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Biomedical subjects

C P Morris

Publications and source records attributed to C P Morris.

At least 37 records · Page 2Linked to original sources
PubMed1994

Molecular genetics of metachromatic leukodystrophy.

Metachromatic leukodystrophy is an autosomal recessive inherited lysosomal storage disease. It can be caused by mutations in two different genes, the arylsulfatase A and the prosaposin gene. These genes encode two proteins that are needed for the proper degradation of cerebroside sulfate, a glycolipid mainly found in the myelin membranes. Deficiency of arylsulfatase A or of a proteolytic product of prosaposin leads to the accumulation of cerebroside sulfate, which causes a lethal progressive demyelination. Mutations in the arylsulfatase A gene are far more frequent than those of the prosaposin gene. So far 31 amino acid substitutions, one nonsense mutation, three small deletions, three splice donor site mutations, and one combined missense/splice donor site mutation have been identified in the arylsulfatase A gene. Two of these mutant alleles are frequent, accounting for about one-half of all mutant alleles, whereas the remainder are heterogeneous. Amino acid substitutions cluster in exons 2 and 3, a region that shows a high degree of conservation among sulfatases of different function and origin. Different mutations are associated with phenotypes of different severity, but there is a remarkable variability of severity when patients with identical genotypes are compared. Demonstration of an arylsulfatase A deficiency is not a proof of metachromatic leukodystrophy, since a substantial deficiency without any clinical consequences is frequent in the general population. This deficiency is caused by an arylsulfatase A allele, which due to certain mutations encodes greatly reduced amounts of functional enzyme. However, these amounts are sufficient to sustain a normal phenotype. In the diagnosis and genetic counseling, these deficiencies must be differentiated from those causing metachromatic leukodystrophy. So far only six patients with mutations in the prosaposin gene have been described, in which three defective alleles two with amino acid substitutions and one with a 33-bp insertion have been identified.

Cerebroside-Sulfatase↗
PubMed1994

Morquio A syndrome: cloning, sequence, and structure of the human N-acetylgalactosamine 6-sulfatase (GALNS) gene.

Deficiency of the lysosomal enzyme, N-acetylgalactosamine 6-sulfatase (GALNS;EC 3.1.6.4), results in the storage of the glycosaminoglycans, keratan sulfate and chondroitin 6-sulfate, which leads to the lysosomal storage disorder Morquio A syndrome. Four overlapping genomic clones derived from a chromosome 16-specific gridded cosmid library containing the entire GALNS gene were isolated. The structure of the gene and the sequence of the exon/intron boundaries and the 5' promoter region were determined. The GALNS gene is split into 14 exons spanning approximately 40 kb. The potential promoter for GALNS lacks a TATA box but contains GC box consensus sequences, consistent with its role as a housekeeping gene. The GALNS gene contains an Alu repeat in intron 5 and a VNTR-like sequence in intron 6.

Base Sequence↗
PubMed1994

Mucopolysaccharidosis type I: identification of 8 novel mutations and determination of the frequency of the two common alpha-L-iduronidase mutations (W402X and Q70X) among European patients.

A group of 46 European patients with mucopolysaccharidosis type I (MPS I) was screened for mutations of the alpha-L-iduronidase gene. The 2 common nonsense mutations, W402X and Q70X, were identified in, respectively, 37% and 35% of mutant alleles. Considerable differences were seen in the frequency of these 2 mutations in patients from North Europe (Norway and Finland) and other European countries (mainly The Netherlands and Germany). In Scandinavia, W402X and Q70X account for 17% and 62% of the MPS I alleles, respectively, while in other European countries W402X is about 2.5 times more frequent (48%) than Q70X (19%). Eight novel mutations are described including 4 missense mutations, 1 nonsense mutation, 1 insertion of 2 base pairs, and 2 deletions of 1 and 12 base pairs.

Alleles↗
PubMed1993

An arylsulfatase A (ARSA) missense mutation (T274M) causing late-infantile metachromatic leukodystrophy.

Metachromatic leukodystrophy (MLD) is an autosomal recessive lysosomal storage disorder caused by a deficiency of arylsulfatase A (ARSA; EC 3.1.6.8). The 8 ARSA exons and adjacent intron boundaries from a patient with late-infantile metachromatic leukodystrophy were polymerase chain reaction (PCR) amplified in seven discrete reactions. Amplified ARSA exons were analysed for the presence of sequence alterations by single-strand conformation polymorphism analysis, followed by direct sequencing of PCR products. The patient was found to be homozygous for a C-->T transition in exon IV that results in the substitution of a highly conserved threonine residue at amino acid 274 with a methionine (T274M). Analysis of a further 29 MLD patients revealed the presence of five additional homozygotes for T274M. All 6 T274M homozygotes (representing four families) were of Lebanese descent, and all were known to be the result of consanguineous marriages. The altered amino acid is rigidly conserved among 10 sulfatases from Escherichia coli to humans; therefore, it is most likely that the resultant mutant protein will have little or no enzyme activity. This is consistent with the very low ARSA activity measured in these patients and their uniformly severe clinical presentation.

Amino Acid Sequence↗
PubMed1993

Molecular basis of mucopolysaccharidosis type II: mutations in the iduronate-2-sulphatase gene.

A number of mutations in the X-chromosomal human iduronate-2-sulphatase gene have now been identified as the primary genetic defect leading to the clinical condition known as Hunter syndrome or mucopolysaccharidosis type II. The mutations that are tabulated include different deletions, splice-site and point mutations. From the group of 319 patients thus far studied by Southern analysis, 14 have a full deletion of the gene and 48 have a partial deletion or other gross rearrangements. All patients with full deletions or gross rearrangements have severe clinical presentations. Twenty-nine different "small" mutations have so far been characterised in a total of 32 patients. These include 4 nonsense and 13 missense mutations, 7 different small deletions from 1 to 3 bp, with most leading to a frameshift and premature chain termination, and 5 different splice-site mutations also leading to small insertions or deletions in the mRNA. A 60 bp deletion, that results from a new donor splice-site, has been observed in five unrelated patients with relatively mild clinical phenotypes. This information will not only be useful for MPS II patient and carrier diagnosis, but also will aid in the understanding of the structure and function of iduronate-2-sulphatase, and possibly in correlating genotype with phenotype.

Gene Deletion↗
PubMed1993

Sequence of the human iduronate 2-sulfatase (IDS) gene.

Deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS; EC 3.1.6.13) results in the storage of the glycosaminoglycans heparan sulfate and dermatan sulfate, which leads to the lysosomal storage disorder mucopolysaccharidosis type II. Three overlapping genomic clones derived from an X-chromosome-specific library containing the entire IDS gene were isolated and the sequences of the intron boundaries and the 5' promoter region were determined. The IDS gene is split into nine exons spanning approximately 24 kb. The potential promoter for IDS lacks a TATA box but contains GC box consensus sequences, consistent with its role as a housekeeping gene. A polypyrimidine-like repeat is found in intron 1.

Base Sequence↗
PubMed1993

Long-term clinical progress in bone marrow transplanted mucopolysaccharidosis type I patients with a defined genotype.

Two mucopolysaccharidosis type I (MPS-I) patients, subjected to bone marrow transplantation (BMT) more than 10 years ago, have recently had their alpha-L-iduronidase genotypes defined. Both patients, homozygous for the relatively common W402X mutation, received BMT when they were 14 and 11 months of age, and are now 12 and 14 years old, respectively. Untreated MPS-I patients, homozygous for W402X, have an extremely severe clinical phenotype with rapid clinical deterioration and death before 6 years of age. The 12-year-old patient, with limited mobility, is coping well at school, while the other patient is wheelchair-bound with severe disability in his lower limbs, and attends a school for the physically handicapped. Both patients have less than normal intelligence with slowly continuing losses. A third MPS-I patients, diagnosed at the age of 6 months, was felt, prior to BMT at 14 months, to have a severe phenotype. Twelve years post-BMT, he is ambulatory, albeit with restricted movement, and has normal intelligence. This patient did not have a defined MPS-I genotype and had alpha-L-iduronidase protein and activity consistent with a less severe outcome than the first two patients. We conclude that BMT has significantly slowed down the clinical regression of the W402X phenotype. We propose that if further gains are to be made, BMT should be performed within the first few months of life. Early diagnosis is therefore essential.

Adolescent↗
PubMed1993

Iduronate-2-sulfatase gene mutations in 16 patients with mucopolysaccharidosis type II (Hunter syndrome).

Mutations of the iduronate-2-sulfatase gene were identified in 16 patients with mucopolysaccharidosis type II (Hunter syndrome). Together with another 10 cases reported by us earlier it emerges that about 20% of the patients have deletions of the whole gene or other major structural alterations. One, two or three base pair deletions are found in about 23% of the cases while the remaining about 57% carry point mutations predicting amino acid replacement, premature termination of translation, or aberrant splicing. Molecular analysis of mRNA in splice site mutants showed that these latter defects frequently resulted in use of cryptic splice sites in exons or introns. 62% of the small deletions and point mutations have occurred in 3 of the 9 iduronate-2-sulfatase gene exons. Knowledge of the primary genetic defect allows fast and reliable carrier detection and prenatal diagnosis as well as insight into the relationship between genotype and phenotype.

Amino Acid Sequence↗
PubMed1993

Identification of mutations in the alpha-L-iduronidase gene (IDUA) that cause Hurler and Scheie syndromes.

Mucopolysaccharidosis type I (MPS-I) is an autosomal recessive genetic disease caused by a deficiency of the lysosomal glycosidase alpha-L-iduronidase. Hurler (severe), Scheie (mild), and Hurler/Scheie (intermediate) syndromes are clinical subtypes of MPS-I, but it is difficult to distinguish between these subtypes by biochemical measurements. Mutation analysis was undertaken to provide a molecular explanation for the clinical variation seen in MPS-I. Using chemical cleavage and direct PCR sequencing, we have defined four previously undescribed mutations for MPS-I (delG1702, 1060 + 2t-->c, R89Q, and 678-7g-->a). R89Q and 678-7g-->a were found to be present in 40% of Scheie syndrome alleles. Expression of R89Q demonstrated reduced stability and activity of the mutant protein. The deleterious effect of R89Q may be potentiated by a polymorphism (A361T) to produce an intermediate phenotype. 678-7g-->a was found to be a mild mutation, since it was present in an index Scheie syndrome patient in combination with a severe allele (W402X). This mutation appears to allow a very small amount of normal mRNA to be produced from the allele which is likely to be responsible for the mild clinical phenotype observed. Both the 5' and 3' splice site mutations (1060 + 2t-->c and 678-7g-->a, respectively) result in high proportions of mature mRNAs containing introns, which has not been observed for other splicing mutations. The frameshift mutation (delG1702) and the 5' splice site mutation (1060 + 2t-->c) are both thought to be associated with severe MPS-I. The identification of these MPS-I mutations begins to document the expected genetic heterogeneity in MPS-I and provides the first molecular explanations for the broad range of clinical phenotypes observed.

Animals↗
PubMed1993

The morquio A syndrome (mucopolysaccharidosis IVA) gene maps to 16q24.3.

The gene for N-acetylgalactosamine-6-sulfatase, the deficiency of which results in Morquio A syndrome (mucopolysaccharidosis type IVA), was assigned to chromosome 16 at band q24.3 by fluorescence in situ hybridization. Localization of this band was confirmed by PCR analysis of a somatic cell hybrid panel used for fine mapping of chromosome 16.

Animals↗
PubMed1992

A cDNA clone for human glucosamine-6-sulphatase reveals differences between arylsulphatases and non-arylsulphatases.

Glucosamine-6-sulphatase is an exo-hydrolase required for the lysosomal degradation of heparan sulphate and keratan sulphate. Deficiency of glucosamine-6-sulphatase activity leads to the lysosomal storage of the glycosaminoglycan, heparan sulphate and the monosaccharide sulphate N-acetylglucosamine 6-sulphate and the autosomal recessive genetic disorder mucopolysaccharidosis type IIID. Glucosamine-6-sulphatase can be classified as a non-arylsulphatase since, relative to arylsulphatase B, it shows negligible activity toward 4-methylumbelliferyl sulphate. We have isolated human cDNA clones and derived amino acid sequence coding for the entire glucosamine-6-sulphatase protein. The predicted sequence has 552 amino acids with a leader peptide of 36 amino acids and contains 13 potential N-glycosylation sites, of which it is likely that 10 are used. Glucosamine-6-sulphatase shows strong sequence similarity to other sulphatases such as the family of arylsulphatases, although the degree of similarity is not as high as that between members of the arylsulphatase family. This pattern of inter- and intra-family similarity delineates regions and amino acid residues that may be critical for sulphatase function and substrate specificity.

Amino Acid Sequence↗
PubMed1992

A common mutation for mucopolysaccharidosis type I associated with a severe Hurler syndrome phenotype.

Mucopolysaccharidosis type I (MPS-I) is an autosomal recessive genetic disease caused by a deficiency of the glycosidase alpha-L-iduronidase which is required for the lysosomal degradation of the glycosaminoglycans heparan sulfate and dermatan sulfate. Patients with MPS-I store these partially degraded glycosaminoglycans in their lysosomes. MPS-I patients have a wide range of clinical presentations, that makes it difficult to predict patient phenotype which is needed for genetic counselling and also impedes the selection and evaluation of patients undergoing therapy such as bone marrow transplantation. We report the presence of a common mutation accounting for 31% of MPS-I alleles in a study of 64 MPS-I patients. The mutation was originally detected by chemical cleavage and then direct PCR sequencing. The mutation is a single base substitution that introduces a stop codon at position 402 (W402X) of the alpha-L-iduronidase protein and is associated with an extremely severe clinical phenotype in homozygotes. Patients who are compound heterozygotes having one allele carrying the W402X mutation have a wide range of clinical phenotypes. Based on polymorphisms within the alpha-L-iduronidase gene, W402X is associated with three different haplotypes, implying that there is more than one origin for the mutation or that intragenic recombination has occurred. W402X introduces a MaeI restriction endonuclease site into MPS-I alleles enabling its simple detection, which should make possible the assessment of the efficacy of bone marrow transplantation in MPS-I patients homozygous for W402X.

Alleles↗
PubMed1992

alpha-L-iduronidase mutations (Q70X and P533R) associate with a severe Hurler phenotype.

Mucopolysaccharidosis type I (MPS-I) is an autosomal recessive genetic disease caused by a deficiency of the glycosidase alpha-L-iduronidase which is required for the lysosomal degradation of the glycosaminoglycans heparan sulfate and dermatan sulfate. Patients with MPS-I store forms of these partially degraded glycosaminoglycans in their lysosomes. MPS-I patients present with a wide range of clinical phenotypes, which makes prognostic predictions and genetic counselling difficult, therefore impeding the selection and evaluation of patients undergoing experimental therapy, such as bone marrow transplantation. We report the presence of two mutations, one that introduces a stop codon at position 70 (Q70X), and the other that alters the proline at position 533 to an arginine (P533R) in the 653 amino acid alpha-L-iduronidase protein. These mutations were originally detected by chemical cleavage and then by direct PCR sequencing. Allele specific oligonucleotides were used to detect the mutations in a group of 73 MPS-I patients and Q70X was found to account for 15% of all MPS-I alleles and P533R for 3% of MPS-I alleles. Both mutations are associated with an extremely severe clinical phenotype in homozygotes. MPS-I patients heterozygous for either mutation may have a wide range of clinical phenotypes. We have now described three mutations, W402X (Scott et al., 1992c), Q70X, and P533R totalling 53% of MPS-I alleles which together define 28% of MPS-I genotypes.

Alleles↗
PubMed1992

An N-acetylgalactosamine-4-sulfatase mutation (delta G238) results in a severe Maroteaux-Lamy phenotype.

Maroteaux-Lamy syndrome (mucopolysaccharidosis type VI, MPS VI) is an autosomally inherited lysosomal storage disorder caused by a deficiency of N-acetylgalactosamine-4-sulfatase (EC 3.1.6.1; 4-sulfatase). In order to determine the gene defect in a clinically severe MPS VI patient, polymerase chain reaction (PCR) products were generated from the patient's fibroblast mRNA and also from a 4-sulfatase cDNA clone and subjected to the chemical cleavage technique to detect mismatched bases, which were then identified by direct DNA sequencing of the PCR products. The patient was homozygous for an early frameshift mutation caused by the deletion of a G at position 238 (delta G238), which produces a truncated 4-sulfatase with an altered amino acid sequence from amino acid 80 to a premature stop codon at codon 113 relative to the normal 4-sulfatase reading frame of 533 amino acids. Since the mutation occurs only 40 amino acids past the signal peptidase cleavage site, it is most likely that this will result in a protein with no 4-sulfatase activity. This is consistent with the severe clinical presentation and the absence of 4-sulfatase enzyme activity or mutant 4-sulfatase protein in the patient. The patient was also found to be homozygous for two polymorphisms, i.e., a G to A transition at nucleotide 1072 resulting in a valine358 to methionine substitution (V358M) and a salient A to G transition in the third base of the proline397 codon at nucleotide 1191.

Amino Acid Sequence↗
PubMed1992

PCR detection of two RFLPs in exon I of the alpha-L-iduronidase (IDUA) gene.

Two polymorphisms were detected within exon I of the alpha-L-iduronidase (IDUA) gene both of which create restriction endonuclease sites and one of which changes an amino acid. The polymorphisms may be detected by digesting the same 245-bp polymerase chain reaction product. The polymorphisms can be used diagnostically in families with IDUA deficiency (mucopolysaccharidosis type I) and Huntington disease, which is closely linked to the IDUA locus.

Base Sequence↗