Mitochondrial DNA depletion syndrome (MDS or MDDS), or Alpers disease, is any of a group of autosomal recessive disorders that cause a significant drop in mitochondrial DNA in affected tissues. Symptoms can be any combination of myopathic, hepatopathic, or encephalomyopathic. These syndromes affect tissue in the muscle, liver, or both the muscle and brain, respectively. The condition is typically fatal in infancy and early childhood, though some have survived to their teenage years with the myopathic variant and some have survived into adulthood with the SUCLA2 encephalomyopathic variant. There is currently no curative treatment for any form of MDDS, though some preliminary treatments have shown a reduction in symptoms. Signs and symptoms
All forms of MDDS are very rare. MDDS causes a wide range of symptoms, which can appear in newborns, infants, children, or adults, depending on the class of MDDS; within each class symptoms are also diverse.In MDDS associated with mutations in TK2, infants generally develop normally, but by around two years of age, symptoms of general muscle weakness (called "hypotonia"), tiredness, lack of stamina, and difficulty feeding begin to appear. Some toddlers start to lose control of the muscles in their face, mouth, and throat, and may have difficulty swallowing.
Bifascicular block is a conduction abnormality in the heart where two of the three main fascicles of the His/Purkinje system are blocked. Most commonly, it refers to a combination of right bundle branch block (RBBB) and either left anterior fascicular block (LAFB) or left posterior fascicular block (LPFB), with the former being more common.Some authors consider left bundle branch block (LBBB) to be a technical bifascicular block, since the block occurs above the bifurcation of the left anterior and left posterior fascicles of the left bundle branch. Diagnosis
Diagnostic criteria:Clinically, bifascicular block presents with one of two ECG patterns:
Right bundle branch block (RBBB) with left anterior fascicular block (LAFB), manifested as left axis deviation (LAD). RBBB and left posterior fascicular block (LPFB), manifested as right axis deviation (RAD) in the absence of other causes. Treatment
In those with bifascicular block and no symptoms, little with respect to treatment is needed. In those with syncope, a pacemaker is recommended. References

Olshansky B. Bradyarrhythmias – Conduction System Abnormalities. In: Arrhythmia Essentials 2e, 2017. Vijayaraman P. Clinical Cardiac Pacing, Defibrillation and Resynchronisation Therapy 5e, 2017
Goldberger A. Ventricular Conduction Disturbances.. In: Goldberger’s Clinical Electrocardiography 9e, 2018. == External links ==