Giulia Polo

Developmental defects and neuromuscular alterations due to mitofusin 2 gene (MFN2) silencing in zebrafish: a new model for Charcot-Marie-Tooth type 2A neuropathy

The development of new animal models is a crucial step in determining the pathological mechanism underlying neurodegenerative diseases and is essential for the development of effective therapies. We have investigated the zebrafish (Danio rerio) as a new model to study CMT2A, a peripheral neuropathy characterized by the selective loss of motor neurons, caused by mutations of mitofusin 2 gene. Using a knock-down approach, we provide evidence that during embryonic development, mitofusin 2 loss of function is responsible of several morphological defects and motility impairment. Immunohistochemical investigations, revealing the presence of severe alterations in both motor neurons and muscles fibres, indicated the central role played by MFN2 in axonal and neuromuscular development. Finally, we demonstrated the ability of human MFN2 to balance the downregulation of endogenous mfn2 in zebrafish, further supporting the conserved function of the MFN2 gene. These results highlight the essential role of mitofusin 2 in the motor axon development and demonstrate the potential of zebrafish as a suitable and complementary platform for dissecting pathogenetic mechanisms of MFN2 mutations in vivo.

Diagnosis of sphingolipidoses: a new simultaneous measurement of lysosphingolipids by LC-MS/MS.

Abstract Background: Lysosphingolipids (LysoSLs) are derivatives of sphingolipids which have lost the amide-linked acyl chain. More recently, LysoSLs have been identified as storage compounds in several sphingolipidoses, including Gaucher, Fabry and Niemann-Pick diseases. To date, different methods have been developed to measure each individual lysosphingolipid in plasma. This report describes a rapid liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) assay for simultaneous quantification of several LysoSLs in plasma. Methods: We analyzed the following compounds: hexosylsphingosine (HexSph), globotriaosylsphingosine (LysoGb3), lysosphingomyelin (LysoSM) and lysosphingomyelin-509 (LysoSM-509). The sample preparation requires only 100 μL of plasma and consists of an extraction with a mixture of MeOH/acetone/H2O (45:45:10, v/v). Results: The method validation showed high sensitivity, an excellent accuracy and precision. Reference ranges were determined in healthy adult and pediatric population. The results demonstrate that the LC-MS/MS method can quantify different LysoSLs and can be used to identify patients with Fabry (LysoGb3), Gaucher and Krabbe (HexSph) diseases, prosaposine deficiency (LysoGb3 and HexSph), and Niemann-Pick disease types A/B and C (LysoSM and LysoSM-509). Conclusions: This LC-MS/MS method allows a rapid and simultaneous quantification of LysoSLs and is useful as a biochemical diagnostic tool for sphingolipidoses.

High-throughput LC-MS/MS method for monitoring sirolimus and everolimus in the routine clinical laboratory.

Abstract Background: Immunosuppressant therapeutic drug monitoring (TDM) is an important requirement in post-transplant patient care. In recent years, high-performance liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) has become a valid alternative to antibody-based immunoassays in TDM due to its high specificity and sensitivity. Furthermore, this technology allows for the simultaneous measurement of several immunosuppressive drugs. The aim of the present study was to establish a straightforward, robust, and high-throughput LC-MS/MS method for the simultaneous determination of sirolimus and everolimus in whole blood in order to replace immunoassays in our routine practice. Methods: Five-level blood calibrators were employed for assay development, while three materials at different concentrations were used for internal quality control. The proposed method uses protein precipitation for sample preparation. Analyses were performed using a triple quadrupole LC-MS/MS, with a C18 held at 60°C. Using an appropriate gradient elution profile and SPE on-line, elution times for all compounds analysed were 2.6 min with a total run-time of 3.5 min. Results: Calibration curves were linear throughout the selected ranges. The intra- and inter-assay CVs (<7%), the limit of quantification (0.2 μg/L) and accuracy were highly satisfactory. On testing the results using the international proficiency testing scheme (UK-NEQAS), the performance of the proposed method was found to be highly reliable. Conclusions: The findings made by us indicate that the proposed method is of value, since it is speedy, straightforward, accurate, and applicable to different LC-MS/MS instruments for the routine TDM of organ transplant recipients.

High level of oxysterols in neonatal cholestasis: a pitfall in analysis of biochemical markers for Niemann-Pick type C disease.

Abstract Background: Niemann-Pick disease type C (NPC) is a rare lipid storage disorder characterized by progressive neurological deterioration. Diagnosing NPC is challenging as clinical signs and symptoms are variable and non-specific. Two oxysterols, cholestane-3β,5α,6β-triol (triol) and 7-ketocholesterol (7KC), have been proposed as biomarkers for aiding diagnosis of NPC. This study evaluated the use of triol and 7KC as biomarkers in cholestatic neonates with suspected NPC. Methods: Plasma triol and 7KC were analysed as dimethylglycine esters using an liquid chromatography – tandem mass spectrometry (LC-MS/MS) assay in selected neonates with severe cholestasis and suspected NPC (n=7), adults with cholestasis (n=15), patients with confirmed NPC (positive controls; n=11 [one child and 10 adults]), healthy subjects (negative controls; n=40 [20 children and 20 adults]), and cholestatic adults (comparative reference; n=15). The LC-MS/MS method was subjected to a number of tests for accuracy and consistency. Results: Triol and 7KC levels were substantially and significantly increased in NPC positive patients compared with healthy controls (p<0.001). However, positive results (markedly increased levels of both oxysterols) were identified in 6/7 (86%) neonates with cholestasis. Genetic testing confirmed NPC only in one neonate who had increased triol and 7KC, and increased oxysterol levels among neonates with no identified NPC gene mutations were considered likely due to biliary atresia (BA). Conclusions: While the potential of oxysterols as NPC biomarkers has been well evaluated in older patient populations (without cholestasis), our data suggest that cholestasis might represent a pitfall in oxysterol measurements intended to aid diagnosis of NPC in affected patients.

Quality of Life (QoL) assessment in a cohort of patients with Phenylketonuria

BackgroundPhenylketonuria (PKU) is a chronic inborn error of amino acid metabolism that requires lifelong follow-up and intervention, which may represent strains on Quality of Life (QoL). This observational study evaluated QoL in a cohort of PKU patients, using updated and detailed instruments.Methods22 patients with mild PKU respondent to BH4 and 21 patients with classical PKU treated with diet were recruited in this study. Adult patients completed WHOQOL questionnaire-100 (WHOQOL-100) and pediatric patients the Pediatric QoL inventory (PedsQLTM). Psychiatric and mood disorders were also evaluated using TAD or BDI and STAI-Y inventories. A multivariable linear regression model was fitted to investigate the predictors of QoL, including age, sex, treatment type, length of current treatment, educational level and employment status (only for adults) as covariates. Results were presented as regression coefficients with 95% confidence interval.ResultsGlobal QoL scores were within normal range both in patients with mild and classical disease but global QoL scores were significantly higher in patients with mild PKU under BH4 treatment as compared to those affected by classical disease who were under diet regimen. Furthermore, QoL significantly increased in long treated PKU patients. Among adult patients, QoL scores were significantly lower in males, in patients with lower education and in those employed or unemployed as compared to students (baseline).ConclusionsBoth diet and medical treatment based upon BH4 seem to be associated with higher QoL in the long run. However, patients with mild PKU can rely on BH4 to achieve a higher Phe tolerance and a better compliance to therapy due to diet relaxation/avoidance. Some specific categories of patients with a lower QoL should be investigated more in depth, engaging with those at risk of lower treatment compliance. The questionnaires employed in the present study seemed to be able to effectively detect criticalities in QoL assessment and represent an advance from previous inventories employed in the past.

Newborn screening for lysosomal storage disorders by tandem mass spectrometry in North East Italy

BackgroundLysosomal storage diseases (LSDs) are inborn errors of metabolism resulting from 50 different inherited disorders. The increasing availability of treatments and the importance of early intervention have stimulated newborn screening (NBS) to diagnose LSDs and permit early intervention to prevent irreversible impairment or severe disability. We present our experience screening newborns in North East Italy to identify neonates with Mucopolysaccharidosis type I (MPS I) and Pompe, Fabry, and Gaucher diseases.MethodsActivities of acid β-glucocerebrosidase (ABG; Gaucher), acid α-glucosidase (GAA; Pompe), acid α-galactosidase (GLA; Fabry), and acid α-L-iduronidase (IDUA; MPS-I) in dried blood spots (DBS) from all newborns during a 17-month period were determined by multiplexed tandem mass spectrometry (MS/MS) using the NeoLSD® assay system. Enzymatic activity cutoff values were determined from 3500 anonymous newborn DBS. In the screening study, samples were retested if the value was below cutoff and a second spot was requested, with referral for confirmatory testing and medical evaluation if a low value was obtained.ResultsFrom September 2015 to January 2017, 44,411 newborns were screened for the four LSDs. We recalled 40 neonates (0.09%) for collection of a second DBS. Low activity was confirmed in 20, who had confirmatory testing. Ten of 20 had pathogenic mutations: two Pompe, two Gaucher, five Fabry, and one MPS-I. The incidences of Pompe and Gaucher diseases were similar (1/22,205), with Fabry disease the most frequent (1/8882) and MPS-I the rarest (1/44411). The combined incidence of the four disorders was 1/4411 births.ConclusionsSimultaneously determining multiple enzyme activities by MS/MS, with a focus on specific biochemical markers, successfully detected newborns with LSDs. The high incidence of these disorders supports this screening program.

Clinical experience with N-carbamylglutamate in a single-centre cohort of patients with propionic and methylmalonic aciduria.

Background The effect of long-term N-carbamylglutamate (NCG) treatment on the rate and severity of decompensations due to propionic aciduria (PA) and methylmalonic aciduria (MMA) is unknown. This paper presents clinical experience from a single-centre cohort of patients with PA and MMA who received continuous long-term treatment with NCG. Methods The effect of oral NCG treatment (initial dose: 50 mg/kg/day) was investigated in patients with PA or MMA who were experiencing frequent progressive episodes of metabolic decompensation, who had pathological levels of ammonia, and who were referred to the Division of Metabolic Diseases, University Hospital of Padova between August 2014 and December 2015. Clinical and biochemical data, including the number of metabolic decompensations, lactic acid, uric acid and plasma ammonia levels, protein intake and body weight, were collected before and after the initiation of NCG treatment. Results Eight patients with PA (n = 4) and MMA (n = 4) aged 2–20 years were treated with NCG (50 mg/kg/day) for 7–16 months. Metabolic decompensation episodes decreased in number and severity, with three of the patients having no episodes (pre-treatment: 24 episodes; post-treatment: 9 episodes). After NCG treatment, all episodes were treated at home and none required hospitalisation, lactic acid values were 1.3–2.1 mmol/L and uric acid values were 0.21–0.36 mmol/L. Significant reductions in blood ammonia levels after NCG initiation were observed in five patients, whereas levels were reduced or maintained in the normal range in the remainder. Over the treatment period, patients had an increase in natural protein intake of 20–50% and gained 0–6.5 kg in bodyweight. Conclusion These observations suggest that, in addition to short-term benefits for the acute treatment of hyperammonaemia, NCG may be effective and well tolerated as a long-term treatment in patients with severe PA and MMA, and that further prospective studies are warranted.

N-Acetylglutamate Synthase Deficiency Due to a Recurrent Sequence Variant in the N-acetylglutamate Synthase Enhancer Region

N-acetylglutamate synthase deficiency (NAGSD, MIM #237310) is an autosomal recessive disorder of the urea cycle that results from absent or decreased production of N-acetylglutamate (NAG) due to either decreased NAGS gene expression or defective NAGS enzyme. NAG is essential for the activity of carbamylphosphate synthetase 1 (CPS1), the first and rate-limiting enzyme of the urea cycle. NAGSD is the only urea cycle disorder that can be treated with a single drug, N-carbamylglutamate (NCG), which can activate CPS1 and completely restore ureagenesis in patients with NAGSD. We describe a novel sequence variant NM_153006.2:c.-3026C > T in the NAGS enhancer that was found in three patients from two families with NAGSD; two patients had hyperammonemia that resolved upon treatment with NCG, while the third patient increased dietary protein intake after initiation of NCG therapy. Two patients were homozygous for the variant while the third patient had the c.-3026C > T variant and a partial uniparental disomy that encompassed the NAGS gene on chromosome 17. The c.-3026C > T sequence variant affects a base pair that is highly conserved in vertebrates; the variant is predicted to be deleterious by several bioinformatics tools. Functional assays in cultured HepG2 cells demonstrated that the c.-3026C > T substitution could result in reduced expression of the NAGS gene. These findings underscore the importance of analyzing NAGS gene regulatory regions when looking for molecular causes of NAGSD.

Newborn Screening and High Risk Screening Population for Neurological Inherited Metabolic Diseases

Nowadays, it is possible to carry on screening tests for many of the inherited metabolic disorders currently recognized. Laboratory investigations are complex and susceptible to technical problems. Since 1970s, batteries of relatively inexpensive tests named screening for metabolic diseases that can be carried out rapidly on a large numbers of specimens have been developed.

Living with phenylketonuria in adulthood: The PKU ATTITUDE study

Dietary treatment is the cornerstone of therapy for phenylketonuria (PKU), but adherence to low- phenylalanine diet progressively decreases after adolescence. We designed a survey to characterize the dietary habits of Italian adult PKU patients and to identify psychological factors influencing disease perception and adherence to diet. Participants to the survey (n = 111; response rate 94%) were asked to complete a structured questionnaire. Patients appeared to have an altered perception and awareness of the disease. About 40% of them did not consider PKU a disease and, despite declaring regular monitoring of phenylalanine levels (85%), nearly half of them reported a high plasma value over the last 6 months (>600 μmol/L, 48%) or were unable to specify it (31%). Adherence to PKU diet was unsatisfactory, with increased consumption of natural protein sources and reduced daily use of amino-acid supplements (<4–5 times/day in 82% patients). In addition to the intrinsic characteristics of AA formula (palatability, ease of use), the most important factor influencing their consumption was the increased social pressure associated with their use (55%). Plasma phenylalanine periodical measurements (61%) and examinations at metabolic centers (49%) were considered relevant for compliance to diet. In Italian adult PKU patients dietary management was found to be inadequate, likely due to inappropriate perception and knowledge of the disease, and lack of awareness of the negative impact of poor metabolic control in adult life. Clinicians should consider implementing more intense and tailored educational measures, as well as structured transitional care processes.