Residual Ataxia Telangiectasia Mutated Protein Function in Cells from Ataxia Telangiectasia Patients, with 5762ins137 and 7271T→G Mutations, Showing a Less Severe Phenotype

Abstract

We have assessed several ataxia Telangiectasia mutated (ATM)-dependent functions in cells derived from ataxia telangiectasia patients, carrying either an ATM5762ins137 splice site or a 7271T→G missense mutation, with a less severe phenotype compared with the classical disorder. ATM kinasein vitro, from 5762ins137 cells, showed the same specific activity as ATM in normal cells, but the protein was present at low levels. In contrast, mutant ATM kinase activity in the 7271T→G cells was only about 6% that of the activity in normal cells, although the level of mutant protein expressed was similar to normal cells. Phosphorylation of the DNA double strand break repair proteins Nbs1 and hMre11, following DNA damage, was observed in normal and 7271T→G cells but was almost absent in both 5762ins137 and classical ataxia telangiectasia cells. The kinetics of p53 response was intermediate between normal and classical ataxia telangiectasia cells in both the 7271T→G and 5762ins137 cells, but interestingly, c-Jun kinase activation following DNA damage was equally deficient in cell lines derived from all the ataxia telangiectasia patients. Our results indicate that levels of ATM kinase activity, but not induction of p53 or c-Jun kinase activity, in these cells correlate with the degree of neurological disorder in the patients. We have assessed several ataxia Telangiectasia mutated (ATM)-dependent functions in cells derived from ataxia telangiectasia patients, carrying either an ATM5762ins137 splice site or a 7271T→G missense mutation, with a less severe phenotype compared with the classical disorder. ATM kinasein vitro, from 5762ins137 cells, showed the same specific activity as ATM in normal cells, but the protein was present at low levels. In contrast, mutant ATM kinase activity in the 7271T→G cells was only about 6% that of the activity in normal cells, although the level of mutant protein expressed was similar to normal cells. Phosphorylation of the DNA double strand break repair proteins Nbs1 and hMre11, following DNA damage, was observed in normal and 7271T→G cells but was almost absent in both 5762ins137 and classical ataxia telangiectasia cells. The kinetics of p53 response was intermediate between normal and classical ataxia telangiectasia cells in both the 7271T→G and 5762ins137 cells, but interestingly, c-Jun kinase activation following DNA damage was equally deficient in cell lines derived from all the ataxia telangiectasia patients. Our results indicate that levels of ATM kinase activity, but not induction of p53 or c-Jun kinase activity, in these cells correlate with the degree of neurological disorder in the patients. ataxia telangiectasia lymphoblastoid cell lines gray c-Jun N-terminal kinase glutathione S-transferase polyacrylamide gel electrophoresis antibody ataxia telangiectasia mutated Ataxia telangiectasia (A-T)1 is a human autosomal recessive disorder in which affected individuals exhibit a diverse range of clinical symptoms affecting multiple organ systems (1Sedgwick R.P. Boder E. Vinken P.J. Bruyn G.W. Klawans H.L. Handbook of Neurology. Elsevier Science Publishers, Amsterdam1991: 347-422Google Scholar). The principal manifestation of A-T presents as a progressive truncal and limb ataxia as a consequence of degeneration of the cerebellum. This ultimately results in the patients being wheelchair-bound from the early teenage years. Other clinical signs of A-T are the presence of oculocutaneous telangiectasia, selective immunodeficiency, an increased sensitivity to ionizing radiation and other radiomimetic chemicals, and a marked prevalence of tumors of the lymphoid system (reviewed in Ref.2Shiloh Y. Annu. Rev. Genet. 1997; 31: 635-662Crossref PubMed Scopus (428) Google Scholar). These features define classical A-T, which results from total absence of functional ATM protein. At the gene level, the vast majority of classical A-T patients in the UK are compound heterozygotes for null mutations, most of which are truncating ATM mutations (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). The clinical diagnosis is unambiguous in these A-T patients. Whether or not clinical and cellular heterogeneity exists within the group of classical A-T patients with two null mutations is unknown, as no careful correlation studies have been undertaken. Across all A-T patients there is a degree of variation between them in both the severity and expression of the clinical features. In particular, the degree of telangiectasia, the extent of immunodeficiency, the susceptibility to recurrent sinopulmonary infections, longevity, the rate of neuronal degeneration, and the development of tumors show the greatest degree of heterogeneity among patients. In some cases this variation presents as a clearly milder form of A-T. These individuals have a combination of the following: a slightly later age of onset of the clinical symptoms, a slower rate of disease progression, an extended life span, when compared with most classical A-T patients, and a reduced or absent hypersensitivity to ionizing radiation (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar, 4McConville C.M. Stankovic T. Byrd P.J. McGuire G.M. Yao Q.-Y. Lennox G.G. Taylor A.M.R. Am. J. Hum. Genet. 1996; 59: 320-330PubMed Google Scholar, 5Gilad S. Chessa L. Khosravi R. Russell P. Galanty Y. Piane M. Gatti R.A. Jorgensen T.J. Shiloh Y. Bar-Shira A. Am. J. Hum. Genet. 1998; 62: 551-561Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar). Given the predominance of null mutations underlying the classical form of ataxia telangiectasia (6Gilad S. Khosravi R. Shkedy D. Uziel T. Ziv Y. Savitsky K. Rotman G. Smith S. Chessa L. Jorgensen T.J. Harnik R. Frydman M. Sanal O. Portnoi S. Goldwicz Z. Jaspers N.G.J. Gatti R.A. Lenoir G. Lavin M. Tatsumi K. Wegner R.D. Shiloh Y. Bar-Shira A. Hum. Mol. Genet. 1996; 5: 433-439Crossref PubMed Scopus (257) Google Scholar), it is highly likely that milder, “variant” forms arise from less severe mutations that retain some normal protein function. In support of this, we have previously reported two different ATM gene mutations that are specifically associated with a milder clinical syndrome (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar, 4McConville C.M. Stankovic T. Byrd P.J. McGuire G.M. Yao Q.-Y. Lennox G.G. Taylor A.M.R. Am. J. Hum. Genet. 1996; 59: 320-330PubMed Google Scholar). The first mutation, present in the heterozygous state in 15% of A-T families in the United Kingdom, is an intronic missense mutation that activates a cryptic splice donor/acceptor site resulting in the insertion of 137 nucleotides of intronic sequence at position 5762. It appears, however, that this mutation is “leaky” and also allows normal splicing to occur, albeit at a reduced level. It was proposed that the presence of some normal ATM protein was sufficient to reduce the severity of the disease (4McConville C.M. Stankovic T. Byrd P.J. McGuire G.M. Yao Q.-Y. Lennox G.G. Taylor A.M.R. Am. J. Hum. Genet. 1996; 59: 320-330PubMed Google Scholar). In a similar context, a leaky splice mutation (3576G→A) was identified in four Italian A-T patients with a milder phenotype (5Gilad S. Chessa L. Khosravi R. Russell P. Galanty Y. Piane M. Gatti R.A. Jorgensen T.J. Shiloh Y. Bar-Shira A. Am. J. Hum. Genet. 1998; 62: 551-561Abstract Full Text Full Text PDF PubMed Scopus (207) Google Scholar), which again allows residual amounts of normally spliced ATM transcript. In contrast, the second ATM mutation we reported, associated with a mild variant A-T phenotype (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar), is a T to G transition at position 7271, which has so far been found in three A-T families, and homozygous in one, in the UK. In this case the genotype-phenotype relationship is thought to result from some normal activity retained the mutant ATM which to expressed at levels to that in a normal at in affected individuals that are homozygous for this mutation (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). The for the milder clinical in both the 5762ins137 and the 7271T→G patients is Our was to and cellular ATM that for the symptoms from of ATM function. cell lines and derived in from normal individuals and patients with ataxia in with and cell as (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). cells in and cellular was in 6% to and with p53 D. P. p53 ATM (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar), hMre11, and G.M. A. L. S. Mol. 1996; PubMed Scopus Google Scholar, M. L. 1998; Full Text Full Text PDF PubMed Scopus Google that amounts of the with an antibody was cells for in was for at of cell was with of in for at a with of or antibody for at a for at with of protein in with with with and with kinase was in of kinase with of and of and at for The kinase was the of and for a and and the gel was and to for in and cellular was for The was for at with either protein or for with Nbs1 antibody or (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google for at with protein or four with in and 6% polyacrylamide and as following with a two in and with of at for The was in cells with of and at at the three in and cell of cell from a gel and protein the with an antibody was cells with of at and for at The cells in and in The cells for and cellular was for at of cell was of antibody or an of was to and for at for at with protein with and with kinase was in of kinase with of and of and at for The kinase was the of and for a and the gel was and to It is that the ATM protein a in that are in response to DNA the majority of of the of the ATM protein functions as a protein a of proteins that and R. Y. D. A. 1997; PubMed Scopus Google Scholar, S. L. S. Y. Chessa L. Y. Shiloh Y. Ziv Y. 1998; PubMed Scopus Google Scholar, Y. K. K. E. 1998; PubMed Scopus Google Scholar, T.J. Mol. 1998; PubMed Scopus Google Scholar, R. R. T. M. Shiloh Y. Shkedy D. S. A. PubMed Scopus Google Scholar, J. Full Text Full Text PDF PubMed Scopus Google Scholar, D. Y. J. PubMed Scopus Google Scholar, S. L. Ziv Y. Shiloh Y. PubMed Scopus Google Scholar, J. PubMed Scopus Google Scholar, S. Rotman G. A. Shiloh Y. K. S. A. PubMed Scopus Google Scholar, Y. D. P. N. J. PubMed Scopus Google Scholar). In an to the underlying for the milder clinical patients with the 5762ins137 and 7271T→G mutations, we to the level of ATM protein expression in these patients and the residual protein for kinase The level of residual ATM protein expression in patients with the 5762ins137 ATM gene mutation from to of the normal level of expression and and all a second truncating mutation with the that the residual protein was protein derived from the leaky 5762ins137 mutation (4McConville C.M. Stankovic T. Byrd P.J. McGuire G.M. Yao Q.-Y. Lennox G.G. Taylor A.M.R. Am. J. Hum. Genet. 1996; 59: 320-330PubMed Google Scholar). The second mutation in was a of three at position which has been found to associated with a classical A-T phenotype (4McConville C.M. Stankovic T. Byrd P.J. McGuire G.M. Yao Q.-Y. Lennox G.G. Taylor A.M.R. Am. J. Hum. Genet. 1996; 59: 320-330PubMed Google Scholar). The gene mutation for the patients has not been the level of ATM expression in that the second mutation was an expressed missense in A-T cell lines in lines with 5762ins137 lines with 7271T→G lines with lines from classical A-T with two truncating ATM in a In contrast, the 7271T→G mutation was expressed at levels to normal in cells from patients and homozygous for the mutation and that of normal in was heterozygous for the mutation and a second null mutation, (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). The normal level of ATM protein in the heterozygous that the second mutation was also an expressed missense mutation that not the of the protein the kinase activity of the residual ATM protein expressed in the 5762ins137 patients, an in was in which the of protein was increased to for the reduced level of of the level of ATM to was and expressed as a of the activity found in normal cells. of four 5762ins137 patients and the same specific activity of ATM kinase as The expressed ATM protein at levels that low to ATM kinase activity not was compound heterozygous for a truncating null ATM and the mutation no ATM kinase activity, in with the classical A-T phenotype this similar was cells from patients with the 7271T→G mutation, that similar amounts of protein in that the level of mutant protein in these patients was to that found in normal cells (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar). The mutant protein expressed in cells from the homozygous patients and showed only of normal ATM kinase activity when as a In this mutant ATM protein was also to not The kinase activity of the mutant ATM protein in the 7271T→G heterozygous was low to and of observed in the not In contrast, the kinase activity in the heterozygous was of normal ATM activity that the second expressed mutant in to the 7271T→G mutation, to the residual ATM in these cells not the residual ATM protein expressed in cells derived from both the 5762ins137 and the 7271T→G patients retained in protein kinase In the mutation present in the cells also the level of the activity of the residual ATM protein in these variant A-T patients in we the of the double strand break repair Nbs1 and hMre11, DNA The of Nbs1 J. PubMed Scopus Google Scholar, M. D. A. K. S. Lavin Gatti R.A. P. K. Genet. PubMed Scopus Google Scholar, G. PubMed Scopus Google Scholar, S. E. Gatti R.A. Ziv Y. Shiloh Y. PubMed Scopus Google and Z. J. Full Text Full Text PDF PubMed Scopus Google a in protein an The of Nbs1 and proteins is clearly in normal cells but not in cells from a classical A-T to of and that the of both and Nbs1 was specifically to of and Nbs1 following of normal and classical A-T cells to ionizing radiation with protein in normal of and Nbs1 that of the and Nbs1 protein DNA damage was specifically to The three 5762ins137 cell lines showed a level of Nbs1 but not following DNA damage and of Nbs1 in of the 5762ins137 cell lines following DNA damage a of Nbs1 of in this cell following to ionizing radiation to show In contrast, of Nbs1 and was observed at a level in cells derived from patients that either homozygous or heterozygous for the 7271T→G mutation, albeit at reduced levels when compared with normal in both the 5762ins137 and the cells, the ATM protein retain some normal as as in vitro, although it was in patients with the 7271T→G mutant protein. ATM activation results in the induction of p53 and A-T cells exhibit a induction of p53 and to ionizing radiation T. Full Text PDF PubMed Scopus Google Scholar). in with the heterogeneity that is of A-T, the kinetics of the p53 in these cells show some It that the in cells from classical A-T patients is either a in the of p53 or in both the of p53 and also a in the level of p53 protein T. Full Text PDF PubMed Scopus Google Scholar, Lavin Google Scholar, Google Scholar, M. A. M. J. Google Scholar). lines derived from normal individuals for the induction of and following to The of p53 induction at with the p53 induction levels between and The induction of the gene and a at not compared with normal the p53 induction kinetics in cells from classical A-T patients showed and reduced when compared with normal not The of and in these cells was also with the 5762ins137 ATM mutation and two with the ATM mutation for to and to ionizing some variation of p53 was observed within the 5762ins137 cells from all patients a p53 induction that was intermediate between normal and classical A-T a of p53 within the first The and in the 5762ins137 showed normal induction kinetics In the two a and response that was from classical A-T cells from all 7271T→G patients an intermediate p53 response following to ionizing again a in p53 protein the first and also normally in all 7271T→G cell at The intermediate p53 following radiation observed in cells derived from both the 5762ins137 and the 7271T→G patients that the residual low level of normal ATM protein or the mutant ATM protein expressed in these patients, was of the severity of the A-T cellular DNA damage, p53 is multiple which allows the p53 protein to and also (reviewed in PubMed Scopus Google Scholar). The of ionizing radiation is ATM and S. L. S. Y. Chessa L. Y. Shiloh Y. Ziv Y. 1998; PubMed Scopus Google Scholar, Y. K. K. E. 1998; PubMed Scopus Google Scholar, Y. PubMed Scopus Google Scholar). It has been proposed that the of p53 is a result of the activation of ATM following DNA damage, and this is at later Y. PubMed Scopus Google Scholar). This is that that in cells to ionizing radiation is but not Y. K. E. 1997; PubMed Scopus Google Scholar). In of the intermediate p53 response observed in cells from both the 5762ins137 and the 7271T→G patients following DNA damage, we the extent of in these cells following p53 was within in normal cells and was at a level In contrast, both the classical A-T cell and cell showed a reduced The 5762ins137 normal kinetics but with the level of being cells from the three 7271T→G patients different from the 7271T→G homozygous showed a although of the first that and cells from the 7271T→G heterozygous also showed some in the from the 7271T→G heterozygous however, a induction of when compared with the other two cell lines of the second in this being as In to DNA cell ATM is also of a of specific cellular response the of ATM in this it that the of ATM with in for some of the in observed in A-T cells. ATM has been to the kinase activity following to ionizing radiation which in the activation of a of and the R. Y. D. A. 1997; PubMed Scopus Google Scholar, S. R. P. PubMed Scopus Google Scholar, A. J. R. S. Google Scholar, T. P. K. S. T. K. M. N. D. M. Shiloh Y. S. D. Lavin 1997; PubMed Scopus Google Scholar). the cellular in the variant A-T patients the 5762ins137 and the 7271T→G the of cells from these patients to was The activity of was ionizing radiation in normal cells, cells from the 5762ins137 the 7271T→G patients showed activation of following DNA damage and the kinetics of activation a in cells from these patients was not different from observed for a classical A-T not the level of activity was in cells derived from the majority of 5762ins137 and 7271T→G patients to observed in classical A-T cells and It was that a in the not the severity of the A-T clinical Our was to and the less severe clinical and cellular features of some A-T patients to residual of expressed ATM protein in cells from these In the A-T is the presence of mutations, and so several families with the same mutation We A-T patients with either the 5762ins137 or 7271T→G mutations in which for the 7271T→G mutation showed a less severe of degeneration compared with patients carrying the 5762ins137 G. Z. Sanal O. E. Chessa L. Gatti R.A. Mol. Genet. PubMed Scopus Google the in and phenotype in a of A-T patients cell and as two Our however, that a correlation that the of A-T patients are that of protein are and that cellular to DNA damage are We show that the of normal ATM protein expressed in patients with the 5762ins137 mutation or carrying in in the correlation of expression of normal ATM with cellular or clinical features in these In contrast, the expression of mutant protein in cells from patients with the mutation an The of expressed normal ATM protein present in cells derived from 5762ins137 patients, has a specific activity of kinase as The of mutant ATM from the 7271T→G homozygous and heterozygous variant A-T patients also kinase activity in but at specific These kinase although correlate with the milder clinical the of patients. In the intermediate p53 response and of in both the 5762ins137 and 7271T→G cells, in with the in of following to ionizing also that the residual ATM protein is of some normal that the severity of the A-T cellular The principal of both the 5762ins137 and 7271T→G patients is a in the severity of the neurological features and a of the degeneration that to the p53 and gene are reported to when ionizing cell in the and system M. P.J. 1998; PubMed Scopus Google Scholar, Russell A. M. P.J. S. A. PubMed Scopus Google Scholar). It has been proposed that of in the of damage that in to functional in later in a specific cell as and cells the presence of functional ATM is this to selective M. P.J. 1998; PubMed Scopus Google Scholar). development of the system that is in null A. L. S. R.A. Y. S. A. PubMed Scopus Google has not been reported in for p53 M. A. PubMed Scopus Google Scholar). the presence of a normal p53 response following of cells to ionizing radiation from patients with ataxia disorder Stankovic T. Jaspers A. Byrd P.J. Taylor A.M. Full Text Full Text PDF PubMed Scopus Google and an to between the 5762ins137 and 7271T→G cells in of p53 response that the is not the for progressive the p53 is only of the ATM response to DNA for ATM is cellular DNA repair The of the system with gene for of the repair for DNA or have that are for normal and system development G. A. T. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, Y. Y. P. Y. J. M. J. L. R. T. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, Y. T. P.J. PubMed Scopus Google Scholar). This is the in ataxia disorder patients the presence of degeneration is associated with mutations in the DNA double strand break repair Stankovic T. Jaspers A. Byrd P.J. Taylor A.M. Full Text Full Text PDF PubMed Scopus Google Scholar). It to that the less severe neurological symptoms the 5762ins137 and 7271T→G variant A-T patients at in for some normal DNA repair in The residual of the DNA double strand break repair proteins Nbs1 and hMre11, following ionizing radiation in cells derived from the 7271T→G patients with a although this has not been The of in the 5762ins137 cell however, this, although it is likely that the level of was the level of sensitivity for It is also the case that the 5762ins137 patients are affected the 7271T→G homozygous mutant patients. The presence of in both the 5762ins137 and 7271T→G patients of a DNA repair for a less severe DNA repair is that of the homozygous patients has a (3Stankovic T. Kidd A.M. Sutcliffe A. McGuire G.M. Robinson P. Weber P. Bedenham T. Bradwell A.R. Easton D.F. Lennox G.G. Haites N. Byrd P.J. Taylor A.M.R. Am. J. Hum. Genet. 1998; 62: 334-345Abstract Full Text Full Text PDF PubMed Scopus (305) Google Scholar), that is not and it is likely that repair are it that the of ATM in is in of the system Ziv Y. Shiloh Y. S. A. 1998; PubMed Scopus Google Scholar). The of a with an to protein progressive degeneration, to the of in cell Full Text PDF PubMed Scopus Google Scholar). The of to these specific the of p53 being for the of neuronal the of some normal for of lymphoid development in these patients. of p53 is a G. 1996; PubMed Scopus Google Scholar, M. A. M. T. 1996; PubMed Scopus Google Scholar, S. A. P. Genet. 1997; PubMed Scopus Google Scholar, P. PubMed Google Scholar, Y. J. J. J. R.A. PubMed Scopus Google Scholar). In to the intermediate p53 response to DNA damage, the activation of the following ionizing radiation is in cells from both the 5762ins137 and the 7271T→G patients. It that the mutant ATM protein is to and it and that the residual normal ATM protein expressed in the 5762ins137 patients is expressed at levels low to in this this at in the case of the 5762ins137 patients, the low levels of normal ATM are sufficient to other cellular as The of a to the A-T phenotype is of the of protein have been reported to in in cells neuronal and lymphoid cells M. P. R.A. 1997; PubMed Scopus Google Scholar, P. R.A. Full Text Full Text PDF PubMed Scopus Google Scholar). the of and of degeneration in both the 5762ins137 and 7271T→G patients that this in the not the severity of the A-T cells from patients, which not show degeneration, also exhibit a in the activation of that this also not the of system Stankovic T. Jaspers A. Byrd P.J. Taylor A.M. Full Text Full Text PDF PubMed Scopus Google Scholar). In these that the ATM protein expressed in cells derived from both the 5762ins137 and the 7271T→G variant A-T patients retain sufficient activity to the severity of the A-T cellular This both kinase activity and resulting in cell the patients are in clinical with classical A-T patients being the most affected and homozygous 7271T→G patients being the the level of residual ATM is greatest in affected The clinical and cellular features of A-T patients carrying either the 5762ins137 or 7271T→G mutation are likely to result from a combination of the cellular level of functional ATM protein the and level of ATM expression from the second mutant the age of the degree of degeneration is in as as a of of these cells is to the that are in the severity of the clinical of these for cellular when We Shiloh for ATM kinase