Brian Kirmse

Newborn screening and early biochemical follow-up in combined methylmalonic aciduria and homocystinuria, cblC type, and utility of methionine as a secondary screening analyte

INTRODUCTION Combined methylmalonic aciduria and homocystinuria, cobalamin C (cblC) type, is an inherited disorder of vitamin B(12) metabolism caused by mutations in MMACHC. CblC typically presents in the neonatal period with neurological deterioration, failure to thrive, cytopenias, and multisystem pathology including renal and hepatic dysfunction. Rarely, affected individuals present in adulthood with gait ataxia and cognitive decline. Treatment with hydroxocobalamin may ameliorate the clinical features of early-onset disease and prevent clinical late-onset disease. Propionic acidemia (PA), methylmalonic acidemia (MMA), and various disorders of cobalamin metabolism are characterized by elevated propionylcarnitine (C3) on newborn screening (NBS). Distinctions can be made between these disorders with secondary analyte testing. Elevated methionine is already routinely used as a NBS marker for cystathionine beta-synthase deficiency. We propose that low methionine may be useful as a secondary analyte for specific detection of cbl disorders among a larger pool of infants with elevated C3 on NBS. METHODS Retrospective analysis of dried blood spot (DBS) data in patients with molecularly confirmed cblC disease. RESULTS Nine out of ten patients with confirmed cblC born in New York between 2005 and 2008 had methionine below 13.4mumol/L on NBS. Elevated C3, elevated C3:C2 ratio, and low methionine were incorporated into a simple screening algorithm that can be used to improve the specificity of newborn screening programs and provide a specific and novel method of distinguishing cblC from other disorders of propionate metabolism prior to recall for confirmatory testing. CONCLUSIONS It is anticipated that this algorithm will aid in early and specific detection of cobalamin C, D, and F diseases, with no additional expense to NBS laboratories screening for organic acidemias and classical homocystinuria.

HIV Protease Inhibitors Inhibit the Development of Preerythrocytic-Stage Plasmodium Parasites

Recent studies have demonstrated that human immunodeficiency virus (HIV) protease inhibitors (PIs) exert inhibitory effects on erythrocytic stages of the human-malaria parasite Plasmodium falciparum in vitro and on erythrocytic stages of the rodent-malaria parasite Plasmodium chabaudi in vivo. Although it remains unclear how HIV PIs inhibit the parasite, the effect seen on parasite development in the erythrocytic stages is potent. The effect on preerythrocytic stages has not yet been investigated. Using the rodent parasite Plasmodium berghei, we screened a panel of HIV PIs in vitro for effects on the preerythrocytic stages. Our data indicated that the HIV PIs lopinavir and saquinavir affect preerythrocytic-stage parasite development in vitro. We then evaluated the effect of HIV PIs on preerythrocytic stages in vivo using the rodent parasite Plasmodium yoelii. We found that lopinavir/ritonavir had a dose-dependent effect on liver-stage parasite development. Given that sub-Saharan Africa is where the HIV/AIDS pandemic intersects with malaria, these results merit analysis in clinical settings.

High prevalence of structural heart disease in children with cblC-type methylmalonic aciduria and homocystinuria.

OBJECTIVE To characterize the frequency and nature of cardiovascular defects in patients with CblC-type methylmalonic aciduria and homocystinuria (cblC), an inborn error of cobalamin (vitamin B12) metabolism resulting in accumulation of methylmalonic acid and homocysteine. STUDY DESIGN A retrospective observational study was conducted investigating 10 patients with cblC ranging in age from 2 weeks to 24 years (mean 4.4 years +/- 7.5 years, median 0.6 years). All patients underwent a complete 2-D echocardiogram including quantitative assessment of left ventricular systolic function. RESULTS Structural heart defects were detected in 50% of patients with cblC. Heart defects included left ventricular (LV) non-compaction (3), secundum atrial septal defect (2), muscular ventricular septal defect (1), dysplastic pulmonary valve without pulmonary stenosis (1) and mitral valve prolapse with mild mitral regurgitation (1). One patient had resolved cor pulmonale and right heart failure secondary to pulmonary embolism. All patients had quantitatively normal LV systolic function. CONCLUSIONS Diverse and clinically significant structural heart defects appear to be highly prevalent in cblC, perhaps due to abnormal DNA and histone methylation during embryogenesis. The specific cardiac defects detected in our cohort were variable, and studies with a larger number of patients are needed to establish which forms are most common. Routine and periodic cardiovascular evaluation may be indicated in patients with cblC.

Novel first-dose adverse drug reactions during a phase I trial of olipudase alfa (recombinant human acid sphingomyelinase) in adults with Niemann-Pick disease type B (acid sphingomyelinase deficiency)

Purpose:Enzyme replacement therapy with olipudase alfa (recombinant human acid sphingomyelinase) is being developed for Niemann–Pick disease type B (NPD B).Methods:A single-center, open-label, nonrandomized, single-ascending-dose trial evaluated the safety of intravenous olipudase alfa (0.03–1.0 mg/kg) in 11 adults with NPD B. Patients were monitored in the hospital for 72 h after infusion and had follow-up visits on days 14 and 28.Results:Plasma ceramide, a product of sphingomyelin catabolism by olipudase alfa, showed dose-dependent elevations by 6 h postdose, or postinfusion. No serious adverse drug reactions (ADRs) occurred during the study. Acute phase reaction-type ADRs, as evidenced by elevated inflammatory biomarkers (high-sensitivity C-reactive protein, interleukin-8, and calcitonin) and constitutional symptoms (fever, pain, nausea, and/or vomiting) emerged 12–24 h following doses ≥0.3 mg/kg olipudase alfa. Three patients experienced hyperbilirubinemia. The study was terminated after a patient dosed at 1 mg/kg exhibited severe hyperbilirubinemia; he was subsequently diagnosed with Gilbert syndrome.Conclusion:The maximum tolerated dose of olipudase alfa in adults with NPD B was 0.6 mg/kg. First-dose ADRs were likely induced by elevated concentrations of ceramide (or its downstream derivatives) generated by the catabolism of accumulated sphingomyelin. Within-patient dose escalation to slowly catabolize sphingomyelin stores may be a strategy to mitigate first-dose ADRs in patients with NPD B.Genet Med 18 1, 34–40.

Abnormal newborn screens and acylcarnitines in HIV-exposed and ARV-exposed infants

Background: Antiretroviral drugs (ARV), specifically nucleoside analogs, are toxic to mitochondrial oxidative phosphorylation. Other metabolic pathways, such as fatty acid oxidation, organic acid metabolism and amino acid metabolism, are dependent on normal oxidative phosphorylation but remain unexamined as potential points of ARV toxicity. Methods: We analyzed newborn screening data from New York and compared proportions of abnormal newborn metabolic screens in HIV antibody screen–positive and HIV screen–negative neonates. Subsequently, we compared acylcarnitine levels in ARV-exposed (n = 16) and ARV-unexposed (n = 14) HIV-exposed infants to assess for dysfunctional fatty and organic acid metabolism. Results: The rate of abnormal newborn metabolic screens in HIV screen–positive infants was higher than that in the general population (2.2% versus 1.2%; P = 0.00025), most of which were for disorders of mitochondria-related metabolism. Abnormal acylcarnitine levels occurred more frequently in ARV-exposed compared with ARV-unexposed infants (43% versus 0%; P = 0.02). Conclusions: A higher proportion of positive metabolic screens in HIV screen–positive neonates suggests that HIV or ARV exposure is associated with dysfunctional intermediary metabolism in newborns. Abnormal acylcarnitine levels were more frequent in ARV-exposed infants, suggesting that ARV may perturb normal fatty acid oxidation in some infants. Studies designed to validate and determine the clinical significance of these findings are warranted.

Resolution of cor pulmonale after medical management in a patient with cblC-type methylmalonic aciduria and homocystinuria: a case report

We describe a 3-year-old Hispanic male with cblC-type methylmalonic aciduria and homocystinuria who presented to the emergency department with progressive tachypnea, vomiting, and edema secondary to pulmonary embolism and cor pulmonale. With aggressive medical management, there was complete resolution of right heart failure and pulmonary hypertension after 3 months. Pulmonary embolism is rare in the pediatric population. Children with cblC-type methylmalonic aciduria and homocystinuria may be at increased risk for thrombus formation and pulmonary embolism due to chronic hyperhomocystinemia, a risk factor for thrombus formation in the adult population. Aspirin therapy may be indicated in children with inborn errors of metabolism that predispose to hyperhomocystinemia.

Malaria in HIV-infected children receiving HIV protease-inhibitor-compared with non-nucleoside reverse transcriptase inhibitor-based antiretroviral therapy, IMPAACT P1068s, substudy to P1060

Background HIV and malaria geographically overlap. HIV protease inhibitors kill malaria parasites in vitro and in vivo, but further evaluation in clinical studies is needed. Methods Thirty-one children from Malawi aged 4–62 months were followed every 3 months and at intercurrent illness visits for ≤47 months (September 2009-December 2011). We compared malaria parasite carriage by blood smear microscopy (BS) and confirmed clinical malaria incidence (CCM, or positive BS with malaria symptoms) in children initiated on HIV antiretroviral therapy (ART) with zidovudine, lamivudine, and either nevirapine (NVP), a non-nucleoside reverse transcriptase inhibitor, or lopinavir-ritonavir (LPV-rtv), a protease inhibitor. Results We found an association between increased time to recurrent positive BS, but not CCM, when anti-malarial treatment and LPV-rtv based ART were used concurrently and when accounting for a LPV-rtv and antimalarial treatment interaction (adjusted HR 0.39; 95% CI (0.17,0.89); p = 0.03). Conclusions LPV-rtv in combination with malaria treatment was associated with lower risk of recurrent positive BS, but not CCM, in HIV-infected children. Larger, randomized studies are needed to confirm these findings which may permit ART optimization for malaria-endemic settings. Trial Registration ClinicalTrials.gov NCT00719602

Complex care of individuals with multiple sulfatase deficiency: Clinical cases and consensus statement

Multiple sulfatase deficiency (MSD) is an ultra-rare neurodegenerative disorder that results in defective sulfatase post-translational modification. Sulfatases in the body are activated by a unique protein, formylglycine-generating enzyme (FGE) that is encoded by SUMF1. When FGE is absent or insufficient, all 17 known human sulfatases are affected, including the enzymes associated with metachromatic leukodystrophy (MLD), several mucopolysaccharidoses (MPS II, IIIA, IIID, IVA, VI), chondrodysplasia punctata, and X-linked ichthyosis. As such, individuals demonstrate a complex and severe clinical phenotype that has not been fully characterized to date. In this report, we describe two individuals with distinct clinical presentations of MSD. Also, we detail a comprehensive systems-based approach to the management of individuals with MSD, from the initial diagnostic evaluation to unique multisystem issues and potential management options. As there have been no natural history studies to date, the recommendations within this report are based on published studies and consensus opinion and underscore the need for future research on evidence-based outcomes to improve management of children with MSD.

A recurrent missense variant in SLC9A7 causes nonsyndromic X-linked intellectual disability with alteration of Golgi acidification and aberrant glycosylation

We report two unrelated families with multigenerational nonsyndromic intellectual disability (ID) segregating with a recurrent de novo missense variant (c.1543C>T:p.Leu515Phe) in the alkali cation/proton exchanger gene SLC9A7 (also commonly referred to as NHE7). SLC9A7 is located on human X chromosome at Xp11.3 and has not yet been associated with a human phenotype. The gene is widely transcribed, but especially abundant in brain, skeletal muscle and various secretory tissues. Within cells, SLC9A7 resides in the Golgi apparatus, with prominent enrichment in the trans-Golgi network (TGN) and post-Golgi vesicles. In transfected Chinese hamster ovary AP-1 cells, the Leu515Phe mutant protein was correctly targeted to the TGN/post-Golgi vesicles, but its N-linked oligosaccharide maturation as well as that of a co-transfected secretory membrane glycoprotein, vesicular stomatitis virus G (VSVG) glycoprotein, was reduced compared to cells co-expressing SLC9A7 wild-type and VSVG. This correlated with alkalinization of the TGN/post-Golgi compartments, suggestive of a gain-of-function. Membrane trafficking of glycosylation-deficient Leu515Phe and co-transfected VSVG to the cell surface, however, was relatively unaffected. Mass spectrometry analysis of patient sera also revealed an abnormal N-glycosylation profile for transferrin, a clinical diagnostic marker for congenital disorders of glycosylation. These data implicate a crucial role for SLC9A7 in the regulation of TGN/post-Golgi pH homeostasis and glycosylation of exported cargo, which may underlie the cellular pathophysiology and neurodevelopmental deficits associated with this particular nonsyndromic form of X-linked ID.

Prevalence of Asymptomatic Parasitemia and Gametocytemia in HIV-Infected Children on Differing Antiretroviral Therapy

Abstract. Laboratory data and prior pediatric reports indicate that HIV protease inhibitor (PI)–based antiretroviral therapy (ARV) kills gametocytes and reduces rates of gametocytemia, but not asymptomatic parasitemia, in a high malaria-transmission area. To determine whether ARV regimen impacts these rates in areas with less-intense malaria transmission, we compared asymptomatic parasitemia and gametocytemia rates in HIV-infected children by ARV regimen in Lilongwe, Malawi, an area of low-to-moderate transmission intensity. HIV PI lopinavir–ritonavir (LPV–rtv) ARV– or non-nucleoside reverse transcriptase inhibitor nevirapine ARV–treated children did not differ in the rates of polymerase chain reaction-detected asymptomatic parasitemia (relative risk [RR] 0.43 95% confidence interval [CI] [0.16, 1.18], P value 0.10) or microscopically detected gametocytemia with LPV–rtv ARV during symptomatic malaria (RR 0.48 95% CI [0.22,1.04] P value 0.06). LPV–rtv ARV was not associated with reduced rates of asymptomatic parasitemia, or gametocytemia on days of symptomatic malaria episodes, in HIV-infected children. Larger studies should evaluate whether ARV impacts transmission.