Browsing by Author "Cirak S."

Now showing 1 - 4 of 4

Biallelic Mutations in ADPRHL2, Encoding ADP-Ribosylhydrolase 3, Lead to a Degenerative Pediatric Stress-Induced Epileptic Ataxia Syndrome
(2018-09-06) Ghosh S.G.; Becker K.; Huang H.; Dixon-Salazar T.; Chai G.; Salpietro V.; Al-Gazali L.; Waisfisz Q.; Wang H.; Vaux K.K.; Stanley V.; Manole A.; Akpulat U.; Weiss M.M.; Efthymiou S.; Hanna M.G.; Minetti C.; Striano P.; Pisciotta L.; De Grandis E.; Altmüller J.; Nürnberg P.; Thiele H.; Yis U.; Okur T.D.; Polat A.I.; Amiri N.; Doosti M.; Karimani E.G.; Toosi M.B.; Haddad G.; Karakaya M.; Wirth B.; van Hagen J.M.; Wolf N.I.; Maroofian R.; Houlden H.; Cirak S.; Gleeson J.G.
ADP-ribosylation, the addition of poly-ADP ribose (PAR) onto proteins, is a response signal to cellular challenges, such as excitotoxicity or oxidative stress. This process is catalyzed by a group of enzymes referred to as poly(ADP-ribose) polymerases (PARPs). Because the accumulation of proteins with this modification results in cell death, its negative regulation restores cellular homeostasis: a process mediated by poly-ADP ribose glycohydrolases (PARGs) and ADP-ribosylhydrolase proteins (ARHs). Using linkage analysis and exome or genome sequencing, we identified recessive inactivating mutations in ADPRHL2 in six families. Affected individuals exhibited a pediatric-onset neurodegenerative disorder with progressive brain atrophy, developmental regression, and seizures in association with periods of stress, such as infections. Loss of the Drosophila paralog Parg showed lethality in response to oxidative challenge that was rescued by human ADPRHL2, suggesting functional conservation. Pharmacological inhibition of PARP also rescued the phenotype, suggesting the possibility of postnatal treatment for this genetic condition.
Choline transporter mutations in severe congenital myasthenic syndrome disrupt transporter localization
(2017-11-01) Wang H.; Salter C.G.; Refai O.; Hardy H.; Barwick K.E.S.; Akpulat U.; Kvarnung M.; Chioza B.A.; Harlalka G.; Taylan F.; Sejersen T.; Wright J.; Zimmerman H.H.; Karakaya M.; Stüve B.; Weis J.; Schara U.; Russell M.A.; Abdul-Rahman O.A.; Chilton J.; Blakely R.D.; Baple E.L.; Cirak S.; Crosby A.H.
The presynaptic, high-affinity choline transporter is a critical determinant of signalling by the neurotransmitter acetylcholine at both central and peripheral cholinergic synapses, including the neuromuscular junction. Here we describe an autosomal recessive presynaptic congenital myasthenic syndrome presenting with a broad clinical phenotype due to homozygous choline transporter missense mutations. The clinical phenotype ranges from the classical presentation of a congenital myasthenic syndrome in one patient (p.Pro210Leu), to severe neurodevelopmental delay with brain atrophy (p.Ser94Arg) and extend the clinical outcomes to a more severe spectrum with infantile lethality (p.Val112Glu). Cells transfected with mutant transporter construct revealed a virtually complete loss of transport activity that was paralleled by a reduction in transporter cell surface expression. Consistent with these findings, studies to determine the impact of gene mutations on the trafficking of the Caenorhabditis elegans choline transporter orthologue revealed deficits in transporter export to axons and nerve terminals. These findings contrast with our previous findings in autosomal dominant distal hereditary motor neuropathy of a dominant-negative frameshift mutation at the C-terminus of choline transporter that was associated with significantly reduced, but not completely abrogated choline transporter function. Together our findings define divergent neuropathological outcomes arising from different classes of choline transporter mutation with distinct disease processes and modes of inheritance. These findings underscore the essential role played by the choline transporter in sustaining acetylcholine neurotransmission at both central and neuromuscular synapses, with important implications for treatment and drug selection.
Clinical and genetic characterization of PYROXD1-related myopathy patients from Turkey
(2021-06-01) Daimagüler H.S.; Akpulat U.; Özdemir Ö.; Yis U.; Güngör S.; Talim B.; Diniz G.; Baydan F.; Thiele H.; Altmüller J.; Nürnberg P.; Cirak S.
Congenital myopathies (CMs) are a heterogeneous group of inherited muscle disorders characterized by muscle weakness at birth, while limb-girdle muscular dystrophies (LGMD) have a later onset and slower disease progression. Thus, detailed clinical phenotyping of genetically defined disease entities are required for the full understanding of genotype–phenotype correlations. A recently defined myopathic genetic disease entity is caused by bi-allelic variants in a gene coding for pyridine nucleotide-disulfide oxidoreductase domain 1 (PYROXD1) with unknown substrates. Here, we present three patients from two consanguineous Turkish families with mild LGMD, facial weakness, normal CK levels, and slow progress. Genomic analyses revealed a homozygous known pathogenic missense variant (c.464A>G, p.Asn155Ser) in family 1 with two affected females. In the affected male of family 2, we found this variant in a compound heterozygous state together with a novel frameshift variant (c.329_332delTCTG, p.Leu112Valfs*8), which is the second frameshift variant known so far in PYROXD1. We have been able to define a large homozygous region in family 1 sharing a common haplotype with family 2 in the critical region. Our data suggest that c.464A>G is a Turkish founder mutation. To gain deeper insights, we performed a systematic review of all published PYROXD1-related myopathy cases. Our analysis showed that the c.464A > G variant was found in 87% (20/23) of the patients and that it may cause either a childhood- or adult-onset phenotype, irrespective of its presence in a homozygous or compound heterozygous state. Interestingly, only four patients had elevated CK levels (up to 1000 U/L), and cardiac involvement was found in few compound heterozygous cases.
Shorter Phosphorodiamidate Morpholino Splice-Switching Oligonucleotides May Increase Exon-Skipping Efficacy in DMD
(2018-12-07) Akpulat U.; Wang H.; Becker K.; Contreras A.; Partridge T.; Novak J.; Cirak S.
Duchenne muscular dystrophy is a fatal muscle disease, caused by mutations in DMD, leading to loss of dystrophin expression. Phosphorodiamidate morpholino splice-switching oligonucleotides (PMO-SSOs) have been used to elicit the restoration of a partially functional truncated dystrophin by excluding disruptive exons from the DMD messenger. The 30-mer PMO eteplirsen (EXONDYS51) developed for exon 51 skipping is the first dystrophin-restoring, conditionally FDA-approved drug in history. Clinical trials had shown a dose-dependent variable and patchy dystrophin restoration. The main obstacle for efficient dystrophin restoration is the inadequate uptake of PMOs into skeletal muscle fibers at low doses. The excessive cost of longer PMOs has limited the utilization of higher dosing. We designed shorter 25-mer PMOs directed to the same eteplirsen-targeted region of exon 51 and compared their efficacies in vitro and in vivo in the mdx52 murine model. Our results showed that skipped-dystrophin induction was comparable between the 30-mer PMO sequence of eteplirsen and one of the shorter PMOs, while the other 25-mer PMOs showed lower exon-skipping efficacies. Shorter PMOs would make higher doses economically feasible, and high dosing would result in better drug uptake into muscle, induce higher levels of dystrophin restoration in DMD muscle, and, ultimately, increase the clinical efficacy.