Biochemical evaluation revealed markedly elevated urinary δ-aminolevulinic acid (ALA), consistent with a porphyria-like metabolic decompensation, together with inappropriately increased plasma copeptin in the setting of hypotonic hyponatremia and clinical euvolemia, fulfilling diagnostic criteria for the syndrome of inappropriate antidiuretic hormone secretion (SIADH). This evidence concerns the gene AVP and inappropriate ADH syndrome.