Allel Chabli

Endogenous hydrogen sulfide overproduction in Down syndrome

The cystathionine beta synthase (CBS) gene is localized on chromosome 21 (21q22.3). This enzyme is one of three enzymes able to produce hydrogen sulfide. CBS is overexpressed in Down syndrome with levels 166% of normal values in fibroblasts [Chadefaux et al., 1985] and 1,200% in myeloblasts [Taub et al., 1999]. The CBS overexpression could induceanoverproduction ofhydrogen sulfide in Down syndrome patients, and this overproduction is potentially able to induce some of the clinical signs of Down syndrome such as hypotonia and mental retardation. As thiosulfate is the main catabolite of hydrogen sulfide [Kangas and Savolainen, 1987], we compared the levels of this molecule in the urine of Down syndrome patients and control subjects. Human erythrocytes containvarious formsofhemoglobin.These include sulfhemoglobin, which is formed by transformation of the ferric derivative of hemoglobin, methemoglobin. Sulfhemoglobin production requires hydrogen sulfide (or another sulfide) andmethemoglobin [Nichols et al., 1968]. The determination of sulfhemoglobin in erythrocytes was therefore also used to assess hydrogen sulfide production in Down syndrome. Informed consent was obtained from Down syndrome patients and their parents and from controls. The subjects were assigned to three groups. Group 1 (diet-matched pairs) consisted of 21 pairs of subjects (17 of them were included in a previously published study [Belardinelli et al., 2001]. In each volunteer family, one Down syndrome subject and one relative (mother or father in most families, brother or sister in rare cases) were given identical diets. This group consisted of 13 male and 8 female Down syndrome subjects and matched controls (10 male and 11 female). Sulfur compounds were excluded from the daily treatments of Downsyndromepatientsandcontrols.Group2consisted of 30 patients with Down syndrome (19 male and 11 female) and 20 controls (volunteers from the laboratory; 10 male and 10 female). In this group, age distribution was similar for Down syndrome patients and controls (Table I). The first urine produced in the morning was collected from the subjects of groups 1 and 2 in vials containing boric acid used as a preservative. Thiosulfate was determined in urine by colorimetry after chromatographic separation [Voroteliak et al., 1993]. Creatinine was determined by the manual Jaffe method. Group 3 consisted of 60 Down syndrome patients (33 male and 27 female) and 60 age-matched controls (35 male and 25 female). Venous blood was withdrawn in fasting subjects of group 3; erythrocytes were separated by centrifugation and hemolysates were frozen until use. Sulfhemoglobin was determined by spectrophotometry and the results are expressed as ratio of absorbance (A) at various wawelengths: (A622 nm A636 nm)/(A535 nmþA560 nm) 0.5 10. This ratio was used because it is not affected by differences between the respective concentrations of oxygenated and unoxygenated hemoglobin. A significant difference was observed in the urinary excretion of thiosulfate between Down syndrome patients and relatives of group 1 (diet-matched pairs) (Table I). In group 2, statistical analysis indicates that the differences in thiosulfate excretion persisted. To confirm that hydrogen sulfide was overproduced in Down syndrome patients, we studied erythrocyte sulfhemoglobin content in subjects of group 3. The wawelength ratios were 2.51 0.04 and 2.00 0.08 (SEM) for patientswithDownsyndrome and controls, respectively (P<0.001). We obtained two different types of evidence for the overproduction of hydrogen sulfide in Down syndrome patients. The main function of CBS is to catalyze the first step of transsulphuration pathway, producing cysteine from homocysteine. In vivo, the high level of CBS activity in Down syndrome results in low concentrations of the substrate of CBS (homocysteine) in plasma [Chadefaux et al., 1988]. CBS also has another enzymatic activity: the production of hydrogen sulfide from cysteine [Stipanuck and Beck, 1982]. The endogenous productionofhydrogensulfidecanbeestimatedbymonitoring thiosulfate excretion in urine (31 mmoles/day in control adults) [Sorbo and Ohman, 1978]. After hydrogen sulfide poisoning, the excretion of thiosulfate in urine increased significantly [Kangas and Savolainen, *Correspondence to: Pierre Kamoun, Biochimie B–Tour Lavoisier, Hôpital Necker Enfants Malades, 149, rue de Sèvres, 75743 Paris Cedex 15, France. E-mail: pierre.kamoun@nck.ap-hop-paris.fr

Heptahelical protein PQLC2 is a lysosomal cationic amino acid exporter underlying the action of cysteamine in cystinosis therapy

Cystinosin, the lysosomal cystine exporter defective in cystinosis, is the founding member of a family of heptahelical membrane proteins related to bacteriorhodopsin and characterized by a duplicated motif termed the PQ loop. PQ-loop proteins are more frequent in eukaryotes than in prokaryotes; except for cystinosin, their molecular function remains elusive. In this study, we report that three yeast PQ-loop proteins of unknown function, Ypq1, Ypq2, and Ypq3, localize to the vacuolar membrane and are involved in homeostasis of cationic amino acids (CAAs). We also show that PQLC2, a mammalian PQ-loop protein closely related to yeast Ypq proteins, localizes to lysosomes and catalyzes a robust, electrogenic transport that is selective for CAAs and strongly activated at low extracytosolic pH. Heterologous expression of PQLC2 at the yeast vacuole rescues the resistance phenotype of an ypq2 mutant to canavanine, a toxic analog of arginine efficiently transported by PQLC2. Finally, PQLC2 transports a lysine-like mixed disulfide that serves as a chemical intermediate in cysteamine therapy of cystinosis, and PQLC2 gene silencing trapped this intermediate in cystinotic cells. We conclude that PQLC2 and Ypq1–3 proteins are lysosomal/vacuolar exporters of CAAs and suggest that small-molecule transport is a conserved feature of the PQ-loop protein family, in agreement with its distant similarity to SWEET sugar transporters and to the mitochondrial pyruvate carrier. The elucidation of PQLC2 function may help improve cysteamine therapy. It may also clarify the origin of CAA abnormalities in Batten disease.

Methylenetetrahydrofolate Reductase Polymorphism in the Etiology of Down Syndrome

A methylenetetrahydrofolate reductase polymorphism (677 C/T mutation) was recently implicated in the etiology of Down syndrome. We studied a cohort of 85 women carrying fetuses with Down syndrome and found no difference in the frequencies of the three groups of subjects (C/C, C/T, T/T) between Down syndrome mothers and controls.

Natural history of Barth syndrome: a national cohort study of 22 patients

BackgroundThis study describes the natural history of Barth syndrome (BTHS).MethodsThe medical records of all patients with BTHS living in France were identified in multiple sources and reviewed.ResultsWe identified 16 BTHS pedigrees that included 22 patients. TAZ mutations were observed in 15 pedigrees. The estimated incidence of BTHS was 1.5 cases per million births (95%CI: 0.2–2.3). The median age at presentation was 3.1 weeks (range, 0–1.4 years), and the median age at last follow-up was 4.75 years (range, 3–15 years). Eleven patients died at a median age of 5.1 months; 9 deaths were related to cardiomyopathy and 2 to sepsis. The 5-year survival rate was 51%, and no deaths were observed in patients ≥3 years. Fourteen patients presented with cardiomyopathy, and cardiomyopathy was documented in 20 during follow-up. Left ventricular systolic function was very poor during the first year of life and tended to normalize over time. Nineteen patients had neutropenia. Metabolic investigations revealed inconstant moderate 3-methylglutaconic aciduria and plasma arginine levels that were reduced or in the low-normal range. Survival correlated with two prognostic factors: severe neutropenia at diagnosis (<0.5 × 109/L) and birth year. Specifically, the survival rate was 70% for patients born after 2000 and 20% for those born before 2000.ConclusionsThis survey found that BTHS outcome was affected by cardiac events and by a risk of infection that was related to neutropenia. Modern management of heart failure and prevention of infection in infancy may improve the survival of patients with BTHS without the need for heart transplantation.

Secondary creatine deficiency in ornithine delta-aminotransferase deficiency

AIMS Ornithine delta-aminotransferase (OAT) deficiency causes gyrate atrophy (GA) of the retina, as a consequence of high plasma ornithine concentrations. Because creatine synthesis requires the conversion of arginine and glycine into ornithine and guanidinoacetate, high ornithine concentration inhibits this reaction thus causing secondary creatine deficiency. The aim of this study was to evaluate the neuropsychological features and creatine metabolism in patients with GA. METHODS The study involved 7 GA patients, aged from 11 to 27 years who underwent neuropsychological evaluation and cerebral proton magnetic resonance spectroscopy (MRS). RESULTS Neurocognitive impairment was found in 5/7 patients, including mental retardation (3/7), school failure (1/7), major visuospatial dyspraxia (1/7), aggressive behavior (3/7) and epilepsy (2/7). Two patients had normal neuropsychological evaluation. Cerebral proton magnetic resonance spectroscopy revealed a profound creatine deficiency in all patients. MRS data were confirmed by decreased levels of creatine and/or guanidinoacetate in plasma and urine in all patients. CONCLUSIONS In our group of patients with GA, we found a high prevalence of neurological impairment, not reported so far, and possibly related to secondary creatine deficiency and hyperornithinemia. We propose to treat mentally retarded GA patients with high doses of creatine, as it may normalize brain creatine levels and help to reduce ornithine levels.

Screening for primary creatine deficiencies in French patients with unexplained neurological symptoms.

A population of patients with unexplained neurological symptoms from six major French university hospitals was screened over a 28-month period for primary creatine disorder (PCD). Urine guanidinoacetate (GAA) and creatine:creatinine ratios were measured in a cohort of 6,353 subjects to identify PCD patients and compile their clinical, 1H-MRS, biochemical and molecular data. Six GAMT [N-guanidinoacetatemethyltransferase (EC 2.1.1.2)] and 10 X-linked creatine transporter (SLC6A8) but no AGAT (GATM) [L-arginine/glycine amidinotransferase (EC 2.1.4.1)] deficient patients were identified in this manner. Three additional affected sibs were further identified after familial inquiry (1 brother with GAMT deficiency and 2 brothers with SLC6A8 deficiency in two different families). The prevalence of PCD in this population was 0.25% (0.09% and 0.16% for GAMT and SLC6A8 deficiencies, respectively). Seven new PCD-causing mutations were discovered (2 nonsense [c.577C > T and c.289C > T] and 1 splicing [c.391 + 15G > T] mutations for the GAMT gene and, 2 missense [c.1208C > A and c.926C > A], 1 frameshift [c.930delG] and 1 splicing [c.1393-1G > A] mutations for the SLC6A8 gene). No hot spot mutations were observed in these genes, as all the mutations were distributed throughout the entire gene sequences and were essentially patient/family specific. Approximately one fifth of the mutations of SLC6A8, but not GAMT, were attributed to neo-mutation, germinal or somatic mosaicism events. The only SLC6A8-deficient female patient in our series presented with the severe phenotype usually characterizing affected male patients, an observation in agreement with recent evidence that is in support of the fact that this X-linked disorder might be more frequent than expected in the female population with intellectual disability.

Creatine and guanidinoacetate reference values in a French population

Creatine and guanidinoacetate are biomarkers of creatine metabolism. Their assays in body fluids may be used for detecting patients with primary creatine deficiency disorders (PCDD), a class of inherited diseases. Their laboratory values in blood and urine may vary with age, requiring that reference normal values are given within the age range. Despite the long known role of creatine for muscle physiology, muscle signs are not necessarily the major complaint expressed by PCDD patients. These disorders drastically affect brain function inducing, in patients, intellectual disability, autistic behavior and other neurological signs (delays in speech and language, epilepsy, ataxia, dystonia and choreoathetosis), being a common feature the drop in brain creatine content. For this reason, screening of PCDD patients has been repeatedly carried out in populations with neurological signs. This report is aimed at providing reference laboratory values and related age ranges found for a large scale population of patients with neurological signs (more than 6 thousand patients) previously serving as a background population for screening French patients with PCDD. These reference laboratory values and age ranges compare rather favorably with literature values for healthy populations. Some differences are also observed, and female participants are discriminated from male participants as regards to urine but not blood values including creatine on creatinine ratio and guanidinoacetate on creatinine ratio values. Such gender differences were previously observed in healthy populations; they might be explained by literature differential effects of testosterone and estrogen in adolescents and adults, and by estrogen effects in prepubertal age on SLC6A8 function. Finally, though they were acquired on a population with neurological signs, the present data might reasonably serve as reference laboratory values in any future medical study exploring abnormalities of creatine metabolism and transport.

Functional and electrophysiological characterization of four non-truncating mutations responsible for creatine transporter (SLC6A8) deficiency syndrome

Intellectual disability coupled with epilepsy are clinical hallmarks of the creatine (Cr) transporter deficiency syndrome resulting from mutations in the SLC6A8 gene. So far characterization of pathogenic mutations of SLC6A8 has been limited to Cr uptake. The aim of our study was to characterize the electrogenic and pharmacological properties of non truncating SLC6A8 mutations identified in patients presenting variable clinical severity. Electrophysiological and pharmacological properties of four mutants (including two novel ones) were studied in X. laevis oocyte expression system. Creatine uptake was assessed with [14C]-Cr in X. laevis and patients’ fibroblasts. Subcellular localization was determined by immunofluorescence and western blot. All mutants were properly targeted to the plasma membrane in both systems. Mutations led to the complete loss of both electrogenic and transport activities in X. laevis and Cr uptake in patients’ fibroblasts. Among the Cr analogs tested, guanidinopropionate induced an electrogenic activity with the normal SLC6A8 transporter similar to creatine whereas a phosphocreatine derivative, PCr-Mg-CPLX, resulted in partial activity. SLC6A8 mutants displayed no electrogenic activity with all Cr analogs tested in X. laevis oocytes. Although the mutations altered various domains of SLC6A8 Cr uptake and electrogenic properties were completely inhibited and could not be dissociated. Besides the metabolic functions of Cr, the loss of SLC6A8 electrogenic activity, demonstrated here for the first time, may also play a role in the altered brain functions of the patients.

Obstructive sleep apnea syndrome after hematopoietic stem cell transplantation in children with mucopolysaccharidosis type I

BACKGROUND Obstructive sleep apnea syndrome (OSAS) is very common in mucopolysaccharidosis I (MPS I). Hematopoietic stem cell transplantation (HSCT) is the preferred treatment for patients with severe MPS I diagnosed early in life. The protective effect of HSCT on the development of long term OSAS is not known. METHODS Overnight polysomnography (PSG) and biomarker data were analyzed during the annual follow-up in consecutive MPS I patients treated with HSCT. RESULTS The data of 13 patients (6 boys) were analyzed. Median age at HSCT was 17 (range 14-19) months, median age at PSG was 9.0 (4.5-14.5) years, and median time elapsed since HSCT was 7.6 (2.4-13.2) years. A significant correlation was observed between time elapsed since HSCT and the apnea-hypopnea index (AHI, r(2)=0.493, p=+0.003) and the oxygen desaturation index (r(2)=0.424, p=+0.02). Patients older than 10 years of age had a higher mean AHI (25.8/h vs 1.4/h, p=0.0008), a lower mean pulse oximetry (94.7% vs 97.2%, p=0.01) and a higher mean hypopnea index (18.8 vs 0.71/h, p=0.016) as compared to those younger than 10 years of age. No correlation was observed between the AHI and the metabolic clearance, assessed by urine glycosaminoglycan (GAG) excretion and residual enzyme activity, although there was a positive trend for the urinary GAG/higher normal value for age ratio (p=0.09). CONCLUSION HSCT does not offer long term protection against OSAS in MPS I with OSAS being documented in all patients after a time elapse since HSCT exceeding 10 years. The potential benefit of additional enzyme replacement therapy needs to be assessed.