Nancy Leslie

Recombinant human acid α-glucosidase: Major clinical benefits in infantile-onset Pompe disease

Background: Pompe disease is a progressive metabolic neuromuscular disorder resulting from deficiency of lysosomal acid α-glucosidase (GAA). Infantile-onset Pompe disease is characterized by cardiomyopathy, respiratory and skeletal muscle weakness, and early death. The safety and efficacy of recombinant human (rh) GAA were evaluated in 18 patients with rapidly progressing infantile-onset Pompe disease. Methods: Patients were diagnosed at 6 months of age and younger and exhibited severe GAA deficiency and cardiomyopathy. Patients received IV infusions of rhGAA at 20 mg/kg (n = 9) or 40 mg/kg (n = 9) every other week. Analyses were performed 52 weeks after the last patient was randomized to treatment. Results: All patients (100%) survived to 18 months of age. A Cox proportional hazards analysis demonstrated that treatment reduced the risk of death by 99%, reduced the risk of death or invasive ventilation by 92%, and reduced the risk of death or any type of ventilation by 88%, as compared to an untreated historical control group. There was no clear advantage of the 40-mg/kg dose with regard to efficacy. Eleven of the 18 patients experienced 164 infusion-associated reactions; all were mild or moderate in intensity. Conclusions: Recombinant human acid α-glucosidase is safe and effective for treatment of infantile-onset Pompe disease. Eleven patients experienced adverse events related to treatment, but none discontinued. The young age at which these patients initiated therapy may have contributed to their improved response compared to previous trials with recombinant human acid α-glucosidase in which patients were older.

Clinical outcomes after long-term treatment with alglucosidase alfa in infants and children with advanced Pompe disease

Purpose: A clinical trial was conducted to evaluate the safety and efficacy of alglucosidase alfa in infants and children with advanced Pompe disease.Methods: Open-label, multicenter study of IV alglucosidase alfa treatment in 21 infants 3–43 months old (median 13 months) with minimal acid α-glucosidase activity and abnormal left ventricular mass index by echocardiography. Patients received IV alglucosidase alfa every 2 weeks for up to 168 weeks (median 120 weeks). Survival results were compared with an untreated reference cohort.Results: At study end, 71% (15/21) of patients were alive and 44% (7/16) of invasive-ventilator free patients remained so. Compared with the untreated reference cohort, alglucosidase alfa reduced the risk of death by 79% (P < 0.001) and the risk of invasive ventilation by 58% (P = 0.02). Left ventricular mass index improved or remained normal in all patients evaluated beyond 12 weeks; 62% (13/21) achieved new motor milestones. Five patients were walking independently at the end of the study and 86% (18/21) gained functional independence skills. Overall, 52% (11/21) of patients experienced infusion-associated reactions; 95% (19/20) developed IgG antibodies to recombinant human lysosomal acid α-glucosidase; no patients withdrew from the study because of safety concerns.Conclusions: In this population of infants with advanced disease, biweekly infusions with alglucosidase alfa prolonged survival and invasive ventilation-free survival. Treatment also improved indices of cardiomyopathy, motor skills, and functional independence.

Early Treatment With Alglucosidase Alfa Prolongs Long-Term Survival of Infants With Pompe Disease

In a previous 52-wk trial, treatment with alglucosidase alfa markedly improved cardiomyopathy, ventilatory function, and overall survival among 18 children <7 mo old with infantile-onset Pompe disease. Sixteen of the 18 patients enrolled in an extension study, where they continued to receive alglucosidase alfa at either 20 mg/kg biweekly (n = 8) or 40 mg/kg biweekly (n = 8), for up to a total of 3 y. These children continued to exhibit the benefits of alglucosidase alfa at the age of 36 mo. Cox regression analyses showed that over the entire study period, alglucosidase alfa treatment reduced the risk of death by 95%, reduced the risk of invasive ventilation or death by 91%, and reduced the risk of any type of ventilation or death by 87%, compared with an untreated historical control group. Cardiomyopathy continued to improve and 11 patients learned and sustained substantial motor skills. No significant differences in either safety or efficacy parameters were observed between the 20 and 40 mg/kg biweekly doses. Overall, long-term alglucosidase alfa treatment markedly extended survival as well as ventilation-free survival and improved cardiomyopathy.

The human galactose-1-phosphate uridyltransferase gene.

Classical galactosemia is an inborn error of metabolism caused by a deficiency of galactose-1-phosphate uridyltransferase (GALT). Standard treatment with dietary galactose restriction will reverse the potentially lethal symptoms of the disease that are manifest in the newborn period. However, the long-term prognosis for these patients is variable. As a first step toward investigating the molecular basis for phenotypic variation in galactosemia, we have cloned and sequenced the entire gene for human galactose-1-phosphate uridyltransferase. This gene is organized into 11 exons spanning 4 kb. In exons 6, 9, and a portion of 10, there is a high degree of amino acid sequence conservation among Escherichia coli, yeast, mouse, and human. We have identified a number of nucleotide changes in the GALT genes of galactosemic patients that alter conserved amino acids. The most common of these is an A to G transition at nucleotide position 1470, converting a glutamine to an arginine at amino acid codon position 188 (Q188R).(ABSTRACT TRUNCATED AT 250 WORDS)

Mutations in the MPV17 gene are responsible for rapidly progressive liver failure in infancy.

MPV17 is a mitochondrial inner membrane protein of unknown function recently recognized as responsible for a mitochondrial DNA depletion syndrome. The aim of this study is to delineate the specific clinical, pathological, biochemical, and molecular features associated with mitochondrial DNA depletion due to MPV17 gene mutations. We report 4 cases from 3 ethnically diverse families with MPV17 mutations. Importantly, 2 of these cases presented with isolated liver failure during infancy without notable neurologic dysfunction. Conclusion: We therefore propose that mutations in the MPV17 gene be considered in the course of evaluating the molecular etiology for isolated, rapidly progressive infantile hepatic failure. (HEPATOLOGY 2007.)

Galactose Metabolism by the Mouse with Galactose-1-Phosphate Uridyltransferase Deficiency

The ability of mice deficient in galactose-1-phosphate uridyltransferase (GALT) to metabolize galactose was determined in animals weaned to a mouse chow diet for a 4-wk period. When given [14C]galactose intraperitoneally, these animals slowly oxidized the sugar, excreting only 5.5% of the dose as 14CO2 in 4 h, whereas normal animals excreted 39.9%. These results mimic those seen in human galactosemic patients given isotopic galactose. When given 10 μmol of [1-13C]galactose, normal animals excrete small amounts of labeled galactose and galactonate but no galactitol in urine whereas GALT-deficient mice excrete significant amounts of all of these as labeled compounds in urine. When challenged with galactose, only about 20% of the dose is excreted in urine, and even on the chow diet, significant amounts of galactose, galactonate, and galactitol are excreted in urine. These compounds are also found to be present in liver, kidney, and brain, except that galactonate is not found in brain. Galactose-1-phosphate accumulates in red blood cells to levels found in humans exposed to large amounts of galactose, and galactose-1-phosphate is found in increased amounts in liver, kidney, and brain of GALT-deficient animals. There was no difference in the hepatic concentration of uridine diphosphate galactose and uridine diphosphate glucose between normal and GALT-deficient mice. The explanation for the presence of galactose and its conversion products in tissues and urine of affected mice appears to be related to the presence of approximately 1.75% of galactose-containing carbohydrates in the chow, which becomes bioavailable to mice. Despite the presence of galactose and its metabolites in tissues and urine and impaired ability to oxidize the sugar, the GALT-deficient animals are indistinguishable from normal animals and do not exhibit the phenotype of humans with GALT-deficiency galactosemia.

Diversity of approaches to classic galactosemia around the world: a comparison of diagnosis, intervention, and outcomes

Without intervention, classic galactosemia is a potentially fatal disorder in infancy. With the benefit of early diagnosis and dietary restriction of galactose, the acute sequelae of classic galactosemia can be prevented or reversed. However, despite early and lifelong dietary treatment, many galactosemic patients go on to experience serious long-term complications including cognitive disability, speech problems, neurological and/or movement disorders and, in girls and women, ovarian dysfunction. Further, there remains uncertainty surrounding what constitutes a ‘best practice’ for treating this disorder. To explore the extent and implications of this uncertainty, we conducted a small but global survey of healthcare providers who follow patients with classic galactosemia, seeking to compare established protocols for diagnosis, intervention, and follow-up, as well as the outcomes and outcome frequencies seen in the patient populations cared for by these providers. We received 13 survey responses representing five continents and 11 countries. Respondents underscored disparities in approaches to diagnosis, management and follow-up care. Notably, we saw no clear relationship between differing approaches to care and long-term outcomes in the populations studied. Negative outcomes occurred in the majority of cases regardless of when treatment was initiated, how tightly galactose intake was restricted, or how closely patients were monitored. We document here what is, to our knowledge, the first global comparison of healthcare approaches to classic galactosemia. These data reinforce the idea that there is currently no one best practice for treating patients with classic galactosemia, and underscore the need for more extensive and statistically powerful comparative studies to reveal potential positive or negative impacts of differing approaches.

Enzyme reconstitution/replacement therapy for lysosomal storage diseases.

Purpose of review Over the past 15 years, the lysosomal storage diseases have become paradigms for the specific treatment of monogenic disorders, particularly those affecting children. This review summarizes the phenotypes and recent literature regarding enzyme reconstitution (replacement) therapy and outcomes for such treatable lysosomal storage diseases: Gaucher disease, Fabry disease, Pompe disease and the mucopolysaccharidoses. Recent findings Recent clinical trials have shown that enzyme reconstitution therapy effectively treats many of the manifestations of the lysosomal storage diseases. When initiated early in the disease course, enzyme reconstitution therapy can reverse some disease manifestations, but may not completely alleviate the disease progression. Enzyme reconstitution therapy is generally well tolerated. Many adverse events are antibody-related, but can be managed without requiring cessation of enzyme reconstitution therapy. Documented IgE reactions, i.e. anaphylactoid, are quite rare (fewer than 1%). Summary Enzyme reconstitution therapy is a safe and effective treatment modality available for several of the lysosomal storage diseases. Owing to the short history of enzyme reconstitution therapy, the long-term outcomes of enzyme reconstitution therapy-treated individuals are unknown and require further investigation. Medical professionals must learn to identify patients likely to benefit from these life-changing therapies so as to prevent many of the devastating, irreversible complications of the lysosomal storage diseases.

Undetectable maternal serum uE3 and postnatal abnormal sterol and steroid metabolism in Antley-Bixler syndrome

Antley–Bixler syndrome (ABS) is a rare condition characterized by radiohumeral synostosis, craniosynostosis, midface hypoplasia, bowing of the femora, multiple joint contractures, and urogenital defects. Several reports have implicated errors of steroid or sterol metabolism in the pathogenesis of ABS. Evidence for this has included association with maternal luteomas, fetal 21‐hydroxylase deficiency, early pregnancy exposure to high‐dose fluconazole, lanosterol 14‐α‐demethylase deficiency, and a unique urinary steroid profile consistent with apparent pregnene hydroxylation deficiency (APHD). We report two sibs with classic ABS. During both pregnancies, mid‐trimester maternal serum screening demonstrated undetectable levels of uncongugated estriol (uE3). The brother had ambiguous genitalia and increased serum levels of progesterone and 17‐α‐hydroxyprogesterone. Postnatal tests performed on the sister demonstrated both the unique urinary steroid profile that defines APHD and evidence of impaired lanosterol 14‐α‐demethylase activity. Our results suggest that in at least some patients with ABS, the skeletal findings and altered steroidogenesis are not associated with genes specific to individual sterol or steroid pathways but rather are related to an element, such as NADPH cytochrome P450 reductase (CPR) or cytochrome b5 (CYb5), that is common to all of these pathways.

Cardiac Disease in Methylmalonic Acidemia

Methylmalonic acidemia (MMA) is a heterogeneous disorder, with onset from infancy to adulthood and varying degrees of organ involvement and severity. Cardiac disease is a known lethal complication of other organic acidemias, but has not been associated with MMA. We identified 3 patients with MMA and cardiac disease.