Expanding the phenotype in argininosuccinic aciduria: need for new therapies.

OBJECTIVES: This UK-wide study defines the natural history of argininosuccinic aciduria and compares long-term neurological outcomes in patients presenting clinically or treated prospectively from birth with ammonia-lowering drugs. METHODS: Retrospective analysis of medical records prior to March 2013, then prospective analysis until December 2015. Blinded review of brain MRIs. ASL genotyping. RESULTS: Fifty-six patients were defined as early-onset (n = 23) if symptomatic < 28 days of age, late-onset (n = 23) if symptomatic later, or selectively screened perinatally due to a familial proband (n = 10). The median follow-up was 12.4 years (range 0-53). Long-term outcomes in all groups showed a similar neurological phenotype including developmental delay (48/52), epilepsy (24/52), ataxia (9/52), myopathy-like symptoms (6/52) and abnormal neuroimaging (12/21). Neuroimaging findings included parenchymal infarcts (4/21), focal white matter hyperintensity (4/21), cortical or cerebral atrophy (4/21), nodular heterotopia (2/21) and reduced creatine levels in white matter (4/4). 4/21 adult patients went to mainstream school without the need of additional educational support and 1/21 lives independently. Early-onset patients had more severe involvement of visceral organs including liver, kidney and gut. All early-onset and half of late-onset patients presented with hyperammonaemia. Screened patients had normal ammonia at birth and received treatment preventing severe hyperammonaemia. ASL was sequenced (n = 19) and 20 mutations were found. Plasma argininosuccinate was higher in early-onset compared to late-onset patients. CONCLUSIONS: Our study further defines the natural history of argininosuccinic aciduria and genotype-phenotype correlations. The neurological phenotype does not correlate with the severity of hyperammonaemia and plasma argininosuccinic acid levels. The disturbance in nitric oxide synthesis may be a contributor to the neurological disease. Clinical trials providing nitric oxide to the brain merit consideration.

Advantages and pitfalls of an extended gene panel for investigating complex neurometabolic phenotypes.

Neurometabolic disorders are markedly heterogeneous, both clinically and genetically, and are characterized by variable neurological dysfunction accompanied by suggestive neuroimaging or biochemical abnormalities. Despite early specialist input, delays in diagnosis and appropriate treatment initiation are common. Next-generation sequencing approaches still have limitations but are already enabling earlier and more efficient diagnoses in these patients. We designed a gene panel targeting 614 genes causing inborn errors of metabolism and tested its diagnostic efficacy in a paediatric cohort of 30 undiagnosed patients presenting with variable neurometabolic phenotypes. Genetic defects that could, at least partially, explain observed phenotypes were identified in 53% of cases. Where biochemical abnormalities pointing towards a particular gene defect were present, our panel identified diagnoses in 89% of patients. Phenotypes attributable to defects in more than one gene were seen in 13% of cases. The ability of in silico tools, including structure-guided prediction programmes to characterize novel missense variants were also interrogated. Our study expands the genetic, clinical and biochemical phenotypes of well-characterized (POMGNT1, TPP1) and recently identified disorders (PGAP2, ACSF3, SERAC1, AFG3L2, DPYS). Overall, our panel was accurate and efficient, demonstrating good potential for applying similar approaches to clinically and biochemically diverse neurometabolic disease cohorts.

Proteomic Discovery and Development of a Multiplexed Targeted MRM-LC-MS/MS Assay for Urine Biomarkers of Extracellular Matrix Disruption in Mucopolysaccharidoses I, II, and VI.

The mucopolysaccharidoses (MPS) are lysosomal storage disorders that result from defects in the catabolism of glycosaminoglycans. Impaired muscle, bone, and connective tissue are typical clinical features of MPS due to disruption of the extracellular matrix. Markers of MPS disease pathology are needed to determine disease severity and monitor effects of existing and emerging new treatments on disease mechanisms. Urine samples from a small cohort of MPS-I, -II, and -VI patients (n = 12) were analyzed using label-free quantative proteomics. Fifty-three proteins including many associated with extracellular matrix organization were differently expressed. A targeted multiplexed peptide MRM LC-MS/MS assay was used on a larger validation cohort of patient samples (MPS-I n = 18, MPS-II n = 12, MPS-VI n = 6, control n = 20). MPS-I and -II groups were further subdivided according to disease severity. None of the markers assessed were altered significantly in the mild disease groups compared to controls. ß-galactosidase, a lysosomal protein, was elevated 3.6-5.7-fold significantly (p < 0.05) in all disease groups apart from mild MPS-I and -II. Collagen type Iα, fatty-acid-binding-protein 5, nidogen-1, cartilage oligomeric matrix protein, and insulin-like growth factor binding protein 7 concentrations were elevated in severe MPS I and II groups. Cartilage oligomeric matrix protein, insulin-like growth factor binding protein 7, and ß-galactosidase were able to distinguish the severe neurological form of MPS-II from the milder non-neurological form. Protein Heg1 was significantly raised only in MPS-VI. This work describes the discovery of new biomarkers of MPS that represent disease pathology and allows the stratification of MPS-II patients according to disease severity.

Paediatric single mitochondrial DNA deletion disorders: an overlapping spectrum of disease.

BACKGROUND: Single large-scale mitochondrial DNA (mtDNA) deletions (SLSMDs) are amongst the most frequently diagnosed mtDNA disorders in childhood, yet their natural history remains poorly understood. We report the natural history of a large multicentre cohort of such children. METHODS: We reviewed case notes from three different UK centres to determine the clinical course of 34 patients (16 female, 18 male) with childhood-onset mitochondrial disease caused by SLSMDs. Kaplan-Meier analysis was used to compare survival of patients presenting with haematological features (Pearson syndrome) and those with nonhaematological presentations. RESULTS: The most frequent initial presentation was with isolated ptosis (16/34, 47%). Eleven (32%) patients presented with transfusion-dependent anaemia soon after birth and were diagnosed with Pearson syndrome, whilst ten were classified as having Kearns-Sayre syndrome, three as having progressive external ophthalmoplegia (PEO) and seven as having PEO-plus. Three patients did not conform to any specific mitochondrial syndrome. The most frequently affected organ during the disease course was the kidney, with documented tubular or glomerular dysfunction in 17 of 20 (85%) cases who had detailed investigations. SLSMDs were present in blood and/or urine cells in all cases tested, indicating that muscle biopsy is not necessary for diagnosis in the paediatric age range. Kaplan-Meier survival analysis revealed significantly worse mortality in patients with Pearson syndrome compared with the rest of the cohort. CONCLUSIONS: Mitochondrial disease caused by SLSMDs is clinically heterogeneous, and not all cases conform to a classical mitochondrial syndrome. Multisystem disease is the norm, with anaemia, renal impairment and endocrine disturbance being the most frequent extraneurological features. SLSMDs should be considered in the differential diagnosis of all children presenting with ptosis.

Treatment of mucopolysaccharidosis type II (Hunter syndrome) with idursulfase: the relevance of clinical trial end points.

The current treatment of mucopolysaccharidosis type II (MPS II, Hunter syndrome) is enzyme replacement therapy with recombinant idursulfase (Elaprase®). The efficacy of ERT was established based primarily on reduction in urine glycosaminoglycans:creatinine (GAG:Cr) ratio and improvement in a composite score of predicted forced vital capacity (FVC% predicted) and 6-min walk-test distance (6MWT). We retrospectively reviewed these parameters in 11 boys with MPS II treated with idursulfase between April 2007 (or the time of diagnosis) and February 2010. Some results were inconsistent with published trial data, and there was only a small number of analyzable results obtained for the FVC% predicted and 6MWT. A major drawback was the high prevalence of neurological involvement and young age of patients in the study cohort compared with the clinical trials. This study emphasizes the limitations of the current tools utilized to monitor ERT efficacy and MPS II disease burden in clinical practice.

HIBCH mutations can cause Leigh-like disease with combined deficiency of multiple mitochondrial respiratory chain enzymes and pyruvate dehydrogenase.

BACKGROUND: Deficiency of 3-hydroxy-isobutyryl-CoA hydrolase (HIBCH) caused by HIBCH mutations is a rare cerebral organic aciduria caused by disturbance of valine catabolism. Multiple mitochondrial respiratory chain (RC) enzyme deficiencies can arise from a number of mechanisms, including defective maintenance or expression of mitochondrial DNA. Impaired biosynthesis of iron-sulphur clusters and lipoic acid can lead to pyruvate dehydrogenase complex (PDHc) deficiency in addition to multiple RC deficiencies, known as the multiple mitochondrial dysfunctions syndrome. METHODS: Two brothers born to distantly related Pakistani parents presenting in early infancy with a progressive neurodegenerative disorder, associated with basal ganglia changes on brain magnetic resonance imaging, were investigated for suspected Leigh-like mitochondrial disease. The index case had deficiencies of multiple RC enzymes and PDHc in skeletal muscle and fibroblasts respectively, but these were normal in his younger brother. The observation of persistently elevated hydroxy-C4-carnitine levels in the younger brother led to suspicion of HIBCH deficiency, which was investigated by biochemical assay in cultured skin fibroblasts and molecular genetic analysis. RESULTS: Specific spectrophotometric enzyme assay revealed HIBCH activity to be below detectable limits in cultured skin fibroblasts from both brothers. Direct Sanger sequence analysis demonstrated a novel homozygous pathogenic missense mutation c.950G

Tuberculous radiculomyelitis presenting as urinary retention in a child with Down's syndrome.

Tuberculous radiculomyelitis (TBRM) is an uncommon complication of TB meningitis. The authors report the case of a 10-year-old Asian girl with trisomy 21, who presented with acute urinary retention and fever. She was initially treated for a urinary tract infection. After an acute neurological deterioration she was found to have evidence of TB meningitis with TBRM. She developed acute hydrocephalus requiring ventriculo-peritoneal shunt. She was treated with quadruple antituberculous therapy and high dose intravenous dexamethasone. She needed tracheostomy with continuous positive airway pressure (CPAP) support. Although she showed gradual neurological improvement in her cognitive functions, she persisted to have quadriparesis with the need for tracheostomy and CPAP support overnight and gastrostomy feeding. Acute urinary retention in children is uncommon, and should serve as a 'red flag' to consideration of further underlying neurological problems. This presentation and subsequent events should serve as a learning point to clinicians.

Group A streptococcal meningitis: case report and review of the literature.

Group A streptococcus is an uncommon cause of meningitis in children. We report a single case of Group A streptococcus meningitis, in an apparently healthy 6-week-old infant. Twenty-five cases in the English-language literature in the last 25 years and our case are reviewed. The commonest associated illness was otitis media. Of the 25 patients, 24 survived. Antibiotic therapy, which consisted of penicillin in the majority of patients, was effective. Ceftriaxone was an alternative agent. Neurological sequelae were not uncommon. This report emphasizes the fact that Group A streptococcus can cause meningitis in healthy children without apparent recognizable foci of infection.