Eli Hershkovitz

Deficiency of the ADP-Forming Succinyl-CoA Synthase Activity Is Associated with Encephalomyopathy and Mitochondrial DNA Depletion

The mitochondrial DNA (mtDNA) depletion syndrome is a quantitative defect of mtDNA resulting from dysfunction of one of several nuclear-encoded factors responsible for maintenance of mitochondrial deoxyribonucleoside triphosphate (dNTP) pools or replication of mtDNA. Markedly decreased succinyl-CoA synthetase activity due to a deleterious mutation in SUCLA2, the gene encoding the beta subunit of the ADP-forming succinyl-CoA synthetase ligase, was found in muscle mitochondria of patients with encephalomyopathy and mtDNA depletion. Succinyl-CoA synthetase is invariably in a complex with mitochondrial nucleotide diphosphate kinase; hence, we propose that a defect in the last step of mitochondrial dNTP salvage is a novel cause of the mtDNA depletion syndrome.

Mutation of TBCE causes hypoparathyroidism- retardation-dysmorphism and autosomal recessive Kenny-Caffey syndrome

The syndrome of congenital hypoparathyroidism, mental retardation, facial dysmorphism and extreme growth failure (HRD or Sanjad–Sakati syndrome; OMIM 241410) is an autosomal recessive disorder reported almost exclusively in Middle Eastern populations1,2,3. A similar syndrome with the additional features of osteosclerosis and recurrent bacterial infections has been classified as autosomal recessive Kenny–Caffey syndrome4 (AR-KCS; OMIM 244460). Both traits have previously been mapped to chromosome 1q43–44 (refs 5,6) and, despite the observed clinical variability, share an ancestral haplotype, suggesting a common founder mutation7. We describe refinement of the critical region to an interval of roughly 230 kb and identification of deletion and truncation mutations of TBCE in affected individuals. The gene TBCE encodes one of several chaperone proteins required for the proper folding of α-tubulin subunits and the formation of α–β-tubulin heterodimers. Analysis of diseased fibroblasts and lymphoblastoid cells showed lower microtubule density at the microtubule-organizing center (MTOC) and perturbed microtubule polarity in diseased cells. Immunofluorescence and ultrastructural studies showed disturbances in subcellular organelles that require microtubules for membrane trafficking, such as the Golgi and late endosomal compartments. These findings demonstrate that HRD and AR-KCS are chaperone diseases caused by a genetic defect in the tubulin assembly pathway, and establish a potential connection between tubulin physiology and the development of the parathyroid.The syndrome of congenital hypoparathyroidism, mental retardation, facial dysmorphism and extreme growth failure (HRD or Sanjad–Sakati syndrome; OMIM 241410) is an autosomal recessive disorder reported almost exclusively in Middle Eastern populations. A similar syndrome with the additional features of osteosclerosis and recurrent bacterial infections has been classified as autosomal recessive Kenny–Caffey syndrome (AR-KCS; OMIM 244460). Both traits have previously been mapped to chromosome 1q43–44 (refs 5,6) and, despite the observed clinical variability, share an ancestral haplotype, suggesting a common founder mutation. We describe refinement of the critical region to an interval of roughly 230 kb and identification of deletion and truncation mutations of TBCE in affected individuals. The gene TBCE encodes one of several chaperone proteins required for the proper folding of α-tubulin subunits and the formation of α–β-tubulin heterodimers. Analysis of diseased fibroblasts and lymphoblastoid cells showed lower microtubule density at the microtubule-organizing center (MTOC) and perturbed microtubule polarity in diseased cells. Immunofluorescence and ultrastructural studies showed disturbances in subcellular organelles that require microtubules for membrane trafficking, such as the Golgi and late endosomal compartments. These findings demonstrate that HRD and AR-KCS are chaperone diseases caused by a genetic defect in the tubulin assembly pathway, and establish a potential connection between tubulin physiology and the development of the parathyroid.

Defective mitochondrial translation caused by a ribosomal protein (MRPS16) mutation

The mitochondrial respiratory chain comprises 85 subunits, 13 of which are mitochondrial encoded. The synthesis of these 13 proteins requires many nuclear‐encoded proteins that participate in mitochondrial DNA replication, transcript production, and a distinctive mitochondrial translation apparatus. We report a patient with agenesis of corpus callosum, dysmorphism, and fatal neonatal lactic acidosis with markedly decreased complex I and IV activity in muscle and liver and a generalized mitochondrial translation defect identified in pulse‐label experiments. The defect was associated with marked reduction of the 12S rRNA transcript level likely attributed to a nonsense mutation in the MRPS16 gene. A new group of mitochondrial respiratory chain disorders is proposed, resulting from mutations in nuclear encoded components of the mitochondrial translation apparatus. Ann Neurol 2004;56:734–738

Autosomal-Recessive Hypophosphatemic Rickets Is Associated with an Inactivation Mutation in the ENPP1 Gene

Human disorders of phosphate (Pi) handling and hypophosphatemic rickets have been shown to result from mutations in PHEX, FGF23, and DMP1, presenting as X-linked recessive, autosomal-dominant, and autosomal-recessive patterns, respectively. We present the identification of an inactivating mutation in the ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) gene causing autosomal-recessive hypophosphatemic rickets (ARHR) with phosphaturia by positional cloning. ENPP1 generates inorganic pyrophosphate (PPi), an essential physiologic inhibitor of calcification, and previously described inactivating mutations in this gene were shown to cause aberrant ectopic calcification disorders, whereas no aberrant calcifications were present in our patients. Our surprising result suggests a different pathway involved in the generation of ARHR and possible additional functions for ENPP1.

Successful immune tolerance induction to enzyme replacement therapy in CRIM-negative infantile Pompe disease

Purpose:Infantile Pompe disease resulting from a deficiency of lysosomal acid α-glucosidase (GAA) requires enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA). Cross-reactive immunologic material negative (CRIM-negative) Pompe patients develop high-titer antibody to the rhGAA and do poorly. We describe successful tolerance induction in CRIM-negative patients.Methods:Two CRIM-negative patients with preexisting anti-GAA antibodies were treated therapeutically with rituximab, methotrexate, and gammaglobulins. Two additional CRIM-negative patients were treated prophylactically with a short course of rituximab and methotrexate, in parallel with initiating rhGAA.Results:In both patients treated therapeutically, anti-rhGAA was eliminated after 3 and 19 months. All four patients are immune tolerant to rhGAA, off immune therapy, showing B-cell recovery while continuing to receive ERT at ages 36 and 56 months (therapeutic) and 18 and 35 months (prophylactic). All patients show clinical response to ERT, in stark contrast to the rapid deterioration of their nontolerized CRIM-negative counterparts.Conclusion:The combination of rituximab with methotrexate ± intravenous gammaglobulins (IVIG) is an option for tolerance induction of CRIM-negative Pompe to ERT when instituted in the naïve setting or following antibody development. It should be considered in other conditions in which antibody response to the therapeutic protein elicits robust antibody response that interferes with product efficacy.Genet Med 2012:14(1):135–142

Mitochondrial Complex I Deficiency Caused by a Deleterious NDUFA11 Mutation

Complex I deficiency is the most common respiratory chain defect, clinically manifesting by severe neonatal lactic acidosis, Leighs disease, or various combinations of cardiac, hepatic, and renal disorders. Using homozygosity mapping, we identified a splice‐site mutation in the NDUFA11 gene in six patients from three unrelated families. The patients presented with encephalocardiomyopathy or fatal infantile lactic acidemia. The mutation is predicted to abolish the first transmembrane domain of the gene product, thereby destabilizing the enzymatic complex. Mutation analysis of the NDUFA11 is warranted in isolated complex I deficiency presenting with infantile lactic acidemia or encephalocardiomyopathy. Ann Neurol 2008

Effects of a twelve-week randomized intervention of exercise and/or diet on weight loss and weight maintenance, and other metabolic parameters in obese preadolescent children.

Aims: To compare the short- and long-term effects of intervention programs on body weight and cardiometabolic risk factors. Methods: 162 obese children (6–11 years) were randomly assigned to three 12-week interventions with a 9-month follow-up period: exercise (E): 90 min moderate exercise 3 days/week (n = 52); diet (D): balanced hypocaloric diet, weekly meetings with dietician (n = 55), and diet + exercise (D+E) (n = 55). Changes in anthropometric variables, cardiometabolic profile and psychological outcome were assessed. Results: At 12 weeks BMI-SDS, cardiometabolic profiles, and psychological score improved in all groups. The decrease in BMI-SDS was greater in D and D+E compared with E (p < 0.001), without a significant difference between the first two groups. Waist circumference and LDL cholesterol decreased more in D+E compared with E (p = 0.026 and p = 0.038, respectively). The increase in adiponectin was greater in D and D+E compared with E (p = 0.004). Anthropometric and cardiometabolic variables regressed without significant differences between groups after 9 months. However, BMI-SDS, body fat percentage and LDL cholesterol were lower compared to baseline. Conclusions: Diet alone or combined with exercise are the most effective short-term interventions for weight loss and improved cardiometabolic profiles, without a difference between them. In the long term, obese children need the long-term support of maintenance approaches.

Homozygous Mutation G539R in the Gene for P450 Oxidoreductase in a Family Previously Diagnosed as Having 17,20-Lyase Deficiency

CONTEXT Very few patients have been described with isolated 17,20-lyase deficiency who have had their mutations in P450c17 (17alpha-hydroxylase/17,20-lyase) proven by DNA sequencing and in vitro characterization of the mutations. Most patients with 17,20-lyase deficiency have mutations in the domain of P450c17 that interact with the electron-donating redox partner, P450 oxidoreductase (POR). OBJECTIVE Our objective was to clarify the genetic and functional basis of isolated 17,20-lyase deficiency in familial cases who were previously reported as having 17,20-lyase deficiency. PATIENTS Four undervirilized males of an extended Bedouin family were investigated. One of these has previously been reported to carry mutations in the CYP17A1 gene encoding P450c17 causing isolated 17,20-lyase deficiency. METHODS Serum hormones were evaluated before and after stimulation with ACTH. Urinary steroid metabolites were profiled by gas chromatography-mass spectrometry. Exons 1 and 8 of CYP17A1 previously reported to harbor mutations in one of these patients and all 15 coding exons of POR were sequenced. RESULTS Gas chromatography-mass spectrometry (GC-MS) urinary steroid profiling and serum steroid measurements showed combined deficiencies of 17,20-lyase and 21-hydroxylase. Sequencing of exons 1 and 8 of CYP17A1 in two different laboratories showed no mutations. Sequencing of POR showed that all four patients were homozygous for G539R, a previously studied mutation that retains 46% of normal capacity to support the 17alpha-hydroxylase activity but only 8% of the 17,20-lyase activity of P450c17. CONCLUSION POR deficiency can masquerade clinically as isolated 17,20-lyase deficiency.

Homozygosity and linkage-disequilibrium mapping of the syndrome of congenital hypoparathyroidism, growth and mental retardation, and dysmorphism to a 1-cM interval on chromosome 1q42-43

The syndrome of hypoparathyroidism associated with growth retardation, developmental delay, and dysmorphism (HRD) is a newly described, autosomal recessive, congenital disorder with severe, often fatal consequences. Since the syndrome is very rare, with all parents of affected individuals being consanguineous, it is presumed to be caused by homozygous inheritance of a single recessive mutation from a common ancestor. To localize the HRD gene, we performed a genomewide screen using DNA pooling and homozygosity mapping for apparently unlinked kindreds. Analysis of a panel of 359 highly polymorphic markers revealed linkage to D1S235. The maximum LOD score obtained was 4.11 at a recombination fraction of 0. Analysis of three additional markers-GGAA6F06, D1S2678, and D1S179-in a 2-cM interval around D1S235 resulted in LOD scores >3. Analysis of additional chromosome 1 markers revealed evidence of genetic linkage disequilibrium and place the HRD locus within an approximately 1-cM interval defined by D1S1540 and D1S2678 on chromosome 1q42-43.

TMEM70 mutations are a common cause of nuclear encoded ATP synthase assembly defect: further delineation of a new syndrome

Background The TMEM70 gene defect was recently identified as a novel cause of autosomal recessive ATP synthase deficiency. Most of the 28 patients with TMEM70 disorder reported to date display a distinctive phenotype characterised by neonatal onset of severe muscular hypotonia hypertrophic cardiomyopathy, facial dysmorphism, profound lactic acidosis, and 3-methylglutaconic aciduria. Almost all share a common Roma descent and are homozygous for a single founder splice site mutation. Methods Six new patients from four separate families, with clinical and biochemical diagnosis of ATP synthase deficiency, were studied. TMEM70 sequence analysis of the three exons and their flanking splice junction consensus sequences was performed in all patients. In addition their clinical phenotype and disease course was strictly studied. Results Four novel deleterious homozygous TMEM70 mutations were identified. The previously described clinical spectrum was expanded to include infantile onset cataract, early onset gastrointestinal dysfunction and congenital hypertonia with multiple contractures resembling arthrogryposis. The first characterisation of fetal presentation of the syndrome is also provided, featuring significant intrauterine growth retardation, severe oligohydramnios, fetal hypotonia, and myocardial wall thickening. Conclusions The current report corroborates the previously described unique phenotype of TMEM70 deficiency. The study identifies TMEM70 gene defect as a pan-ethnic disorder and further redefines it as the most common cause of nuclear-origin ATP synthase deficiency.