In this study population, treatment with alglucosidase alfa was associated with improved walking distance and stabilization of pulmonary function over an 18-month period. (ClinicalTrials.gov number, NCT00158600.)
Tyrosinemia type I (hepatorenal tyrosinemia, HT-1) is an autosomal recessive condition resulting in hepatic failure with comorbidities involving the renal and neurologic systems and long term risks for hepatocellular carcinoma. An effective medical treatment with 2-[2-nitro-4-trifluoromethylbenzoyl]-1,3-cyclohexanedione (NTBC) exists but requires early identification of affected children for optimal long-term results. Newborn screening (NBS) utilizing blood succinylacetone as the NBS marker is superior to observing tyrosine levels as a way of identifying neonates with HT-1. If identified early and treated appropriately, the majority of affected infants can remain asymptomatic. A clinical management scheme is needed for infants with HT-1 identified by NBS or clinical symptoms. To this end, a group of 11 clinical practitioners, including eight biochemical genetics physicians, two metabolic dietitian nutritionists, and a clinical psychologist, from the United States and Canada, with experience in providing care for patients with HT-1, initiated an evidence- and consensus-based process to establish uniform recommendations for identification and treatment of HT-1. Recommendations were developed from a literature review, practitioner management survey, and nominal group process involving two face-to-face meetings. There was strong consensus in favor of NBS for HT-1, using blood succinylacetone as a marker, followed by diagnostic confirmation and early treatment with NTBC and diet. Consensus recommendations for both immediate and long-term clinical follow-up of positive diagnoses via both newborn screening and clinical symptomatic presentation are provided.
ABSTRACT. Objectives. Type B Niemann-Pick disease (NPD-B) caused by acid sphingomyelinase deficiency is a rare, autosomal recessive, lysosomal storage disorder with a broad range of disease severity. The objectives of this study were to document the natural history of the disease in a large, clinically heterogeneous patient population that was followed for a period of 10 years and to determine how genotype influences phenotype.Methods. Twenty-nine patients with NPD-B had serial evaluations at least 9 months apart. Organ volumes, hematologic indices, lipid concentrations, pulmonary function, and hepatic activity were studied, and individual phenotypic severity was compared with genotype.Results. All patients with intact spleens had splenomegaly (mean value: 12.7 multiples of normal [MN]; range: 4.5-27.3 MN), and all but 1 had hepatomegaly (mean volume: 1.91 MN; range: 0.93-3.21 MN). At initial visit, 39% had thrombocytopenia and 3% had leukopenia. At final visit, the percentages increased to 54% and 34%, respectively. Mean annual decreases in platelet count and leukocyte count were 7 ؋ 10 3 and 0.2 ؋ 10 3 per mm 3 , respectively. The typical atherogenic lipid profile was worse in older patients. A total of 69% of patients had low diffusion capacity for carbon monoxide, and more than one third had low forced expiratory volume in 1 second, forced vital capacity, and forced expiratory volume in 1 second/forced vital capacity at initial visit. All measurements of pulmonary function showed a gradual deterioration over time. Liver dysfunction was characterized by stable elevation of hepatic transaminases and bilirubin. Homozygotes for ⌬R608, P323A, and P330R had milder disease than patients with all other genotypes.Conclusions. N iemann-Pick disease (NPD) is a lysosomal storage disease caused by deficient activity of acid sphingomyelinase (ASM; sphingomyelin phosphodiesterase; EC 3.1.4.12) and the accumulation of sphingomyelin within cells of the monocyte-macrophage system. 1 Types A and B NPD are inherited as autosomal recessive traits and result from allelic mutations in the ASM gene. Type A disease (NPD-A), which has an Ashkenazi Jewish predilection, is a fatal neurodegenerative disorder of infancy. In contrast, type B NPD (NPD-B), which is panethnic, is a nonneuronopathic disease characterized by hepatosplenomegaly, hyperlipidemia, and pulmonary involvement, with most patients living into adulthood. Other, more variable features of NPD-B may include liver dysfunction, cardiac disease, retinal stigmata, and growth retardation. [2][3][4][5][6] There is a broad spectrum of disease manifestations among NPD-B patients, ranging from onset in childhood with massive organomegaly, secondary hypersplenism, growth restriction, and later pulmonary involvement or liver failure to a milder, attenuated course. As in other lysosomal storage diseases, this marked phenotypic variability is influenced by genotype, 7,8 although other factors such as gender and age may also contribute to disease severity. To date, the phenotypic variab...
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