All five deficiencies share a common core: fatigue, weakness, and impaired energy production. Beyond that core, each one has a characteristic cluster that reflects the specific step it blocks.
Thiamine deficiency (beriberi) blocks decarboxylation, hitting the nervous system and heart hardest: peripheral neuropathy, muscle wasting, and high-output cardiac failure. In its acute neurological form it produces confusion, ataxia, and eye movement abnormalities. Riboflavin deficiency impairs FAD-dependent redox reactions, producing angular stomatitis, cheilosis, and a scaly dermatitis, often with anemia. Niacin deficiency blocks NAD-dependent dehydrogenases across many tissues, giving the classic dermatitis, diarrhea, and dementia triad. Pantothenate deficiency is rare but would impair acyl transfer and the citric acid cycle, causing general weakness and neurological disturbance. Biotin deficiency blocks carboxylation, producing dermatitis, hair loss, and neurological symptoms.
The overlap comes from the shared dependence on ATP production. The differences come from which reaction class is blocked: decarboxylation (thiamine), redox (riboflavin, niacin), acyl transfer (pantothenate), or carboxylation (biotin). That is why the syndromes resemble each other in their general features but diverge in their specific tissue signs.