Type of TP53 Mutations Affects Subclonal Configuration and Selection Pressure for Acquisition of Additional Hits in Contralateral Alleles

Somatic TP53 mutations are found in 10% of adult patients with MDS and de novo AML and in up to 20% of patients with therapy-related myeloid neoplasms. TP53 status is associated with complex karyotype (CK), aberrations of chromosome 5 and poor survival. Moreover, mutated TP53 (TP53MT) may be an indication for hematopoietic cell transplantation, but also predictive of relapse following the procedure, making this particular category of myeloid neoplasms (MN) a conundrum of clinical management. Unlike other tumor suppressor genes, missense (ms) mutations within the DNA-binding domain (DBD) are the most common genetic alterations in TP53 gene representing up to 80% of somatic hits, with involvement of canonical hotspots (R175H, Y220C, M237I, R248Q, R273H, R282W) in around 30% of cases. A loss-of-function (LOF) dominant-negative effect (DN) may explain the ability of TP53MT to interfere with wild type (WT) functions. Moreover, TP53 germ line (GL) mutations are responsible for Li-Fraumeni syndrome, and GL contamination may also exist in adult MN. Here we comprehensively characterize TP53MT MNs to better dissect the role of specific mutational configurations and identify the selective forces affecting outcomes in this poor prognostic MN category. A total of 764 TP53 mutations were found in 632 MN patients. Ms mutations were the most common (75%) followed by frameshift (11%), splice site (7%), nonsense (5%) and insertion/deletions (2%), with 20% of patients harboring more than 1 lesion. Topographical annotation revealed that ms mutations typically (98%) occurred within the DBD (residues 102-292) and only 2% occurred outside this region (vs. 28% in case of truncating mutations, p<.0001). Overall, 22% of patients displayed a mutation in the canonical hotspot regions. Among TP53MT, 36 cases (6%) were of possible GL origin. Focusing on the somatic lesions, a male preponderance (1.42 vs. 1.1 M:F, p=.0069) and a younger age at presentation (median 68.9 vs 71, p<.00001) were found in WT vs. mutant cases, which were also less enriched in coincident de novo leukemia-driver genes mutations (e.g. NPM1, FLT3). When compared to WT MN, TP53MT cases were more likely to have CK (8% vs. 70%, p<.00001), del(5q) (4% vs. 40%, p<.00001), del(7q)/-7 (6% vs. 18%, p<.00001) and trisomy 8 (8% vs. 49%, p<.00001). Of note, deletion of the TP53 locus was found in 27% of mutated cases vs only 1% of WT counterparts (p<.00001). Conversely, 77% of all MN cases with CK had either TP53 mutations (61%), del(17p) (3%) or both (36%). When classifying patients according to TP53 genomic context (30% single vs. 70% double hit, defined as a presence of biallelic, hemizigous or UPD configuration) progressive inactivation had an adverse impact on survival (p<.0001). We then hypothesized that truncating (frameshift/nonsense/deletion) alterations require additional hits as the presence of one allele may be partially protective. Consequently, the VAF for these lesions may be a result of a UPD in a smaller fraction of cells; biallelic truncation hits thus may be truly biallelic rather than clonally mosaic, which can be demonstrated only by single cell DNA sequencing. In contrast, DN mutations in canonical hotspots decrease the function beyond 50% of the activity, with further inactivation would having less of an effect, thus exerting less selection pressure for acquisition of additional lesions. Indeed, second truncating hits (including UPD and del(17p)) were common (30%), while none of the dominant ms hits had a double-mutant hotspot configuration (vs. 14% of non-canonical ms double mutant), and these canonical dominant hits were less likely to be paired with del(17p) or truncating mutations (8%). Only 25% of CK had a WT configuration of TP53, consistent with our theory that dominant ms hits were more likely to be present without del(17p). It is possible that the inability to assert clear survival differences according to the number or types of TP53 lesions may be due to an inability to resolve the intraclonal configuration of mutations using VAF calculations. We also conclude that non-canonical ms mutations (many of them classified as VUS) may have a variable impact, with functional consequences ranging from those that are less severe than truncations to various degrees of negative dominance. Analyses of the impact of ms mutations on TP53 tetramers (which may contain various doses of mutant vs WT monomer), will shed further light on the biology of TP53MT MN. Disclosures Voso: Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding. Sekeres:Takeda/Millenium: Consultancy; BMS: Consultancy; Pfizer: Consultancy. Carraway:Abbvie: Other: Independent Advisory Committe (IRC); Stemline: Consultancy, Speakers Bureau; ASTEX: Other: Independent Advisory Committe (IRC); BMS: Consultancy, Other: Research support, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Jazz: Consultancy, Speakers Bureau; Takeda: Other: Independent Advisory Committe (IRC). Maciejewski:Alexion, BMS: Speakers Bureau; Novartis, Roche: Consultancy, Honoraria.

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TP53 Mutations Are the Most Unfavorable Genetic Alteration in AML

Blood ◽

10.1182/blood.v120.21.660.660 ◽

2012 ◽

Vol 120 (21) ◽

pp. 660-660 ◽

Cited By ~ 1

Author(s):

Claudia Haferlach ◽

Vera Grossmann ◽

Christiane Eder ◽

Alexander Kohlmann ◽

Wolfgang Kern ◽

...

Keyword(s):

Cox Regression ◽

Close Association ◽

Tp53 Gene ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Complex Karyotype ◽

Cox Regression Analysis ◽

Tp53 Mutations ◽

Equity Ownership ◽

The Impact

Abstract Abstract 660 Background: TP53 is the most frequently mutated gene in cancer. An association of TP53 mutations and adverse prognosis was shown in multiple malignancies. In AML, a high frequency of TP53 alterations has been reported in cases with complex karyotype. However, thus far, a comprehensive study analyzing the impact of TP53 alterations has been lacking. Aims: 1. Determine the frequency of TP53 mutations (TP53mut) and TP53 deletions (TP53del) in a large cohort of AML. 2. Analyze the relation of TP53mut and TP53del with cytogenetics and other molecular mutations. 3. Evaluate the impact of TP53 alterations on outcome. Patients and methods: In 1,000 AML patients (median age 66.8 yrs) the TP53 gene (exons 4–11) was analyzed to detect mutations by either DHPLC with subsequent direct Sanger sequencing (n=190) or a next-generation amplicon deep-sequencing assay (n=810) (454 Life Sciences, Branford, CT). All cases with available material (n=858) were analyzed by interphase FISH for TP53del. In all cases the karyotype was available and categorized according to the refined MRC classification (Grimwade et al., Blood 2010). Cases were also screened for mutations in NPM1 (n=966), CEPBA (n=997), RUNX1 (n=907), ASXL1 (n=937) as well as for FLT3-ITD (n=999) and MLL-PTD (n=952). Clinical follow-up data was available in 841 patients. Results: Frequency of TP53 mutations and deletions: In 115 patients (11.5%) a total of 131 TP53mut were detected. 99 patients showed one and 16 cases two TP53 mutations. Heterozygous deletions of the TP53 gene were detected by FISH in 55/858 (6.4%) patients. In 97/115 cases with TP53mut also the TP53del status was available: 41/97 (42.3%) cases harbored both a TP53mut and a TP53del. 32 of the 56 (57.1%) TP53mut cases without TP53del showed heterozygous and 24 (42.8%) homozygous TP53mut. 13/32 (40.6%) cases with heterozygous mutations harbored two distinct TP53mut, whereas only 19/32 (59.3%) were affected by one mutation suggesting a dominant negative effect of these mutations. In patients with homozygous mutations and no TP53del a copy neutral loss of heterozygosity (CN-LOH) can be assumed. In 2 of these patients SNP microarray data was available revealing in both cases a CN-LOH spanning from 17p11.2 to 17p13.3. Association with cytogenetics and other molecular markers: TP53mut were observed in 1/106 cases with favorable, 12/688 with intermediate (1.7%), and 17/90 (18.9%) with adverse cytogenetics. In cases with complex karyotype TP53mut frequency was 73.3% (85/116). TP53mut were mutually exclusive of CEPBA and NPM1 mutations. In patients harboring TP53mut FLT3-ITD, MLL-PTD, RUNX1 and ASXL1 mutations were detected at low frequencies (2.6%, 4.3%, 7.8% and 4.3%, respectively). TP53del were observed in 2/88 (2.3%) patients with favorable, in 6/601 (1.0%) with intermediate, and in 47/169 (27.8%) cases with adverse cytogenetics. 39/47 (83.0%) patients with adverse cytogenetics and TP53del harbored a complex karyotype. 41/55 (74.5%) cases with TP53del also harbored a TP53mut. Clinical impact: Median OS in patients with TP53mut (n=80) vs TP53 wild-type (wt) cases (n=761) was 4.6 vs 35.6 months (mo) (P<0.001), median EFS was 3.1 vs 13.3 mo (P<0.001); OS and EFS at 3 yrs was 0% vs 49.6% and 0% vs 33.8%. Within the complex karyotype cohort, patients with TP53mut (n=56/80) showed an inferior outcome compared to TP53wt cases (n=24/80) (OS and EFS at 3 yrs: 0% vs 27.9%, P=0.002, 0% vs 25.7%, P=0.002). In univariable Cox regression analyses TP53mut and TP53del were significantly associated with shorter OS (hazard ratio (HR) 3.49; P<0.001 and 2.33; P<0.001). Additionally, in multivariable Cox regression analysis the following parameters were included (which were also significantly associated with OS in univariable analysis): favorable and adverse cytogenetics, complex karyotype, monosomal karyotype, CEPBA double-mutations, NPM1mut/FLT3-ITD-, MLL-PTD, RUNX1, and ASXL1 mutations. Independent prognostic factors were: complex karyotype (HR 1.64, P=0.05), CEPBA double-mutations (HR 0.30; P=0.002), NPM1mut/FLT3-ITD- status (HR 0.62; P=0.004), ASXL1mut (HR 1.46; P=0.016), and TP53mut (HR 2.17; P<0.001). Conclusions: 1. TP53mut occurred in 11.5% and TP53del in 6.4% of AML patients and both showed a close association with adverse karyotype, especially complex karyotype. 2. TP53mut was the parameter with highest risk for adverse outcome compared to any other known genetic risk marker in AML thus far. Disclosures: Haferlach: MLL Munich Leukemia Laboratory: Equity Ownership. Grossmann:MLL Munich Leukemia Laboratory: Employment. Eder:MLL Munich Leukemia Laboratory: Employment. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Equity Ownership. Schnittger:MLL Munich Leukemia Laboratory: Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership.

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DNM1 encephalopathy

Neurology ◽

10.1212/wnl.0000000000004152 ◽

2017 ◽

Vol 89 (4) ◽

pp. 385-394 ◽

Cited By ~ 31

Author(s):

Sarah von Spiczak ◽

Katherine L. Helbig ◽

Deepali N. Shinde ◽

Robert Huether ◽

Manuela Pendziwiat ◽

...

Keyword(s):

Functional Data ◽

De Novo ◽

Structural Modeling ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Global Developmental Delay ◽

Epilepsy Syndrome ◽

De Novo Mutations ◽

Phenotypic Data ◽

Phenotypic Spectrum

Objective:To evaluate the phenotypic spectrum caused by mutations in dynamin 1 (DNM1), encoding the presynaptic protein DNM1, and to investigate possible genotype-phenotype correlations and predicted functional consequences based on structural modeling.Methods:We reviewed phenotypic data of 21 patients (7 previously published) with DNM1 mutations. We compared mutation data to known functional data and undertook biomolecular modeling to assess the effect of the mutations on protein function.Results:We identified 19 patients with de novo mutations in DNM1 and a sibling pair who had an inherited mutation from a mosaic parent. Seven patients (33.3%) carried the recurrent p.Arg237Trp mutation. A common phenotype emerged that included severe to profound intellectual disability and muscular hypotonia in all patients and an epilepsy characterized by infantile spasms in 16 of 21 patients, frequently evolving into Lennox-Gastaut syndrome. Two patients had profound global developmental delay without seizures. In addition, we describe a single patient with normal development before the onset of a catastrophic epilepsy, consistent with febrile infection-related epilepsy syndrome at 4 years. All mutations cluster within the GTPase or middle domains, and structural modeling and existing functional data suggest a dominant-negative effect on DMN1 function.Conclusions:The phenotypic spectrum of DNM1-related encephalopathy is relatively homogeneous, in contrast to many other genetic epilepsies. Up to one-third of patients carry the recurrent p.Arg237Trp variant, which is now one of the most common recurrent variants in epileptic encephalopathies identified to date. Given the predicted dominant-negative mechanism of this mutation, this variant presents a prime target for therapeutic intervention.

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Clinical and molecular analysis of three families with autosomal dominant neurohypophyseal diabetes insipidus associated with a novel and recurrent mutations in the vasopressin-neurophysin II gene

Acta Endocrinologica ◽

10.1530/eje.0.1460649 ◽

2002 ◽

pp. 649-656 ◽

Cited By ~ 26

Author(s):

J Rutishauser ◽

P Kopp ◽

MB Gaskill ◽

TJ Kotlar ◽

GL Robertson

Keyword(s):

Diabetes Insipidus ◽

Autosomal Dominant ◽

De Novo ◽

Index Patient ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Heterozygous Mutation ◽

Posterior Pituitary ◽

Recurrent Mutations ◽

Neurophysin Ii

OBJECTIVE: To test further the hypothesis that autosomal dominant neurohypophyseal diabetes insipidus (adFNDI) is caused by heterozygous mutations in the vasopressin-neurophysin II (AVP-NPII) gene that exert a dominant negative effect by producing a precursor that misfolds, accumulates and eventually destroys the neurosecretory neurons. METHODS: Antidiuretic function, magnetic resonance imaging (MRI) of the posterior pituitary and AVP-NPII gene analysis were performed in 10 affected members of three unreported families with adFNDI. RESULTS: As in previously studied patients, adFNDI apparently manifested after birth, was due to a partial or severe deficiency of AVP, and was associated with absence or diminution of the hyperintense MRI signal normally emitted by the posterior pituitary, and with a heterozygous mutation in the AVP-NPII gene. In family A, a transition 275G-->A, which predicts replacement of cysteine 92 by tyrosine (C92Y), was found in the index patient, but not in either parent, indicating that it arose de novo. The six affected members of family B had a transversion 160G-->C, which predicts replacement of glycine 54 by arginine (G54R). It appeared de novo in the oldest affected member, and was transmitted in a dominant manner. In family C, six of 15 living affected members were tested and all had a novel transition, 313T-->C, which predicts replacement of cysteine 105 by arginine (C105R). It, too, was transmitted in a dominant manner. As in other patients with adFNDI, the amino acids replaced by the mutations in these three families are known to be particularly important for correct and efficient folding of the precursor. CONCLUSIONS: These findings are consistent with the malfolding/toxicity hypothesis underlying the pathogenesis of adFNDI. Moreover, they illustrate the value of genetic analysis in all patients who develop idiopathic diabetes insipidus in childhood, even if no other family members are affected.

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Sensing through Non-Sensing Ocular Ion Channels

International Journal of Molecular Sciences ◽

10.3390/ijms21186925 ◽

2020 ◽

Vol 21 (18) ◽

pp. 6925

Author(s):

Meha Kabra ◽

Bikash Ranjan Pattnaik

Keyword(s):

Ion Channels ◽

Visual Processing ◽

Signal Transmission ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Cone Dystrophy ◽

Wide Range ◽

The Impact

Ion channels are membrane-spanning integral proteins expressed in multiple organs, including the eye. In the eye, ion channels are involved in various physiological processes, like signal transmission and visual processing. A wide range of mutations have been reported in the corresponding genes and their interacting subunit coding genes, which contribute significantly to an array of blindness, termed ocular channelopathies. These mutations result in either a loss- or gain-of channel functions affecting the structure, assembly, trafficking, and localization of channel proteins. A dominant-negative effect is caused in a few channels formed by the assembly of several subunits that exist as homo- or heteromeric proteins. Here, we review the role of different mutations in switching a “sensing” ion channel to “non-sensing,” leading to ocular channelopathies like Leber’s congenital amaurosis 16 (LCA16), cone dystrophy, congenital stationary night blindness (CSNB), achromatopsia, bestrophinopathies, retinitis pigmentosa, etc. We also discuss the various in vitro and in vivo disease models available to investigate the impact of mutations on channel properties, to dissect the disease mechanism, and understand the pathophysiology. Innovating the potential pharmacological and therapeutic approaches and their efficient delivery to the eye for reversing a “non-sensing” channel to “sensing” would be life-changing.

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Heterozygous Missense Pathogenic Variants Within the Second Spectrin Repeat of SPTBN2 Lead to Infantile-Onset Cerebellar Ataxia

Journal of Child Neurology ◽

10.1177/0883073819878917 ◽

2019 ◽

Vol 35 (2) ◽

pp. 106-110 ◽

Cited By ~ 1

Author(s):

Andrea Accogli ◽

Judith St-Onge ◽

Nassima Addour-Boudrahem ◽

Joël Lafond-Lapalme ◽

Alexandre Dionne Laporte ◽

...

Keyword(s):

Cognitive Impairment ◽

Cerebellar Ataxia ◽

De Novo ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Adult Onset ◽

Spinocerebellar Ataxias ◽

Spectrin Repeat ◽

Missense Variants ◽

Pathogenic Variants

The term spinocerebellar ataxia encompasses a heterogeneous group of neurodegenerative disorders due to pathogenic variants in more than 100 genes, underlying 2 major groups of ataxia: autosomal dominant cerebellar ataxias (ADCA, also known as spinocerebellar ataxias [SCAs]) due to heterozygous variants or polyglutamine triplet expansions leading to adult-onset ataxia, and autosomal recessive spinocerebellar ataxias (ARCAs, also known as SCARs) due to biallelic variants, usually resulting in more severe and earlier-onset cerebellar ataxia. Certain ataxia genes, including SPTBN2 which encodes β-III spectrin, are responsible for both SCA and SCAR, depending on whether the pathogenic variant occurs in a monoallelic or biallelic state, respectively. Accordingly, 2 major phenotypes have been linked to SPTBN2: pathogenic heterozygous in-frame deletions and missense variants result in an adult-onset, slowly progressive ADCA (SCA5) through a dominant negative effect, whereas biallelic loss-of-function variants cause SCAR14, an allelic disorder characterized by infantile-onset cerebellar ataxia and cognitive impairment. Of note, 2 heterozygous missense variants (c.1438C>T, p.R480 W; c.1309C>G, p.R437G), both lying in the second spectrin repeat of SPTBN2, have been linked to infantile-onset cerebellar ataxia, similar to SCAR14. Here, we report a novel de novo heterozygous pathogenic missense variant (c.1310G>A) in SPTBN2 in a child with infantile-onset cerebellar ataxia and mild cognitive impairment. This variant affects the same R437 residue of the second spectrin repeat but results in a different amino acid change (p.R437Q). We review previously reported cases and discuss possible pathomechanisms responsible for the early-onset cerebellar phenotype due to disease-causing variants in the second spectrin repeat.

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Epilepsy and neurobehavioral abnormalities in mice with a KCNB1 pathogenic variant that alters conducting and non-conducting functions of KV2.1

10.1101/770206 ◽

2019 ◽

Author(s):

Nicole A. Hawkins ◽

Sunita N. Misra ◽

Manuel Jurado ◽

Nicholas C. Vierra ◽

Kimberly Nguyen ◽

...

Keyword(s):

Endoplasmic Reticulum ◽

Plasma Membrane ◽

De Novo ◽

Pathogenic Variant ◽

Repetitive Behaviors ◽

Dominant Negative ◽

Dominant Negative Effect ◽

Delayed Rectifier ◽

Eeg Abnormalities ◽

Surface Ecg

AbstractDevelopmental and epileptic encephalopathies (DEE) are a group of severe epilepsies that usually present with intractable seizures, developmental delay and are at a higher risk for premature mortality. Numerous genes have been identified as a monogenic cause of DEE, including KCNB1. The voltage-gated potassium channel KV2.1, encoded by KCNB1, is primarily responsible for delayed rectifier potassium currents that are important regulators of excitability in electrically excitable cells, including neurons and cardiomyocytes. The de novo pathogenic variant KCNB1-p.G379R was identified in an infant with epileptic spasms, atonic, focal and tonic-clonic seizures that were refractory to treatment with standard antiepileptic drugs. Previous work demonstrated deficits in potassium conductance, but did not assess non-conducting functions. To determine if the G379R variant affected clustering at endoplasmic reticulum-plasma membrane junctions KV2.1-G379R was expressed in HEK293T cells. KV2.1-G379R expression did not induce formation of endoplasmic reticulum-plasma membrane junctions, and co-expression of KV2.1-G379R with KV2.1-WT lowered induction of these structures relative to KV2.1-WT alone, suggesting a dominant negative effect. To model this variant in vivo, we introduced Kcnb1G379R into mice using CRISPR/Cas9 genome editing. We characterized neurological and neurobehavioral phenotypes of Kcnb1G379R/+ (Kcnb1R/+) and Kcnb1G379R/G379R (Kcnb1R/R) mice, and screened for cardiac abnormalities. Immunohistochemistry studies on brains from Kcnb1+/+ (WT), Kcnb1R/+ and Kcnb1R/R mice revealed genotype-dependent differences in the levels and subcellular localization of KV2.1, with reduced plasma membrane expression of the KV2.1-G379R protein, consistent with in vitro data. Kcnb1R/+ and Kcnb1R/R mice displayed profound hyperactivity, repetitive behaviors, impulsivity and reduced anxiety. In addition, both Kcnb1R/+ and Kcnb1R/R mice exhibited abnormal interictal EEG abnormalities, including isolated spike and slow waves. Spontaneous seizure events were observed in Kcnb1R/R mice during exposure to novel environments and/or handling, while both Kcnb1R/+ and Kcnb1R/R mutants were more susceptible to induced seizures. Kcnb1R/+ and Kcnb1R/R mice exhibited prolonged rate-corrected QT interval on surface ECG recording. Overall, the Kcnb1G379R mice recapitulate many features observed in individuals with DEE due to pathogenic variants in KCNB1. This new mouse model of KCNB1 associated DEE will be valuable for improving the understanding of the underlying pathophysiology and will provide a valuable tool for the development of therapies to treat this pharmacoresistant DEE.

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Impaired turnover of hyperfused mitochondria in severe axonal neuropathy due to a novel DRP1 mutation

Human Molecular Genetics ◽

10.1093/hmg/ddz211 ◽

2019 ◽

Vol 29 (2) ◽

pp. 177-188 ◽

Cited By ~ 2

Author(s):

Fabiana Longo ◽

Sara Benedetti ◽

Alberto A Zambon ◽

Maria Grazia Natali Sora ◽

Chiara Di Resta ◽

...

Keyword(s):

Molecular Mechanisms ◽

De Novo ◽

Mitochondrial Fission ◽

Axonal Neuropathy ◽

Sensory Neuropathy ◽

Early Death ◽

Cellular Level ◽

Dominant Negative ◽

Giant Mitochondria ◽

The Impact

Abstract Mitochondria undergo continuous cycles of fusion and fission in response to physiopathological stimuli. The key player in mitochondrial fission is dynamin-related protein 1 (DRP1), a cytosolic protein encoded by dynamin 1-like (DNM1L) gene, which relocalizes to the outer mitochondrial membrane, where it assembles, oligomerizes and drives mitochondrial division upon guanosine-5′-triphosphate (GTP) hydrolysis. Few DRP1 mutations have been described so far, with patients showing complex and variable phenotype ranging from early death to encephalopathy and/or optic atrophy. The disease is the consequence of defective mitochondrial fission due to faulty DRP1 function. However, the underlying molecular mechanisms and the functional consequences at mitochondrial and cellular level remain elusive. Here we report on a 5-year-old girl presenting psychomotor developmental delay, global hypotonia and severe ataxia due to axonal sensory neuropathy harboring a novel de novo heterozygous missense mutation in the GTPase domain of DRP1 (NM_012062.3:c.436G>A, NP_036192.2: p.D146N variant in DNM1L). Patient’s fibroblasts show hyperfused/balloon-like giant mitochondria, highlighting the importance of D146 residue for DRP1 function. This dramatic mitochondrial rearrangement phenocopies what observed overexpressing DRP1-K38A, a well-known experimental dominant negative version of DRP1. In addition, we demonstrated that p.D146N mutation has great impact on peroxisomal shape and function. The p.D146N mutation compromises the GTPase activity without perturbing DRP1 recruitment or assembly, causing decreased mitochondrial and peroxisomal turnover. In conclusion, our findings highlight the importance of sensory neuropathy in the clinical spectrum of DRP1 variants and, for the first time, the impact of DRP1 mutations on mitochondrial turnover and peroxisomal functionality.

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Complex Translocation (8;16;21); a New Variant of t(8;21), with t(13;22) in Acute Myeloid Leukemia.

Blood ◽

10.1182/blood.v106.11.4342.4342 ◽

2005 ◽

Vol 106 (11) ◽

pp. 4342-4342

Author(s):

Shiphali Gupta ◽

Judith Brody ◽

Veena John ◽

Prasad Koduru

Keyword(s):

Sex Chromosome ◽

Chromosome Region ◽

Genetic Alterations ◽

Dominant Negative ◽

Hematopoietic Cell ◽

Hematopoietic Progenitor Cell ◽

Dominant Negative Effect ◽

Complex Translocation ◽

New Variant ◽

Acute Myeloid

Abstract The translocation (8;21)(q22;q22) is a common recurrent chromosome aberration present in 10% to 15% of all acute myeloid leukemias. In approximately 3% of all cases with t(8;21), a variant of t(8;21) involving chromosomes 8,21 and other chromosomes is present. We report here a case of AML-M2 with a new complex translocation (8;16;21)(q22;p16.3;q22) associated with additional abnormality t(13;22)(q22;q13) not described before. Fluorescent in-situ hybridization analysis with probes for ETO and AML1 genes, and probes for the subtelomeric regions of chromosome 16 demonstrated an ETO-AML1 fusion signal on der(8). The 5′ region of ETO gene with chromosome arm distal to translocation breakpoint had moves to der(16) while region of AML1 probe proximal to translocation brealpoint stayed on der(21). The signal for the subtelomeric probe for 16p was present on der(21). Use of painting probe for chromosome 13 confirmed t(13;22). In a hematopoietic cell the expression of chimeric AML1- ETO protein resulting from t(8;21) plays a key role in leukemic transformation by targeting AML1-CBFB transcription factor complex, an essential regulator of genes required for normal hematopoietic cell development, by dominant negative effect on normal AML1 protein. However, the expression of AML1- ETO does not block normal differentiation of stem cells. Additional mutational events must occur in hematopoietic progenitor cell to block normal path of differentiation. Although clinical features of variant translocation is same as cases with conventional t(8;21), prognostic implications of variant (8;21) are yet to be established. Chromosome region 16p13 has been involved in clinically important translocations with poor prognosis such as t(8;16)(p11;p13) and t(11;16)(q23;p13) and may have similar implications. Translocation (8;21) is frequently accompanied by additional chromosome abnormalities i.e. loss of sex chromosome, trisomy 8 and structural abnormalities of 9q. Additional reports on secondary genetic alterations accompanying t(8;21) are needed to understand their cumulative effect. Chromosome region 16p13, 13q22 and 22q13 may harbor putative genes influencing normal path of differentiation.

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Mutational Analysis of PHEX Gene in X-Linked Hypophosphatemia1

The Journal of Clinical Endocrinology & Metabolism ◽

10.1210/jcem.83.10.5180 ◽

1998 ◽

Vol 83 (10) ◽

pp. 3615-3623 ◽

Cited By ~ 4

Author(s):

Peter H. Dixon ◽

Paul T. Christie ◽

Carol Wooding ◽

Dorothy Trump ◽

Marvin Grieff ◽

...

Keyword(s):

Untranslated Region ◽

De Novo ◽

Mutational Analysis ◽

Extracellular Domain ◽

Phosphate Transport ◽

Dominant Negative ◽

Hypophosphatemic Rickets ◽

Dominant Negative Effect ◽

Conformational Polymorphism ◽

Single Stranded Conformational Polymorphism

Hypophosphatemic rickets is commonly an X-linked dominant disorder (XLH or HYP) associated with a renal tubular defect in phosphate transport and bone deformities. The XLH gene, referred to as PHEX, or formerly as PEX (phosphate regulating gene with homologies to endopeptidases on the X-chromosome), encodes a 749-amino acid protein that putatively consists of an intracellular, transmembrane, and extracellular domain. PHEX mutations have been observed in XLH patients, and we have undertaken studies to characterize such mutations in 46 unrelated XLH kindreds and 22 unrelated patients with nonfamilial XLH by single stranded conformational polymorphism and DNA sequence analysis. We identified 31 mutations (7 nonsense, 6 deletions, 2 deletional insertions, 1 duplication, 2 insertions, 4 splice site, 8 missense, and 1 within the 5′ untranslated region), of which 30 were scattered throughout the putative extracellular domain, together with 6 polymorphisms that had heterozygosity frequencies ranging from less than 1% to 43%. Single stranded conformational polymorphism was found to detect more than 60% of these mutations. Over 20% of the mutations were observed in nonfamilial XLH patients, who represented de novo occurrences of PHEX mutations. The unique point mutation (a→g) of the 5′untranslated region together with the other mutations indicates that the dominant XLH phenotype is unlikely to be explained by haplo-insufficiency or a dominant negative effect.

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Essential Nonredundant Function of the Catalytic Activity of Histone Deacetylase 2 in Mouse Development

Molecular and Cellular Biology ◽

10.1128/mcb.00639-15 ◽

2015 ◽

Vol 36 (3) ◽

pp. 462-474 ◽

Cited By ~ 8

Author(s):

Astrid Hagelkruys ◽

Katharina Mattes ◽

Verena Moos ◽

Magdalena Rennmayr ◽

Manuela Ringbauer ◽

...

Keyword(s):

Histone Deacetylases ◽

Regulation Of Gene Expression ◽

Dominant Negative ◽

Mutant Mice ◽

Dominant Negative Effect ◽

Mouse Development ◽

Histone Deacetylase 2 ◽

Histone Hyperacetylation ◽

Negative Effect ◽

The Impact

The class I histone deacetylases (HDACs) HDAC1 and HDAC2 play partially redundant roles in the regulation of gene expression and mouse development. As part of multisubunit corepressor complexes, these two deacetylases exhibit both enzymatic and nonenzymatic functions. To examine the impact of the catalytic activities of HDAC1 and HDAC2, we generated knock-in mice expressing catalytically inactive isoforms, which are still incorporated into the HDAC1/HDAC2 corepressor complexes. Surprisingly, heterozygous mice expressing catalytically inactive HDAC2 die within a few hours after birth, while heterozygous HDAC1 mutant mice are indistinguishable from wild-type littermates. Heterozygous HDAC2 mutant mice show an unaltered composition but reduced associated deacetylase activity of corepressor complexes and exhibit a more severe phenotype than HDAC2-null mice. They display changes in brain architecture accompanied by premature expression of the key regulator protein kinase C delta. Our study reveals a dominant negative effect of catalytically inactive HDAC2 on specific corepressor complexes resulting in histone hyperacetylation, transcriptional derepression, and, ultimately, perinatal lethality.

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