Myasthenic syndromes, congenital

Congenital myasthenic syndromes impair the operation of the acetylcholine receptor 719... 

Engel, A. G., Ohno, K. and Sine, S. M. Congenital myasthenic syndromes a diverse array of molecular targets. /. Neurocytol. 32 1017-1037,2003. 

Key words Motor neuron diseases, amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), peripheral neuropathies, Charcot-Marie-Tooth diseases, hereditary motor and/or sensory neuropathies (HSMNs), congenital myasthenic syndromes, neuromuscular junction, muscular dystrophies, Duchenne s disease. 

The 3 end of an intron and the 5 end of an exon carry a consensus sequence of CAG G, where the vertical line represents the intron/exon boundary. The AG dinucleotide is scanned from the branch point and the first AG is recognized as the 3 end of the intron (Chen et al 2000). In a patient with congenital myasthenic syndrome, we identified duplication of a 16-nt segment comprised of 8 intronic and 8 exonic nucleotides at the intron 10/exon 10 boundary of CHRNE encoding the acetylcholine receptor epsilon subunit (Ohno et al 2005). We found that the upstream AG of the duplicated segment is exclusively used for splicing and that one or two mutations in the upstream BPS had no effect whereas complete deletion of the upstream BPS partially activated the downstream AG. Similar exclusive activation of the upstream AG is reported in HEXB (Dlott et al., 1990) and SLC4A1 (Bianchi et al, 1997). Creation of a cryptic AG dinucleotide close to the 3 end of an intron should be carefully scrutinized in mutation analysis. 

In a patient with congenital myasthenic syndrome, we identified that CHRNAl IVS3-8G>A attenuates binding of hnRNP /f 100-fold and causes exclusive inclusion of the downstream exon P3A (Masuda et al., 2008) (Fig. 4). We also identified that polypyrimidine tract binding protein (PTB) silences recognition of exon P3A and tannic acid facilitates the expression of PTB by activating its promoter region (Gao et al., 2009). 

Fig. 4 CHRNAl carries a 75-nt exon P3A. Its inclusion generates a nonfunctional alpha subunit of the acetylcholine receptor. hnRNP H and PTB silence recognition of exon PSA and induce its skipping. The IVS3-8G>A mutation identified in a patient with congenital myasthenic syndrome weakens the binding of hnRNP H and causes inclusion of exon PSA. Tannic add facilitates the expression of PTB and partially ameliorates aberrant spUcing due to IVS3-8G>A...

CHRNAl 2q24-32 uAChRAl Congenital myasthenic syndrome D/R G/L... 

Engel AG, Ohno K, Milone M et al 1996 New mutations in acetylcholine receptor subunit genes reveal heterogeneity in the slow-channel congenital myasthenic syndrome. Hum Mol Genet 5 1217-1227 ... 

Ohno K, Wang HL, Milone M et al 1996 Congenital myasthenic syndrome caused by decreased agonist binding affinity due to a mutation in the acetylcholine receptor epsilon subunit. Neuron 17 157-170... 

Uchitel O, Engel AG, Walls TJ, Nagel A, Atassi MZ, Bril V 1993 Congenital myasthenic syndromes II. Syndrome attributed to abnormal interaction of acetylcholine with its receptor. Muscle Nerve 16 1293—1301... 

Acetylcholine receptor (skeletal muscle) CHRNAl Congenital myasthenic syndrome... 

Lashley D, Palace J, Jayawant S, Robb S, Beeson D (2010) Ephedrine treatment in congenital myasthenic syndrome due to mutations in DOK7. Neurology 74 1517-1523... 

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