RPA engages telomeric G-quadruplexes more effectively than CST.

G-quadruplexes (G4s) are a set of stable secondary structures that form within guanine-rich regions of single-stranded nucleic acids that pose challenges for DNA maintenance. The G-rich DNA sequence at telomeres has a propensity to form G4s of various topologies. The human protein complexes Replication Protein A (RPA) and CTC1-STN1-TEN1 (CST) are implicated in managing G4s at telomeres, leading to DNA unfolding and allowing telomere replication to proceed. Here, we use fluorescence anisotropy equilibrium binding measurements to determine the ability of these proteins to bind various telomeric G4s. We find that the ability of CST to specifically bind G-rich ssDNA is substantially inhibited by the presence of G4s. In contrast, RPA tightly binds telomeric G4s, showing negligible changes in affinity for G4 structure compared to linear ssDNAs. Using a mutagenesis strategy, we found that RPA DNA-binding domains work together for G4 binding, and simultaneous disruption of these domains reduces the affinity of RPA for G4 ssDNA. The relative inability of CST to disrupt G4s, combined with the greater cellular abundance of RPA, suggests that RPA could act as a primary protein complex responsible for resolving G4s at telomeres.

Replication Protein A Utilizes Differential Engagement of Its DNA-Binding Domains to Bind Biologically Relevant ssDNAs in Diverse Binding Modes.

Replication protein A (RPA) is a ubiquitous ssDNA-binding protein that functions in many DNA processing pathways to maintain genome integrity. Recent studies suggest that RPA forms a highly dynamic complex with ssDNA that can engage with DNA in many modes that are orchestrated by the differential engagement of the four DNA-binding domains (DBDs) in RPA. To understand how these modes influence RPA interaction with biologically relevant ligands, we performed a comprehensive and systematic evaluation of RPA's binding to a diverse set of ssDNA ligands that varied in sequence, length, and structure. These equilibrium binding data show that WT RPA binds structured ssDNA ligands differently from its engagement with minimal ssDNAs. Next, we investigated each DBD's contributions to RPA's binding modes through mutation of conserved, functionally important aromatic residues. Mutations in DBD-A and -B have a much larger effect on binding when ssDNA is embedded into DNA secondary structures compared to their association with unstructured minimal ssDNA. As our data support a complex interplay of binding modes, it is critical to define the trimer core DBDs' role in binding these biologically relevant ligands. We found that DBD-C is important for engaging DNA with diverse binding modes, including, unexpectedly, at short ssDNAs. Thus, RPA uses its constituent DBDs to bind biologically diverse ligands in unanticipated ways. These findings lead to a better understanding of how RPA carries out its functions at diverse locations of the genome and suggest a mechanism through which dynamic recognition can impact differential downstream outcomes.

MTHFR and ACE Polymorphisms Do Not Increase Susceptibility to Migraine Neither Alone Nor in Combination.

OBJECTIVE: The aim of this study was to confirm previous reports in order to substantiate the hypothesis that functional variants of two genes, namely methylenetetrahydrofolate reductase and angiotensin I converting enzyme, both involved in an important pathway of migraine, increase migraine susceptibility when present in combination. BACKGROUND: Migraine is a complex genetic disease. The migraine attack is thought to be the result of an interaction of neuronal and vascular events, possibly originating in the brainstem leading to activation of the pain processing trigeminovascular system. Functional variants in the methylenetetrahydrofolate gene and the angiotensin I converting enzyme have influence on vascular mechanism and have been investigated intensively in migraine. The published results were inconsistent; however, both polymorphisms in combination have been shown to increase migraine susceptibility. METHODS: In this genetic association study, the prevalence of the functionally relevant polymorphisms C677T in the MTHFR gene and I/D polymorphism in the ACE gene was compared in 420 patients with migraine vs 258 migraine-free controls using a chi-square statistic and binary logistic regression. RESULTS: Susceptibility to any type of migraine (migraine with aura, migraine without aura, and both types combined) was neither increased by each polymorphism on its own, nor in combination (MTHFR: X(2) = 0.18 [P = .91]; ACE: X(2) = 1.62 [P = .45]; combined: OR = 1.02 [95% CI 0.98-1.05] P = .97). CONCLUSIONS: We could not replicate a previous study that showed significant increase in migraine susceptibility for two functional polymorphisms in genes affecting relevant pathways.

A novel locus for familial migraine on Xp22.

INTRODUCTION: Migraine is thought to be genetically complex. There is evidence of an X-linked dominant genetic component. A locus at Xq24-q28 has already been described supporting this hypothesis. METHODS: The X chromosome in 61 migraine families was screened using markers spanning the entire chromosome. Alleles were assigned using the GeneScan Analysis software, analysis for affected relative allele sharing and linkage was performed using Genehunter X and ALLEGRO. For linkage analysis we chose a model based on epidemiological data as well as assumptions drawn on other complex disorders. RESULTS: Linkage analysis of combined families showed a parametric 2-point logarithm of the odds (LOD) of 2.86 at theta 0.1 between markers DXS8051 and DXS1223, as well as excess allele sharing at marker DXS8051 with a non-parametric LOD score of 2.85. CONCLUSION: These results provide suggestive evidence for a susceptibility locus for migraine on Xp22. Families with different types of migraine contributed to this LOD score.

No influence of 5-HTTLPR gene polymorphism on migraine symptomatology, comorbid depression, and chronification.

BACKGROUND: The serotonergic system is thought to play an important role for mediating susceptibility to migraine and depression, which is frequently found comorbid in migraine. The functional polymorphism in the serotonin transporter gene linked polymorphic region (5-HTTLPR/SLC6A4) was previously associated with attack frequency and, thus, possibly with chronification. OBJECTIVE: We hypothesized that patients with the "s" allele have higher attack frequency and, paralleling results in depression research, higher scores of depression. METHODS: Genetic analysis of the SLC6A4 44 bp insertion/deletion polymorphism (5-HTTLPR) was performed in 293 patients with migraine with and without aura. Self-rating questionnaires were used for assessment of depression. RESULTS: Multinomial logistic regression analysis found no evidence for association of the 5-HTTLPR polymorphism with either depression or migraine attack frequency. CONCLUSION: We were not able to demonstrate any influence of the serotonin transporter 5-HTTLPR polymorphism on migraine phenomenology (attack frequency or comorbid depression), thereby excluding this variant to be a common genetic denominator for chronic migraine and depression.

No carnitine palmitoyltransferase deficiency in skeletal muscle in 18 malignant hyperthermia susceptible individuals.

Malignant hyperthermia is a rare, potentially life threatening pharmacogenetic disorder triggered by volatile anaesthetics and depolarizing muscle relaxants. The clinical picture comprises rhabdomyolysis, metabolic and respiratory acidosis, and hyperthermia. Carnitine palmitoyltransferase II deficiency is a metabolic myopathy affecting the transport of fatty acids into the mitochondria, leading to impaired energy supply under stressful conditions resulting in muscle weakness and rhabdomyolysis. It was postulated in a previous study that some patients with the MH phenotype have a carnitine palmitoyltransferase deficiency. To investigate a potential association, we tested 18 individuals with proven MH susceptibility for impairment of carnitine palmitoyltransferase enzyme activity in muscle. Enzyme activity was normal in all individuals tested indicating no impairment of the CPT system in this sample of malignant hyperthermia susceptible individuals. Thus our data do not support the hypothesis that susceptibility to malignant hyperthermia has an effect on the carnitine palmitoyltransferase enzyme system.

Muscle carnitine palmitoyltransferase II deficiency: clinical and molecular genetic features and diagnostic aspects.

Muscle carnitine palmitoyltransferase (CPT) II deficiency is an autosomal recessive disorder of fatty acid oxidation characterized by attacks of myalgia and myoglobinuria. This review summarizes the clinical features of this disease, analyzing data of 28 patients with biochemically and genetically confirmed CPT II deficiency. The review shows that exercise-induced myalgia is the most frequent symptom, whereas myoglobinuria, known as the clinical hallmark, is missing in 21% of the patients. Typically, myalgia starts in childhood, whereas attacks with myoglobinuria mostly emerge in adolescence or early adulthood. However, there are also patients with only myalgia, patients with attacks triggered by factors other than exercise, and patients with late-onset disease. Molecular or biochemical analysis is necessary for diagnosis, since no myopathologic hallmark exists. For screening patients, analysis of not only the common S113L mutation but also the P50H and Q413fs-F448L mutations is recommended. The phenotype of muscle CPT II deficiency might be influenced by the underlying mutation, and patients with a truncating mutation on 1 allele might be affected more severely.

Confirmation of the type 2 myotonic dystrophy (CCTG)n expansion mutation in patients with proximal myotonic myopathy/proximal myotonic dystrophy of different European origins: a single shared haplotype indicates an ancestral founder effect.

Myotonic dystrophy (DM), the most common form of muscular dystrophy in adults, is a clinically and genetically heterogeneous neuromuscular disorder. DM is characterized by autosomal dominant inheritance, muscular dystrophy, myotonia, and multisystem involvement. Type 1 DM (DM1) is caused by a (CTG)(n) expansion in the 3' untranslated region of DMPK in 19q13.3. Multiple families, predominantly of German descent and with clinically variable presentation that included proximal myotonic myopathy (PROMM) and type 2 DM (DM2) but without the DM1 mutation, showed linkage to the 3q21 region and were recently shown to segregate a (CCTG)(n) expansion mutation in intron 1 of ZNF9. Here, we present linkage to 3q21 and mutational confirmation in 17 kindreds of European origin with PROMM and proximal myotonic dystrophy, from geographically distinct populations. All patients have the DM2 (CCTG)(n) expansion. To study the evolution of this mutation, we constructed a comprehensive physical map of the DM2 region around ZNF9. High-resolution haplotype analysis of disease chromosomes with five microsatellite and 22 single-nucleotide polymorphism markers around the DM2 mutation identified extensive linkage disequilibrium and a single shared haplotype of at least 132 kb among patients from the different populations. With the exception of the (CCTG)(n) expansion, the available markers indicate that the DM2 haplotype is identical to the most common haplotype in normal individuals. This situation is reminiscent of that seen in DM1. Taken together, these data suggest a single founding mutation in DM2 patients of European origin. We estimate the age of the founding haplotype and of the DM2 (CCTG) expansion mutation to be approximately 200-540 generations.

Absence of known familial hemiplegic migraine (FHM) mutations in the CACNA1A gene in patients with common migraine: implications for genetic testing.

Mutations in the gene CACNA1A have been known to cause familial hemiplegic migraine (FHM); it has been suggested, based on indirect genetic studies, that this gene may also be involved in common forms of migraine. To obtain data from direct gene analysis to test this hypothesis, we investigated 143 patients with common migraine, irrespective of their family history, for the presence of mutations known to result in the FHM phenotype; the mutations V714A, R192Q, R583Q, T666M, V1457L, and 11811L were absent in our patient sample. Furthermore, exons 4, 16, 17, and 36 were completely screened by single-strand conformation polymorphism (SSCP), and no other, hitherto unknown, mutations were detected. Bearing in mind that, in particular, the T666M mutation contributes to a large proportion of FHM linked to chromosome 19, we conclude that common migraine is distinct from FHM in its molecular basis and, therefore, most likely also in its pathophysiology. The possibility, however, of the existence of allelic disorders, with mutations located in other regions of the CACNA1A gene, cannot be ruled out. Molecular testing, therefore, is at present not a feasible option for the diagnosis and classification of migraine.

A novel nonsense mutation (515del4) in muscle carnitine palmitoyltransferase II deficiency.

We identified a novel nonsense mutation in the carnitine palmitoyltransferase (CPT; EC 2.3.1.21) II gene in a patient with biochemical evidence of CPT II deficiency. The 39-year-old man suffered from the muscle form of CPT II deficiency. Attacks of myalgia and muscle weakness started in childhood and led to renal failure five times. A mild proximal weakness of the lower limbs was left as a residue. Molecular genetic analysis revealed the common S113L mutation on one allele. On the other allele a novel 4-bp deletion starting at codon 515 (515del4) was found leading to frameshift that results in a stop codon 15 codons upstream. Our data further expand the genetic heterogeneity in patients with CPT II deficiency.