Annette Feigenbaum

Efficacy of sapropterin dihydrochloride (tetrahydrobiopterin, 6R-BH4) for reduction of phenylalanine concentration in patients with phenylketonuria: a phase III randomised placebo-controlled study

BACKGROUND Early and strict dietary management of phenylketonuria is the only option to prevent mental retardation. We aimed to test the efficacy of sapropterin, a synthetic form of tetrahydrobiopterin (BH4), for reduction of blood phenylalanine concentration. METHODS We enrolled 89 patients with phenylketonuria in a Phase III, multicentre, randomised, double-blind, placebo-controlled trial. We randomly assigned 42 patients to receive oral doses of sapropterin (10 mg/kg) and 47 patients to receive placebo, once daily for 6 weeks. The primary endpoint was mean change from baseline in concentration of phenylalanine in blood after 6 weeks. Analysis was on an intention-to-treat basis. The study is registered with ClinicalTrials.gov, number NCT00104247. FINDINGS 88 of 89 enrolled patients received at least one dose of study drug, and 87 attended the week 6 visit. Mean age was 20 (SD 9.7) years. At baseline, mean concentration of phenylalanine in blood was 843 (300) micromol/L in patients assigned to receive sapropterin, and 888 (323) micromol/L in controls. After 6 weeks of treatment, patients given sapropterin had a decrease in mean blood phenylalanine of 236 (257) micromol/L, compared with a 3 (240) micromol/L increase in the placebo group (p<0.0001). After 6 weeks, 18/41 (44%) patients (95% CI 28-60) in the sapropterin group and 4/47 (9%) controls (95% CI 2-20) had a reduction in blood phenylalanine concentration of 30% or greater from baseline. Blood phenylalanine concentrations fell by about 200 micromol/L after 1 week in the sapropterin group and this reduction persisted for the remaining 5 weeks of the study (p<0.0001). 11/47 (23%) patients in the sapropterin group and 8/41 (20%) in the placebo group experienced adverse events that might have been drug-related (p=0.80). Upper respiratory tract infections were the most common disorder. INTERPRETATION In some patients with phenylketonuria who are responsive to BH4, sapropterin treatment to reduce blood phenylalanine could be used as an adjunct to a restrictive low-phenylalanine diet, and might even replace the diet in some instances.

A new leukoencephalopathy with brainstem and spinal cord involvement and high lactate

We identified eight patients with a distinct magnetic resonance imaging pattern of inhomogeneous cerebral white matter abnormalities and selective involvement of brainstem and spinal tracts. Proton magnetic resonance imaging showed increased lactate in the abnormal white matter. Clinically, the patients had slowly progressive pyramidal, cerebellar, and dorsal column dysfunction. The uniform, highly characteristic magnetic resonance imaging pattern and the similarities in clinical and magnetic resonance spectroscopy findings provide evidence for a new disease entity. Autosomal recessive inheritance is likely.

Mitochondrial DNA depletion and dGK gene mutations

Mitochondrial DNA depletion syndrome is a clinically heterogeneous group of disorders characterized by a reduction in mitochondrial DNA copy number. The recent discovery of mutations in the deoxyguanosine kinase (dGK) gene in patients with the hepatocerebral form of mitochondrial DNA depletion syndrome prompted us to screen 21 patients to determine the frequency of dGK mutations, further characterize the clinical spectrum, and correlate genotypes with phenotypes. We detected mutations in three patients (14%). One patient had a homozygous GATT duplication (nucleotides 763–766), and another had a homozygous GT deletion (nucleotides 609–610); both mutations lead to truncated proteins. The third patient was a compound heterozygote for two missense mutations (R142K and E227K) that affect critical residues of the protein. These mutations were associated with variable phenotypes, and their low frequencies suggests that dGK is not the only gene responsible for mitochondrial DNA depletion in liver. The patient with the missense mutations had isolated liver failure and responded well to liver transplantation, which may be a therapeutic option in selected cases.

IDH2 Mutations in Patients with d-2-Hydroxyglutaric Aciduria

A mutation that changes the specificity of an enzyme in human cancer is also found in an inherited metabolic disorder. Heterozygous somatic mutations in the genes encoding isocitrate dehydrogenase-1 and -2 (IDH1 and IDH2) were recently discovered in human neoplastic disorders. These mutations disable the enzymes’ normal ability to convert isocitrate to 2-ketoglutarate (2-KG) and confer on the enzymes a new function: the ability to convert 2-KG to d-2-hydroxyglutarate (D-2-HG). We have detected heterozygous germline mutations in IDH2 that alter enzyme residue Arg140 in 15 unrelated patients with d-2-hydroxyglutaric aciduria (D-2-HGA), a rare neurometabolic disorder characterized by supraphysiological levels of D-2-HG. These findings provide additional impetus for investigating the role of D-2-HG in the pathophysiology of metabolic disease and cancer.

Mutation Characterization and Genotype-Phenotype Correlation in Barth Syndrome

Barth syndrome is an X-linked cardiomyopathy with neutropenia and 3-methylglutaconic aciduria. Recently, mutations in the G4.5 gene, located in Xq28, have been described in four probands with Barth syndrome. We have now evaluated 14 Barth syndrome pedigrees for mutations in G4.5 and have identified unique mutations in all, including four splice-site mutations, three deletions, one insertion, five missense mutations, and one nonsense mutation. Nine of the 14 mutations are predicted to significantly disrupt the protein products of G4.5. The occurrence of missense mutations in exons 3 and 8 suggests that these exons encode essential portions of the G4. 5 proteins, whose functions remain unknown. We found no correlation between the location or type of mutation and any of the clinical or laboratory abnormalities of Barth syndrome, which suggests that additional factors modify the expression of the Barth phenotype. The characterization of mutations of the G4.5 gene will be useful for carrier detection, genetic counseling, and the identification of patients with Barth syndrome who do not manifest all of the cardinal features of this disorder.

Screening for carriers of Tay-Sachs disease among Ashkenazi Jews

BACKGROUND AND METHODS The prevention of Tay-Sachs disease (GM2 gangliosidosis, type 1) depends on the identification of carriers of the gene for this autosomal recessive disorder. We compared the enzyme-based test widely used in screening for Tay-Sachs disease with a test based on analysis of DNA. We developed methods to detect the three mutations in the HEXA gene that occur with high frequency among Ashkenazi Jews: two mutations cause infantile Tay-Sachs disease, and the third causes the adult-onset form of the disease. DNA segments containing these mutation sites were amplified with the polymerase chain reaction and analyzed for the presence of the mutations. RESULTS Among 62 Ashkenazi obligate carriers of Tay-Sachs disease, the three specific mutations accounted for all but one of the mutant alleles (98 percent). In 216 Ashkenazi carriers identified by the enzyme test, DNA analysis showed that 177 (82 percent) had one of the identified mutations. Of the 177, 79 percent had the exon 11 insertion mutation, 18 percent had the intron 12 splice-junction mutation, and 3 percent had the less severe exon 7 mutation associated with adult-onset disease. The results of the enzyme tests in the 39 subjects (18 percent) who were defined as carriers but in whom DNA analysis did not identify a mutant allele were probably false positive (although there remains some possibility of unidentified mutations). In addition, of 152 persons defined as noncarriers by the enzyme-based test, 1 was identified as a carrier by DNA analysis (i.e., a false negative enzyme-test result). CONCLUSIONS The increased specificity and predictive value of the DNA-based test make it a useful adjunct to the diagnostic tests currently used to screen for carriers of Tay-Sachs disease. Although some false positive results may be desirable on an enzyme-based test that is used in screening, the DNA test allows precise definition of the carrier state for the known mutations.

A Delphi clinical practice protocol for the management of very long chain acyl-CoA dehydrogenase deficiency

INTRODUCTION Very long chain acyl-CoA dehydrogenase (VLCAD) deficiency is a disorder of oxidation of long chain fat, and can present as cardiomyopathy or fasting intolerance in the first months to years of life, or as myopathy in later childhood to adulthood. Expanded newborn screening has identified a relatively high incidence of this disorder (1:31,500), but there is a dearth of evidence-based outcomes data to guide the development of clinical practice protocols. This consensus protocol is intended to assist clinicians in the diagnosis and management of screen-positive newborns for VLCAD deficiency until evidence-based guidelines are available. METHOD The Oxford Centre for Evidence-based Medicine system was used to grade the literature review and create recommendations graded from A (evidence level of randomized clinical trials) to D (expert opinion). Delphi was used as the consensus tool. A panel of 14 experts (including clinicians, diagnostic laboratory directors and researchers) completed three rounds of survey questions and had a face-to-face meeting. RESULT Panelists reviewed the initial evaluation of the screen-positive infant, diagnostic testing and management of diagnosed patients. Grade C and D consensus recommendations were made in each of these three areas. The panel did not reach consensus on all issues, particularly in the dietary management of asymptomatic infants diagnosed by newborn screening.

Molecular basis of lipoamide dehydrogenase deficiency in Ashkenazi Jews

We studied 13 patients with lipoamide dehydrogenase (LAD) deficiency, originating from seven Ashkenazi Jewish families. Their disease was characterized by recurrent attacks of vomiting, abdominal pain, and encephalopathy accompanied by elevated liver transaminases, prolonged prothrombin time, and occasionally associated with lactic and ketoacidemia or with myoglobinuria. Two patients who presented neonatally suffered from residual neurological damage with attention deficit hyperactive disorder, mild ataxia, motor incoordination, muscle hypotonia, and weakness. Nine patients who presented in early childhood or later suffered from exertional fatigue between decompensation episodes but were otherwise asymptomatic. Two patients died because of intractable metabolic acidosis and multi-organ failure. In all patients LAD activity was reduced to 8 to 21% of the control in muscle or lymphocytes. In four patients LAD protein in muscle was reduced to 20 to 60% of the control. Direct sequencing of the cDNA of the LAD gene showed that 12 of the 14 mutated alleles carried the G229C mutation and two carried an insertion mutation 105insA (Y35X). The patients who presented neonatally and had more severe sequelae were compound heterozygotes for the two mutations; patients who presented in early childhood or later were homozygous for the G229C mutation. Using an allele-specific oligonucleotide hybridization technique, nine heterozygotes for the G229C mutation were identified among 845 anonymous individuals of Ashkenazi Jewish origin disclosing a carrier rate of 1:94. Because of the significant morbidity associated with the disease, screening for the G229C mutation among Ashkenazi Jewish couples should be considered.

Inner Ear Dysplasia is Common in Children With Down Syndrome (trisomy 21)

Objectives/Hypothesis: Middle and external ear anomalies are well recognized in Down syndrome (DS, trisomy 21). Inner ear anomalies are much less frequently described. This study reviews inner ear morphology on imaging to determine the prevalence of cochlear and vestibular anomalies in children with DS.

AMMONIA CONTROL AND NEUROCOGNITIVE OUTCOME AMONG UREA CYCLE DISORDER PATIENTS TREATED WITH GLYCEROL PHENYLBUTYRATE

Glycerol phenylbutyrate is under development for treatment of urea cycle disorders (UCDs), rare inherited metabolic disorders manifested by hyperammonemia and neurological impairment. We report the results of a pivotal Phase 3, randomized, double‐blind, crossover trial comparing ammonia control, assessed as 24‐hour area under the curve (NH3‐AUC0‐24hr), and pharmacokinetics during treatment with glycerol phenylbutyrate versus sodium phenylbutyrate (NaPBA) in adult UCD patients and the combined results of four studies involving short‐ and long‐term glycerol phenylbutyrate treatment of UCD patients ages 6 and above. Glycerol phenylbutyrate was noninferior to NaPBA with respect to ammonia control in the pivotal study, with mean (standard deviation, SD) NH3‐AUC0‐24hr of 866 (661) versus 977 (865) μmol·h/L for glycerol phenylbutyrate and NaPBA, respectively. Among 65 adult and pediatric patients completing three similarly designed short‐term comparisons of glycerol phenylbutyrate versus NaPBA, NH3‐AUC0‐24hr was directionally lower on glycerol phenylbutyrate in each study, similar among all subgroups, and significantly lower (P < 0.05) in the pooled analysis, as was plasma glutamine. The 24‐hour ammonia profiles were consistent with the slow‐release behavior of glycerol phenylbutyrate and better overnight ammonia control. During 12 months of open‐label glycerol phenylbutyrate treatment, average ammonia was normal in adult and pediatric patients and executive function among pediatric patients, including behavioral regulation, goal setting, planning, and self‐monitoring, was significantly improved. Conclusion: Glycerol phenylbutyrate exhibits favorable pharmacokinetics and ammonia control relative to NaPBA in UCD patients, and long‐term glycerol phenylbutyrate treatment in pediatric UCD patients was associated with improved executive function (ClinicalTrials.gov NCT00551200, NCT00947544, NCT00992459, NCT00947297). (HEPATOLOGY 2012)