A missense mutation (His42Arg) in the T-protein gene from a large Israeli-Arab kindred with nonketotic hyperglycinemia

Nonketotic hyperglycinemia (NKH) is caused by a mutation in the genes encoding the components of the glycine cleavage multi-enzyme system. More than 80% of the patients have defects in the gene encoding P-protein, whereas the rest of the patints have defects in the gene encoding T-protein. We have found a large Israeli-Arab kindred with NKH. At least 14 children were affected, and all the patients had seizures and respiratory failure within 2 days after birth. Enzymatic analysis revealed that T-protein activity was deficient in the liver specimen from one propositus. We screened this family for a mutation in the protein-coding region and exon/intron boundaries of T-protein gene by direct sequencing analysis. A missense mutation was found in exon 2; this resulted in an amino acid substitution from histidine to arginine at position 42 (H42R). Histidine 42 is conserved in human, bovine, chicken, pea, and Escherichia coli, suggesting that it has an important role in catalytic functions. Genotype analyses of 26 family members confirmed that the homozygous H42R mutation was completely associated with the onset of NKH. The availability of DNA testing facilitates the prenatal diagnosis of NKH and the identification of carriers, which is necessary for genetic counseling in the affected families. Received: 28 October 1997 / Accepted: 6 January 1998     

Mutations of the tyrosinase gene in patients with oculocutaneous albinism from various ethnic groups in Israel.

We have analyzed the tyrosinase (TYR) gene in 38 unrelated patients with oculocutaneous albinism (OCA), derived from several different ethnic groups of the diverse population of Israel. We detected TYR gene mutations in 23 of the 34 patients with apparent type I (i.e., tyrosinase-deficient) OCA and in none of the patients with other clinical forms of albinism. Among Moroccan Jews with type IA (i.e., tyrosinase-negative) OCA, we detected a highly predominant mutant allele containing a missense substitution, Gly47Asp (G47D). This mutation occurs on the same haplotype as in patients from the Canary Islands and Puerto Rico, suggesting that the G47D mutation in these ethnically distinct populations may stem from a common origin.     

Identification of a mutation in the arylsulfatase A gene of a patient with adult-type metachromatic leukodystrophy.

To analyze the genetic abnormality in a Japanese patient with adult-type metachromatic leukodystrophy (MLD), we first elucidated the genomic organization of the human arylsulfatase A (ASA) gene and then compared the nucleotide sequences of exons and splice junctions of the mutant ASA gene to those of a normal control. We have identified a new mutation, a G-to-A transition in exon 2, which results in amino acid substitution of Asp for 99Gly. In a transient expression study, COS cells transfected with the mutant cDNA carrying 99Gly----Asp did not show an increase of ASA activity, which confirms that the mutation is a cause of adult-type MLD.     

Molecular screening of Batten disease: identification of a missense mutation (E295K) in the CLN3 gene

Batten disease, the juvenile form of neuronal ceroid lipofuscinosis, is a prevalent neuron degenerative disorder of childhood. A 1.02-kb genomic deletion in the Batten disease gene CLN3 has been determined to be a common mutation. We developed a PCR method to screen for this deletion and tested 43 Batten disease probands. We found 36% (31/86) of Batten disease chromosomes did not carry the 1.02-kb deletion. Of the three heterozygotes for the 1.02-kb deletion, a novel G-to-A missense mutation at nucleotide 1020 of the CLN3 cDNA sequence was found on two of the non-1.02-kb deletion chromosomes. The missense mutation resulted in a substitution of glutamic acid (E) by lysine (K) at position 295 (E295 K). The E295 K mutation causes a change in predicted local protein conformation. This glutamic acid is a highly conserved acidic amino acid, being present in human, mouse, dog and yeast, which suggests it may play an important role in the function of the Batten disease protein. Received: 12 May 1997 / Accepted: 21 August 1997     

A Gly1127Ser mutation in an EGF-like domain of the fibrillin-1 gene is a risk factor for ascending aortic aneurysm and dissection.

Ascending aortic disease, ranging from mild aortic root enlargement to aneurysm and/or dissection, has been identified in 10 individuals of a kindred, none of whom had classical Marfan syndrome (MFS). Single-strand conformation analysis of the entire fibrillin-1 (FBN1) cDNA of an affected family member revealed a G-to-A transition at nucleotide 3379, predicting a Gly1127Ser substitution. The glycine in this position is highly conserved in EGF-like domains of FBN1 and other proteins. This mutation was present in 9 of 10 affected family members and in 1 young unaffected member but was not found in other unaffected members, in 168 chromosomes from normal controls, and in 188 chromosomes from other individuals with MFS or related phenotypes. FBN1 intragenic marker haplotypes ruled out the possibility that the other allele played a significant role in modulating the phenotype in this family. Pulse-chase studies revealed normal fibrillin synthesis but reduced fibrillin deposition into the extracellular matrix in cultured fibroblasts from a Gly1127Ser carrier. We postulate that the Gly1127Ser FBN1 mutation is responsible for reduced matrix deposition. We suggest that mutations such as this one may disrupt EGF-like domain folding less drastically than do substitutions of cysteine or of other amino acids important for calcium-binding that cause classical MFS. The Gly1127Ser mutation, therefore, produces a mild form of autosomal dominantly inherited weakness of elastic tissue, which predisposes to ascending aortic aneurysm and dissection later in life.     

delta-Aminolevulinate dehydratase deficient porphyria: identification of the molecular lesions in a severely affected homozygote.

delta-Aminolevulinate dehydratase deficient porphyria, a recently recognized inborn error of heme biosynthesis, results from the markedly deficient activity of the heme biosynthetic enzyme, delta-aminolevulinate dehydratase (ALA-D). The four homozygotes described to date with this disorder have remarkably distinct phenotypes, ranging from a severely affected infant with failure to thrive to an essentially asymptomatic 68-year-old male. To investigate the molecular nature of the lesions causing the severe infantile-onset form, total RNA was isolated from cultured lymphoblasts of the affected homozygote, RNA was reverse-transcribed to cDNA, and the 990-bp ALA-D-coding region was amplified by the PCR. Heterozygosity for an RsaI RFLP within the ALA-dehydratase-coding region permitted identification of the paternal and maternal mutant alleles prior to sequencing. The maternal mutation (designated G133R), a G-to-A transition of nucleotide 397, predicted a glycine-to-arginine substitution at residue 133 at the carboxyl end of the highly conserved zinc-binding site in the enzyme subunit. The G133R mutation created a PstI site and permitted the confirmation and rapid detection of this lesion in amplified genomic DNA from maternal relatives. The paternal mutation, a G-to-A transition of nucleotide 823, predicted a valine-to-methionine substitution of residue 275 (designated V275M). This mutation was confirmed in genomic DNA from family members by the competitive PCR technique. Both missense mutations, which occurred at CpG dinucleotides, resulted in the synthesis of enzyme subunits such that the activity of the homooctameric enzyme was markedly reduced, thereby causing the severe infantile-onset phenotype in the affected homozygote.     

A dominant interfering mutation (CYR3) of the Saccharomyces cerevisiae RAS2 gene.

The dominant cyclic AMP-requiring mutation CYR3 had been previously reported as a mutation in the regulatory subunit of cyclic AMP-dependent protein kinase. However, recharacterization revealed that the CYR3 mutation was a nonconditional dominant lethal mutation and was a missense allele of RAS2 which results from the substitution of aspartic acid for glycine at amino acid 22.     

Identification of point mutations in the alpha-galactosidase A gene in classical and atypical hemizygotes with Fabry disease

Efforts were directed to identify the specific mutations in the alpha-galactosidase A (alpha-Gal A) gene which cause Fabry disease in families of Japanese origin. By polymerase-chain-reaction-amplification of DNA from reverse-transcribed mRNA and genomic DNA, different point mutations were found in two unrelated Fabry hemizygotes. A hemizygote with classic disease manifestations and no detectable alpha-Gal A activity had a G-to-A transition in exon 1 (codon 44) which substituted a termination codon (TAG) for a tryptophan codon (TGG) and created an NheI restriction site. This point mutation would predict a truncated alpha-Gal A polypeptide, consistent with the observed absence of enzymatic activity and a classic Fabry phenotype. In an unrelated Japanese hemizygote who had an atypical clinical course characterized by late-onset cardiac involvement and significant residual alpha-Gal activity, a G-to-A transition in exon 6 (codon 301) resulted in the replacement of a glutamine for an arginine residue. This amino acid substitution apparently altered the properties of the enzyme such that sufficient enzymatic activity was retained to markedly alter the disease course. Identification of these mutations permitted accurate molecular heterozygote diagnosis in these families.     

Non-phenotypic selection of N-methyl-N′-nitro-N-nitrosoguanidine-directed mutation at a predicted hotspot site

The striking mutational specificity of N-methyl-N′-nitro-N-nitrosoguanidine (MNNG) exhibited in the lacI gene in Escherichia coli allows comment on the phenotypic consequences of mutation at specific sequences that are not recovered after MNNG mutagenesis. We predict that the I⁺ phenotype is maintained when such silent positions are substituted by amino acids whose codons are generated by the MNNG-directed G:C → A:T transition. We chose the mutationally silent Gly200 codon (an MNNG hotspot motif sequence) to test this prediction. Through MNNG mutagenesis we have generated, identified and isolated a G:C → A:T transition at position 627 (5′-GG-C3′) under non-selective conditions which creates the Gly200→Asp substitution. The I⁺ phenotype is retained for this altered repressor.     

alpha-Mannosidosis in the guinea pig: cloning of the lysosomal alpha-mannosidase cDNA and identification of a missense mutation causing alpha-mannosidosis

alpha-Mannosidosis is a lysosomal storage disorder caused by deficient activity of the lysosomal alpha-mannosidase. We report here the sequencing and expression of the lysosomal alpha-mannosidase cDNA from normal and alpha-mannosidosis guinea pigs. The amino acid sequence of the guinea pig enzyme displayed 82-85% identity to the lysosomal alpha-mannosidase in other mammals. The cDNA of the alpha-mannosidosis guinea pig contained a missense mutation, 679C>T, leading to substitution of arginine by tryptophan at amino acid position 227 (R227W). The R227W allele segregated with the alpha-mannosidosis genotype in the guinea pig colony and introduction of R227W into the wild-type sequence eliminated the production of recombinant alpha-mannosidase activity in heterologous expression studies. Furthermore, the guinea pig mutation has been found in human patients. Our results strongly indicate that the 679C>T mutation causes alpha-mannosidosis and suggest that the guinea pig will be an excellent model for investigation of pathogenesis and evaluation of therapeutic strategies for human alpha-mannosidosis.     

Identification of a missense mutation in one allele of a patient with Pompe disease, and use of endonuclease digestion of PCR-amplified RNA to demonstrate lack of mRNA expression from the second allele.

Infantile-onset glycogen storage disease type II, or Pompe disease, results from a genetic deficiency of the lysosomal enzyme acid alpha glucosidase (GAA). Sequencing of the cDNA from a cell line (GM 244) derived from a patient with Pompe disease demonstrated a T953-to-C transition that predicted a methionine-to-threonine substitution at codon 318. The basepair substitution resulted in loss of restriction-endonuclease sites for NcoI and StyI. Analysis of genomic DNA revealed both a normal and an abnormal NcoI fragment, indicating that the patient was a genetic compound. NcoI and StyI digestion of cDNA, amplified by PCR from reverse-transcribed RNA, demonstrated that greater than 95% of the GAA mRNA in GM 244 was derived from the allele carrying the missense mutation. The missense mutation was uncommon, since it was not detected in 37 additional GAA-deficient chromosomes, as determined by digestion of genomic DNA with NcoI and hybridization. The amino acid substitution predicts a new potential site for N-linked glycosylation, as well as major changes in secondary structure of the protein. We could confirm that the mutation was responsible for the enzyme deficiency by demonstrating that a hybrid minigene containing the mutation did not express GAA enzyme activity after transient gene expression. We have therefore now provided the first identification of a single-basepair missense mutation in a patient with Pompe disease and furthermore have demonstrated that the patient is a genetic compound with the second allele barely expressing mRNA.     

Acid alpha-glucosidase deficiency: Identification and expression of a missense mutation (S529V) in a Japanese adult phenotype

We report a missense mutation in an adult Japanese patient with acid alpha-glucosidase (GAA) deficiency. A TC to GT transition at nucleotides 1585–1586, was identified. This transition resulted in an amino acid substitution of Ser-529 to Val (S529V) in exon 11. We also have demonstrated that the S529V mutation abolishes the catalytic activity of the enzyme. Our data suggest that this mutation is the cause of the clinical manifestation known as adult-onset GAA deficiency. The missense mutation described here is a new mutation, and the first identified in Japanese patients with GAA deficiency. Received: 23 May 1995     

The molecular basis of homocystinuria due to cystathionine beta-synthase deficiency in Italian families, and report of four novel mutations.

Four new mutations in the cystathionine beta-synthase (CBS) gene have been identified in Italian patients with homocystinuria. The first mutation is a G-to-A transition at base 374 in exon 3, causing an arginine-to-glutamic acid substitution at position 125 of the protein (R125Q). This mutation has been found in homozygosity in a patient partially responsive to pyridoxine treatment. The second mutation is a C-to-T transition at base 770 in exon 7, causing a threonine-to-methionine substitution at amino acid 257 of the protein (T257M). This mutation has been observed in homozygosity in a patient nonresponsive to the cofactor treatment. The third mutation, found in heterozygosity in a patient responsive to pyridoxine treatment, is an insertion of 68 bp in exon 8 at base 844, which introduces a premature termination codon. The fourth mutation is C-to-T transition in exon 2 at base 262, causing a proline-to-serine substitution at position 88 of the protein (P88S). This mutation is carried on a single allele in three affected sisters responsive to the cofactor treatment. In addition, six previously reported mutations (A114V, E131D, P145L, I278T, G307S, and A1224-2C) have been tested in 14 independent Italian families. Mutations A114V and I278T are carried by three and by seven independent alleles, respectively. The other four mutations--including G307S and A1224-2C, common among northern European patients--have not been detected.     

A germ line mutation within the coding sequence for the putative 5-phosphoribosyl-1-pyrophosphate binding site of hypoxanthine-guanine phosphoribosyltransferase (HPRT) in a Lesch-Nyhan patient: missense mutations within a functionally important region probably cause disease

Lesch-Nyhan syndrome caused by a complete deficiency of hypoxanthine guanine phosphoribosyltransferase (HPRT) is the result of a heterogeneous group of germ line mutations. Identification of each mutant gene provides valuable information as to the type of mutation that occurs spontaneously. We report here a newly identified HPRT mutation in a Japanese patient with Lesch-Nyhan syndrome. This gene, designated HPRT Tokyo, had a single nucleotide change from G to A, as identified by sequencing cDNA amplified by the polymerase chain reaction. Allele specific oligonucleotide hybridization analysis using amplified genomic DNA showed that the mutant gene was transmitted from the maternal germ line. This mutation would lead to an amino acid substitution of Asp for Gly at the amino acid position 140 located within the putative 5-phosphoribosyl-1-pyrophosphate (PRPP) binding region. Missense mutations in human HPRT deficient patients thus far reported tend to accumulate in this functionally active region. However, a comparison of the data suggested that both missense and synonymous mutations can occur at any coding sequence of the human germ line HPRT gene, but that a limited percentage of all the missense mutations cause disease. The probability that a mutation will cause disease tends to be higher when the missense mutation is within a functionally important sequence.     

T-protein of the glycine decarboxylase multienzyme complex: evidence for partial similarity to formyltetrahydrofolate synthetase

We have isolated and sequenced cDNA clones encoding T-protein of the glycine decarboxylase complex from three plant species, Flaveria pringlei, Solanum tuberosum and Pisum sativum. The predicted amino acid sequences of these clones are at least 87% identical and all are similar to the predicted sequences of the bovine, human, chicken and Escherichia coli T-proteins. Alignment of all these sequences revealed conserved domains, one of which showed a significant similarity to a part of the formyltetrahydrofolate synthetases from procaryotes and eucaryotes. This suggests that the T-protein sequence is not as unique as previously thought.     

A frequent tyrosinase gene mutation associated with type I-A (tyrosinase-negative) oculocutaneous albinism in Puerto Rico.

We have determined the mutations in the tyrosinase gene from 12 unrelated Puerto Rican individuals who have type I-A (tyrosinase-negative) oculocutaneous albinism (OCA). All but one individual are of Hispanic descent. Nine individuals were homozygous for a missense mutation (G47D) in exon I at codon 47. Two individuals were heterozygous for the G47D mutation, with one having a missense mutation at codon 373 (T373K) in the homologous allele and the other having an undetermined mutation in the homologous allele. One individual with negroid features was homozygous for a nonsense mutation (W236X). The population migration between Puerto Rico and the Canary Islands is well recognized. Analysis of three individuals with OCA from the Canary Islands showed that one was a compound heterozygote for the G47D mutation and for a novel missense mutation (L216M), one was homozygous for a missense mutation (P81L), and one was heterozygous for the missense mutation P81L. The G47D and P81L missense mutations have been previously described in extended families in the United States. Haplotypes were determined using four polymorphisms linked to the tyrosinase locus. Haplotype analysis showed that the G47D mutation occurred on a single haplotype, consistent with a common founder for all individuals having this mutation. Two different haplotypes were found associated with the P81L mutation, suggesting that this may be either a recurring mutation for the tyrosinase gene or a recombination between haplotypes.     

The same amino acid substitution in orthologous esterases confers organophosphate resistance on the house fly and a blowfly.

Organophosphate (OP) insecticide resistance in certain strains of Musca domestica is associated with reduction in the carboxylesterase activity of a particular esterase isozyme. This has been attributed to a 'mutant ali-esterase hypothesis', which invokes a structural mutation to an ali-esterase resulting in the loss of its carboxylesterase activity but acquisition of OP hydrolase activity. It has been shown that the mutation in Lucilia cuprina is a Gly137-->Asp substitution in the active site of an esterase encoded by the Lc alpha E7 gene (Newcomb, R.D., Campbell, P.M., Ollis, D.L., Cheah, E., Russell, R.J., Oakeshott, J.G., 1997. A single amino acid substitution converts a carboxylesterase to an organophosphate hydrolase and confers insecticide resistance on a blowfly. Proc. Natl. Acad. Sci. USA 94, 7464-7468). We now report the cloning and characterisation of the orthologous M. domestica Md alpha E7 gene, including the sequencing of cDNAs from the OP resistant Rutgers and OP susceptible sbo and WHO strains. The Md alpha E7 gene has the same intron structure as Lc alpha E7 and encodes a protein with 76% amino acid identity to Lc alpha E7. Comparisons between susceptible and resistance alleles show resistance in M. domestica is associated with the same Gly137-->Asp mutation as in L. cuprina. Bacterial expression of the Rutgers allele shows its product has OP hydrolase activity. The data indicate identical catalytic mechanisms have evolved in orthologous Md alpha E7 and Lc alpha E7 molecules to endow diazinon-type resistance on the two species of higher Diptera.     

Characterization of a novel missense mutation on murine Pax3 through ENU mutagenesis

N-ethyl-N-nitrosourea (ENU) mutagenesis has led to the elucidation of several regulator genes for melanocyte and skin development.Here we characterized a mutant from ENU mutagenesis with similar phenotype as that of Splotch mutant,including exencephaly,spina bifida and abnormal limbs in homozygotes as well as white belly spotting and occasionally loop-tail in heterozygotes.This novel mutant was named as SpxG..Through genome-wide linkage analysis in backcross progenies with microsatellite markers,the SpxG was confined to a region between D1MIT415 and D1M IT7 on chromosome 1,where notable Pax3 gene was located.Direct sequencing revealed that SpxG carried a nucleotide A894G missense transition in exon 6 of Pax3 gene that resulted in Asn to Asp substitution at amino acid 269 within the highly-conserved homeodomain (HD) DNA recognition module,which was the first point mutation found in this domain in mice.This N269D mutation impaired the transactivation capacity of Pax3 protein,but exerted no effect on Pax3 protein translation.The characterization of the new mutation expanded our understanding the transactivation and DNA-binding structure of Pax3 protein.