ABSTRACT
Hereditary myopathy with lactic acidosis (HML) is an autosomal recessive disease caused by an intronic one-base mutation in the iron-sulfur cluster assembly (ISCU) gene, resulting in aberrant splicing. The incorrectly spliced transcripts contain a 100 or 86 bp intron sequence encoding a non-functional ISCU protein, which leads to defects in several Fe-S containing proteins in the respiratory chain and the TCA cycle. The symptoms in HML are restricted to skeletal muscle, and it has been proposed that this effect is due to higher levels of incorrectly spliced ISCU in skeletal muscle compared with other energy-demanding tissues. In this study, we confirm that skeletal muscle contains the highest levels of incorrect ISCU splice variants compared with heart, brain, liver and kidney using a transgenic mouse model expressing human HML mutated ISCU. We also show that incorrect splicing occurs to a significantly higher extent in the slow-twitch soleus muscle compared with the gastrocnemius and quadriceps. The splicing factor serine/arginine-rich splicing factor 3 (SRSF3) was identified as a potential candidate for the slow fiber specific regulation of ISCU splicing since this factor was expressed at higher levels in the soleus compared to the gastrocnemius and quadriceps. We identified an interaction between SRSF3 and the ISCU transcript, and by overexpressing SRSF3 in human myoblasts we observed increased levels of incorrectly spliced ISCU, while knockdown of SRSF3 resulted in decreased levels. We therefore suggest that SRSF3 may participate in the regulation of the incorrect splicing of mutant ISCU and may, at least partially, explain the muscle-specific symptoms of HML.
Subject(s)
Acidosis, Lactic/congenital , Iron-Sulfur Proteins/genetics , Muscle, Skeletal/metabolism , Muscular Diseases/congenital , RNA Splicing , Serine-Arginine Splicing Factors/genetics , Acidosis, Lactic/genetics , Acidosis, Lactic/pathology , Animals , Cells, Cultured , Humans , Iron-Sulfur Proteins/metabolism , Mice , Mice, Inbred CBA , Mice, Transgenic , Muscular Diseases/genetics , Muscular Diseases/pathology , Mutagenesis, Site-Directed , Myoblasts/cytology , Myoblasts/metabolism , RNA/isolation & purification , RNA/metabolism , RNA Interference , RNA, Small Interfering/metabolism , Real-Time Polymerase Chain Reaction , Serine-Arginine Splicing Factors/antagonists & inhibitors , Serine-Arginine Splicing Factors/metabolismABSTRACT
PURPOSE: To investigate the socioeconomic prognosis after a newly diagnosed unprovoked epileptic seizure in adults. METHODS: Sixty-three patients 17 years or older with a newly diagnosed unprovoked epileptic seizure from 1985 through 1987 and 107 sex- and age- matched controls were followed up for 10 years to 1996. Studied variables were income, source of income, sickness periods, incapacity rate, diagnosis-specific incapacity rate, vocational status, and education. RESULTS: Relative growth of income was similar between patients and controls during follow-up. Patients had lower income than did controls 2 years before seizure onset and during the entire follow-up. This was related to higher morbidity among patients, as measured by sickness periods and incapacity rate. Employment rates did not evolve negatively among patients after seizure onset and were close to employment rates of controls during follow-up time. There was no difference between patients and controls regarding education. CONCLUSIONS: After a newly diagnosed unprovoked epileptic seizure in adults, no negative development regarding employment and education occurs. Income development is positive unless refractory seizures evolve. However, income is lower among patients with epilepsy than among controls, and this difference can be related to overall morbidity.
