HHIP and pulmonary arterial hypertension: Previously reported associations of these genetic variants include: airflow limitation (CHRNA3/5, IREB2, HHIP), [76] emphysema susceptibility and severity (CHRNA3/5, BICD1), [77] chronic bronchitis phenotype, [78] exacerbation rate (HHIP) [79] and pulmonary hypertension pathogenesis [80].