Faculty Bibliography

The exponential expansion of the publicly available human DNA sequence database has increasingly facilitated cloning by homology of genes for biochemically defined, functionally similar proteins. We hypothesized that an as-yet uncloned human alpha-glucosidase (human neutral alpha-glucosidase C or GANC) is a previously uncharacterized member of a paralogous human glycosyl hydrolase gene family 31, sharing sequence homology and related, but not identical, functions with other cloned human alpha-glucosidases. We now report both the in silico and physical cloning of two alleles of human neutral alpha-glucosidase (designated GANC on the human gene map). This cloning and correct identification and annotation as GANC was successful only because of the application of the biochemical and genetic information we had previously developed regarding this gene to the results of the in silico method. Of note, this glucosidase, a member of family 31 glycosyl hydrolases, has multiple alleles, including a 'null' allele and is potentially significant because it is involved in glycogen metabolism and localizes to a chromosomal region (15q15) reported to confer susceptibility to diabetes

Purine nucleoside phosphorylase (PNP) deficiency results in an autosomal recessive immunodeficiency disease characterized by initial involvement of cellular immunity and neurological manifestations with subsequent abnormalities of humoral immunity. The initial presentation and clinical course has varied widely in the relatively few published cases. The molecular basis has been reported in only 10 patients, precluding evaluation of phenotype-genotype relationships. We now report clinical, immunologic, and molecular findings in a new case of relatively early onset that emphasizes hypotonia and developmental delay as early manifestations. The patient carried two novel missense mutations (Gly56A1a and Val217Ile) on the same allele in apparent homozygosity. Expression of each of the mutant enzymes in vitro demonstrated that the Gly156A1a mutation abolished enzyme activity while the Val217Ile mutation was without obvious effect and is therefore a normal variant. Such 'normal' polymorphisms might be associated with a variable response to the immunosuppressive PNP inhibitors currently in clinical trials

Current methods for detection of mutations by polymerase chain reaction (PCR) and sequence analysis frequently are not able to detect heterozygous large deletions. We report the successful use of a novel approach to identify such deletions, based on detection of apparent homozygosity of contiguous single-nucleotide polymorphisms (SNPs). The sequence analysis of genomic DNA PCR products containing all coding exons and flanking introns identified only a single heterozygous mutation (IVS18+2t-->a) in a patient with classic infantile-onset autosomal recessive glycogen storage disease type II (GSDII). Apparent homozygosity for multiple contiguous SNPs detected by this sequencing suggested presence of a large deletion as the second mutation; primers flanking the region of homozygous SNPs permitted identification and characterization by PCR of a large genomic deletion (8.26 kb) extending from IVS7 to IVS15. The data clearly demonstrate the utility of SNPs as markers for large deletions in autosomal recessive diseases when only a single mutation is found, thus complementing currently standard DNA PCR sequence methods for identifying the molecular basis of disease

Glycogen storage disease type II is an autosomal recessive muscle disorder due to deficiency of lysosomal acid alpha-glucosidase and the resulting intralysosomal accumulation of glycogen. We found six novel mutations in three Spanish classic infantile onset glycogen storage disease type II patients with involvement of both cardiac and skeletal muscle; three missense mutations (G219R, E262K, M408V), a nonsense mutation (Y191X), a donor splice site mutation (IVS18 +2gt>ga) and an in frame deletion of an asparagine residue (nt1408-1410). The missense mutations were not found in 100 normal chromosomes and therefore are not normal polymorphic variants. The splice site mutation was subsequently detected in an additional 'Spanish' infantile onset glycogen storage disease type II patient from El Salvador. Further studies will be required to determine if the IVS18 +2gt>ga splice site mutation might in fact be a relatively common Spanish mutation. Mutations among Spanish glycogen storage disease type II patients appear to be genetically heterogeneous and differ from common mutations in neighboring countries

We recently described the incidence of a SCID disease in a litter of Jack Russell terriers. In this study, we show that the molecular defect in these animals is faulty V(D)J recombination. Furthermore, we document a complete deficit in DNA-dependent protein kinase activity that can be explained by a marked diminution in the expression of the catalytic subunit DNA-dependent protein kinase catalytic subunit (DNA-PKcs). We conclude that as is the case in C.B-17 SCID mice and in Arabian SCID foals, the defective factor in these SCID puppies is DNA-PKcs. In mice, it has been clearly established that DNA-PKcs deficiency produces an incomplete block in V(D)J recombination, resulting in 'leaky' coding joint formation and only a modest defect in signal end ligation. In contrast, DNA-PKcs deficiency in horses profoundly blocks both coding and signal end joining. Here, we show that although DNA-PKcs deficiency in canine lymphocytes results in a block in both coding and signal end joining, the deficit in both is intermediate between that seen in SCID mice and SCID foals. These data demonstrate significant species variation in the absolute necessity for DNA-PKcs during V(D)J recombination. Furthermore, the severity of the V(D)J recombination deficits in these three examples of genetic DNA-PKcs deficiency inversely correlates with the relative DNA-PK enzymatic activity expressed in normal fibroblasts derived from these three species

Pompe disease is a lethal cardioskeletal myopathy in infants and results from genetic deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA). Genetic replacement of the cDNA for human GAA (hGAA) is one potential therapeutic approach. Three months after a single intramuscular injection of 10(8) plaque-forming units (PFU) of E1-deleted adenovirus encoding human GAA (Ad-hGAA), the activity in whole muscle lysates of immunodeficient mice is increased to 20 times the native level. Direct transduction of a target muscle, however, may not correct all deficient cells. Therefore, the amount of enzyme that can be transferred to deficient cells from virally transduced cells was studied. Fibroblasts from an affected patient were transduced with AdhGAA, washed, and plated on transwell culture dishes to serve as donors of recombinant enzyme. Deficient fibroblasts were plated as acceptor cells, and were separated from the donor monolayer by a 22-microm pore size filter. Enzymatic and Western analyses demonstrate secretion of the 110-kDa precursor form of hGAA from the donor cells into the culture medium. This recombinant, 110-kDa species reaches the acceptor cells, where it can be taken up by mannose 6-phosphate receptor-mediated endocytosis. It then trafficks to lysosomes, where Western analysis shows proteolytic processing to the 76- and 70-kDa lysosomal forms of the enzyme. Patient fibroblasts receiving recombinant hGAA by this transfer mechanism reach levels of enzyme activity that are comparable to normal human fibroblasts. Skeletal muscle cell cultures from an affected patient were also transduced with Ad-hGAA. Recombinant hGAA is identified in a lysosomal location in these muscle cells by immunocytochemistry, and enzyme activity is transferred to deficient skeletal muscle cells grown in coculture. Transfer of the precursor protein between muscle cells again occurs via mannose 6-phosphate receptors, as evidenced by competitive inhibition with 5 mM mannose 6-phosphate. In vivo studies in GAA-knockout mice demonstrate that hepatic transduction with adenovirus encoding either murine or human GAA can provide a depot of recombinant enzyme that is available to heart and skeletal muscle through this mechanism. Taken together, these data show that the mannose 6-phosphate receptor pathway provides a useful strategy for cell-to-cell distribution of virally derived recombinant GAA

We screened 22 Japanese patients with acid maltase deficiency (seven with the infantile type, eight with the juvenile type and seven with the adult type) for three previously described mutations, D645E, S529V and R672Q, and a novel mutation, R600C. Although D645E has been reported to be common in Chinese patients with the infantile type, only three of 44 alleles (two of 14 infantile type alleles) from Japanese patients harbored the D645E mutation. The S529V mutation was identified in six of 14 alleles from adult-onset patients. None of the infantile or juvenile patients harbored the S529V mutation. Therefore, S529V apparently results in the adult type disease and is common in Japanese adult-onset patients. R672Q was identified in two pairs of siblings with the juvenile type. A novel mutation, R600C, was identified in eight of 22 patients (nine of 44 alleles). Therefore, R600C is another common Japanese mutation occurring at a CpG dinucleotide 'hot spot'. Homozygosity for this mutation apparently results in the infantile phenotype. Genetic diagnosis by detecting these four mutations might be feasible for most Japanese patients with acid maltase deficiency

Genetic deficiency of lysosomal acid alpha-glucosidase (acid maltase) results in the autosomal recessive disorder glycogen storage disease type II (GSDII) in which intralysosomal accumulation of glycogen primarily affects function of skeletal and cardiac muscle. During an earlier review we noted 3 in 100 cases of GSDII with incidental description of cleft lip. In addition, we identified 2 of 35 GSDII patients referred to us for molecular studies with co-occurence of cleft lip, considerably greater than the estimated frequency of nonsyndromic cleft lip with or without cleft palate of 1 in 700 to 1,000. Because several lines of evidence support a minor cleft lip/palate (Cl/P) locus on chromosome 17q close to the locus for GSDII, we defined the molecular basis for the GSDII in these two patients to determine if they represented a contiguous gene syndrome. Patient I (of Dutch descent) was homozygous and the parents heterozygous for an intragenic deletion of exon 18 (deltaex18), common in Dutch patients. Patient II was heterozygous for delta525T, a mutation also common in Dutch patients and a novel nonsense mutation (172 [corrected] C-->T; Gln58Stop) in exon 2, the first coding exon. The mother was heterozygous for the delta525T and the father for the 172 [corrected] C-->T; Gln58Stop. The finding that both patients carried intragenic mutations eliminates a contiguous gene syndrome. Whereas the presence of cleft lip/cleft palate in a patient with GSDII could be coincidental, these co-occurences could represent a modifying action of acid alpha-glucosidase deficiency on unlinked or linked genes that result in increased susceptibility for cleft lip

Acid alpha-glucosidase (GAA) cleaves the alpha1-4 and alpha1-6 glycosidic linkages of glycogen and related alpha-glucosyl substrates within lysosomes. Its deficiency results in glycogen storage disease type II (GSDII) variants including Pompe disease. To gain insight into the tissue patterns of involvement by glycogen storage in GSDII, GAA mRNA expression in mouse tissues was evaluated by Northern blot and in situ hybridization analyses. Extensive temporal and spatial variation of GAA mRNA was observed. During preterm maturation, GAA mRNA levels of whole mice progressively increased as assessed by Northern analysis. By in situ hybridization with GAA antisense mRNA, low signals were detected in most tissues throughout gestation. However, increased expression in specific cell types of different tissues was observed beginning at 16 days post coitum in developing brain neurons, primitive inner ear cells, and seminiferous tubular epithelium. In adult mice, whole-organ GAA mRNA levels were highest in brain, moderate in heart, liver, and skeletal muscle, and lowest in the series kidney > lung > testis > spleen. By in situ hybridization, the highest-intensity signals were in neurons of the central and peripheral nervous systems whereas neuroglial cells had only low-level signal. Signals of moderate intensity were in cardiomyocytes whereas low signals were in hepatocytes and skeletal muscle myocytes and very low in cells of the lungs, thymus, pancreas, spleen, and adrenal glands. However, testicular Sertoli cells and kidney tubular epithelial cells had significant signals even though surrounding cells had very low signals. The discrete temporal and spatial variations of GAA mRNA during development indicate different physiological roles for this enzyme in various cell types and developmental stages

Some recent publications indicate that inherited disorders can ameliorate or possibly disappear if mutations responsible for the disease revert to normal. This review tries to summarize our current knowledge about reverse mutations as this information may be of special interest for attempts at somatic gene therapy.