1016/j.ajhg.2017.09.019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5673654PMC
November 2017

Expression of RMRP RNA is regulated in chondrocyte hypertrophy and determines chondrogenic differentiation.

Sci Rep 2017 07 25;7(1):6440. Epub 2017 Jul 25.

Laboratory for Experimental Orthopedics, Department of Orthopedic Surgery, Maastricht University Medical Centre, Maastricht, The Netherlands.

Mutations in the RMRP-gene, encoding the lncRNA component of the RNase MRP complex, are the origin of cartilage-hair hypoplasia. Cartilage-hair hypoplasia is associated with severe dwarfism caused by impaired skeletal development. However, it is not clear why mutations in RMRP RNA lead to skeletal dysplasia. Since chondrogenic differentiation of the growth plate is required for development of long bones, we hypothesized that RMRP RNA plays a pivotal role in chondrogenic differentiation. Expression of Rmrp RNA and RNase MRP protein subunits was detected in the murine growth plate and during the course of chondrogenic differentiation of ATDC5 cultures, where Rmrp RNA expression was found to be correlated with chondrocyte hypertrophy. Genetic interference with Rmrp RNA expression in ATDC5 cultures caused a deregulation of chondrogenic differentiation, with a prominent impact on hypertrophy and changes in pre-rRNA processing and rRNA levels. Promoter reporter studies showed that Rmrp RNA expression responds to chondrogenic morphogens. Chondrogenic trans-differentiation of cartilage-hair hypoplasia fibroblasts was impaired with a pronounced impact on hypertrophic differentiation. Together, our data show that RMRP RNA expression is regulated during different stages of chondrogenic differentiation and indicate that RMRP RNA may play a pivotal role in chondrocyte hypertrophy, with potential consequences for CHH pathobiology.
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http://dx.doi.org/10.1038/s41598-017-06809-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5527100PMC
July 2017

CMG2/ANTXR2 regulates extracellular collagen VI which accumulates in hyaline fibromatosis syndrome.

Nat Commun 2017 06 12;8:15861. Epub 2017 Jun 12.

Global Health Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne 1015, Switzerland.

Loss-of-function mutations in capillary morphogenesis gene 2 (CMG2/ANTXR2), a transmembrane surface protein, cause hyaline fibromatosis syndrome (HFS), a severe genetic disorder that is characterized by large subcutaneous nodules, gingival hypertrophy and severe painful joint contracture. Here we show that CMG2 is an important regulator of collagen VI homoeostasis. CMG2 loss of function promotes accumulation of collagen VI in patients, leading in particular to nodule formation. Similarly, collagen VI accumulates massively in uteri of Antxr2 mice, which do not display changes in collagen gene expression, and leads to progressive fibrosis and sterility. Crossing Antxr2 with Col6a1 mice leads to restoration of uterine structure and reversion of female infertility. We also demonstrate that CMG2 may act as a signalling receptor for collagen VI and mediates its intracellular degradation.
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http://dx.doi.org/10.1038/ncomms15861DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5472780PMC
June 2017

Clinical and Molecular Heterogeneity of RTEL1 Deficiency.

Front Immunol 2017 1;8:449. Epub 2017 May 1.

Department of Pediatrics and Adolescent Medicine, Division of Pediatric Hematology and Oncology, Medical Centre, Faculty of Medicine, University of Freiburg, Freiburg, Germany.

Typical features of dyskeratosis congenita (DC) resulting from excessive telomere shortening include bone marrow failure (BMF), mucosal fragility, and pulmonary or liver fibrosis. In more severe cases, immune deficiency and recurring infections can add to disease severity. RTEL1 deficiency has recently been described as a major genetic etiology, but the molecular basis and clinical consequences of RTEL1-associated DC are incompletely characterized. We report our observations in a cohort of six patients: five with novel biallelic mutations p.Trp456Cys, p.Ile425Thr, p.Cys1244ProfsX17, p.Pro884_Gln885ins53X13, and one with novel heterozygous mutation p.Val796AlafsX4. The most unifying features were hypocellular BMF in 6/6 and B-/NK-cell lymphopenia in 5/6 patients. In addition, three patients with homozygous mutations p.Trp456Cys or p.Ile425Thr also suffered from immunodeficiency, cerebellar hypoplasia, and enteropathy, consistent with Hoyeraal-Hreidarsson syndrome. Chromosomal breakage resembling a homologous recombination defect was detected in patient-derived fibroblasts but not in hematopoietic compartment. Notably, in both cellular compartments, differential expression of 1243aa and 1219/1300aa RTEL1 isoforms was observed. In fibroblasts, response to ionizing irradiation and non-homologous end joining were not impaired. Telomeric circles did not accumulate in patient-derived primary cells and lymphoblastoid cell lines, implying alternative pathomechanisms for telomeric loss. Overall, RTEL1-deficient cells exhibited a phenotype of replicative exhaustion, spontaneous apoptosis and senescence. Specifically, CD34 cells failed to expand , B-cell development was compromised, and T-cells did not proliferate in long-term culture. Finally, we report on the natural history and outcome of our patients. While two patients died from infections, hematopoietic stem cell transplantation (HSCT) resulted in sustained engraftment in two patients. Whether chemotherapy negatively impacts on the course and onset of other DC-related symptoms remains open at present. Early-onset lung disease occurred in one of our patients after HSCT. In conclusion, RTEL deficiency can show a heterogeneous clinical picture ranging from mild hypocellular BMF with B/NK cell lymphopenia to early-onset, very severe, and rapidly progressing cellular deficiency.
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http://dx.doi.org/10.3389/fimmu.2017.00449DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5410638PMC
May 2017

Involution von Cherubismus im MRT unter Therapie mit Imatinib.

Rofo 2017 Jul 26;189(7):675-677. Epub 2017 Apr 26.

Dept. of Neuroradiology, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Germany.

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http://dx.doi.org/10.1055/s-0043-105074DOI Listing
July 2017

Loss of Functional Osteoprotegerin: More Than a Skeletal Problem.

J Clin Endocrinol Metab 2017 01;102(1):210-219

Department of Endocrinology and Diabetes, Birmingham Children's Hospital, Birmingham B4 6 NH, United Kingdom; and.

Introduction: Juvenile Paget's disease (JPD), an ultra-rare, debilitating bone disease due to loss of functional osteoprotegerin (OPG), is caused by recessive mutations in TNFRFSF11B. A genotype-phenotype correlation spanning from mild to very severe forms is described.

Aim: This study aimed to describe the complexity of the human phenotype of OPG deficiency in more detail and to investigate heterozygous mutation carriers for clinical signs of JPD.

Patients: We investigated 3 children with JPD from families of Turkish, German, and Pakistani descent and 19 family members (14 heterozygous).

Results: A new disease-causing 4 bp-duplication in exon 1 was detected in the German patient, and a microdeletion including TNFRFSF11B in the Pakistani patient. Skeletal abnormalities in all affected children included bowing deformities and fractures, contractures, short stature and skull involvement. Complex malformation of the inner ear and vestibular structures (2 patients) resulted in early deafness. Patients were found to be growth hormone deficient (2), displayed nephrocalcinosis (1), and gross motor (3) and mental (1) retardation. Heterozygous family members displayed low OPG levels (12), elevated bone turnover markers (7), and osteopenia (6). Short stature (1), visual impairment (2), and hearing impairment (1) were also present.

Conclusion: Diminished OPG levels cause complex changes affecting multiple organ systems, including pituitary function, in children with JPD and may cause osteopenia in heterozygous family members. Diagnostic and therapeutic measures should aim to address the complex phenotype.
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http://dx.doi.org/10.1210/jc.2016-2905DOI Listing
January 2017

GenToS: Use of Orthologous Gene Information to Prioritize Signals from Human GWAS.

PLoS One 2016 9;11(9):e0162466. Epub 2016 Sep 9.

Division of Genetic Epidemiology, Institute for Medical Biometry and Statistics, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.

Genome-wide association studies (GWAS) evaluate associations between genetic variants and a trait or disease of interest free of prior biological hypotheses. GWAS require stringent correction for multiple testing, with genome-wide significance typically defined as association p-value <5*10-8. This study presents a new tool that uses external information about genes to prioritize SNP associations (GenToS). For a given list of candidate genes, GenToS calculates an appropriate statistical significance threshold and then searches for trait-associated variants in summary statistics from human GWAS. It thereby allows for identifying trait-associated genetic variants that do not meet genome-wide significance. The program additionally tests for enrichment of significant candidate gene associations in the human GWAS data compared to the number expected by chance. As proof of principle, this report used external information from a comprehensive resource of genetically manipulated and systematically phenotyped mice. Based on selected murine phenotypes for which human GWAS data for corresponding traits were publicly available, several candidate gene input lists were derived. Using GenToS for the investigation of candidate genes underlying murine skeletal phenotypes in data from a large human discovery GWAS meta-analysis of bone mineral density resulted in the identification of significantly associated variants in 29 genes. Index variants in 28 of these loci were subsequently replicated in an independent GWAS replication step, highlighting that they are true positive associations. One signal, COL11A1, has not been discovered through GWAS so far and represents a novel human candidate gene for altered bone mineral density. The number of observed genes that contained significant SNP associations in human GWAS based on murine candidate gene input lists was much greater than the number expected by chance across several complex human traits (enrichment p-value as low as 10-10). GenToS can be used with any candidate gene list, any GWAS summary file, runs on a desktop computer and is freely available.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0162466PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5017755PMC
August 2017

Chondroitin Sulfate N-acetylgalactosaminyltransferase-1 (CSGalNAcT-1) Deficiency Results in a Mild Skeletal Dysplasia and Joint Laxity.

Hum Mutat 2017 01 22;38(1):34-38. Epub 2016 Sep 22.

Department of Pediatrics I, Medical University of Innsbruck, Innsbruck, Austria.

Mutations in genes encoding enzymes responsible for the biosynthesis and structural diversity of glycosaminoglycans (GAGs) cause a variety of disorders affecting bone and connective tissues, including Desbuquois dysplasia (DD). In an infant with prenatal-onset disproportionate short stature, joint laxity, and radiographic findings typical for DD compound-heterozygosity for a large intragenic deletion, and a p.Pro384Arg missense mutation in CSGALNACT1 was found. CSGALNACT1 encodes chondroitin sulfate N-acetylgalactosaminyltransferase-1 (CSGalNAcT-1, ChGn-1), which initiates chondroitin sulfate (CS) chain biosynthesis on the so-called GAG-protein linker region tetrasaccharide. Biochemical studies revealed a reduced GalNAc-transferase activity of the Arg-384 mutant protein, whereas no differences in proteoglycan synthesis in fibroblasts and the GAG content in the urine were found between patient and controls. This is the first description of bi-allelic loss-of-function mutations in CSGALNACT1 that produce a skeletal dysplasia reminiscent of the skeletal dysplasia of Csgalnact1 mice, and adds to the genetic heterogeneity of DD.
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http://dx.doi.org/10.1002/humu.23070DOI Listing
January 2017

Chest Radiograph as Diagnostic Clue in a Floppy Infant.

J Pediatr 2016 Oct 26;177:324-324.e1. Epub 2016 Jul 26.

Department of Neonatology Department of Pediatrics University Medical Center of the Johannes Gutenberg-University Mainz Mainz, Germany.

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http://dx.doi.org/10.1016/j.jpeds.2016.06.065DOI Listing
October 2016

Severe Hypertriglyceridemia in Glut1D on Ketogenic Diet.

Neuropediatrics 2016 Apr 22;47(2):132-6. Epub 2016 Feb 22.

Children's Hospital Klinikum Fürth, Fürth, Germany.

High-fat ketogenic diets are the only treatment available for Glut1 deficiency (Glut1D). Here, we describe an 8-year-old girl with classical Glut1D responsive to a 3:1 ketogenic diet and ethosuximide. After 3 years on the diet a gradual increase of blood lipids was followed by rapid, severe asymptomatic hypertriglyceridemia (1,910 mg/dL). Serum lipid apheresis was required to determine liver, renal, and pancreatic function. A combination of medium chain triglyceride-oil and a reduction of the ketogenic diet to 1:1 ratio normalized triglyceride levels within days but triggered severe myoclonic seizures requiring comedication with sultiam. Severe hypertriglyceridemia in children with Glut1D on ketogenic diets may be underdiagnosed and harmful. In contrast to congenital hypertriglyceridemias, children with Glut1D may be treated effectively by dietary adjustments alone.
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http://dx.doi.org/10.1055/s-0036-1572413DOI Listing
April 2016

Against all odds: blended phenotypes of three single-gene defects.

Eur J Hum Genet 2016 08 27;24(9):1274-9. Epub 2016 Jan 27.

Center for Pediatrics and Adolescent Medicine, Medical Center, University of Freiburg, Freiburg, Germany.

Whole-exome sequencing allows for an unbiased and comprehensive mutation screening. Although successfully used to facilitate the diagnosis of single-gene disorders, the genetic cause(s) of a substantial proportion of presumed monogenic diseases remain to be identified. We used whole-exome sequencing to examine offspring from a consanguineous marriage featuring a novel combination of congenital hypothyroidism, hypomagnesemia and hypercholesterolemia. Rather than identifying one causative variant, we report the first instance in which three independent autosomal-recessive single-gene disorders were identified in one patient. Together, the causal variants give rise to a blended and seemingly novel phenotype: we experimentally characterized a novel splice variant in the thyroglobulin gene (c.638+5G>A), resulting in skipping of exon 5, and detected a pathogenic splice variant in the magnesium transporter gene TRPM6 (c.2667+1G>A), causing familial hypomagnesemia. Based on the third variant, a stop variant in ABCG5 (p.(Arg446*)), we established a diagnosis of sitosterolemia, confirmed by elevated blood plant sterol levels and successfully initiated targeted lipid-lowering treatment. We propose that blended phenotypes resulting from several concomitant single-gene disorders in the same patient likely account for a proportion of presumed monogenic disorders of currently unknown cause and contribute to variable genotype-phenotype correlations.
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http://dx.doi.org/10.1038/ejhg.2015.285DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4989199PMC
August 2016

Molecular mechanism of CHRDL1-mediated X-linked megalocornea in humans and in Xenopus model.

Hum Mol Genet 2015 Jun 23;24(11):3119-32. Epub 2015 Feb 23.

Institute of Human Genetics, Martin Luther University Halle-Wittenberg, 06112 Halle, Saale, Germany

Chordin-Like 1 (CHRDL1) mutations cause non-syndromic X-linked megalocornea (XMC) characterized by enlarged anterior eye segments. Mosaic corneal degeneration, presenile cataract and secondary glaucoma are associated with XMC. Beside that CHRDL1 encodes Ventroptin, a secreted bone morphogenetic protein (BMP) antagonist, the molecular mechanism of XMC is not well understood yet. In a family with broad phenotypic variability of XMC, we identified the novel CHRDL1 frameshift mutation c.807_808delTC [p.H270Wfs*22] presumably causing CHRDL1 loss of function. Using Xenopus laevis as model organism, we demonstrate that chrdl1 is specifically expressed in the ocular tissue at late developmental stages. The chrdl1 knockdown directly resembles the human XMC phenotype and confirms CHRDL1 deficiency to cause XMC. Interestingly, secondary to this bmp4 is down-regulated in the Xenopus eyes. Moreover, phospho-SMAD1/5 is altered and BMP receptor 1A is reduced in a XMC patient. Together, we classify these observations as negative-feedback regulation due to the deficient BMP antagonism in XMC. As CHRDL1 is preferentially expressed in the limbal stem cell niche of adult human cornea, we assume that CHRDL1 plays a key role in cornea homeostasis. In conclusion, we provide novel insights into the molecular mechanism of XMC as well as into the specific role of CHRDL1 during cornea organogenesis, among others by the establishment of the first XMC in vivo model. We show that unravelling monogenic cornea disorders like XMC-with presumably disturbed cornea growth and differentiation-contribute to the identification of potential limbal stem cell niche factors that are promising targets for regenerative therapies of corneal injuries.
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http://dx.doi.org/10.1093/hmg/ddv063DOI Listing
June 2015

Reversible pancytopenia and immunodeficiency in a patient with hereditary folate malabsorption.

Pediatr Blood Cancer 2015 Jun 11;62(6):1091-4. Epub 2014 Dec 11.

Department of Pediatrics and Adolescent Medicine, University Medical Center, Freiburg, Germany.

Mutations in SLC46A1 result in a defect of the proton coupled folate transporter (PCFT) and are the basis of hereditary folate malabsorption (HFM). Patients with HFM frequently present with neurodevelopmental delay and megaloblastic anemia. Some cases may be complicated by additional lymphopenia and immunodeficiency. We report a patient with a new homozygous mutation in the SLC46A1 gene. The boy presented with early-onset pancytopenia and secondary immunodeficiency. We provide clinical and molecular observations that extend the phenotypic description of HFM and highlight diagnostic as well as therapeutic pitfalls in this rare condition.
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http://dx.doi.org/10.1002/pbc.25364DOI Listing
June 2015

A founder CEP120 mutation in Jeune asphyxiating thoracic dystrophy expands the role of centriolar proteins in skeletal ciliopathies.

Hum Mol Genet 2015 Mar 30;24(5):1410-9. Epub 2014 Oct 30.

Department of Genetics, King Faisal Specialist Hospital and Research Center, Riyadh 11211, Saudi Arabia, Department of Anatomy and Cell Biology, College of Medicine, Alfaisal University, Riyadh 11533, Saudi Arabia

Jeune asphyxiating thoracic dystrophy (JATD) is a skeletal dysplasia characterized by a small thoracic cage and a range of skeletal and extra-skeletal anomalies. JATD is genetically heterogeneous with at least nine genes identified, all encoding ciliary proteins, hence the classification of JATD as a skeletal ciliopathy. Consistent with the observation that the heterogeneous molecular basis of JATD has not been fully determined yet, we have identified two consanguineous Saudi families segregating JATD who share a single identical ancestral homozygous haplotype among the affected members. Whole-exome sequencing revealed a single novel variant within the disease haplotype in CEP120, which encodes a core centriolar protein. Subsequent targeted sequencing of CEP120 in Saudi and European JATD cohorts identified two additional families with the same missense mutation. Combining the four families in linkage analysis confirmed a significant genome-wide linkage signal at the CEP120 locus. This missense change alters a highly conserved amino acid within CEP120 (p.Ala199Pro). In addition, we show marked reduction of cilia and abnormal number of centrioles in fibroblasts from one affected individual. Inhibition of the CEP120 ortholog in zebrafish produced pleiotropic phenotypes characteristic of cilia defects including abnormal body curvature, hydrocephalus, otolith defects and abnormal renal, head and craniofacial development. We also demonstrate that in CEP120 morphants, cilia are shortened in the neural tube and disorganized in the pronephros. These results are consistent with aberrant CEP120 being implicated in the pathogenesis of JATD and expand the role of centriolar proteins in skeletal ciliopathies.
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http://dx.doi.org/10.1093/hmg/ddu555DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4321448PMC
March 2015

PGM3 mutations cause a congenital disorder of glycosylation with severe immunodeficiency and skeletal dysplasia.

Am J Hum Genet 2014 Jul 12;95(1):96-107. Epub 2014 Jun 12.

Section of Immunology, Allergy, and Rheumatology, Department of Pediatrics, Baylor College of Medicine and Texas Children's Hospital, Houston, TX 77030, USA; Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA.

Human phosphoglucomutase 3 (PGM3) catalyzes the conversion of N-acetyl-glucosamine (GlcNAc)-6-phosphate into GlcNAc-1-phosphate during the synthesis of uridine diphosphate (UDP)-GlcNAc, a sugar nucleotide critical to multiple glycosylation pathways. We identified three unrelated children with recurrent infections, congenital leukopenia including neutropenia, B and T cell lymphopenia, and progression to bone marrow failure. Whole-exome sequencing demonstrated deleterious mutations in PGM3 in all three subjects, delineating their disease to be due to an unsuspected congenital disorder of glycosylation (CDG). Functional studies of the disease-associated PGM3 variants in E. coli cells demonstrated reduced PGM3 activity for all mutants tested. Two of the three children had skeletal anomalies resembling Desbuquois dysplasia: short stature, brachydactyly, dysmorphic facial features, and intellectual disability. However, these additional features were absent in the third child, showing the clinical variability of the disease. Two children received hematopoietic stem cell transplantation of cord blood and bone marrow from matched related donors; both had successful engraftment and correction of neutropenia and lymphopenia. We define PGM3-CDG as a treatable immunodeficiency, document the power of whole-exome sequencing in gene discoveries for rare disorders, and illustrate the utility of genomic analyses in studying combined and variable phenotypes.
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http://dx.doi.org/10.1016/j.ajhg.2014.05.007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4085583PMC
July 2014

Up-regulation of RUNX2 in acute myeloid leukemia in a patient with an inherent RUNX2 haploinsufficiency and cleidocranial dysplasia.

Leuk Lymphoma 2014 Aug 24;55(8):1930-2. Epub 2014 Feb 24.

Department of Hematology, Oncology and Stem Cell Transplantation.

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http://dx.doi.org/10.3109/10428194.2013.855310DOI Listing
August 2014

FAM111A mutations result in hypoparathyroidism and impaired skeletal development.

Am J Hum Genet 2013 Jun 16;92(6):990-5. Epub 2013 May 16.

Department of Pediatrics, Lausanne University Hospital, University of Lausanne, 1011 Lausanne, Switzerland; Medical Genetics Service, Lausanne University Hospital, University of Lausanne, 1011 Lausanne, Switzerland.

Kenny-Caffey syndrome (KCS) and the similar but more severe osteocraniostenosis (OCS) are genetic conditions characterized by impaired skeletal development with small and dense bones, short stature, and primary hypoparathyroidism with hypocalcemia. We studied five individuals with KCS and five with OCS and found that all of them had heterozygous mutations in FAM111A. One mutation was identified in four unrelated individuals with KCS, and another one was identified in two unrelated individuals with OCS; all occurred de novo. Thus, OCS and KCS are allelic disorders of different severity. FAM111A codes for a 611 amino acid protein with homology to trypsin-like peptidases. Although FAM111A has been found to bind to the large T-antigen of SV40 and restrict viral replication, its native function is unknown. Molecular modeling of FAM111A shows that residues affected by KCS and OCS mutations do not map close to the active site but are clustered on a segment of the protein and are at, or close to, its outer surface, suggesting that the pathogenesis involves the interaction with as yet unidentified partner proteins rather than impaired catalysis. FAM111A appears to be crucial to a pathway that governs parathyroid hormone production, calcium homeostasis, and skeletal development and growth.
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http://dx.doi.org/10.1016/j.ajhg.2013.04.020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3675238PMC
June 2013

Identification of a Ninein (NIN) mutation in a family with spondyloepimetaphyseal dysplasia with joint laxity (leptodactylic type)-like phenotype.

Matrix Biol 2013 Oct-Nov;32(7-8):387-92. Epub 2013 May 9.

Institute of Human Genetics, University Hospital Erlangen, Friedrich-Alexander University Erlangen-Nürnberg, Erlangen, Germany.

Spondyloepimetaphyseal dysplasia with joint laxity-leptodactylic type (SEMDJL2) is an autosomal dominant skeletal dysplasia which is characterized by midface hypoplasia, short stature, joint laxity with dislocations, genua valga, progressive scoliosis, and slender fingers. Recently, heterozygous missense mutations in KIF22, a gene which encodes a member of the kinesin-like protein family, have been identified in sporadic as well as familial cases of SEMDJL2. In the present study homozygosity mapping and whole-exome sequencing were combined to analyze a consanguineous family with a phenotype resembling SEMDJL2. We identified homozygous missense mutations in the two nearby genes NIN (Ninein) and POLE2 (DNA polymerase epsilon subunit B) which segregate with the disease in the family and were not present in 500 healthy control individuals and in the 1094 control individuals contained within the 1000-genomes database. We present several lines of evidence that mutant Ninein is most likely causative for the SEMDJL2-like phenotype. The centrosomal protein NIN shows a functional relationship with KIF22 and other proteins associated with chromosome congression/movement, centrosomal function, and ciliogenesis, which have been associated with skeletal dysplasias. Moreover, compound heterozygous missense mutations at more N-terminal positions of Ninein have very recently been identified in a family with microcephalic primordial dwarfism. Together with the present report this strongly supports a fundamental role of Ninein in skeletal development.
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http://dx.doi.org/10.1016/j.matbio.2013.05.001DOI Listing
July 2014

Mutations in B3GALT6, which encodes a glycosaminoglycan linker region enzyme, cause a spectrum of skeletal and connective tissue disorders.

Am J Hum Genet 2013 Jun 9;92(6):927-34. Epub 2013 May 9.

Laboratory for Bone and Joint Diseases, Center for Integrative Medical Sciences, RIKEN, Tokyo 108-8639, Japan.

Proteoglycans (PGs) are a major component of the extracellular matrix in many tissues and function as structural and regulatory molecules. PGs are composed of core proteins and glycosaminoglycan (GAG) side chains. The biosynthesis of GAGs starts with the linker region that consists of four sugar residues and is followed by repeating disaccharide units. By exome sequencing, we found that B3GALT6 encoding an enzyme involved in the biosynthesis of the GAG linker region is responsible for a severe skeletal dysplasia, spondyloepimetaphyseal dysplasia with joint laxity type 1 (SEMD-JL1). B3GALT6 loss-of-function mutations were found in individuals with SEMD-JL1 from seven families. In a subsequent candidate gene study based on the phenotypic similarity, we found that B3GALT6 is also responsible for a connective tissue disease, Ehlers-Danlos syndrome (progeroid form). Recessive loss-of-function mutations in B3GALT6 result in a spectrum of disorders affecting a broad range of skeletal and connective tissues characterized by lax skin, muscle hypotonia, joint dislocation, and spinal deformity. The pleiotropic phenotypes of the disorders indicate that B3GALT6 plays a critical role in a wide range of biological processes in various tissues, including skin, bone, cartilage, tendon, and ligament.
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http://dx.doi.org/10.1016/j.ajhg.2013.04.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3675233PMC
June 2013

In-depth analysis of hyaline fibromatosis syndrome frameshift mutations at the same site reveal the necessity of personalized therapy.

Hum Mutat 2013 Jul 19;34(7):1005-17. Epub 2013 Apr 19.

Global Health Institute, Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland.

Hyaline fibromatosis syndrome is an autosomal recessive disease caused by mutations in ANTXR2, a gene involved in extracellular matrix homeostasis. Sixty percent of patients carry frameshift mutations at a mutational hotspot in exon 13. We show in patient cells that these mutations lead to low ANTXR2 mRNA and undetectable protein levels. Ectopic expression of the proteins encoded by the mutated genes reveals that a two base insertion leads to the synthesis of a protein that is rapidly targeted to the ER-associated degradation pathway due to the modified structure of the cytosolic tail, which instead of being hydrophilic and highly disordered as in wild type ANTXR2, is folded and exposes hydrophobic patches. In contrast, one base insertion leads to a truncated protein that properly localizes to the plasma membrane and retains partial function. We next show that targeting the nonsense mediated mRNA decay pathway in patient cells leads to a rescue of ANTXR2 protein in patients carrying one base insertion but not in those carrying two base insertions. This study highlights the importance of in-depth analysis of the molecular consequences of specific patient mutations, which even when they occur at the same site can have drastically different consequences.
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http://dx.doi.org/10.1002/humu.22324DOI Listing
July 2013

Mutations in WNT1 cause different forms of bone fragility.

Am J Hum Genet 2013 Apr 14;92(4):565-74. Epub 2013 Mar 14.

Institute of Human Genetics, University Hospital Cologne, University of Cologne, 50931 Cologne, Germany.

We report that hypofunctional alleles of WNT1 cause autosomal-recessive osteogenesis imperfecta, a congenital disorder characterized by reduced bone mass and recurrent fractures. In consanguineous families, we identified five homozygous mutations in WNT1: one frameshift mutation, two missense mutations, one splice-site mutation, and one nonsense mutation. In addition, in a family affected by dominantly inherited early-onset osteoporosis, a heterozygous WNT1 missense mutation was identified in affected individuals. Initial functional analysis revealed that altered WNT1 proteins fail to activate canonical LRP5-mediated WNT-regulated β-catenin signaling. Furthermore, osteoblasts cultured in vitro showed enhanced Wnt1 expression with advancing differentiation, indicating a role of WNT1 in osteoblast function and bone development. Our finding that homozygous and heterozygous variants in WNT1 predispose to low-bone-mass phenotypes might advance the development of more effective therapeutic strategies for congenital forms of bone fragility, as well as for common forms of age-related osteoporosis.
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http://dx.doi.org/10.1016/j.ajhg.2013.02.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3617378PMC
April 2013

Exome sequencing identifies DYNC2H1 mutations as a common cause of asphyxiating thoracic dystrophy (Jeune syndrome) without major polydactyly, renal or retinal involvement.

J Med Genet 2013 May 1;50(5):309-23. Epub 2013 Mar 1.

Molecular Medicine Unit, Birth Defects Research Centre, University College London UCL Institute of Child Health, 30 Guilford Street, London WC1N 1EH, UK.

Background: Jeune asphyxiating thoracic dystrophy (JATD) is a rare, often lethal, recessively inherited chondrodysplasia characterised by shortened ribs and long bones, sometimes accompanied by polydactyly, and renal, liver and retinal disease. Mutations in intraflagellar transport (IFT) genes cause JATD, including the IFT dynein-2 motor subunit gene DYNC2H1. Genetic heterogeneity and the large DYNC2H1 gene size have hindered JATD genetic diagnosis.

Aims And Methods: To determine the contribution to JATD we screened DYNC2H1 in 71 JATD patients JATD patients combining SNP mapping, Sanger sequencing and exome sequencing.

Results And Conclusions: We detected 34 DYNC2H1 mutations in 29/71 (41%) patients from 19/57 families (33%), showing it as a major cause of JATD especially in Northern European patients. This included 13 early protein termination mutations (nonsense/frameshift, deletion, splice site) but no patients carried these in combination, suggesting the human phenotype is at least partly hypomorphic. In addition, 21 missense mutations were distributed across DYNC2H1 and these showed some clustering to functional domains, especially the ATP motor domain. DYNC2H1 patients largely lacked significant extra-skeletal involvement, demonstrating an important genotype-phenotype correlation in JATD. Significant variability exists in the course and severity of the thoracic phenotype, both between affected siblings with identical DYNC2H1 alleles and among individuals with different alleles, which suggests the DYNC2H1 phenotype might be subject to modifier alleles, non-genetic or epigenetic factors. Assessment of fibroblasts from patients showed accumulation of anterograde IFT proteins in the ciliary tips, confirming defects similar to patients with other retrograde IFT machinery mutations, which may be of undervalued potential for diagnostic purposes.
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http://dx.doi.org/10.1136/jmedgenet-2012-101284DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3627132PMC
May 2013

TRPV4-associated skeletal dysplasias.

Am J Med Genet C Semin Med Genet 2012 Aug 12;160C(3):190-204. Epub 2012 Jul 12.

Génétique Médicale, CHUV, Av. Decker 2, 1011 Lausanne, Switzerland.

Dominant mutations in the TRPV4 gene result in a bone dysplasia family and form a continuous phenotypic spectrum that includes, in decreasing severity, lethal, and nonlethal metatropic dysplasia (MD), spondylometaphyseal dysplasia Kozlowski type (SMDK), and autosomal dominant brachyolmia. Several rare variant phenotypes that have some overlap but deviate in some ways from the general pattern have also been described. The known variant phenotypes are spondyloepiphyseal dysplasia Maroteaux type (Pseudo-Morquio type 2), parastremmatic dysplasia, and familial digital arthropathy with brachydactyly. Interestingly, different TRPV4 mutations have been associated with dominantly inherited neurologic disorders such as congenital spinal muscular atrophy and hereditary motor and sensory neuropathy. Finally, a small number of patients have been identified in whom a TRPV4 mutation results in a phenotype combining skeletal dysplasia with peripheral neuropathy. The TRPV4 gene encodes a regulated calcium channel implicated in multiple and diverse cellular processes. Over 50 different TRPV4 mutations have been reported, with two codons appearing to be mutational hot spots: P799 in exon 15, mostly associated with MD, and R594 in exon 11, associated with SMDK. While most pathogenic mutations tested so far result in activation of the calcium channel in vitro, the mechanisms through which TRPV4 activation results in skeletal dysplasia and/or peripheral neuropathy remain unclear and the genotype-phenotype correlations in this group of disorders remains somewhat mysterious. Since the phenotypic expression of most mutations seems to be relatively constant, careful clinical and radiographic assessment is useful in directing molecular analysis.
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http://dx.doi.org/10.1002/ajmg.c.31335DOI Listing
August 2012

Choline-releasing glycerophosphodiesterase EDI3 drives tumor cell migration and metastasis.

Proc Natl Acad Sci U S A 2012 May 8;109(21):8155-60. Epub 2012 May 8.

Leibniz Research Centre for Working Environment and Human Factors (IfADO), University of Dortmund, 44139 Dortmund, Germany.

Metastasis from primary tumors remains a major problem for tumor therapy. In the search for markers of metastasis and more effective therapies, the tumor metabolome is relevant because of its importance to the malignant phenotype and metastatic capacity of tumor cells. Altered choline metabolism is a hallmark of cancer. More specifically, a decreased glycerophosphocholine (GPC) to phosphocholine (PC) ratio was reported in breast, ovarian, and prostate cancers. Improved strategies to exploit this altered choline metabolism are therefore required. However, the critical enzyme cleaving GPC to produce choline, the initial step in the pathway controlling the GPC/PC ratio, remained unknown. In the present work, we have identified the enzyme, here named EDI3 (endometrial differential 3). Purified recombinant EDI3 protein cleaves GPC to form glycerol-3-phosphate and choline. Silencing EDI3 in MCF-7 cells decreased this enzymatic activity, increased the intracellular GPC/PC ratio, and decreased downstream lipid metabolites. Downregulating EDI3 activity inhibited cell migration via disruption of the PKCα signaling pathway, with stable overexpression of EDI3 showing the opposite effect. EDI3 was originally identified in our screening study comparing mRNA levels in metastasizing and nonmetastasizing endometrial carcinomas. Both Kaplan-Meier and multivariate analyses revealed a negative association between high EDI3 expression and relapse-free survival time in both endometrial (P < 0.001) and ovarian (P = 0.029) cancers. Overall, we have identified EDI3, a key enzyme controlling GPC and choline metabolism. Because inhibition of EDI3 activity corrects the GPC/PC ratio and decreases the migration capacity of tumor cells, it represents a possible target for therapeutic intervention.
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http://dx.doi.org/10.1073/pnas.1117654109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3361409PMC
May 2012