Diagnostic Challenge in PLIN1-Associated Familial Partial Lipodystrophy.

CONTEXT: Heterozygous frameshift variants in PLIN1 encoding perilipin-1, a key protein for lipid droplet formation and triglyceride metabolism, have been implicated in familial partial lipodystrophy type 4 (FPLD4), a rare entity with only six families reported worldwide. The pathogenicity of other PLIN1 null variants identified in patients with diabetes and/or hyperinsulinemia was recently questioned because of the absence of lipodystrophy in these individuals and the elevated frequency of PLIN1 null variants in the general population. OBJECTIVES: To reevaluate the pathogenicity of PLIN1 frameshift variants owing to new data obtained in the largest series of patients with FPLD4. METHODS: We performed histological and molecular studies for patients referred to our French National Reference Center for Rare Diseases of Insulin Secretion and Insulin Sensitivity for lipodystrophy and/or insulin resistance and carrying PLIN1 frameshift variants. RESULTS: We identified two heterozygous PLIN1 frameshift variants segregating with the phenotype in nine patients from four unrelated families. The FPLD4 stereotypical signs included postpubertal partial lipoatrophy of variable severity, muscular hypertrophy, acromegaloid features, polycystic ovary syndrome and/or hirsutism, metabolic complications (e.g., hypertriglyceridemia, liver steatosis, insulin resistance, diabetes), and disorganized subcutaneous fat lobules with fibrosis and macrophage infiltration. CONCLUSIONS: These data suggest that some FPLD4-associated PLIN1 variants are deleterious. Thus, the evidence for the pathogenicity of each variant ought to be carefully considered before genetic counseling, especially given the importance of an early diagnosis for optimal disease management. Thus, we recommend detailed familial investigation, adipose tissue-focused examination, and follow-up of metabolic evolution.

Complex dynamics under tension in a high-efficiency frameshift stimulatory structure.

Specific structures in mRNA can stimulate programmed ribosomal frameshifting (PRF). PRF efficiency can vary enormously between different stimulatory structures, but the features that lead to efficient PRF stimulation remain uncertain. To address this question, we studied the structural dynamics of the frameshift signal from West Nile virus (WNV), which stimulates -1 PRF at very high levels and has been proposed to form several different structures, including mutually incompatible pseudoknots and a double hairpin. Using optical tweezers to apply tension to single mRNA molecules, mimicking the tension applied by the ribosome during PRF, we found that the WNV frameshift signal formed an unusually large number of different metastable structures, including all of those previously proposed. From force-extension curve measurements, we mapped 2 mutually exclusive pathways for the folding, each encompassing multiple intermediates. We identified the intermediates in each pathway from length changes and the effects of antisense oligomers blocking formation of specific contacts. Intriguingly, the number of transitions between the different conformers of the WNV frameshift signal was maximal in the range of forces applied by the ribosome during -1 PRF. Furthermore, the occupancy of the pseudoknotted conformations was far too low for static pseudoknots to account for the high levels of -1 PRF. These results support the hypothesis that conformational heterogeneity plays a key role in frameshifting and suggest that transitions between different conformers under tension are linked to efficient PRF stimulation.

FRIZZY PANICLE drives supernumerary spikelets in bread wheat.

Bread wheat (Triticum aestivum) inflorescences, or spikes, are characteristically unbranched and normally bear one spikelet per rachis node. Wheat mutants on which supernumerary spikelets (SSs) develop are particularly useful resources for work towards understanding the genetic mechanisms underlying wheat inflorescence architecture and, ultimately, yield components. Here, we report the characterization of genetically unrelated mutants leading to the identification of the wheat FRIZZY PANICLE (FZP) gene, encoding a member of the APETALA2/Ethylene Response Factor transcription factor family, which drives the SS trait in bread wheat. Structural and functional characterization of the three wheat FZP homoeologous genes (WFZP) revealed that coding mutations of WFZP-D cause the SS phenotype, with the most severe effect when WFZP-D lesions are combined with a frameshift mutation in WFZP-A. We provide WFZP-based resources that may be useful for genetic manipulations with the aim of improving bread wheat yield by increasing grain number.

Transcriptional frameshifting rescues Citrobacter rodentium type VI secretion by the production of two length variants from the prematurely interrupted tssM gene.

The Type VI secretion system (T6SS) mediates toxin delivery into both eukaryotic and prokaryotic cells. It is composed of a cytoplasmic structure resembling the tail of contractile bacteriophages anchored to the cell envelope through a membrane complex composed of the TssL and TssM inner membrane proteins and of the TssJ outer membrane lipoprotein. The C-terminal domain of TssM is required for its interaction with TssJ, and for the function of the T6SS. In Citrobacter rodentium, the tssM1 gene does not encode the C-terminal domain. However, the stop codon is preceded by a run of 11 consecutive adenosines. In this study, we demonstrate that this poly-A tract is a transcriptional slippery site that induces the incorporation of additional adenosines, leading to frameshifting, and hence the production of two TssM1 variants, including a full-length canonical protein. We show that both forms of TssM1, and the ratio between these two forms, are required for the function of the T6SS in C. rodentium. Finally, we demonstrate that the tssM gene associated with the Yersinia pseudotuberculosis T6SS-3 gene cluster is also subjected to transcriptional frameshifting.

Myoclonus-dystonia and epilepsy in a family with a novel epsilon-sarcoglycan mutation.

Seizures have been reported in two families with myoclonus-dystonia due to epsilon-sarcoglycan (SGCE) mutations. We report a Norwegian family with myoclonus-dystonia and epilepsy associated with a novel SGCE mutation. All six manifesting SGCE mutation carriers had myoclonus, and dystonia was present in two patients. Sequencing of the SGCE gene in the proband identified a novel frameshift c.372delG mutation that predicts the amino acid change [p.Lys125SerfsX7] and the formation of a premature stop codon. The mutation segregated with myoclonus-dystonia in the family. The typical motor symptoms were accompanied by generalized seizures in four of six affected mutation carriers. The seizure type included febrile, absence and generalized tonic-clonic seizures. One deceased patient with severe epilepsy and myoclonus could not be tested for the SGCE mutation. Seizures are rarely observed in myoclonus-dystonia patients with SGCE mutations, and may not be a part of the phenotype. The co-occurrence of seizures and myoclonus-dystonia suggests that they are both due to the same underlying SGCE mutation. However, with epilepsy being a relatively common disorder and lack of complete co-segregation in our and previous families, it is possible that some patients suffer from two different genetic disorders. The presence of seizures and EEG abnormalities should not be considered exclusion criteria for the diagnosis of myoclonus-dystonia.

A balanced ratio of proteins from gene G and frameshift-extended gene GT is required for phage lambda tail assembly.

In bacteriophage λ, the overlapping open reading frames G and T are expressed by a programmed translational frameshift similar to that of the gag-pol genes of many retroviruses to produce the proteins gpG and gpGT. An analogous frameshift is widely conserved among other dsDNA tailed phages in their corresponding "G" and "GT" tail genes even in the absence of detectable sequence homology. The longer protein gpGT is known to be essential for tail assembly, but the requirement for the shorter gpG remained unclear because mutations in gene G affect both proteins. A plasmid system that can direct the efficient synthesis of tails was created and used to show that gpG and gpGT are both essential for correct tail assembly. Phage complementation assays under conditions where levels of plasmid-expressed gpG or gpGT could be altered independently revealed that the correct molar ratio of these two related proteins, normally determined by the efficiency of the frameshift, is also crucial for efficient assembly of functional tails. Finally, the physical connection between the G and T domains of gpGT, a consequence of the frameshift mechanism of protein expression, appears to be important for efficient tail assembly.

Expanding the mutation spectrum for Fraser syndrome: identification of a novel heterozygous deletion in FRAS1.

Fraser syndrome (FS) is a rare autosomal recessive inherited disorder characterized by cryptophthalmos, laryngeal defects and oral clefting, mental retardation, syndactyly, and urogenital defects. To date, 250 patients have been described in the literature. Mutations in the FRAS1 gene on chromosome 4 have been identified in patients with Fraser syndrome. So far, 26 mutations have been identified, most of them are truncating mutations. The mutational spectrum includes nucleotide substitutions, splicing defects, a large insertion, and small deletions/insertions. Moreover, single heterozygous missense mutations in FRAS1 seem to be responsible for non-syndromic unilateral renal agenesis. Here we report the first case of a family with two patients affected by Fraser syndrome due to a deletion of 64 kb (deletion 4q21.21) and an additional novel frameshift mutation in exon 66 of the FRAS1 gene. To date, large deletions of the FRAS1 gene have not yet been described. Large deletions seem to be a rare cause for Fraser syndrome, but should be considered in patients with a single heterozygous mutation.

A novel frame shift mutation in the GHRH receptor gene in familial isolated GH deficiency: early occurrence of anterior pituitary hypoplasia.

BACKGROUND: Mutations in the genes encoding for GHRH receptor (GHRHR) and GH (GH1) are the most common cause of familial isolated GH deficiency (IGHD). GHRHR mutations are often associated with anterior pituitary hypoplasia (APH), but this has been reported almost exclusively in children older than 8 yr. We analyzed the GHRHR and measured pituitary size in a consanguineous family with the father and three of the five siblings with IGHD. OBJECTIVE: The aim of the study was to find the mutated gene in a family with severe IGHD. METHODS: We sequenced the whole GHRHR coding regions and the intron-exon boundaries from peripheral DNA of the index patient. After identifying the novel mutation, we sequenced the region of interest in the other members of the family. We measured the anterior pituitary volume from magnetic resonance imaging (MRI). RESULTS: The father and the three affected children were homozygous for a new frame-shift mutation in the coding sequence of exon 4 (corresponding to the extracellular domain of the receptor) (c.340delG) that places the downstream sequence out of frame [corrected]. The mother and two unaffected siblings were heterozygous for the mutation. Two of the affected children had MRI evidence of APH before reaching 6 yr of age. CONCLUSIONS: We describe a new mutation in the GHRHR in a family with IGHD. The presence of frank APH before age 6 yr shows that MRI-evident reduced pituitary size can be present in GHRHR mutations even in children younger than 8 yr of age.

Alexander disease causing mutations in the C-terminal domain of GFAP are deleterious both to assembly and network formation with the potential to both activate caspase 3 and decrease cell viability.

Alexander disease is a primary genetic disorder of astrocyte caused by dominant mutations in the astrocyte-specific intermediate filament glial fibrillary acidic protein (GFAP). While most of the disease-causing mutations described to date have been found in the conserved α-helical rod domain, some mutations are found in the C-terminal non-α-helical tail domain. Here, we compare five different mutations (N386I, S393I, S398F, S398Y and D417M14X) located in the C-terminal domain of GFAP on filament assembly properties in vitro and in transiently transfected cultured cells. All the mutations disrupted in vitro filament assembly. The mutations also affected the solubility and promoted filament aggregation of GFAP in transiently transfected MCF7, SW13 and U343MG cells. This correlated with the activation of the p38 stress-activated protein kinase and an increased association with the small heat shock protein (sHSP) chaperone, αB-crystallin. Of the mutants studied, D417M14X GFAP caused the most significant effects both upon filament assembly in vitro and in transiently transfected cells. This mutant also caused extensive filament aggregation coinciding with the sequestration of αB-crystallin and HSP27 as well as inhibition of the proteosome and activation of p38 kinase. Associated with these changes were an activation of caspase 3 and a significant decrease in astrocyte viability. We conclude that some mutations in the C-terminus of GFAP correlate with caspase 3 cleavage and the loss of cell viability, suggesting that these could be contributory factors in the development of Alexander disease.

Strains of the East Asian (W/Beijing) lineage of Mycobacterium tuberculosis are DosS/DosT-DosR two-component regulatory system natural mutants.

As part of our ongoing efforts to uncover the phenotypic consequences of genetic variability among clinical Mycobacterium tuberculosis isolates, we previously reported that isolates of the "East Asian" or "W/Beijing" lineage constitutively overexpress the coordinately regulated transcriptional program known as the DosR regulon under standard in vitro conditions. This phenotype distinguishes the W/Beijing lineage from all other M. tuberculosis lineages, which normally induce expression of this regulon only once exposed to low oxygen or nitric oxide, both of which result in inhibition of bacterial respiration and replication. Transcription of the DosR regulon is controlled through a two-component regulatory system comprising the transcription factor DosR and two possible cognate histidine sensor kinases, DosS and DosT. Through sequence analysis of a carefully selected set of isolates representing each of the major M. tuberculosis lineages, we describe herein a naturally occurring frameshift mutation in the gene encoding the DosT sensor kinase for isolates of the most recently evolved W/Beijing sublineages. Intriguingly, the occurrence of the frameshift mutation correlates precisely with the appearance of the constitutive DosR regulon phenotype displayed by the same "modern" W/Beijing strains. However, complementation studies have revealed that the mutation in dosT alone is not directly responsible for the constitutive DosR regulon phenotype. Our data serve to highlight the evolutionary pressure that exists among distinct M. tuberculosis lineages to maintain tight control over DosR regulon expression.

A frame shift due to a two-nucleotide deletion results in an HLA-B null allele, B*9549N.

This report describes the identification of a new human leukocyte antigen (HLA) class I null allele, B*9549N, resulting from a premature stop codon in exon 3.

Dissecting the molecular mechanisms in craniofrontonasal syndrome: differential mRNA expression of mutant EFNB1 and the cellular mosaic.

Craniofrontonasal syndrome (CFNS) is an X-linked malformation syndrome with variable phenotype that is caused by mutations in the ephrin-B1 gene (EFNB1). Over 50% of EFNB1 mutations result in premature termination codons that may elicit mRNA degradation by the nonsense-mediated decay pathway. To assess the effects of various mutations at the transcript level, expression of EFNB1 mRNA was studied by RT-PCR in fibroblast cultures established from CFNS female patients. Compared to the wild-type and two missense mutation alleles, severe depletion of transcripts was observed for mutant alleles harbouring either splice site mutation c.407-2A>T at the exon 2/3 boundary or frameshift mutation c.377_384delTCAAGAAG in exon 2. In contrast, escape from mRNA decay was observed for mutation c.614_615delCT, which generates a premature termination codon close to the 3'-end of the penultimate exon 4 disobeying the '50-55 bp' rule. These results suggest differential degradation of mutant EFNB1 transcripts by the nonsense-mediated mRNA decay pathway. Although the clinical phenotypes of the patients were not highly suggestive of a phenotype-genotype correlation, the two female patients were diagnosed with diaphragmatic hernia harbouring putative ephrin-B1 truncating mutations. Previously, disease manifestation in heterozygous females had been attributed mainly to cellular interference of divergent cell populations expressing wild-type or mutant EFNB1, depending on the pattern of X-inactivation. Upon clonal expansion of patient cells with either the wild-type or mutant EFNB1 on the active X-chromosome, we were able to separate mutant and wild-type EFNB1-expressing cells in vitro, further supporting the concept of cellular interference in CFNS.

[Phenotype-genotype study in 154 French NF2 mutation carriers]. / Analyse phénotypique de 154 patients porteurs d'une mutation constitutionnelle du gène NF2.

INTRODUCTION: Germline mutations in the NF2 gene are responsible for 80 p.cent of neurofibromatosis type 2 typical cases. Mutations are mainly truncating mutations or deletions, missense mutations having been reported in few cases. An important phenotypic variability is observed among gene carriers. To assess whether the phenotypic variability of neurofibromatosis 2 could be linked to genotype, clinical data of 154 patients whose NF2 germline alteration had been identified in our laboratory have been collected. METHODS: A retrospective questionnaire was sent to the physicians in charge of these patients. Statistical analyses regarding genotypic and phenotypic data were performed by comparisons of average values and correlation tests. RESULTS: In French patients, type of mutation was correlated neither with patients' sex, nor with disease occurrence mode (de novo or inherited mutation). Disease associated with missense mutations occurred later, with a less severe symptomatology. Patients with nonsense or frameshift mutations were more frequently affected with meningiomas and spinal tumours, in addition to VIII nerve schwannomas, an observation that underlies the genetic determination of the number and type of NF2-related tumours. CONCLUSION: Results from the literature as well as from our study tend to show that only few correlations exist between genotype and phenotype in the NF2 disease. It also recognizes that missense mutations have a lower level of evolution, severity and mortality risk. Nonsense and frameshift mutations seem to be associated with a higher number of meningiomas and spinal tumours. Therefore, NF2 gene screening keeps its indications in both typical and moderate forms of the disease. Mutations are responsible of 80 p.cent of typical forms; in moderate forms, identification of a missense mutation seems linked to a lower disease evolution. In any case, assessment and supervision should be identical. Finally, in a small number of cases, the NF2 gene appears to be implicated in clinical forms different from those defined by NIH and it might be of interest to enlarge the clinical features suggestive of the disease.

A novel beta-Thalassemic allele due to a two nucleotide deletion: beta76 (-GC).

We have identified and characterized a novel beta-thalassemic mutation in a North African adult. The molecular defect consists of a two nucleotide (nt) deletion in the beta-globin gene at codon 76 [beta76 (-GC), c.229-230delGC]. This frameshift mutation generates a TGA stop codon at position 89. The carrier presented with mild microcytic anemia (Hb 12.8 g/dL, MCV 60 fL), no detectable Hb F, an elevated Hb A2 level (5.5%) with no other mutation in the beta-globin gene and none of the more common known deletions in the alpha-globin cluster. No abnormal hemoglobin (Hb) was present in routine electrophoresis or in high performance liquid chromatography (HPLC) analyses. Pathologic inclusions were absent in both mature red cells and in reticulocytes. This observation reinforces the hypothesis that nonsense and frameshift mutations that result in a premature stop codon in exon 1 or exon 2 inherited in the heterozygous state do not generate dominant beta-thalassemia (thal). This is the first example of a premature stop codon at position 89.

Overexpression of DNA polymerase beta results in an increased rate of frameshift mutations during base excision repair.

DNA polymerase beta (Pol beta) is important for the base excision repair (BER) pathway. Overexpression of Pol beta is frequently found in cancer cells and is thought to be associated with tumorigenesis. In this study, we examined BER fidelity in extracts derived from a human lymphoblastoid cell line that over expresses Pol beta compared to normal control cells. Using an in vitro mutagenesis assay, we found an increased rate of frameshift mutations arising during DNA repair in whole-cell extracts derived from the Pol beta-overexpressing cells. We demonstrate that the addition of excess Pol beta to a control cell extract enhances the mutagenic potential of the extract. Furthermore, using cell extracts and purified Pol beta, we demonstrate that the mechanism of frameshift formation involves slippage of Pol beta during the one-nucleotide gap-filling step of BER and that this slippage is fixed by strand-displacement synthesis stimulated by an excess of Pol beta.

Long-term follow-up of combined pituitary hormone deficiency in two siblings with a Prophet of Pit-1 gene mutation.

Combined pituitary hormone deficiency (CPHD) is a rare disorder resulting from an impaired pituitary function due to different causes, characterized by impaired secretion of growth hormone (GH) and one or more of the other anterior pituitary hormones. To date, 16 distinct human Prophet of Pit-1 (Prop1) gene mutations have been identified in patients with CPHD, inducing a phenotype involving GH, follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin and thyroid-stimulating hormone (TSH), and rarely adrenocorticotropic hormone, deficiency. Herein we present two siblings of different sexes from a family with parental consanguinity presenting the 301-302delAG mutation in the Prop1 gene. The female presented failure of growth from the age of 6 years and was treated for 10 years with GH, ending in a final height (standard deviation score) of -0.28. TSH deficiency was manifested after the initiation of GH and was treated with thyroxine while puberty was initiated with conjugated estrogens. The male presented TSH deficiency since childhood, treated with thyroxine, and growth failure at the age of 14 years, treated for a period of 2 years with GH. Puberty was initiated with increasing doses of testosterone, while human chorionic gonadotropin was added in order to achieve increased testicular volume. In conclusion, these two siblings of different sexes with CPHD carrying the 301-302delAG mutation in the Prop1 gene presented a variable phenotype characterized by GH, TSH, LH and FSH deficiency.

Accumulation of recessive lethal mutations in Saccharomyces cerevisiae mlh1 mismatch repair mutants is not associated with gross chromosomal rearrangements.

We examined mismatch repair (MMR)-defective diploid strains of budding yeast grown for approximately 160 generations to determine whether decreases in spore viability due to the uncovering of recessive lethal mutations correlated with an increase in gross chromosomal rearrangements (GCRs). No GCRs were detected despite dramatic decreases in spore viability, suggesting that frameshift and/or other unrepaired DNA replication lesions play a greater role than chromosomal instability in decreasing viability in MMR-defective strains.

A novel thyroid hormone receptor-beta mutation that fails to bind nuclear receptor corepressor in a patient as an apparent cause of severe, predominantly pituitary resistance to thyroid hormone.

CONTEXT: Resistance to thyroid hormone (RTH) is a dominantly inherited syndrome of variable tissue hyporesponsiveness to thyroid hormone (TH). OBJECTIVE: We report a newborn who presented with severe RTH (Mkar) with serum TSH 1500 mU/liter and free T(3) greater than 50 pm (normal 3.1-9.4) and free T(4) 25.3 pm (normal 12-22). We hypothesized that the RTH was due to reduced ligand binding and/or abnormal interaction with nuclear cofactors. DESIGN: These were prospective in vivo and in vitro studies. SETTING: The study was conducted at a tertiary care university hospital. PATIENTS: Patients included a newborn child and two other subjects with RTH. INTERVENTION: The effect of various TH-lowering agents in the subject with RTH was studied. In vitro studies including EMSA and mammalian two-hybrid assay as well as in vitro transfection studies were conducted. MAIN OUTCOME MEASURES: Sequencing of the TH receptor (TR)beta and in vitro measurements of receptor-cofactor interaction were measured. RESULTS: Sequencing of the TRbeta demonstrated a de novo heterozygous mutation, 1590_1591insT, resulting in a frameshift producing a mutant TRbeta (mutTR)-beta with a 28-amino acid (aa) nonsense sequence and 2-amino acid carboxyl-terminal extension. The Mkar mutation was evaluated in comparison to three other TRbeta frameshift mutations in the carboxyl terminus. EMSA demonstrated that the Mkar mutTRbeta1 had impaired ability to recruit nuclear receptor corepressor but intact association with silencing mediator of retinoid and thyroid receptor (SMRT). CONCLUSION: Our data suggest that alterations in codons 436-453 in helix 11 result in significantly diminished association with nuclear receptor corepressor but not SMRT. This novel mutTRbeta demonstrates nuclear corepressor specificity that results in severe predominantly pituitary RTH due to impaired release of SMRT.

Crohn's disease-associated NOD2 variants share a signaling defect in response to lipopolysaccharide and peptidoglycan.

BACKGROUND & AIMS: The NOD2 variants R702W, G908R, and L1007fsinsC are strongly associated with Crohn's disease (CD) in both European and American populations, but whether this susceptibility extends to all ethnic groups remains unknown. Except for the L1007fsinsC mutation, which produces a truncated NOD2 protein, the functional activity of the major CD-associated variants G908R and R702W is unknown. METHODS: Individuals were genotyped for R702W, G908R, and L1007fsinsC. The ability of G908R, R702W, and L1007fsinsC variants in the presence and absence of P268S to confer responsiveness to lipopolysaccharide (LPS) and peptidoglycan (PGN) was determined in HEK293T kidney cells. RESULTS: G908R and L1007fsinsC, but not R702W, were associated with disease susceptibility in Ashkenazi Jews. Ashkenazi Jews with CD had significantly higher allele frequency carriage of G908R and lower carriage of R702W compared with non-Jewish whites with CD. Functional studies revealed that the G908R, R702W, and L1007fsinsC variants in the presence and absence of P268S are defective in their ability to respond to bacterial LPS and PGN, whereas P268S alone exhibited wild-type activity. CONCLUSIONS: R702W is not associated with susceptibility to CD in Ashkenazi Jews. The G908R, R702W, and L1007fsinsC variants share a common signaling defect in response to bacterial components, providing evidence for a unifying molecular mechanism whereby NOD2 mutations contribute to disease susceptibility.