Kristina Cusmano-Ozog

22q13.3 deletion syndrome: a recognizable malformation syndrome associated with marked speech and language delay.

The 22q13.3 deletion syndrome is a recognizable malformation syndrome associated with developmental delay, hypotonia, delayed or absent speech, autistic‐like behavior, normal to accelerated growth and dysmorphic facies. The prevalence of this disorder is unknown, but it is likely under‐diagnosed. Age at diagnosis has varied widely, from cases diagnosed prenatally to 46 years. Males and females are equally affected. The distal 22q deletion can be detected occasionally by routine or high resolution chromosome analysis; however, the majority of cases are detected by FISH analysis, associated with deletion of the ARSA (control) probe when performing a FISH analysis for the velocardiofacial syndrome (del 22q11.2). The 22q13.3 deletion syndrome can accompany a simple chromosome deletion, an unbalanced translocation, or a ring chromosome. Primary care physicians, in addition to numerous specialists, play an important role in caring for patients with this disorder. Although the dysmorphic features observed in this condition are nonspecific, it is an important consideration in the differential diagnosis of children with developmental delay, hypotonia, marked speech and language disability, autistic‐like features, multiple minor anomalies, and normal growth and head circumference.

The role of vanin-1 and oxidative stress-related pathways in distinguishing acute and chronic pediatric ITP.

Pediatric immune thrombocytopenia (ITP) is usually self-limited. However, approximately 20% of children develop chronic ITP, which can be associated with significant morbidity because of long-term immunosuppression and splenectomy in refractory cases. To explore the molecular mechanism of chronic ITP compared with acute ITP, we studied 63 pediatric patients with ITP. Gene expression analysis of whole blood revealed distinct signatures for acute and chronic ITP. Oxidative stress-related pathways were among the most significant chronic ITP-associated pathways. Overexpression of VNN1, an oxidative stress sensor in epithelial cells, was most strongly associated with progression to chronic ITP. Studies of normal persons demonstrated VNN1 expression in a variety of blood cells. Exposure of blood mononuclear cells to oxidative stress inducers elicited dramatic up-regulation of VNN1 and down-regulation of PPARγ, indicating a role for VNN1 as a peripheral blood oxidative stress sensor. Assessment of redox state by tandem mass spectrometry demonstrated statistically significant lower glutathione ratios in patients with ITP versus healthy controls; lower glutathione ratios were also seen in untreated patients with ITP compared with recently treated patients. Our work demonstrates distinct patterns of gene expression in acute and chronic ITP and implicates oxidative stress pathways in the pathogenesis of chronic pediatric ITP.

A rapid, sensitive method for quantitative analysis of underivatized amino acids by liquid chromatography-tandem mass spectrometry (LC-MS/MS).

The quantitation of free amino acids from physiologic samples is essential for diagnosing and monitoring patients with inherited metabolic disorders. Current methods are hindered by long preparative and/or analysis times, expensive reagents, and often suboptimal performance characteristics. To overcome these challenges, a improved method for amino acid analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) has been developed and validated. Samples were deproteinized with sulfosalicylic acid and supernatants diluted with tridecafluoroheptanoic acid. Chromatographic separation of amino acids occurred using two columns, with conditions favoring resolution of isobaric compounds and minimizing ion suppression. Eluted compounds were detected by selective reaction monitoring, and quantitated by relating peak areas of amino acids to externally run standards. Validation studies evaluated linearity, within- and between-run imprecision, lower limits of detection and quantification for 33 amino acids, and correlation with the Biochrom 30 Amino Acid Analyzer. Total run time including re-equilibration was 15min per sample. Within-run precision averaged 2.8% for all compounds, with an average linear correlation coefficient of 0.995. The majority of compounds were reliably quantitated at ≤0.1μM. Between-run precision averaged 4.0%. Results showed excellent correlation with the Biochrom 30 amino acid analyzer with an average overall correlation of 0.908. We conclude that our method is extremely sensitive, specific and reproducible and represents an improvement over other currently available technologies.

Targeting proximal tubule mitochondrial dysfunction attenuates the renal disease of methylmalonic acidemia

Isolated methylmalonic acidemia (MMA), caused by deficiency of the mitochondrial enzyme methylmalonyl-CoA mutase (MUT), is often complicated by end stage renal disease that is resistant to conventional therapies, including liver transplantation. To establish a viable model of MMA renal disease, Mut was expressed in the liver of Mut−/− mice as a stable transgene under the control of an albumin (INS-Alb-Mut) promoter. Mut−/−;TgINS-Alb-Mut mice, although completely rescued from neonatal lethality that was displayed by Mut−/− mice, manifested a decreased glomerular filtration rate (GFR), chronic tubulointerstitial nephritis and ultrastructural changes in the proximal tubule mitochondria associated with aberrant tubular function, as demonstrated by single-nephron GFR studies. Microarray analysis of Mut−/−;TgINS-Alb-Mut kidneys identified numerous biomarkers, including lipocalin-2, which was then used to monitor the response of the GFR to antioxidant therapy in the mouse model. Renal biopsies and biomarker analysis from a large and diverse patient cohort (ClinicalTrials.gov identifier: NCT00078078) precisely replicated the findings in the animals, establishing Mut−/−;TgINS-Alb-Mut mice as a unique model of MMA renal disease. Our studies suggest proximal tubular mitochondrial dysfunction is a key pathogenic mechanism of MMA-associated kidney disease, identify lipocalin-2 as a biomarker of increased oxidative stress in the renal tubule, and demonstrate that antioxidants can attenuate the renal disease of MMA.

Degree of Glutathione Deficiency and Redox Imbalance Depend on Subtype of Mitochondrial Disease and Clinical Status

Mitochondrial disorders are associated with decreased energy production and redox imbalance. Glutathione plays a central role in redox signaling and protecting cells from oxidative damage. In order to understand the consequences of mitochondrial dysfunction on in vivo redox status, and to determine how this varies by mitochondrial disease subtype and clinical severity, we used a sensitive tandem mass spectrometry assay to precisely quantify whole blood reduced (GSH) and oxidized (GSSG) glutathione levels in a large cohort of mitochondrial disorder patients. Glutathione redox potential was calculated using the Nernst equation. Compared to healthy controls (n = 59), mitochondrial disease patients (n = 58) as a group showed significant redox imbalance (redox potential −251 mV±9.7, p<0.0001) with an increased level of oxidation by ∼9 mV compared to controls (−260 mV±6.4). Underlying this abnormality were significantly lower whole blood GSH levels (p = 0.0008) and GSH/GSSG ratio (p = 0.0002), and significantly higher GSSG levels (p<0.0001) in mitochondrial disease patients compared to controls. Redox potential was significantly more oxidized in all mitochondrial disease subgroups including Leigh syndrome (n = 15), electron transport chain abnormalities (n = 10), mitochondrial encephalomyopathy, lactic acidosis and stroke-like episodes (n = 8), mtDNA deletion syndrome (n = 7), mtDNA depletion syndrome (n = 7), and miscellaneous other mitochondrial disorders (n = 11). Patients hospitalized in metabolic crisis (n = 7) showed the greatest degree of redox imbalance at −242 mV±7. Peripheral whole blood GSH and GSSG levels are promising biomarkers of mitochondrial dysfunction, and may give insights into the contribution of oxidative stress to the pathophysiology of the various mitochondrial disorders. In particular, evaluation of redox potential may be useful in monitoring of clinical status or response to redox-modulating therapies in clinical trials.

Expansion of the TARP syndrome phenotype associated with de novo mutations and mosaicism

The TARP syndrome (Talipes equinovarus, Atrial septal defect, Robin sequence, and Persistent left superior vena cava) is an X‐linked disorder that was determined to be caused by mutations in RBM10 in two families, and confirmed in a subsequent case report. The first two original families were quite similar in phenotype, with uniform early lethality although a confirmatory case report showed survival into childhood. Here we report on five affecteds from three newly recognized families, including patients with atypical manifestations. None of the five patients had talipes and others also lacked cardinal TARP features of Robin sequence and atrial septal defect. All three families demonstrated de novo mutations, and one of the families had two recurrences, with demonstrable maternal mosaicism.

Outcome of infants diagnosed with 3-methyl-crotonyl-CoA-carboxylase deficiency by newborn screening

INTRODUCTION 3-Methyl CoA carboxylase (3-MCC) deficiency is an inborn error of metabolism in the catabolism of the amino acid leucine. Original reports suggested this disorder was associated with significant neurological and biochemical effects. However newborn screening has identified a higher than expected incidence of this disorder with apparent normal outcome in most cases. METHOD A retrospective analysis of thirty-five cases of 3-MCC deficiency identified by newborn screening and diagnosed by enzyme or molecular analysis. RESULTS There was a strong inverse correlation between initial C5OH level and residual enzyme activity. A few reports of hypoglycemia, ketosis, poor feeding/failure to thrive or fasting intolerance were reported, but there was no clear relationship between symptoms and residual enzyme activity. Developmental outcome included several children with mental retardation (including one with Down syndrome and one with schizencephaly) and two with Autism Spectrum disorders but there was no apparent relationship to residual enzyme activity. Free carnitine deficiency was relatively common. DISCUSSION Although residual enzyme activity was clearly related to metabolite elevation, there was no apparent relationship with other measures of outcome. The number of reports of neurologic abnormalities or metabolic symptoms (poor feeding, hypoglycemia, fasting intolerance, etc.) is concerning, but the significance is unclear in this retrospective sample.

Thiamine pyrophosphokinase deficiency causes a Leigh disease like phenotype in a sibling pair: Identification through whole exome sequencing and management strategies

We present a sibling pair with Leigh-like disease, progressive hypotonia, regression, and chronic encephalopathy. Whole exome sequencing in the younger sibling demonstrated a homozygous thiamine pyrophosphokinase (TPK) mutation. Initiation of high dose thiamine, niacin, biotin, α-lipoic acid and ketogenic diet in this child demonstrated improvement in neurologic function and re-attainment of previously lost milestones. The diagnosis of TPK deficiency was difficult due to inconsistent biochemical and diagnostic parameters, rapidity of clinical demise and would not have been made in a timely manner without the use of whole exome sequencing. Molecular diagnosis allowed for attempt at dietary modification with cofactor supplementation which resulted in an improved clinical course.

Dopa-Responsive Dystonia Presenting as Delayed and Awkward Gait

Dopa-responsive dystonia is a hereditary disease characterized by inadequate dopamine production. Autosomal-dominant cases result from mutations in the GCH1 gene, encoding guanosine triphosphate (GTP)-cyclohydrolase 1. The most common presenting manifestation is dystonia of a lower extremity, often worsening late in the day. The onset and clinical severity are variable, sometimes even within a single family. Gender effects on allele penetrance have been reported. We present a male toddler with dopa-responsive dystonia caused by an autosomal-dominant GCH1 mutation. Three other family members were also found to carry the mutation, with widely different functional consequences.

Kupffer cells modulate hepatic fatty acid oxidation during infection with PR8 influenza

In response to infection, patients with inborn errors of metabolism may develop a functional deterioration termed metabolic decompensation. The biochemical hallmarks of this disruption of metabolic homeostasis are disease specific and may include acidosis, hyperammonemia or hypoglycemia. In a model system previously published by our group, we noted that during influenza infection, mice displayed a depression in hepatic mitochondrial enzymes involved in nitrogen metabolism. Based on these findings, we hypothesized that this normal adaptation may extend to other metabolic pathways, and as such, may impact various inborn errors of metabolism. Since the liver is a critical organ in inborn errors of metabolism, we carried out untargeted metabolomic profiling of livers using mass spectrometry in C57Bl/6 mice infected with influenza to characterize metabolic adaptation. Pathway analysis of metabolomic data revealed reductions in CoA synthesis, and long chain fatty acyl CoA and carnitine species. These metabolic adaptations coincided with a depression in hepatic long chain β-oxidation mRNA and protein. To our surprise, the metabolic changes observed occurred in conjunction with a hepatic innate immune response, as demonstrated by transcriptional profiling and flow cytometry. By employing an immunomodulation strategy to deplete Kupffer cells, we were able to improve the expression of multiple genes involved in β-oxidation. Based on these findings, we are the first to suggest that the role of the liver as an immunologic organ is central in the pathophysiology of hepatic metabolic decompensation in inborn errors of metabolism due to respiratory viral infection.