BACKGROUND: Remethylation defects are rare inherited disorders in which impaired remethylation of homocysteine to methionine leads to accumulation of homocysteine and perturbation of numerous methylation reactions. OBJECTIVE: To summarise clinical and biochemical characteristics of these severe disorders and to provide guidelines on diagnosis and management. DATA SOURCES: Review, evaluation and discussion of the medical literature (Medline, Cochrane databases) by a panel of experts on these rare diseases following the GRADE approach. KEY RECOMMENDATIONS: We strongly recommend measuring plasma total homocysteine in any patient presenting with the combination of neurological and/or visual and/or haematological symptoms, subacute spinal cord degeneration, atypical haemolytic uraemic syndrome or unexplained vascular thrombosis. We strongly recommend to initiate treatment with parenteral hydroxocobalamin without delay in any suspected remethylation disorder; it significantly improves survival and incidence of severe complications. We strongly recommend betaine treatment in individuals with MTHFR deficiency; it improves the outcome and prevents disease when given early.

• MeSH
• homocystein genetika   MeSH
• lidé MeSH
• methionin genetika   MeSH
• methylentetrahydrofolátreduktasa (NADPH2) nedostatek   MeSH
• metylace účinky léků   MeSH
• protoonkogenní proteiny c-cbl nedostatek   MeSH
• vitamin B 12 farmakologie   terapeutické užití   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• Názvy látek
• homocystein MeSH
• methionin MeSH
• methylentetrahydrofolátreduktasa (NADPH2) MeSH
• protoonkogenní proteiny c-cbl MeSH
• vitamin B 12 MeSH

Newborn screening (NBS) is justified if early intervention is effective in a disorder generally not detected early in life on a clinical basis, and if sensitive and specific biochemical markers exist. Experience with NBS for homocystinurias and methylation disorders is limited. However, there is robust evidence for the success of early treatment with diet, betaine and/or pyridoxine for CBS deficiency and good evidence for the success of early betaine treatment in severe MTHFR deficiency. These conditions can be screened in dried blood spots by determining methionine (Met), methionine-to-phenylanine (Met/Phe) ratio, and total homocysteine (tHcy) as a second tier marker. Therefore, we recommend NBS for cystathionine beta-synthase and severe MTHFR deficiency. Weaker evidence is available for the disorders of intracellular cobalamin metabolism. Early treatment is clearly of advantage for patients with the late-onset cblC defect. In the early-onset type, survival and non-neurological symptoms improve but the effect on neurocognitive development is uncertain. The cblC defect can be screened by measuring propionylcarnitine, propionylcarnitine-to-acetylcarnitine ratio combined with the second tier markers methylmalonic acid and tHcy. For the cblE and cblG defects, evidence for the benefit of early treatment is weaker; and data on performance of Met, Met/Phe and tHcy even more limited. Individuals homozygous or compound heterozygous for MAT1A mutations may benefit from detection by NBS using Met, which on the other hand also detects asymptomatic heterozygotes. Clinical and laboratory data is insufficient to develop any recommendation on NBS for the cblD, cblF, cblJ defects, glycineN-methyltransferase-, S-adenosylhomocysteinehydrolase- and adenosine kinase deficiency.

• MeSH
• acylkarnitin krev   MeSH
• betain terapeutické užití   MeSH
• homocystinurie diagnóza   MeSH
• karnitin analogy a deriváty   krev   MeSH
• kyselina methylmalonová krev   MeSH
• lidé MeSH
• methionin krev   MeSH
• methylentetrahydrofolátreduktasa (NADPH2) nedostatek   účinky léků   MeSH
• metylace MeSH
• novorozenec MeSH
• novorozenecký screening * MeSH
• směrnice pro lékařskou praxi jako téma MeSH
• Check Tag
• lidé MeSH
• novorozenec MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH
• systematický přehled MeSH
• Názvy látek
• acylkarnitin MeSH
• betain MeSH
• karnitin MeSH
• kyselina methylmalonová MeSH
• methionin MeSH
• methylentetrahydrofolátreduktasa (NADPH2) MeSH
• propionylcarnitine MeSH Prohlížeč

The prevalent c.903+469T>C mutation in MTRR causes the cblE type of homocystinuria by strengthening an SRSF1 binding site in an ESE leading to activation of a pseudoexon. We hypothesized that other splicing regulatory elements (SREs) are also critical for MTRR pseudoexon inclusion. We demonstrate that the MTRR pseudoexon is on the verge of being recognized and is therefore vulnerable to several point mutations that disrupt a fine-tuned balance between the different SREs. Normally, pseudoexon inclusion is suppressed by a hnRNP A1 binding exonic splicing silencer (ESS). When the c.903+469T>C mutation is present two ESEs abrogate the activity of the ESS and promote pseudoexon inclusion. Blocking the 3'splice site or the ESEs by SSOs is effective in restoring normal splicing of minigenes and endogenous MTRR transcripts in patient cells. By employing an SSO complementary to both ESEs, we were able to rescue MTRR enzymatic activity in patient cells to approximately 50% of that in controls. We show that several point mutations, individually, can activate a pseudoexon, illustrating that this mechanism can occur more frequently than previously expected. Moreover, we demonstrate that SSO blocking of critical ESEs is a promising strategy to treat the increasing number of activated pseudoexons.

• MeSH
• buněčné linie MeSH
• exony * MeSH
• ferredoxin-NADP-reduktasa genetika   metabolismus   MeSH
• HEK293 buňky MeSH
• homocystinurie enzymologie   genetika   MeSH
• kultivované buňky MeSH
• lidé MeSH
• megaloblastová anemie enzymologie   genetika   MeSH
• místa sestřihu RNA MeSH
• mutace * MeSH
• oligonukleotidy * MeSH
• regulační sekvence ribonukleových kyselin * MeSH
• sestřih RNA * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ferredoxin-NADP-reduktasa MeSH
• methionine synthase reductase MeSH Prohlížeč
• místa sestřihu RNA MeSH
• oligonukleotidy * MeSH
• regulační sekvence ribonukleových kyselin * MeSH

Deep intronic mutations are often ignored as possible causes of human diseases. A deep intronic mutation in the MTRR gene, c.903+469T>C, is the most frequent mutation causing the cblE type of homocystinuria. It is well known to be associated with pre-mRNA mis-splicing, resulting in pseudoexon inclusion; however, the pathological mechanism remains unknown. We used minigenes to demonstrate that this mutation is the direct cause of MTRR pseudoexon inclusion, and that the pseudoexon is normally not recognized due to a suboptimal 5' splice site. Within the pseudoexon we identified an exonic splicing enhancer (ESE), which is activated by the mutation. Cotransfection and siRNA experiments showed that pseudoexon inclusion depends on the cellular amounts of SF2/ASF and in vitro RNA-binding assays showed dramatically increased SF2/ASF binding to the mutant MTRR ESE. The mutant MTRR ESE sequence is identical to an ESE of the alternatively spliced MST1R proto-oncogene, which suggests that this ESE could be frequently involved in splicing regulation. Our study conclusively demonstrates that an intronic single nucleotide change is sufficient to cause pseudoexon activation via creation of a functional ESE, which binds a specific splicing factor. We suggest that this mechanism may cause genetic disease much more frequently than previously reported.

• MeSH
• Cercopithecus aethiops MeSH
• COS buňky MeSH
• exony genetika   MeSH
• ferredoxin-NADP-reduktasa genetika   MeSH
• homocystinurie klasifikace   enzymologie   genetika   MeSH
• introny genetika   MeSH
• jaderné proteiny metabolismus   MeSH
• messenger RNA genetika   metabolismus   MeSH
• místa sestřihu RNA genetika   MeSH
• molekulární sekvence - údaje MeSH
• mutace genetika   MeSH
• mutantní proteiny genetika   MeSH
• proteiny vázající RNA metabolismus   MeSH
• protoonkogen Mas MeSH
• sekvence nukleotidů MeSH
• serin-arginin sestřihové faktory MeSH
• sestřih RNA genetika   MeSH
• vazba proteinů MeSH
• vitamin B 12 metabolismus   MeSH
• výpočetní biologie MeSH
• zesilovače transkripce genetika   MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ferredoxin-NADP-reduktasa MeSH
• jaderné proteiny MeSH
• MAS1 protein, human MeSH Prohlížeč
• messenger RNA MeSH
• methionine synthase reductase MeSH Prohlížeč
• místa sestřihu RNA MeSH
• mutantní proteiny MeSH
• proteiny vázající RNA MeSH
• protoonkogen Mas MeSH
• serin-arginin sestřihové faktory MeSH
• vitamin B 12 MeSH