Splicing mutation

In the history of drug metabolism, prominent were the discoveries of genetic variability of the metabolism of debrisoquine (14) and of sparteine (15). Subsequent studies indicated that both drugs are metabolized by the same enzyme (16), which turned out to be the P450 cytochrome CYP2D6 (17). The enzyme s variations were found to be complex (18) enzyme activity could be absent because of frameshift mutations, splicing defects, gene deletion, or the presence of a stop codon. The enzyme may function slowly because of various kinds of mutation, whereby some mutations affected only the interaction with specific substrates. Enzyme duplication or multiplication could lead to very fast action. 

Lesch-Nyhan syndrome, an overproduction hyperuricemia characterized by frequent episodes of uric acid hthiasis and a bizarre syndrome of self-mutilation, reflects a defect in hypoxanthme-guanine phosphoribo-syl transferase, an enzyme of purine salvage (Figure 34—4). The accompanying rise in intracellular PRPP results in purine overproduction. Mutations that decrease or abohsh hypoxanthine-guanine phosphoribosyltrans-ferase activity include deletions, frameshift mutations, base substitutions, and aberrant mRNA splicing. 

P-Thalassemla (MIM 141900) A very wide variety of mutations in the p-globin gene, including deletions, nonsense and frameshift mutations, and others affecting every aspect of its structure (eg, splice sites, promoter mutants)... 

The distribution of open channel times is mainly determined by the rate constants S and K (2 is assumed to be very small). Mutations which change the C to O transition (e.g., the burst size of channel opening) have not been characterized yet. However, structural alterations which affect k and thereby the level of steady state inactivation have been described for Sh channels [29,60]. Different splice variants of Sh channels... 

To date, 15 GPI variants have been analyzed at the molecular level, and 16 mis-sense mutations, 1 nonsense mutation, and 1 splicing mutation due to a four-nucleotide deletion have been reported (Fig. 7) (B9, F13, K14, Wl, XI). The GPI gene mutations were heterogeneous, although most GPI variants had common biochemical characteristics such as heat instability and normal kinetic properties. We have determined the molecular abnormalities of four homozygous variants, GPI Matsumoto, GPI Iwate, GPI Narita, and GPI Fukuoka (K14). GPI Narita has a homozygous mutation from A to G at position 1028 (343 Gin to Arg), and the same mutation was reported in an Italian patient, GPI Moscone (B9). The substituted Gin is adjacent to the reported active site residue, 341 Asp. Homozygous missense mutations, C to T at position 14 (5 Thr to lie) and C to T at position 671 (224 Thr to Met) have been identified in GPI Matsumoto and GPI Iwate, respectively. GPI... 

GSH-S deficiency is a more frequent cause of GSH deficiency (HI7), and more than 20 families with this enzyme deficiency have been reported since the first report by Oort et al. (05). There are two distinct types of GSH-S deficiency with different clinical pictures. In the red blood cell type, the enzyme defect is limited to red blood cells and the only clinical presentation is mild hemolysis. In the generalized type, the deficiency is also found in tissues other than red blood cells, and the patients show not only chronic hemolytic anemia but also metabolic acidosis with marked 5-oxoprolinuria and neurologic manifestations including mental retardation. The precise mechanism of these two different phenotypes remains to be elucidated, because the existence of tissue-specific isozymes is not clear. Seven mutations at the GSH-S locus on six alleles—four missense mutations, two deletions, and one splice site mutation—have been identified (S14). 

Hereditary methemoglobinemia is classified into three types a red blood cell type (type I), a generalized type (type II), and a blood cell type (type HI). Enzyme deficiency of type I is limited to red blood cells, and these patients show only the diffuse, persistent, slate-gray cyanosis not associated with cardiac or pulmonary disease. In type II, the enzyme deficiency occurs in all cells, and patients of this type have a severe neurological disorder with mental retardation that predisposes them to early death. Patients with type III show symptoms similar to those of patients with type I. The precise nature of type III is not clear, but decreased enzyme activity is observed in all cells (M9). It is considered that uncomplicated hereditary methemoglobinemia without neurological involvement arises from a defect limited to the soluble cytochrome b5 reductase and that a combined deficiency of both the cytosolic and the microsomal cytochrome b5 reductase occurs in subjects with mental retardation. Up to now, three missense mutations in type I and three missense mutations, two nonsense mutations, two in-frame 3-bp deletions, and one splicing mutation in type n have been identified (M3, M8, M31). 

Low levels or absence of adenosine deaminase (ADA) is associated with one form of severe combined immunodeficiency disease (SCID) characterized by B-andT-lymphocyte dysfunction due to toxic effects of deoxyadenosine (HI9). Most patients present as infants with failure to thrive, repeated infections, severe lymphopenia, and defective cellular and humoral immunity. Disease severity is correlated with the degree of deoxyadenosine nucleotide pool expansion and inactivation of S-adenosylhomocysteine hydrolase in red blood cells. Up to now, more than 40 mutations have been identified (A4, H20, S5, S6). The majority of the basic molecular defects underlying ADA deficiency of all clinical phenotypes are missense mutations. Nonsense mutations, deletions ranging from very large to single nucleotides, and splicing mutations have also been reported. It is likely that severe... 

Purine nucleoside phosphorylase (PNP) deficiency engenders a combined immunodeficiency and neurologic abnormalities and is usually fatal in childhood (G4). Patients with PNP deficiency have profound lymphopenia and a small thymus with poorly formed Hassall corpuscles. Lymphocyte enumeration shows markedly decreased numbers of T cells and T-cell subsets, with normal percentages of B cells. Point mutations and a splicing mutation have been identified in some PNP-deficient patients (H4). 

Acatalasemia is a rare hereditary deficiency of tissue catalase and is inherited as an autosomal recessive trait (03). This enzyme deficiency was discovered in 1948 by Takahara and Miyamoto (Tl). Two different types of acatalasemia can be distinguished clinically and biochemically. The severe form, Japanese-type acatalasemia, is characterized by nearly total loss of catalase activity in the red blood cells and is often associated with an ulcerating lesion of the oral cavity. The asymptomatic Swiss-type acatalasemia is characterized by residual catalase activity with aberrant biochemical properties. In four unrelated families with Japanese-type acatalasemia, a splicing mutation due to a G-to-A transition at the fifth nucleotide in intron 4 was elucidated (K20, W5). We have also determined a single base deletion resulting in the frameshift and premature translational termination in the Japanese patient (HI6). 

A4. Arredondo-Vega, F. X., Santisteban, I., Kelly, S., Schlossman, C., Umetsu, D and Hershfield, M. S., Correct splicing despite a G- A mutation at the invariant first nucleotide of a 5 splice site A possible basis for disparate clinical phenotypes in siblings with adenosine deaminase (ADA) deficiency. Am. J. Hum. Genet. 54,820-830 (1994). 

K9. Kanno, H., Wei, D. C. C., Miwa, S., Chan, L. C., and Fujii, H., Identification of a 5 -splice site mutation and a missense mutation in homozygous pyruvate kinase deficiency cases found in Hong Kong. Blood 82 (Suppl. 1), 97a (1993). 

N2. Nakajima, H., Kono, N Yamasaki, T Hotta, K., Kawachi, M Kuwajima, M., Noguchi, T., Tanaka, T., and Tarui, S Genetic defect in muscle phosphofructokinase deficiency Abnormal splicing of the muscle phosphofructokinase gene due to a point mutation at the 5 -splice site. J. Biol. Chem. 265, 9392-9395 (1990). 

Ookawara, T., Dave, V., Willems, P Martin, J.-J., de Barsy, T., Matthys, E., and Yoshida, A., Retarded and aberrant splicings caused by single exon mutation in a phosphoglycerate kinase variant. Arch. Biochem. Biophys. 327, 35-40 (1996). 

Rl. Raben, N., Sherman, J., Miller, E, Mena, H., and Plotz, P., A5 splice junction mutation leading to exon deletion in an Ashkenazic Jewish family with phosphofructokinase deficiency (Tarui disease). J. Biol. Chem. 268,4963-4967 (1993). 

Santisteban, I., Arredondo-Vega, F. X., Kelly, S., Debre, M., Fischer, A., Pdrignon, J. L., Hilman, B., Eldahr, J., Dreyfus, D. H., Howell, P. L., and Hershfield, M. S Four new adenosine deaminase mutations, altering a zinc-binding histidine, two conserved alanine, and a 5 splice site. Hum. Mutat. 5,243-250 (1995). 

T24. Tsujino, S., Tonin, P Shanske, S., Nohria, V., Boustany, R.-M., Lewis, D Chen, Y.-T., and DiMauro, S., A splice junction mutation in a new myopathic variant of phosphoglycerate kinase deficiency (PGK North Carolina). Ann. Neurol. 35,349-353 (1994). 

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