Mutations disrupting the Kennedy phosphatidylcholine pathway in humans with congenital lipodystrophy and fatty liver disease

Phosphatidylcholine (PC) is the major glycerophospholipid in eukaryotic cells and is an essential component in all cellular membranes. The biochemistry of de novo PC synthesis by the Kennedy pathway is well established, but less is known about the physiological functions of PC. We identified two unrelated patients with defects in the Kennedy pathway due to biallellic loss-of-function mutations in phosphate cytidylyltransferase 1 alpha (PCYT1A), the rate-limiting enzyme in this pathway. The mutations lead to a marked reduction in PCYT1A expression and PC synthesis. The phenotypic consequences include some features, such as severe fatty liver and low HDL cholesterol levels, that are predicted by the results of previously reported liver-specific deletion of murine Pcyt1a. Both patients also had lipodystrophy, severe insulin resistance, and diabetes, providing evidence for an additional and essential role for PCYT1A-generated PC in the normal function of white adipose tissue and insulin action.All living cells are surrounded by a lipid membrane. Eukaryotic cells also contain several internal membrane-bound organelles, which enable them to compartmentalize related biological functions and thereby to enhance the efficiency of these processes. Phospholipids are the predominant component of these membranes. Their hydrophilic head groups interact with the cytosol, whereas their hydrophobic side chains are either buried within the hydrophobic interior of a typical membrane bilayer or interact with the hydrophobic neutral lipid core of lipoproteins and lipid droplets (LDs). Phospholipids are generally defined by their organic head group with phosphatidylcholine (PC) constituting over 50% of all membrane phospholipids. PC was first isolated in the 19th century and the major enzymatic pathway involved in its synthesis was revealed by Kennedy and Weiss (1) in the 1950s. Cells synthesize PC in three consecutive steps (Fig. 1A): choline kinase phosphorylates choline before choline phosphate cytidylyltransferase 1 α (encoded by the PCYT1A gene) generates the high-energy donor CDP-choline in the rate-limiting step of the pathway. In the last step, DAG:CDP-choline cholinephosphotransferase (CPT) uses CDP-choline and diacylglycerol (DAG) to form PC (2, 3).Open in a separate windowFig. 1.Cosegregation of biallelic PCYT1A mutations with fatty liver, low HDL cholesterol levels, lipodystrophy, insulin-resistant diabetes, and short stature. (A) Schematic illustration of the Kennedy PC synthesis pathway. CK, choline kinase; CPT, CDP-choline:1,2-diacylglycerol cholinephosphotransferase; PCYT1A, choline-phosphate cytidylyltransferase A, CTP:phosphocholine-cytidylyltransferase. (B) Family pedigrees of both probands demonstrating that only compound heterozygous carriers of PCYT1A mutations manifest fatty liver (red), low HDL cholesterol (blue), lipodystrophy (yellow), and insulin resistance/type 2 diabetes (T2DM) (green). PCYT1A mutation status, height (Ht.), and body mass index (BMI) are indicated below each individual’s symbol. ND, not determined; WT, wild type. (C) The location of PCYT1A mutations E280del, V142M, and 333fs in relation to known functional domains of PCYT1A. Domain M, membrane binding domain; domain P, phosphorylated region. (D) Conservation around the V142(red*) and E280(red*) mutation sites. Sequence alignment of representative metazoan sequences in the region surrounding the mutated residues. Hydrophobic (blue) and polar (green) residues interacting with V142 are highlighted. Only residues different from the human sequence are shown. Sequence IDs: human (Homo sapiens) {"type":"entrez-protein","attrs":{"text":"P49585","term_id":"166214967"}}P49585, zebrafish (Danio rerio) F1QEN6, sea squirt (Ciona intestinalis) {"type":"entrez-protein","attrs":{"text":"XP_002130773.1","term_id":"198437270"}}XP_002130773.1, sea urchin (Strongylocentrotus purpuratus) H3I3V9, water flee (Daphnia pulex) E9G1P5, Drosophila (D. melanogaster) Q9W0D9, Caenorhabditis (C. elegans) {"type":"entrez-protein","attrs":{"text":"P49583","term_id":"32172439"}}P49583, Trichoplax (T. adherens) B3RI62. (E and F) Structure of the catalytic domain of PCYT1A highlighting the role of V142M in the core packing. The two chains in the dimer are shown in yellow and gray; the residues and the secondary structure units are highlighted in color in the yellow monomer A: loop L3 with V142, red; α-helix, green; and the interacting β-sheet, blue. The residues packing with V142 are shown in ball-and-stick and space-filling representations, the dimer stabilizing R140 is shown in ball-and-stick colored according to the atom type. E is a global view, and F is a zoomed-in view of the catalytic core.Membrane phospholipids are a defining feature of advanced life-forms so it is perhaps not surprising that the pathways involved in their synthesis are ancient, and mutations affecting them are rarely tolerated in evolution. Here, we describe the identification and characterization of pathogenic human loss-of-function mutations affecting the eponymous Kennedy pathway.     

Repeat percutaneous coronary revascularization: Indications and outcomes in a “Real World” cohort

Objectives : To investigate rates of and reasons for second and subsequent stent procedures in an unselected, “real‐world” population. Background : Repeat stenting is the primary difference reported in clinical trials of alternative revascularization strategies. The incidence, indication, and outcome for repeat stenting in contemporary practice outside the more selective populations of trials and registries has not been described. Method : All patients undergoing a first percutaneous coronary intervention (PCI) procedure with stenting from January 2001 to August 2009 (10,509) from a large UK tertiary referral and district general hospital were identified. Mortality and the incidence, timing, and indication for repeat revascularization in this population were investigated from patient records. Results : Of 10,509 patients undergoing a first PCI and stent implant 23.5% underwent repeat angiography of which 11.2% required repeat PCI and 2% coronary artery bypass grafting (median follow‐up of 3.8 years). A total of 1.3% went on to a third PCI. The commonest indication for repeat stenting was disease progression remote from the original stent (46%) and planned staged PCI (23%); 21% had a stent‐related indication. Functional assessment before repeat stenting was used in one‐third of stable patients. Mortality was 2.5% per annum. Conclusions : In contemporary practice, patients undergoing a first stenting procedure have a low subsequent mortality, and the substantial majority (86.4%) requires no further revascularization over a median 3.8 year follow‐up. For those who do require repeat stenting, this is most commonly at a site remote from the first stent. © 2012 Wiley Periodicals, Inc.     

Brief Report: Do Service Dog Providers Placing Dogs with Children with Developmental Disabilities Use Outcome Measures and, If So, What Are they?

The aim of this study was to identify the outcomes expected and assessed by those providing service dogs to children with developmental disabilities. Seventeen registered service dog providers were invited to complete a mixed methods online survey. Five providers, who prepared dogs to work with a wide range of conditions and behaviours, mainly Asperger’s syndrome, autism and communication disorders, completed the survey. All five participants reported that they expected to see positive changes as a consequence of the service dog placement, in both the recipient child and their family, including improvements in attention span and language skills, as well as increased familial cohesion. Survey responses indicated that not all desired outcomes were routinely assessed. The range of assessments used were interviews, intake conversations, pre-placement questionnaires, child social dairies filled in by parents, follow up surveys after placement, and child observation by parents. No specifically named valid and reliable clinical or research measures were referred to, showing an emphasis on assessments from parents and service dog providers. It is not clear whether pre-intervention assessments are repeated systematically at follow-up, which could show robust intervention effects. There is scope for professionals in developmental disability to work with service dog providers to improve the evidence base in this field.     

Impairment‐ and activity/participation‐directed interventions in progressive language impairment: Clinical and theoretical issues

Abstract

The most salient and discussed features of agrammatism are the omission and substitution of grammatical morphemes, whether bound or free, in speech production. Cross-linguistic studies have shown that language-specific features determine the pattern of omissions and substitutions found; morphological markers are almost never omitted if the resulting form is a non-word; substitutions are mis-selections from existing paradigms. In the present paper we investigate the ways in which agrammatism is manifested in Algerian Arabic, a Semitic language where simple (Ø-prefixed and Ø-suffixed) words are described as consisting of three morphemes: the discontinuous consonantal root, the discontinuous vocalic base and a CV template or skeleton (McCarthy 1975). Our findings are comparable to those previously reported, in that the three agrammatic subjects who participated in this study do omit and substitute free-standing and bound grammatical markers, and never produce non-words. More specifically, their performance is characterized by omissions of linear bound morphemes in prefixed and suffixed words, as well as substitutions of morphologically complex forms by simpler and more frequent ones. An interpretation of the subjects' performance in the light of current linguistic and psycholinguistic theories on the lexicon is proposed.     

A patient with a macrodont, transposition and supplemental tooth in the upper anterior segment: a case report

This case report describes the presence of multiple dental anomalies in the upper labial segment of a 7-year-old boy; a macrodont, transposition and supplemental tooth. CLINICAL RELEVANCE:This case highlights the need for careful treatment planning in patients with mutiple dental anomalies.     

A case report and review of the locked metacarpophalangeal joint

A 59-year-old female with metacarpal joint locking is presented. The successful closed manipulation is described with a review of the literature.