Psychosine, a marker of Krabbe phenotype and treatment effect.

Newborn screening (NBS) for Krabbe disease, a rare neurodegenerative disorder caused by deficient galactocerebrosidase (GALC) enzyme activity, has recently been implemented in a number of US states. However, the spectrum of phenotypic manifestations associated with deficient GALC activity complicates the management of screen-positive newborns and underscores the need to identify clinically relevant biomarkers. Earlier studies with a small number of patients identified psychosine, a substrate of the GALC enzyme, as a potential biomarker for Krabbe disease. In this study, we provide, for the first time, longitudinal data on dried blood spot (DBS) psychosine concentrations in different Krabbe disease phenotypes for both untreated patients and those treated with hematopoietic stem cell transplantation (HSCT). Our cohort included patients previously identified by NBS to be at high risk to develop Krabbe disease. Substantially elevated DBS psychosine concentration during the newborn period was found to be a highly specific marker for infantile Krabbe disease. This finding supports the use of DBS psychosine concentration as a second-tier NBS test to aid in the identification of patients who require urgent evaluation for HSCT. In addition, longitudinal assessments showed that both natural disease progression and treatment with HSCT were associated with decreases in DBS psychosine concentrations. Based on these findings we provide recommendations for the interpretation of psychosine concentrations in DBS specimens collected during the first year of life. Future studies should aim to better delineate the relationship between DBS psychosine concentration and disease onset in patients with later-onset forms of Krabbe disease.

Thiopurine methyltransferase screening before azathioprine prescription: a physician survey.

BACKGROUND: In patients treated with azathioprine, deficient thiopurine methyltransferase (TPMT) activity has been associated with haematologic toxicity. OBJECTIVES: To determine how many Saskatchewan rheumatologists routinely pre-screen TPMT activity before prescribing azathioprine. Further, to retrospectively review TPMT activity levels from pre-screening in one patient cohort. METHODS: All rheumatologists practicing in the province of Saskatchewan were surveyed by questionnaire. The questionnaire scrutinized prevalence of routine TPMT screening pre-azathioprine initiation, response to abnormal test results, monitoring frequencies, starting dosages, and attitudes towards potential consensus guidelines or practice standards. For the second objective of this study, health region laboratory database retrieval identified 42 patients who had undergone TPMT phenotype testing within a single rheumatology practice. Chart review of all 42 patients was performed to verify test results. RESULTS: In a survey of all eleven Saskatchewan rheumatologists, 55% reported routinely pre-screening, compared to 45% who never screen pre-azathioprine. Half of those who pre-screen, report avoidance of azathioprine in both patients with deficiency and those with intermediate activity levels. The majority of respondents indicated they would adjust their practice to conform to future national rheumatology clinical guidelines. A retrospective review in one practice revealed TPMT activity values consistent with deficiency, carrier status, and normal ranges in 2.4%, 21.4%, and 76.2% of patients pre-screened, respectively. CONCLUSIONS: Provincial rheumatologists were divided on the practice of pre-screening TPMT status prior to initiation of azathioprine. Azathioprine may be underutilized by half of those who pre-screen. A need for practice guidelines was recognized by the participants. In this patient group, diminished TPMT activity was observed in 23.8% of those who were tested.

Reduction of the false-positive rate in newborn screening by implementation of MS/MS-based second-tier tests: the Mayo Clinic experience (2004-2007).

The continued expansion of newborn screening programmes to include additional conditions increases the responsibility of newborn screening laboratories to provide testing with the highest sensitivity and specificity to allow for identification of affected patients while minimizing the false-positive rate. Some assays and analytes are particularly problematic. Over recent years, our laboratory tried to improve this situation by developing second-tier tests to reduce false-positive results in the screening for congenital adrenal hyperplasia (CAH), tyrosinaemia type I, methylmalonic acidaemias, homocystinuria, and maple syrup urine disease (MSUD). Beginning in 2004, this approach was applied to Mayo's newborn screening programme and resulted in a false-positive rate of 0.09%, a positive predictive value of 41%, and a positive detection rate of 1 affected case in 1672 babies screened.

FH-Freiburg: a novel missense mutation (C317Y) in growth factor repeat A of the low density lipoprotein receptor gene in a German patient with homozygous familial hypercholesterolemia.

We describe the characterization of a novel mutation in the low density lipoprotein receptor (LDL-R) gene in a patient with true homozygous familial hypercholesterolemia (FH). The combined use of denaturing gradient gel electrophoresis (DGGE) and sequencing of genomic DNA revealed a guanine to adenine base substitution at nucleotide position 1013 of the LDL-R cDNA. This point mutation results in a change from cysteine to tyrosine at amino acid residue 317 of repeat A of the epidermal growth factor (EGF) precursor homology domain. Binding, uptake and degradation of iodinated LDL in skin fibroblasts from the homozygous patient were less than 10% of normal. In contrast, binding, uptake and degradation of iodinated VLDL was reduced by only 60, 30, and 38%, respectively. Incubation of the patient's fibroblasts in the presence of cholesterol diminished the residual binding of VLDL by 50%, suggesting that the loss of the highly conserved cysteine at position 317 results in a LDL-R that fails to bind LDL, but retains some ability to bind VLDL by interacting with the apolipoprotein E. Both parents were heterozygous for the C317Y mutation. Interestingly, however, the father presented with markedly elevated levels of triglycerides and VLDL cholesterol, whereas his LDL cholesterol was unexpectedly low. The mother of the index patient had only slightly elevated LDL cholesterol. These observations testify to the biological complexity of genotype-environment interactions in individuals carrying mutations at the LDL-R locus and indicate that genetic analysis importantly complements the clinical and biochemical diagnosis of patients with hyperlipidemia.

Molecular genetic analysis of 40 patients with glycogen storage disease type Ia: 100% mutation detection rate and 5 novel mutations.

Molecular genetic analysis of 40 patients with glycogen storage disease type Ia (GSD Ia) revealed mutations on all 80 alleles and verified the diagnosis in all patients. At least 7 patients were diagnosed with GSD Ia solely on the basis of clinical findings prior to our analysis. Five mutations, Q20R, W50X, G81R, W156L, and G188D have not been reported so far. This study underscores that molecular genetic analysis is a reliable and convenient alternative to the enzyme assay in a fresh liver biopsy specimen to diagnose GSD Ia.

Liver transplantation for glycogen storage disease types I, III, and IV.

UNLABELLED: Glycogen storage disease (GSD) types I, III, and IV can be associated with severe liver disease. The possible development of hepatocellular carcinoma and/or hepatic failure make these GSDs potential candidates for liver transplantation. Early diagnosis and initiation of effective dietary therapy have dramatically improved the outcome of GSD type I by reducing the incidence of liver adenoma and renal insufficiency. Nine type I and 3 type III patients have received liver transplants because of poor metabolic control, multiple liver adenomas, or progressive liver failure. Metabolic abnormalities were corrected in all GSD type I and type III patients, while catch-up growth was reported only in two patients. Whether liver transplantation results in reversal and/or prevention of renal disease remains unclear. Neutropenia persisted in both GSDIb patients post liver transplantation necessitating continuous granulocyte colony stimulating factor treatment. Thirteen GSD type IV patients were liver transplanted because of progressive liver cirrhosis and failure. All but one patient have not had neuromuscular or cardiac complications during follow-up periods for as long as 13 years. Four have died within a week and 5 years after transplantation. Caution should be taken in selecting GSD type IV candidates for liver transplantation because of the variable phenotype, which may include life-limiting extrahepatic manifestations. It remains to be evaluated, whether a genotype-phenotype correlation exists for GSD type IV, which may aid in the decision making. CONCLUSION: Liver transplantation should be considered for patients with glycogen storage disease who have developed liver malignancy or hepatic failure, and for type IV patients with the classical and progressive hepatic form.