Conditions such as hypertrophic cardiomyopathy, cardiac amyloidosis (including both transthyretin [ATTR] and light-chain [AL] subtypes), Fabry disease, cardiac sarcoidosis, constrictive pericarditis, and pulmonary hypertension associated with WHO groups 1, 3, 4, and 5 necessitate distinct diagnostic pathways and therapeutic strategies [61,62]. The gene discussed is TTR; the disease is pulmonary arterial hypertension.