Regarding extraocular non-neurological abnormalities, endocrine disorders primarily due to WFS1 mutations are the most common in patients with optic atrophy, while digestive abnormalities, such as liver failure (primarily linked to POLG and NBAS mutations) and gastrointestinal stromal tumours (primarily linked to SDHA mutations), are predominant in patients without optic atrophy. The gene discussed is NBAS; the disease is liver failure.