Amyotrophic lateral sclerosis is considered a genetic disorder for those with familial ALS. While the causes of sporadic ALS and ALS/dementia have been unknown, a recent study published in Nature showed that there is a defect in a protein degradation pathway involving ubiquilin2, which normally clears misfolded proteins in all three forms of ALS. Is this the true underlying cause of all ALS or does expression of the disease actually require a viral infection to be present as well?

Here your intuition is working beautifully to look beyond the surface of things, what is known by science currently, and their bias to turn to genetics in understanding origin of illnesses. While this is often a clue as to why some people develop a disease and others not, it is not definitive proof of actual causation but only association and a starting point for further investigation always, so as to not close the book on true understanding prematurely. Analogous to what we have told you about the dementias, that they are all viral in actual causation, and that the accumulation of plaques and tau tangles in the brain are an end product of the infection and not a cause of the dementia, the same is true in ALS patients, that the associated misfolded proteins are a symptom, not a cause. The cause is, in all cases, an underlying viral presence causing dysregulation of normal physiologic functioning and this will aggravate genetic predisposition and vulnerability in how the disease manifests with respect to specific cellular and functional changes.