In a study known as the ‘Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints’, in which a total of 1,888 patients with COPD were recruited, the serum SP-D levels were not associated with COPD disease severity according to the GOLD guidelines, radiology emphysema score or areas of low attenuation on computed tomography scans (15). This evidence concerns the gene SFTPD and chronic obstructive pulmonary disease.