C. Ronald Scott

Effectiveness of Enzyme replacement therapy in 1028 patients with type 1 Gaucher disease after 2 to 5 years of treatment: A report from the Gaucher registry

PURPOSE Gaucher disease is the first lysosomal storage disorder to be treated with macrophage-targeted enzyme replacement therapy. Previous studies in relatively small numbers of patients demonstrated short-term efficacy of this treatment. This study describes the effects of 2 to 5 years of treatment on specific manifestations of type 1 Gaucher disease. SUBJECTS AND METHODS Physicians reported data from 1028 patients to the Gaucher Registry. Assessment of response included serial measurements of hemoglobin concentration, platelet count, liver and spleen volumes, and the occurrence of bone pain and bone crises. RESULTS Among anemic patients, hemoglobin concentration increased to normal or near normal within 6 to 12 months, with a sustained response through 5 years. In thrombocytopenic patients with intact spleens, the most rapid response occurred during the first 2 years, with slower improvement thereafter. The likelihood of achieving a normal platelet count decreased with increasing severity of baseline thrombocytopenia. In patients who had undergone splenectomy, platelet counts returned to normal within 6 to 12 months. Hepatomegaly decreased by 30% to 40% during follow-up; splenomegaly decreased 50% to 60%, but rarely to volumes below five times normal size. In patients with pretreatment bone pain or bone crises, 52% (67/128) were pain free after 2 years and 94% (48/51) reported no additional crises. CONCLUSION Enzyme replacement therapy prevents progressive manifestations of Gaucher disease, and ameliorates Gaucher disease-associated anemia, thrombocytopenia, organomegaly, bone pain, and bone crises.

Gaucher disease: mutation and polymorphism spectrum in the glucocerebrosidase gene (GBA).

Gaucher disease (GD) is an autosomal recessive disorder caused by the deficiency of glucocerebrosidase, a lysosomal enzyme that catalyses the hydrolysis of the glycolipid glucocerebroside to ceramide and glucose. Lysosomal storage of the substrate in cells of the reticuloendothelial system leads to multisystemic manifestations, including involvement of the liver, spleen, bone marrow, lungs, and nervous system. Patients with GD have highly variable presentations and symptoms that, in many cases, do not correlate well with specific genotypes. Almost 300 unique mutations have been reported in the glucocerebrosidase gene (GBA), with a distribution that spans the gene. These include 203 missense mutations, 18 nonsense mutations, 36 small insertions or deletions that lead to either frameshifts or in‐frame alterations, 14 splice junction mutations, and 13 complex alleles carrying two or more mutations in cis. Recombination events with a highly homologous pseudogene downstream of the GBA locus also have been identified, resulting from gene conversion, fusion, or duplication. In this review we discuss the spectrum of GBA mutations and their distribution in the patient population, evolutionary conservation, clinical presentations, and how they may affect the structure and function of glucocerebrosidase. Hum Mutat 29(5), 567–583, 2008. Published 2008 Wiley‐Liss, Inc.

Actionable exomic incidental findings in 6503 participants: challenges of variant classification

Recommendations for laboratories to report incidental findings from genomic tests have stimulated interest in such results. In order to investigate the criteria and processes for assigning the pathogenicity of specific variants and to estimate the frequency of such incidental findings in patients of European and African ancestry, we classified potentially actionable pathogenic single-nucleotide variants (SNVs) in all 4300 European- and 2203 African-ancestry participants sequenced by the NHLBI Exome Sequencing Project (ESP). We considered 112 gene-disease pairs selected by an expert panel as associated with medically actionable genetic disorders that may be undiagnosed in adults. The resulting classifications were compared to classifications from other clinical and research genetic testing laboratories, as well as with in silico pathogenicity scores. Among European-ancestry participants, 30 of 4300 (0.7%) had a pathogenic SNV and six (0.1%) had a disruptive variant that was expected to be pathogenic, whereas 52 (1.2%) had likely pathogenic SNVs. For African-ancestry participants, six of 2203 (0.3%) had a pathogenic SNV and six (0.3%) had an expected pathogenic disruptive variant, whereas 13 (0.6%) had likely pathogenic SNVs. Genomic Evolutionary Rate Profiling mammalian conservation score and the Combined Annotation Dependent Depletion summary score of conservation, substitution, regulation, and other evidence were compared across pathogenicity assignments and appear to have utility in variant classification. This work provides a refined estimate of the burden of adult onset, medically actionable incidental findings expected from exome sequencing, highlights challenges in variant classification, and demonstrates the need for a better curated variant interpretation knowledge base.

Genetic counseling and screening of consanguineous couples and their offspring: Recommendations of the national society of genetic counselors

The objective of this document is to provide recommendations for genetic counseling and screening for consanguineous couples (related as second cousins or closer) and their offspring with the goals of1. providing preconception reproductive options2. improving pregnancy outcome and identifying reproductive choices3. reducing morbidity and mortality in the 1st years of life, and4. respecting psychosocial and multicultural issues.The recommendations are the opinions of a multicenter working group (the Consanguinity Working Group (CWG)) with expertise in genetic counseling, medical genetics, biochemical genetics, genetic epidemiology, pediatrics, perinatology, and public health genetics, which was convened by the National Society of Genetic Counselors (NSGC). The consensus of the CWG and NSGC reviewers is that beyond a thorough medical family history with follow-up of significant findings, no additional preconception screening is recommended for consanguineous couples. Consanguineous couples should be offered similar genetic screening as suggested for any couple of their ethnic group. During pregnancy, consanguineous couples should be offered maternal–fetal serum marker screening and high-resolution fetal ultrasonography. Newborns should be screened for impaired hearing and detection of treatable inborn errors of metabolism. These recommendations should not be construed as dictating an exclusive course of management, nor does use of such recommendations guarantee a particular outcome. The professional judgment of a health care provider, familiar with the facts and circumstances of a specific case, will always supersede these recommendations.

Familial neurovisceral lipidosis

Histochemical studies on renal tissue obtained from an infant with familial neurovisceral lipidosis indicate that a mucopolysaccharide rather than a glycolipid is the major storage material contained within the vacuoles of the glomerular epithelium. Electron microscopic studies indicate that the storage vacuoles are probably lysosomes. Because of the clinical similarity to Hurlers syndrome and the storage of a mucopolysaccharide, it is suggested that familial neurovisceral lipidosis may be related to the genetic mucopolysaccharidoses.

The genetic tyrosinemias.

The genetic tyrosinemias are characterized by the accumulation of tyrosine in body fluids and tissues. The most severe form of tyrosinemia, Type I, is a devastating disorder of childhood that causes liver failure, painful neurologic crises, rickets, and hepatocarcinoma. This disorder is caused by a deficiency of fumarylacetoacetate hydrolase (FAH). If untreated, death typically occurs at less than 2 years of age, with some chronic forms allowing longer survival. It has a prevalence of about 1 in 100,000 newborns in the general population. Oculocutaneous tyrosinemia, Type II, is caused by a deficiency of tyrosine aminotransferase (TAT). It clinically presents with hyperkeratotic plaques on the hands and soles of the feet and photophobia due to deposition of tyrosine crystals within the cornea. Tyrosinemia Type III is an extremely rare disorder caused by a deficiency of 4‐hydroxyphenylpyruvic dioxygenase. It has been associated with ataxia and mild mental retardation. These disorders are diagnosed by observing elevated tyrosine by plasma amino acid chromatography and characteristic tyrosine metabolites by urine organic acid analysis. In tyrosinemia Type I, methionine is also elevated, reflecting impaired hepatocellular function. Urine organic acids show elevated p‐hydroxy‐phenyl organic acids in each type of tyrosinemia, and the pathognomic succinylacetone in tyrosinemia Type I. Diagnosis can be confirmed by enzyme or molecular studies in tyrosinemia Type I. Therapy consists of a diet low in phenylalanine and tyrosine for each of the tyrosinemias and 2‐(2‐nitro‐4‐trifluoromethylbenzoyl)‐1,3‐cyclohexanedione (NTBC) for tyrosinemia Type I.

Identification of infants at risk for developing Fabry, Pompe or Mucopolysaccharidosis-I from newborn blood spots by tandem mass spectrometry

OBJECTIVE To assess the performance of a tandem mass spectrometry (MS/MS) technology in a newborn screening laboratory to simultaneously measure α-galactosidase, acid-α-glucosidase, and α-L-iduronidase for the detection of infants at risk to develop Fabry, Pompe, or mucopolysaccharidosis (MPS)-I diseases. STUDY DESIGN Enzyme activity was assayed from a 3.2-mm punch from 100,000+ anonymous newborn blood spots. Punches with low enzyme activity were further evaluated by nucleotide sequence analysis of the responsible gene. Confirmation of affected infants was dependent on identification of mutations compatible with diminished enzyme activity. RESULTS The technology for simultaneously measuring multiple enzyme activities by MS/MS was successful. The confirmation of diagnosis for Fabry, Pompe, or MPS-I, by DNA sequencing estimated the prevalence of Fabry disease at 1/7800 males (95% CI 1/17,800-1/3600); Pompe disease at 1/27,800 newborns (95% CI 1/90,000-1/10,200); and MPS-I at 1/35,500 newborns (95% CI 1/143,000-1/11,100). These estimates of prevalence are 2 to 4 times greater than the prevalence estimated by clinical diagnosis. The combined prevalence for the 3 disorders was 1/7500 newborns (95% CI 1/13,500-1/4500). CONCLUSIONS MS/MS for the simultaneous assay of multiple lysosomal enzymes can be successfully introduced into a routine newborn screening laboratory. The technology has a positive predictive value equal to, or better, than methods currently used for the detection of nonlysosomal disorders. Using newborn blood spots, the combined prevalence of Fabry, Pompe, and MPS-I is estimated at 1/7500 newborns based on low-enzyme activity and confirmation by mutation analysis.

Tandem Mass Spectrometry for the Direct Assay of Lysosomal Enzymes in Dried Blood Spots:Application to Screening Newborns for Mucopolysaccharidosis IVA

BACKGROUND Treatments are being developed for an increasing number of mucopolysaccharidoses, and early diagnosis is expected to be necessary to maximize the benefits of therapy. Therefore, we developed an assay for N-acetylgalactosamine-6-sulfate sulfatase (GALNS), the enzyme deficient in mucopolysaccharidosis IVA (Morquio A syndrome), that is applicable for clinical diagnosis. METHODS A novel substrate for GALNS was synthesized for a new enzyme activity assay that is based on tandem mass spectrometry and uses dried blood spots (DBSs) as the enzyme source. We optimized the assay conditions, including the substrate concentration, reaction pH, lead formate concentration, incubation time, punch size of the DBS, and mass spectrometer conditions. We also assessed inter- and intraassay variation. RESULTS The assay uses either solid-phase or liquid-phase extraction before analysis by mass spectrometry. An evaluation of blood spots from 90 randomly chosen healthy newborns and 9 patients with Morquio A syndrome showed a well-defined interval between their respective enzyme activities. Inter- and intraassay imprecision was <10%. CONCLUSIONS This tandem mass spectrometry assay requires a minimal number of sample-preparation steps, thus making it easy to implement. The assay has the potential to be adopted for early diagnosis of Morquio A syndrome. We believe this assay could be performed in a multiplex fashion with assays for other lysosomal enzymes.

Ten-year outcome of enzyme replacement therapy with agalsidase beta in patients with Fabry disease

Background Fabry disease results from deficient α-galactosidase A activity and globotriaosylceramide accumulation causing renal insufficiency, strokes, hypertrophic cardiomyopathy and early demise. We assessed the 10-year outcome of recombinant α-galactosidase A therapy. Methods The outcomes (severe clinical events, renal function, cardiac structure) of 52/58 patients with classic Fabry disease from the phase 3 clinical trial and extension study, and the Fabry Registry were evaluated. Disease progression rates for patients with low renal involvement (LRI, n=32) or high renal involvement (HRI, n=20) at baseline were assessed. Results 81% of patients (42/52) did not experience any severe clinical event during the treatment interval and 94% (49/52) were alive at the end of the study period. Ten patients reported a total of 16 events. Patients classified as LRI started therapy 13 years younger than HRI (mean 25 years vs 38 years). Mean slopes for estimated glomerular filtration rate for LRI and HRI were −1.89 mL/min/1.73 m2/year and −6.82 mL/min/1.73 m2/year, respectively. Overall, the mean left ventricular posterior wall thickness and interventricular septum thickness remained unchanged and normal. Patients who initiated treatment at age ≥40 years exhibited significant increase in left ventricular posterior wall thickness and interventricular septum thickness. Mean plasma globotriaosylceramide normalised within 6 months. Conclusions This 10-year study documents the effectiveness of agalsidase beta (1 mg/kg/2 weeks) in patients with Fabry disease. Most patients remained alive and event-free. Patients who initiated treatment at a younger age and with less kidney involvement benefited the most from therapy. Patients who initiated treatment at older ages and/or had advanced renal disease experienced disease progression.

Individualization of long-term enzyme replacement therapy for Gaucher disease

Gaucher disease, the most common lysosomal storage disorder, is a heterogeneous condition affecting multiple organ systems. Patients with nonneuronopathic (type 1) Gaucher disease may suffer from hepatomegaly, splenomegaly, thrombocytopenia, bleeding tendencies, anemia, hypermetabolism, skeletal pathology, growth retardation, pulmonary disease, and decreased quality of life. Enzyme replacement therapy (ERT) with mannose-terminated glucocerebrosidase (imiglucerase, Cerezyme, Genzyme Corporation, Cambridge, MA) reverses or ameliorates many of the manifestations of type 1 Gaucher disease. However, due to the variable pattern and severity of disease, and the uncertain manner of progression, implementation of treatment, choice of initial and maintenance imiglucerase dose, and evaluation of the therapeutic response must be tailored to the individual patient. For the past 14 years, the US Regional Coordinators of the International Collaborative Gaucher Group have individually and collectively developed extensive clinical experience in managing patients with Gaucher disease. In this review, we present recommendations for initial imiglucerase treatment and subsequent dose adjustments based on a schedule of regular assessment and monitoring, and achievement and maintenance of defined therapeutic goals.