A new multiplex analysis of glucosylsphingosine and globotriaosylsphingosine in dried blood spots by tandem mass spectrometry

Background

Gaucher's and Fabry's disease are two of the most common treatable lysosomal storage diseases, and have a wide spectrum of clinical symptoms. Early detection is important, because timely initiation of treatments can improve the disease status and prevent complications. However disease manifestations develop in childhood, diagnosis is delayed until adulthood partly due to the limitations of the currently used diagnostic pathway. The aim of this research is to develop and validate a multiplex assay and defining reference ranges, which do not exist at this moment, to improve and facilitate the entire diagnostic work up and enable treatment in an earlier stage of disease.

Methods and findings

Biomarkers glucosylsphingosine (GlcSph) and globotriaosylsphingosine (Lyso-Gb3) were detected and quantified using LC-MS/MS on dried blood spots. We developed an improved and new extraction method that allowed to measure GlcSph and Lyso-Gb3 in a multiplex analytical platform. After validation of the method, samples of 1480 individuals with normal enzymatic activity were collected to determine age and gender-related reference ranges.Our combination method showed a good linearity, precision, accuracy and limit of quantification with lack of carry-over following the specific international CLSI guidelines. The suggested protocol is robust, efficient, sensitive, specific, comprehensive and relatively cheap in order to accelerate the diagnostic process for both lysosomal storage diseases. The samples, with normal enzymatic activity, defined statistical relevant and clinical correct reference ranges for each specific age group by gender.

Conclusion

We report a multiplex LC-MS/MS method and relevant reference ranges that are appropriate for the targeted screening, diagnosis and follow-up of Fabry and Gaucher disease.

What Mothers Know about Newborn Bloodspot Screening and the Sources They Use to Acquire This Knowledge: A Pilot Study in Flanders

To learn what mothers know about newborn bloodspot screening (NBS), the procedure, and the sources used, a pilot study was performed. An online questionnaire was developed, with the first part focused on characteristics and the NBS procedure, and the second on knowledge, information sources, and health care providers (HCPs). This questionnaire was accessible until 200 answers were received. The characteristics of respondents were representative for the population. Mothers gave verbal consent in 69.5% of cases, 12.5% did not, and 18% stated that no consent was requested. The 'knowledge' part contained 12 closed questions, five multiple-choice questions on sources, and assessments (5-point Likert scores) of the information transfer. The mean knowledge level was 7.2/12. Screening concepts (consequences, likelihood, sensitivity, carrier) and absence of notification of normal findings were well known. The fact that NBS is not compulsory was poorly known, and post-analysis sample handling procedures were poorly understood. Key HCPs were midwifes (80.5%) and nurses (38.5%). When the leaflet (44%) was provided, the majority read it. Mean Likert scores were 3.36, 3.38, 3.11 and 3.35 for clarity, timing appropriateness, sufficiency, and usefulness. The knowledge level and consent practices were reasonably good. Key HCP were midwives and nurses, the leaflets were supporting. This should enable a quality improvement program to a sustainable NBS program in Flanders.

Metachromatic leukodystrophy: To screen or not to screen?

Metachromatic leukodystrophy (MLD) is a neurodegenerative lysosomal storage disorder caused by biallelic pathogenic variants in the gene encoding arylsulfatase A. Disease onset is variable (with late infantile, early and late juvenile, and adult forms) and treatment options depend on age and disease symptoms at onset. In the past, allo-hematopoietic stem cell transplantation (allo-HSCT) has been the best treatment option, following strict selection criteria. The outcome however is variable and morbidity remains high. This paved the way to the development of new treatment options, some of them aiming to be curative. In the light of this changing therapeutic field, newborn screening is becoming a valuable option. This narrative review aims to describe the outcome of allo-HSCT in the different MLD disease forms, and, in addition, reviews new treatment options. Finally, the shift of the field towards newborn screening for MLD is discussed.

Severe dilated cardiomyopathy as an unusual clinical presentation in an infant with sialidosis type II

We report a unique case of an infant with a severe dilated cardiomyopathy as the clinical presentation of sialidosis type II (OMIM 256550), a rare autosomal recessive inherited lysosomal storage disease that is characterized by partial or complete deficiency of α-neuraminidase, following mutations in the gene neuraminidase 1 (NEU1), located on the short arm of chromosome 6 (6p21.3). Accumulation of metabolic intermediates leads to severe morbidity, especially myoclonus, gait disturbances, cherry-red macules with secondary loss of visual acuity, impaired color vision and night blindness, and sometimes additional neurological findings such as seizures. Dilated cardiomyopathies are characterized by dilation and impaired contraction of the left or both ventricles, whereas most of the metabolic cardiomyopathies are hypertrophic forms appearing with diastolic dysfunction and, in case of lysosomal storage diseases, often associated with valvular thickening and prolapse. Cardiac manifestations in systemic storage disorders are common although rarely described in mucolipidoses. In mucolipidosis type 2 or I-cell disease only three cases were presented with severe dilated cardiomyopathy and endocardial fibroelastosis in infancy, as opposed to sialidosis type II, by which to the best of our knowledge no presentation of dilated cardiomyopathy was previously reported in literature.

Long-term efficacy and safety of sapropterin in patients who initiated sapropterin at < 4 years of age with phenylketonuria: results of the 3-year extension of the SPARK open-label, multicentre, randomised phase IIIb trial

BACKGROUND

During the initial 26-week SPARK (Safety Paediatric efficAcy phaRmacokinetic with Kuvan®) study, addition of sapropterin dihydrochloride (Kuvan®; a synthetic formulation of the natural cofactor for phenylalanine hydroxylase, tetrahydrobiopterin; BH4), to a phenylalanine (Phe)-restricted diet, led to a significant improvement in Phe tolerance versus a Phe-restricted diet alone in patients aged 0-4 years with BH4-responsive phenylketonuria (PKU) or mild hyperphenylalaninaemia (HPA). Based on these results, the approved indication for sapropterin in Europe was expanded to include patients < 4 years of age. Herein, we present results of the SPARK extension study (NCT01376908), evaluating the long-term safety, dietary Phe tolerance, blood Phe concentrations and neurodevelopmental outcomes in patients < 4 years of age at randomisation, over an additional 36 months of treatment with sapropterin.

RESULTS

All 51 patients who completed the 26-week SPARK study period entered the extension period. Patients who were previously treated with a Phe-restricted diet only ('sapropterin extension' group; n = 26), were initiated on sapropterin at 10 mg/kg/day, which could be increased up to 20 mg/kg/day. Patients previously treated with sapropterin plus Phe-restricted diet, remained on this regimen in the extension period ('sapropterin continuous' group; n = 25). Dietary Phe tolerance increased significantly at the end of the study versus baseline (week 0), by 38.7 mg/kg/day in the 'sapropterin continuous' group (95% CI 28.9, 48.6; p < 0.0001). In the 'sapropterin extension' group, a less pronounced effect was observed, with significant differences versus baseline (week 27) only observed between months 9 and 21; dietary Phe tolerance at the end of study increased by 5.5 mg/kg/day versus baseline (95% CI - 2.8, 13.8; p = 0.1929). Patients in both groups had normal neuromotor development and growth parameters.

CONCLUSIONS

Long-term treatment with sapropterin plus a Phe-restricted diet in patients who initiated sapropterin at < 4 years of age with BH4-responsive PKU or mild HPA maintained improvements in dietary Phe tolerance over 3.5 years. These results continue to support the favourable risk/benefit profile for sapropterin in paediatric patients (< 4 years of age) with BH4-responsive PKU. Frequent monitoring of blood Phe levels and careful titration of dietary Phe intake to ensure adequate levels of protein intake is necessary to optimise the benefits of sapropterin treatment. Trial registration ClinicalTrials.gov, NCT01376908. Registered 17 June 2011, https://clinicaltrials.gov/ct2/show/NCT01376908 .

Belgian rare diseases plan in clinical pathology: identification of key biochemical diagnostic tests and establishment of reference laboratories and financing conditions

Background

One objective of the Belgian Rare Diseases plan is to improve patients’ management using phenotypic tests and, more specifically, the access to those tests by identifying the biochemical analyses used for rare diseases, developing new financing conditions and establishing reference laboratories.

Methods

A feasibility study was performed from May 2015 until August 2016 in order to select the financeable biochemical analyses, and, among them, those that should be performed by reference laboratories. This selection was based on an inventory of analyses used for rare diseases and a survey addressed to the Belgian laboratories of clinical pathology (investigating the annual analytical costs, volumes, turnaround times and the tests unavailable in Belgium and outsourced abroad). A proposal of financeable analyses, financing modalities, reference laboratories’ scope and budget estimation was developed and submitted to the Belgian healthcare authorities. After its approval in December 2016, the implementation phase took place from January 2017 until December 2019.

Results

In 2019, new reimbursement conditions have been published for 46 analyses and eighteen reference laboratories have been recognized. Collaborations have also been developed with 5 foreign laboratories in order to organize the outsourcing and financing of 9 analyses unavailable in Belgium.

Conclusions

In the context of clinical pathology and rare diseases, this initiative enabled to identify unreimbursed analyses and to meet the most crucial financial needs. It also contributed to improve patients’ management by establishing Belgian reference laboratories and foreign referral laboratories for highly-specific analyses and a permanent surveillance, quality and financing framework for those tests.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01728-1.

The natural history of classic galactosemia: lessons from the GalNet registry

BACKGROUND

Classic galactosemia is a rare inborn error of carbohydrate metabolism, caused by a severe deficiency of the enzyme galactose-1-phosphate uridylyltransferase (GALT). A galactose-restricted diet has proven to be very effective to treat the neonatal life-threatening manifestations and has been the cornerstone of treatment for this severe disease. However, burdensome complications occur despite a lifelong diet. For rare diseases, a patient disease specific registry is fundamental to monitor the lifespan pathology and to evaluate the safety and efficacy of potential therapies. In 2014, the international Galactosemias Network (GalNet) developed a web-based patient registry for this disease, the GalNet Registry. The aim was to delineate the natural history of classic galactosemia based on a large dataset of patients.

METHODS

Observational data derived from 15 countries and 32 centers including 509 patients were acquired between December 2014 and July 2018.

RESULTS

Most affected patients experienced neonatal manifestations (79.8%) and despite following a diet developed brain impairments (85.0%), primary ovarian insufficiency (79.7%) and a diminished bone mineral density (26.5%). Newborn screening, age at onset of dietary treatment, strictness of the galactose-restricted diet, p.Gln188Arg mutation and GALT enzyme activity influenced the clinical picture. Detection by newborn screening and commencement of diet in the first week of life were associated with a more favorable outcome. A homozygous p.Gln188Arg mutation, GALT enzyme activity of ≤ 1% and strict galactose restriction were associated with a less favorable outcome.

CONCLUSION

This study describes the natural history of classic galactosemia based on the hitherto largest data set.

Galactosidase Alpha p.A143T Variant Fabry Disease May Result in a Phenotype With Multifocal Microvascular Cerebral Involvement at a Young Age

Introduction

A 16-year-old male presented with episodic headaches and a brain magnetic resonance imaging (MRI) that showed multifocal punctate to patchy white matter lesions. The diagnosis of Fabry disease (FD) was suggested upon the finding of significantly reduced plasma alpha-galactosidase A activity (0.62 µmol/L or 13% of normal; normal range ≥ 1.65 μmol/L) and genetic investigation confirmed the presence of a hemizygous missense variant in the galactosidase alpha (GLA) gene (p.A143T). Baseline assessment of other systemic involvement showed only a discrete proteinuria.

Background

FD is a rare lysosomal storage disorder. Genetic screening studies have revealed over 600 variants in the GLA gene. The p.A143T variant is a genetic variant of unknown significance, with its associated phenotype ranging from classical FD to healthy unaffected patients. Some authors, however, deem this variant non-pathogenic. We describe the case of a 16-year-old male with multifocal white matter lesions on brain MRI, who was diagnosed with FD and carried this genetic variant.

Discussion

The causative p.A143T mutation can be associated with a more severe subclinical phenotype than has been reported to date. Furthermore, a diagnosis of FD should be considered when finding asymptomatic cerebral white matter lesions in a young patient.

Dietary practices in propionic acidemia: A European survey

Background

The definitive dietary management of propionic acidaemia (PA) is unknown although natural protein restriction with adequate energy provision is of key importance.

Aim

To describe European dietary practices in the management of patients with PA prior to the publication of the European PA guidelines.

Methods

This was a cross-sectional survey consisting of 27 questions about the dietary practices in PA patients circulated to European IMD dietitians and health professionals in 2014.

Results

Information on protein restricted diets of 186 PA patients from 47 centres, representing 14 European countries was collected. Total protein intake [PA precursor-free L-amino acid supplements (PFAA) and natural protein] met WHO/FAO/UNU (2007) safe protein requirements for age in 36 centres (77%). PFAA were used to supplement natural protein intake in 81% (n = 38) of centres, providing a median of 44% (14–83%) of total protein requirement. Seventy-four per cent of patients were prescribed natural protein intakes below WHO/FAO/UNU (2007) safe levels in one or more of the following age groups: 0–6 m, 7–12 m, 1–10 y, 11–16 y and > 16 y. Sixty-three per cent (n = 117) of patients were tube fed (74% gastrostomy), but only 22% received nocturnal feeds.

Conclusions

There was high use of PFAA with intakes of natural protein commonly below WHO/FAO/UNU (2007) safe levels. Optimal dietary management can only be determined by longitudinal, multi-centre, prospective case controlled studies. The metabolic instability of PA and small patient cohorts in each centre ensure that this is a challenging undertaking.

Efficacy, safety and population pharmacokinetics of sapropterin in PKU patients <4 years: results from the SPARK open-label, multicentre, randomized phase IIIb trial

BACKGROUND

Sapropterin dihydrochloride, a synthetic formulation of BH4, the cofactor for phenylalanine hydroxylase (PAH, EC 1.14.16.1), was initially approved in Europe only for patients ≥4 years with BH4-responsive phenylketonuria. The aim of the SPARK (Safety Paediatric efficAcy phaRmacokinetic with Kuvan®) trial was to assess the efficacy (improvement in daily phenylalanine tolerance, neuromotor development and growth parameters), safety and pharmacokinetics of sapropterin dihydrochloride in children <4 years.

RESULTS

In total, 109 male or female children <4 years with confirmed BH4-responsive phenylketonuria or mild hyperphenylalaninemia and good adherence to dietary treatment were screened. 56 patients were randomly assigned (1:1) to 10 mg/kg/day oral sapropterin plus a phenylalanine-restricted diet or to only a phenylalanine-restricted diet for 26 weeks (27 to the sapropterin and diet group and 29 to the diet-only group; intention-to-treat population). Of these, 52 patients with ≥1 pharmacokinetic sample were included in the pharmacokinetic analysis, and 54 patients were included in the safety analysis. At week 26 in the sapropterin plus diet group, mean phenylalanine tolerance was 30.5 (95% confidence interval 18.7-42.3) mg/kg/day higher than in the diet-only group (p < 0.001). The safety profile of sapropterin, measured monthly, was acceptable and consistent with that seen in studies of older children. Using non-linear mixed effect modelling, a one-compartment model with flip-flop pharmacokinetic behaviour, in which the effect of weight was substantial, best described the pharmacokinetic profile. Patients in both groups had normal neuromotor development and stable growth parameters.

CONCLUSIONS

The addition of sapropterin to a phenylalanine-restricted diet was well tolerated and led to a significant improvement in phenylalanine tolerance in children <4 years with BH4-responsive phenylketonuria or mild hyperphenylalaninemia. The pharmacokinetic model favours once per day dosing with adjustment for weight. Based on the SPARK trial results, sapropterin has received EU approval to treat patients <4 years with BH4-responsive phenylketonuria.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01376908 . Registered June 17, 2011.

International clinical guideline for the management of classical galactosemia: diagnosis, treatment, and follow-up

Classical galactosemia (CG) is an inborn error of galactose metabolism. Evidence-based guidelines for the treatment and follow-up of CG are currently lacking, and treatment and follow-up have been demonstrated to vary worldwide. To provide patients around the world the same state-of-the-art in care, members of The Galactosemia Network (GalNet) developed an evidence-based and internationally applicable guideline for the diagnosis, treatment, and follow-up of CG. The guideline was developed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. A systematic review of the literature was performed, after key questions were formulated during an initial GalNet meeting. The first author and one of the working group experts conducted data-extraction. All experts were involved in data-extraction. Quality of the body of evidence was evaluated and recommendations were formulated. Whenever possible recommendations were evidence-based, if not they were based on expert opinion. Consensus was reached by multiple conference calls, consensus rounds via e-mail and a final consensus meeting. Recommendations addressing diagnosis, dietary treatment, biochemical monitoring, and follow-up of clinical complications were formulated. For all recommendations but one, full consensus was reached. A 93 % consensus was reached on the recommendation addressing age at start of bone density screening. During the development of this guideline, gaps of knowledge were identified in most fields of interest, foremost in the fields of treatment and follow-up.

Dietary practices in isovaleric acidemia: A European survey

Background

In Europe, dietary management of isovaleric acidemia (IVA) may vary widely. There is limited collective information about dietetic management.

Aim

To describe European practice regarding the dietary management of IVA, prior to the availability of the E-IMD IVA guidelines (E-IMD 2014).

Methods

A cross-sectional questionnaire was sent to all European dietitians who were either members of the Society for the Study of Inborn Errors of Metabolism Dietitians Group (SSIEM-DG) or whom had responded to previous questionnaires on dietetic practice (n = 53). The questionnaire comprised 27 questions about the dietary management of IVA.

Results

Information on 140 patients with IVA from 39 centres was reported. 133 patients (38 centres) were given a protein restricted diet. Leucine-free amino acid supplements (LFAA) were routinely used to supplement protein intake in 58% of centres. The median total protein intake prescribed achieved the WHO/FAO/UNU [2007] safe levels of protein intake in all age groups. Centres that prescribed LFAA had lower natural protein intakes in most age groups except 1 to 10 y. In contrast, when centres were not using LFAA, the median natural protein intake met WHO/FAO/UNU [2007] safe levels of protein intake in all age groups. Enteral tube feeding was rarely prescribed.

Conclusions

This survey demonstrates wide differences in dietary practice in the management of IVA across European centres. It provides unique dietary data collectively representing European practices in IVA which can be used as a foundation to compare dietary management changes as a consequence of the first E-IMD IVA guidelines availability.

Can psychiatric childhood disorders be due to inborn errors of metabolism?

Many patients who visit a centre for hereditary metabolic diseases remarkably also suffer from a child psychiatric disorder. Those child psychiatric disorders may be the first sign or manifestation of an underlying metabolic disorder. Lack of knowledge of metabolic disorders in child psychiatry may lead to diagnoses being missed. Patients therefore are also at risk for not accessing efficacious treatment and proper counselling. To search the literature for the co-occurrence of child psychiatric disorders, such as ADHD, autism, psychosis, learning disorders and eating disorders and metabolic disorders. A search of the literature was conducted by performing a broad search on PubMed, using the terms "ADHD and metabolic disorders", "autism and metabolic disorders", "psychosis and metabolic disorders", "learning disorders and metabolic disorders", and "eating disorders and metabolic disorders". Based on inclusion criteria (concerning a clear psychiatric disorder and concerning a metabolic disorder) 4441 titles and 249 abstracts were screened and resulted in 71 relevant articles. This thorough literature search provides child and adolescent psychiatrists with an overview of metabolic disorders associated with child psychiatric symptoms, their main characteristics and recommendations for further investigations.

Bone Health in Classic Galactosemia: Systematic Review and Meta-Analysis

INTRODUCTION

Previous studies have reported an association between classic galactosemia (CG) and decreased bone mass. The primary objective of this systematic review with meta-analysis was to determine the extent of bone mineral density (BMD) Z-score reduction. Low BMD was defined as a Z-score ≤-2 standard deviations (SD). The secondary objective was to evaluate other indicators of bone status through a descriptive analysis.

METHODS

Systematic search strategies were developed by an experienced clinical librarian. Selection of relevant manuscripts, risk of bias assessment, and data extraction were performed independently by two investigators.

RESULTS

Four studies were included in the meta-analysis. BMD Z-scores in children and adults with CG measured at the lumbar spine (LBMD; 4 studies; n  = 112), total hip (HBMD; 2 studies; n = 58), and femoral neck (FBMD; 2 studies; n = 73) were assessed. Mean BMD Z-scores in the CG population were LBMD -0.70 (95% CI: -0.88, -0.52); HBMD -0.89 (95% CI: -1.14, -0.64); and FBMD -0.63 (95% CI -1.29, 0.02). Results from studies included in the descriptive analysis (n = 7) show that vitamin D levels were frequently in the low reference range, whereas serum calcium levels were within reference range.

CONCLUSION

The mean BMD Z-score in the CG population is -0.7, which is lower than in the general population, though still within two SD of the reference mean of zero. This indicates that bone health is mildly affected in CG and that more patients, compared to the general population, are at risk for a BMD Z-score ≤-2 SD. In conclusion, clinicians should ensure appropriate preventive and therapeutic measures for CG patients.

Oral pharmacological chaperone migalastat compared with enzyme replacement therapy in Fabry disease: 18-month results from the randomised phase III ATTRACT study

Background

Fabry disease is an X-linked lysosomal storage disorder caused by GLA mutations, resulting in α-galactosidase (α-Gal) deficiency and accumulation of lysosomal substrates. Migalastat, an oral pharmacological chaperone being developed as an alternative to intravenous enzyme replacement therapy (ERT), stabilises specific mutant (amenable) forms of α-Gal to facilitate normal lysosomal trafficking.

Methods

The main objective of the 18-month, randomised, active-controlled ATTRACT study was to assess the effects of migalastat on renal function in patients with Fabry disease previously treated with ERT. Effects on heart, disease substrate, patient-reported outcomes (PROs) and safety were also assessed.

Results

Fifty-seven adults (56% female) receiving ERT (88% had multiorgan disease) were randomised (1.5:1), based on a preliminary cell-based assay of responsiveness to migalastat, to receive 18 months open-label migalastat or remain on ERT. Four patients had non-amenable mutant forms of α-Gal based on the validated cell-based assay conducted after treatment initiation and were excluded from primary efficacy analyses only. Migalastat and ERT had similar effects on renal function. Left ventricular mass index decreased significantly with migalastat treatment (−6.6 g/m² (−11.0 to −2.2)); there was no significant change with ERT. Predefined renal, cardiac or cerebrovascular events occurred in 29% and 44% of patients in the migalastat and ERT groups, respectively. Plasma globotriaosylsphingosine remained low and stable following the switch from ERT to migalastat. PROs were comparable between groups. Migalastat was generally safe and well tolerated.

Conclusions

Migalastat offers promise as a first-in-class oral monotherapy alternative treatment to intravenous ERT for patients with Fabry disease and amenable mutations.

Trial registration number:

NCT00925301; Pre-results.

Neurocognitive outcome in tyrosinemia type 1 patients compared to healthy controls

Background

Hereditary Tyrosinemia type 1 (HT1) is a rare metabolic disorder caused by a defect in the enzyme Fumarylacetoacetate Hydrolase. Due to this defect, toxic products accumulate which, in turn, cause liver and kidney dysfunction. Treatment with 2-(2-nitro-4-trifluoromethylbenoyl)-1,3-cyclohexanedione (NTBC) and diet has diminished these problems, but recent data indicate that HT1 patients have neurocognitive problems. However, the neuropsychological profile of these patients is unknown. Therefore, this study aimed to investigate this neuropsychological profile by comparing HT1 patients with healthy controls.

Methods

Neurocognitive testing was performed in a heterogeneous group of 19 NTBC and dietary treated HT1 patients (five female, fourteen male; mean age 12.9 ± 4.8 years; range 7.9–23.6 years) and 19 age and gender matched controls (five female, fourteen male; mean age 13.2 ± 4.6 years; range 8.1–24.8 years). IQ scores were estimated and all participants performed the Amsterdam Neuropsychological Tasks, measuring executive functions (inhibition, cognitive flexibility and working memory) and social cognition (face recognition and identification of facial emotions).

Results

HT1 patients showed poorer estimated IQ, executive functioning (working memory and cognitive flexibility), and social cognition compared to healthy controls. Lower IQ scores in HT1 patients were mostly unrelated to scores on executive function- and social cognition tasks and therefore did not account for group differences in these domains. Further analyses within the HT1 patient group (comparing different groups of patients based on the age at diagnosis and the clinical symptoms at diagnosis) did not reveal any significant results. The duration of NTBC treatment was negatively correlated with IQ.

Conclusions

Despite the heterogeneity of the patient group, these data clearly show that IQ, executive functioning and social cognition are affected in HT1 patients, and that IQ screening is not sufficient for cognitive monitoring of these patients. Further research should focus on the underlying pathophysiological mechanisms of these impairments to consequently try to improve treatment strategies.

Identifying Non-Duchenne Muscular Dystrophy-Positive and False Negative Results in Prior Duchenne Muscular Dystrophy Newborn Screening Programs: A Review

IMPORTANCE

Duchenne muscular dystrophy (DMD) is a candidate for the recommended universal screening panel based on evidence that early corticosteroid treatment improves outcomes and on new genetic therapies that require early diagnosis for effectiveness. Elevated creatine kinase levels in the neonatal period are the initial screening marker in DMD newborn screening programs but is found in inherited muscle disorders other than DMD. Data are needed to inform protocols for future screening and follow-up testing and care in these patients.

OBJECTIVES

To review non-DMD muscle disorders identified by prior DMD screening programs and to investigate whether these programs failed to identify patients later diagnosed as having DMD (false-negative findings).

EVIDENCE REVIEW

Since 1975, 10 DMD newborn screening programs have provided opportunities to study screening protocols, outcomes, and parental responses. These programs used elevated creatine kinase levels in dried blood spots for the initial screening, with the diagnosis of DMD based on findings of clinical follow-up, muscle biopsy, or direct mutational testing of the DMD gene. Literature regarding these prior programs was reviewed in PubMed, and the programs were discussed directly with the directors when possible to identify diagnoses of non-DMD disorders and false negative results from 1975 to July 12, 2015. Data were collected from screening programs, which were active between 1975 and December 2011. Data were analyzed from March 26, 2015, to August 24, 2015.

FINDINGS

The 10 screening programs screened more than 1.8 million newborns between 1975 and 2011, and 344 were diagnosed with DMD. Of those screened, the majority were boys. Across all programs, 80 patients had positive results for non-DMD disorders, including Becker muscular dystrophy and forms of limb-girdle and congenital muscular dystrophies, and 21 patients had false-negative findings for DMD.

CONCLUSIONS AND RELEVANCE

Screening for DMD will result in identification of other muscle diseases. Future screening protocols should include infants of both sexes and include follow-up testing algorithms to evaluate patients who do not have DMD gene mutations but may have another muscle disorder associated with elevated neonatal creatine kinase levels. These programs will need to be aware that false-negative results are a possibility.

Dietary management of urea cycle disorders: European practice

BACKGROUND

There is no published data comparing dietary management of urea cycle disorders (UCD) in different countries.

METHODS

Cross-sectional data from 41 European Inherited Metabolic Disorder (IMD) centres (17 UK, 6 France, 5 Germany, 4 Belgium, 4 Portugal, 2 Netherlands, 1 Denmark, 1 Italy, 1 Sweden) was collected by questionnaire describing management of patients with UCD on prescribed protein restricted diets.

RESULTS

Data for 464 patients: N-acetylglutamate synthase (NAGS) deficiency, n=10; carbamoyl phosphate synthetase (CPS1) deficiency, n=29; ornithine transcarbamoylase (OTC) deficiency, n=214; citrullinaemia, n=108; argininosuccinic aciduria (ASA), n=80; arginase deficiency, n=23 was reported. The majority of patients (70%; n=327) were aged 0-16y and 30% (n=137) >16y. Prescribed median protein intake/kg body weight decreased with age with little variation between disorders. The UK tended to give more total protein than other European countries particularly in infancy. Supplements of essential amino acids (EAA) were prescribed for 38% [n=174] of the patients overall, but were given more commonly in arginase deficiency (74%), CPS (48%) and citrullinaemia (46%). Patients in Germany (64%), Portugal (67%) and Sweden (100%) were the most frequent users of EAA. Only 18% [n=84] of patients were prescribed tube feeds, most commonly for CPS (41%); and 21% [n=97] were prescribed oral energy supplements.

CONCLUSIONS

Dietary treatment for UCD varies significantly between different conditions, and between and within European IMD centres. Further studies examining the outcome of treatment compared with the type of dietary therapy and nutritional support received are required.

Dietary practices in pyridoxine non-responsive homocystinuria: a European survey

BACKGROUND

Within Europe, the management of pyridoxine (B6) non-responsive homocystinuria (HCU) may vary but there is limited knowledge about treatment practice.

AIM

A comparison of dietetic management practices of patients with B6 non-responsive HCU in European centres.

METHODS

A cross-sectional audit by questionnaire was completed by 29 inherited metabolic disorder (IMD) centres: (14 UK, 5 Germany, 3 Netherlands, 2 Switzerland, 2 Portugal, 1 France, 1 Norway, 1 Belgium).

RESULTS

181 patients (73% >16 years of age) with HCU were identified. The majority (66%; n=119) were on dietary treatment (1-10 years, 90%; 11-16 years, 82%; and >16 years, 58%) with or without betaine and 34% (n=62) were on betaine alone. The median natural protein intake (g/day) on diet only was, by age: 1-10 years, 12 g; 11-16 years, 11 g; and >16 years, 45 g. With diet and betaine, median natural protein intake (g/day) by age was: 1-10 years, 13 g; 11-16 years, 20 g; and >16 years, 38 g. Fifty-two percent (n=15) of centres allocated natural protein by calculating methionine rather than a protein exchange system. A methionine-free l-amino acid supplement was prescribed for 86% of diet treated patients. Fifty-two percent of centres recommended cystine supplements for low plasma concentrations. Target treatment concentrations for homocystine/homocysteine (free/total) and frequency of biochemical monitoring varied.

CONCLUSION

In B6 non-responsive HCU the prescription of dietary restriction by IMD centres declined with age, potentially associated with poor adherence in older patients. Inconsistencies in biochemical monitoring and treatment indicate the need for international consensus guidelines.

Mutation of the iron-sulfur cluster assembly gene IBA57 causes severe myopathy and encephalopathy

Two siblings from consanguineous parents died perinatally with a condition characterized by generalized hypotonia, respiratory insufficiency, arthrogryposis, microcephaly, congenital brain malformations and hyperglycinemia. Catalytic activities of the mitochondrial respiratory complexes I and II were deficient in skeletal muscle, a finding suggestive of an inborn error in mitochondrial biogenesis. Homozygosity mapping identified IBA57 located in the largest homozygous region on chromosome 1 as a culprit candidate gene. IBA57 is known to be involved in the biosynthesis of mitochondrial [4Fe-4S] proteins. Sequence analysis of IBA57 revealed the homozygous mutation c.941A > C, p.Gln314Pro. Severely decreased amounts of IBA57 protein were observed in skeletal muscle and cultured skin fibroblasts from the affected subjects. HeLa cells depleted of IBA57 showed biochemical defects resembling the ones found in patient-derived cells, including a decrease in various mitochondrial [4Fe-4S] proteins and in proteins covalently linked to lipoic acid (LA), a cofactor produced by the [4Fe-4S] protein LA synthase. The defects could be complemented by wild-type IBA57 and partially by mutant IBA57. As a result of the mutation, IBA57 protein was excessively degraded, an effect ameliorated by protease inhibitors. Hence, we propose that the mutation leads to partial functional impairment of IBA57, yet the major pathogenic impact is due to its proteolytic degradation below physiologically critical levels. In conclusion, the ensuing lethal complex biochemical phenotype of a novel metabolic syndrome results from multiple Fe/S protein defects caused by a deficiency in the Fe/S cluster assembly protein IBA57.

Phenotypical characterization of α-galactosidase A gene mutations identified in a large Fabry disease screening program in stroke in the young

OBJECTIVE

In the Belgian Fabry Study (BeFaS), the prevalence of Fabry disease was assessed in 1000 young patients presenting with stroke, unexplained white matter lesions or vertebrobasilar dolichoectasia. The results of the BeFaS suggested that Fabry disease may play a role in up to 1% of young patients presenting with cerebrovascular disease. However, the clinical relevance was unclear in all cases. We report on detailed phenotyping in subjects identified with α-galactosidase A (α-Gal A) enzyme deficiency or GLA mutations identified in the BeFaS (n=10), and on the results of family screening in this population.

METHODS

Family screening was performed to identify additional mutation carriers. Biochemical and/or clinical evaluation of all subjects (BeFaS index patients and relatives carrying a GLA mutation) was performed.

RESULTS

Genetic family screening revealed 18 additional GLA mutation carriers. Bloodspot α-Gal A enzyme activity was normal in all GLA mutation carriers, even in 2 males with the p.A143T mutation. Plasma Gb3 and lyso-Gb3 levels were normal in all subjects. Elevated Gb3 in urine was detected in 2 subjects. Some classic clinical signs of Fabry disease, like angiokeratoma or cornea verticillata, could not be detected in our population. Cardiac symptoms of Fabry disease were found in 6 out of 10 p.A143T carriers. No signs of cerebrovascular disease were found in the relatives with a GLA mutation.

CONCLUSIONS

We could not identify mutations causing the classical clinical phenotype of Fabry disease in our cerebrovascular disease population. Enzyme activity analysis in bloodspots and plasma may fail to identify late-onset variants of Fabry disease. We recommend genetic testing when an atypical, late-onset variant of Fabry disease is suspected in a male cerebrovascular disease patient. However, this may lead to the identification of non-disease causing or controversial genetic variants.

Fabry disease: a review of current management strategies

Fabry disease is an X-linked inherited condition due to the absence or reduction of alpha-galactosidase activity in lysosomes, that results in accumulation of globotriaosylceramide (Gb3) and related neutral glycosphingolipids. Manifestations of Fabry disease include serious and progressive impairment of renal and cardiac function. In addition, patients experience pain, gastrointestinal disturbance, transient ischaemic attacks and strokes. Additional effects on the skin, eyes, ears, lungs and bones are often seen. The first symptoms of classic Fabry disease usually appear in childhood. Despite being X-linked, females can suffer the same severity of symptoms as males, and life expectancy is reduced in both females and males. Enzyme replacement therapy (ERT) can stabilize the progression of the disease. The rarity of the classic form of Fabry disease, however, means that there is a need to improve the knowledge and understanding that the majority of physicians have concerning Fabry disease, in order to avoid misdiagnosis and/or delayed diagnosis. This review aims to raise awareness of the signs and symptoms of Fabry disease; to provide a general diagnostic algorithm and to give an overview of the effects of ERT and concomitant treatments. We highlight a need to develop comprehensive international guidelines to optimize ERT and adjunctive therapy in patients with Fabry disease, including females and children.

Belgian Fabry study: prevalence of Fabry disease in a cohort of 1000 young patients with cerebrovascular disease

BACKGROUND AND PURPOSE

Data on the prevalence of Fabry disease in patients with central nervous system pathology are limited and controversial. In this study, we assessed the prevalence of Fabry disease in young patients presenting with cerebrovascular disease in Belgium.

METHODS

In this national, prospective, multicenter study, we screened for Fabry disease in 1000 patients presenting with ischemic stroke, transient ischemic attack, or intracranial hemorrhage; unexplained white matter lesions; or vertebrobasilar dolichoectasia. In male patients, we measured alpha-galactosidase A (alpha-GAL A) activity in dried blood spots. Female patients were screened for mutations by exonic DNA sequencing of the alpha-GAL A gene.

RESULTS

alpha-GAL A activity was deficient in 19 men (3.5%), although all had normal alpha-GAL A gene sequences. Enzymatic deficiency was confirmed on repeat assessment in 2 male patients (0.4%). We identified missense mutations in 8 unrelated female patients (1.8%): Asp313Tyr (n=5), Ala143Thr (n=2), and Ser126Gly (n=1). The pathogenicity of the 2 former missense mutations is controversial. Ser126Gly is a novel mutation that can be linked to late-onset Fabry disease.

CONCLUSIONS

alpha-GAL A deficiency may play a role in up to 1% of young patients presenting with cerebrovascular disease. These findings suggest that atypical variants of Fabry disease with late-onset cerebrovascular disease exist, although the clinical relevance is unclear in all cases.

Fabry disease in a patient with Turner syndrome

We report a unique case with co-occurrence of Turner syndrome and Fabry disease (OMIM #301500). The latter is a rare X-linked lysosomal storage disease that is characterized by partial or complete deficiency of alpha-galactosidase A (GLA; EC 3.2.1.22) following mutations in the gene (GLA) localized at Xq22.1. Accumulation of metabolic intermediates can occur in many tissues and leads to severe morbidity, especially due to renal failure, cardiac involvement and stroke. It is well established that hemizygous male mutation carriers with Fabry disease are generally more severely affected than heterozygous female mutation carriers, but disabling clinical features and disease progression often occur in female Fabry patients as well. The majority of this patient's cells are of the 45,X type, making her a hemizygous GLA mutation carrier displaying a very severe Fabry disease phenotype.

Mitochondrial mosaics in the liver of 3 infants with mtDNA defects

Background

In muscle cytochrome oxidase (COX) negative fibers (mitochondrial mosaics) have often been visualized.

Methods

COX activity staining of liver for light and electron microscopy, muscle stains, blue native gel electrophoresis and activity assays of respiratory chain proteins, their immunolocalisation, mitochondrial and nuclear DNA analysis.

Results

Three unrelated infants showed a mitochondrial mosaic in the liver after staining for COX activity, i.e. hepatocytes with strongly reactive mitochondria were found adjacent to cells with many negative, or barely reactive, mitochondria. Deficiency was most severe in the patient diagnosed with Pearson syndrome. Ragged-red fibers were absent in muscle biopsies of all patients. Enzyme biochemistry was not diagnostic in muscle, fibroblasts and lymphocytes. Blue native gel electrophoresis of liver tissue, but not of muscle, demonstrated a decreased activity of complex IV; in both muscle and liver subcomplexes of complex V were seen. Immunocytochemistry of complex IV confirmed the mosaic pattern in two livers, but not in fibroblasts. MRI of the brain revealed severe white matter cavitation in the Pearson case, but only slight cortical atrophy in the Alpers-Huttenlocher patient, and a normal image in the 3rd. MtDNA in leucocytes showed a common deletion in 50% of the mtDNA molecules of the Pearson patient. In the patient diagnosed with Alpers-Huttenlocher syndrome, mtDNA was depleted for 60% in muscle. In the 3rd patient muscular and hepatic mtDNA was depleted for more than 70%. Mutations in the nuclear encoded gene of POLG were subsequently found in both the 2nd and 3rd patients.

Conclusion

Histoenzymatic COX staining of a liver biopsy is fast and yields crucial data about the pathogenesis; it indicates whether mtDNA should be assayed. Each time a mitochondrial disorder is suspected and muscle data are non-diagnostic, a liver biopsy should be recommended. Mosaics are probably more frequent than observed until now. A novel pathogenic mutation in POLG is reported.

Tentative explanations for the mitochondrial mosaics are, in one patient, unequal partition of mutated mitochondria during mitoses, and in two others, an interaction between products of several genes required for mtDNA maintenance.

Middelheim Fabry Study (MiFaS): a retrospective Belgian study on the prevalence of Fabry disease in young patients with cryptogenic stroke

OBJECTIVE

To assess the prevalence of Fabry disease in young patients with cryptogenic stroke.

PATIENTS AND METHODS

We retrospectively assessed the prevalence of Fabry disease in patients aged 16-60 years that were admitted to ZNA Middelheim Hospital from January 1, 2000 to December 31, 2004 for cryptogenic stroke. We screened for Fabry disease by measurement of alpha-galactosidase A and beta-glucuronidase activity on blood spot. In all patients with abnormal enzymatic activity and in all female patients with low normal values, genetic sequencing of the alpha-GAL-gene was performed.

RESULTS

In a population of 103 young patients with cryptogenic stroke that met the in- and exclusion criteria, we were unable to identify any patient with Fabry disease.

CONCLUSION

Based on the results of alpha-galactosidase A and beta-glucuronidase activity, genetic sequencing and the low prevalence of clinical signs and symptoms of Fabry disease in this population, we believe that the true prevalence of Fabry disease in patients with cryptogenic stroke may be less than currently accepted in literature.

Cognitive functioning and psychiatric disorders in children with a metabolic disease

OBJECTIVE

To report on the intelligence scores and the psychiatric pathology of distinct groups of children with metabolic diseases.

METHODS

The study population consists of 53 children between 0 and 18 years of age. Diagnostic assessment included a semi-structured interview, self-report questionnaires and a standard intelligence test.

RESULTS

In 40% of the children older than 5 years, a child psychiatric diagnosis was made. While CBCL total and internalizing scores did not differ between metabolic disease groups, the CBCL externalizing scores for some groups did. Two fifths of the children showed a below normal intelligence, while a performal-verbal IQ discrepancy was found in half of the children. Of the school aged children almost one third attended a special needs school.

CONCLUSION

In spite of the small sample size, the results suggest substantial psychiatric problems in children with a metabolic disease. Further study on larger groups is warranted, which should enable further comparison of patients affected by specific metabolic diseases.

Multiplex ligation-dependent probe amplification to detect subtelomeric rearrangements in routine diagnostics

Subtelomeric rearrangements are believed to be responsible for 5-7% of idiopathic mental retardation cases. Due to the relative complexity and high cost of the screening methods used till now, only preselected patient populations including mostly the more severely affected cases have been screened. Recently, multiplex ligation-dependent probe amplification (MLPA) has been adapted for use in subtelomeric screening, and we have incorporated this technique into routine diagnostics of our laboratory. Since the evaluation of MLPA as a screening method, we tested 275 unselected patients with idiopathic mental retardation and detected 12 possible subtelomeric aberrations: a der(11)t(11;20)(qter;qter), a 19pter duplication, a der(18)t(18;10)(qter; pter), a 15qter deletion, a 8pter deletion, a 6qter deletion, a der(X)t(X;1)(pter;qter), a der(X)t(X;3)(pter;pter), a 5qter duplication, a 3pter deletion, and two 3qter duplications. The patients can be subdivided into two groups: the first containing de novo rearrangements that are likely related to the clinical presentation of the patient and the second including aberrations also present in one of the parents that may or may not be causative of the mental retardation. In our patient cohort, five (1.8%) subtelomeric rearrangements were de novo, three (1.1%) rearrangements were familial and suggestively disease causing, and four (1.5%) were possible polymorphisms. This high frequency of subtelomeric abnormalities detected in an unselected population warrants further investigation about the feasibility of routine screening for subtelomeric aberrations in mentally retarded patients.

Novel mutations in the PEX2 gene of four unrelated patients with a peroxisome biogenesis disorder

The peroxisome biogenesis disorders (PBDs) form a genetically and clinically heterogeneous group of disorders due to defects in at least 11 distinct genes. The prototype of this group of disorders is Zellweger syndrome (ZS) with neonatal adrenoleukodystrophy (NALD) and infantile Refsum disease (IRD) as milder variants. Common to PBDs are liver disease, variable neurodevelopmental delay, retinopathy and perceptive deafness. PBD patients belonging to complementation group 10 (CG10) have mutations in the PEX2 gene (PXMP3), which codes for a protein (PEX2) that contains two transmembrane domains and a zinc-binding domain considered to be important for its interaction with other proteins of the peroxisomal protein import machinery. We report on the identification of four PBD patients belonging to CG10. Sequence analysis of their PEX2 genes revealed 4 different mutations, 3 of which have not been reported before. Two of the patients had homozygous mutations leading to truncated proteins lacking both transmembrane domains and the zinc-binding domain. These mutations correlated well with their severe phenotypes. The third patient had a homozygous mutation leading to the absence of the zinc-binding domain (W223X) and the fourth patient had a homozygous mutation leading to the change of the second cysteine residue of the zinc-binding domain (C247R). Surprisingly, the patient lacking the domain had a mild phenotype, whereas the C247R patient had a severe phenotype. This might be due to an increased instability of PEX2 due to the R for C substitution or to a dominant negative effect on interacting proteins.

Respiratory chain complex V deficiency due to a mutation in the assembly gene ATP12

In patients with mitochondrial encephalomyopathies an increasing number of causative gene defects have been detected. The number of identified pathogenic mitochondrial DNA mutations has largely increased over the past 15 years. Recently, much attention has turned to the investigation of nuclear oxidative phosphorylation (OXPHOS) gene defects. Within the OXPHOS defects, complex V deficiency is rarely found and, so far, these defects have only been attributed to mutations in the mitochondrial MTATP6 gene. Mutation analysis of the complete coding regions at the cDNA level of the nuclear ATP11, ATP12, ATPalpha, ATPbeta and ATPgamma genes and the mitochondrial MTATP6 and MTAT8 genes was undertaken in two unrelated patients. Blue Native polyacrylamide gel electrophoresis followed by catalytic staining had already documented their complex V decreased activity. Extensive molecular analysis of five nuclear and two mitochondrial genes revealed a mutation in the ATP12 assembly gene in one patient. This mutation is believed to be the cause of the impaired complex V activity. To our knowledge, this is the first report of a pathogenic mutation in a human nuclear encoded ATPase assembly gene.

A nonsense mutation in the 3-hydroxy-3-methylglutaryl-CoA lyase gene produces exon skipping in two patients of different origin with 3-hydroxy-3-methylglutaryl-CoA lyase deficiency

A novel nonsense mutation associated with the skipping of constitutive exon 2 of the 3-hydroxy-3-methylglutaryl-CoA lyase gene was found in two patients, from Portugal and Morocco, with 3-hydroxy-3-methylglutaric acidemia. By reverse transcriptase PCR and single-strand conformational polymorphism a G-T transversion was located, at nucleotide 109, of the 3-hydroxy-3-methylglutaryl-CoA lyase cDNA, within exon 2. Two mRNAs were produced as a result of this nonsense mutation: one of the expected size that contains the premature stop codon UAA, and the other with a deletion of 84 bp corresponding to the whole of exon 2. This deletion produced the loss of the last seven amino acids of the leader peptide and the first 21 amino acids of the mature protein. The nonsense mutation was found in a purine-rich GGAAG sequence, which is equal to, or similar to, others reported to be exonic splicing enhancers (ESE). We suggest that the nonsense mutation may affect a possible ESE on exon 2, which would hinder the splice site selection and facilitate an aberrant splice with the skipping of this exon. Determination by quantitative PCR shows that the ratio of mRNA with the nonsense mutation to the mRNA with the deletion is approx. 3:1.

Carbohydrate-deficient glycoprotein syndrome with previously unreported features

A boy with carbohydrate-deficient glycoprotein syndrome died at five months of age in status epilepticus. Postmortem examination failed to show the classically observed olivopontocerebellar atrophy. Two previously unreported features were present: cataracts from the first week of life and lysosomal storage affecting mainly the anterior horn neurons of the spinal cord.