BACKGROUND Congenital disorders of glycosylation are genetic syndromes that result in impaired glycoprotein production. We evaluated patients who had a novel recessive disorder of glycosylation, with a range of clinical manifestations that included hepatopathy, bifid uvula, malignant hyperthermia, hypogonadotropic hypogonadism, growth retardation, hypoglycemia, myopathy, dilated cardiomyopathy, and cardiac arrest. METHODS Homozygosity mapping followed by whole-exome sequencing was used to identify a mutation in the gene for phosphoglucomutase 1 (PGM1) in two siblings. Sequencing identified additional mutations in 15 other families. Phosphoglucomutase 1 enzyme activity was assayed on cell extracts. Analyses of glycosylation efficiency and quantitative studies of sugar metabolites were performed. Galactose supplementation in fibroblast cultures and dietary supplementation in the patients were studied to determine the effect on glycosylation. RESULTS Phosphoglucomutase 1 enzyme activity was markedly diminished in all patients. Mass spectrometry of transferrin showed a loss of complete N-glycans and the presence of truncated glycans lacking galactose. Fibroblasts supplemented with galactose showed restoration of protein glycosylation and no evidence of glycogen accumulation. Dietary supplementation with galactose in six patients resulted in changes suggestive of clinical improvement. A new screening test showed good discrimination between patients and controls. CONCLUSIONS Phosphoglucomutase 1 deficiency, previously identified as a glycogenosis, is also a congenital disorder of glycosylation. Supplementation with galactose leads to biochemical improvement in indexes of glycosylation in cells and patients, and supplementation with complex carbohydrates stabilizes blood glucose. A new screening test has been developed but has not yet been validated. (Funded by the Netherlands Organization for Scientific Research and others.)

Purpose: To examine the enzyme kinetics of gefitinib and erlotinib metabolism by individual cytochrome P450 (CYP) enzymes, and to compare their effects on CYP3A activity, with the aim to better understand mechanisms underlying pharmacokinetic variability and clinical effects. Experimental Design: Enzyme kinetics were examined by incubating gefitinib or erlotinib (1.5-50 Amol/L) with recombinant human CYP3A4, CYP3A5, CYP2D6, CYP1A1, CYP1A2, and CYP1B1 (10-160 pmol/mL). Their effects on CYP3A activity were examined by comparing midazolam metabolism in the presence and absence of gefitinib or erlotinib in human liver and intestinal microsomes. Parent compounds and metabolites were monitored by high-performance liquid chromatography with a photodiode detector or tandem mass spectrometer. Results: Both drugs were metabolized primarily by CYP3A4, CYP3A5, and CYP1A1, with respective maximum clearance (Cl max ) values for metabolism of 0.41, 0.39, and 0.57 mL/min/nmol for gefitinib and 0.24, 0.21, 0.31 mL/min/nmol for erlotinib. CYP2D6 was involved in gefitinib metabolism (Cl max , 0.63 mL/min/nmol) to a large extent, whereas CYP1A2 was considerably involved in erlotinib metabolism (Cl max , 0.15 mL/min/nmol). Both drugs stimulated CYP3A-mediated midazolam disappearance and 1-hydroxymidazolam formation in liver and intestinal microsomes. Conclusions: Gefitinib is more susceptible to CYP3A-mediated metabolism than erlotinib, which may contribute to the higher apparent oral clearance observed for gefitinib. Metabolism by hepatic and extrahepatic CYP1A may represent a determinant of pharmacokinetic variability and response for both drugs. The differential metabolizing enzyme profiles suggest that there may be differences in drug-drug interaction potential and that stimulation of CYP3A4 may likely play a role in drug interactions for erlotinib and gefitinib.Gefitinib and erlotinib are orally bioavailable synthetic anilinoquinazolines that selectively and reversibly bind to the intracellular ATP-binding site of the epidermal growth factor receptor (EGFR) tyrosine kinase, and have shown activity in patients with non -small-cell lung cancer (1). Gefitinib and erlotinib share a common chemical backbone structure and exhibit similar disposition characteristics in humans after oral administration (1). They are reported to have similar oral bioavailability (f60%; refs. 2, 3) and undergo extensive metabolism primarily by cytochrome P450 (CYP) 3A4 (4, 5), with >80% of the administered dose excreted in feces (4, 6). Both drugs are associated with wide interindividual pharmacokinetic variability in cancer patients (7,8). Administration of erlotinib at the maximum tolerated dose (MTD) and approved dose of 150 mg once daily achieved an approximate 3.5-fold higher steady-state plasma trough concentration than gefitinib administered at the recommended dose but approximately one third the MTD, of 250 mg once daily (1.5 versus 0.41 Ag/mL; refs. 7, 9). As food intake has been shown to increase erlotinib bioavailability to f100% (1),...

Purpose The endoplasmic reticulum-associated degradation (ERAD) pathway is responsible for the translocation of misfolded proteins across the ER membrane into the cytosol for subsequent degradation by the proteasome. In order to understand the spectrum of clinical and molecular findings in a complex neurological syndrome, we studied a series of eight patients with inherited deficiency of N-glycanase 1 (NGLY1), a novel disorder of cytosolic ERAD dysfunction. Methods Whole-genome, whole-exome or standard Sanger sequencing techniques were employed. Retrospective chart reviews were performed in order to obtain clinical data. Results All patients had global developmental delay, a movement disorder, and hypotonia. Other common findings included hypo- or alacrima (7/8), elevated liver transaminases (6/7), microcephaly (6/8), diminished reflexes (6/8), hepatocyte cytoplasmic storage material or vacuolization (5/6), and seizures (4/8). The nonsense mutation c.1201A>T (p.R401X) was the most common deleterious allele. Conclusions NGLY1 deficiency is a novel autosomal recessive disorder of the ERAD pathway associated with neurological dysfunction, abnormal tear production, and liver disease. The majority of patients detected to date carry a specific nonsense mutation that appears to be associated with severe disease. The phenotypic spectrum is likely to enlarge as cases with a more broad range of mutations are detected.

Bupropion is primarily metabolized in human liver by cytochrome P450 (CYP) 2B6, an isoform that shows high interindividual variability in expression and catalysis. The aim of this study was to identify mechanisms underlying this variability through comprehensive phenotype-genotype analysis of a well-characterized human liver bank (n = 54). There was substantial variability in microsomal bupropion hydroxylation activities (over 45-fold) and CYP2B6 protein content (over 288-fold), with excellent correlation between protein and activity values (rs = 0.88). CYP2B6 mRNA levels showed less variability (13-fold) and poorer correlation (rs = 0.44) to CYP2B6 protein resulting from 20-30% of livers that contained substantial CYP2B6 mRNA, but low CYP2B6 protein. Livers were genotyped for the common coding polymorphisms (Q172H, K262R and R487C) and 14 additional variations identified by sequencing of the gene promoter to -3000 bp. Of 14 haplotypes that were inferred, *1A (reference), *1H (-2320t>c; -750t>c) and *6B (-1456t>c; -750t>c; Q172H; K262R) were most common with frequencies of 0.28, 0.20 and 0.26, respectively. Alcohol use history (P = 0.011) and *6B haplotype (P = 0.011) were identified as significant predictors of bupropion hydroxylation. A consideration of the effects of these variables on CYP2B6 mRNA and protein levels suggests that alcohol use is associated with enhanced CYP2B6 gene transcription, but the presence of at least one *6B allele reduces this effect on bupropion hydroxylation at the post-transcriptional level. In conclusion, the results of this study indicate that interindividual variability in bupropion hydroxylation is a consequence of interactions between environmental and genetic influences on CYP2B6 gene function.