NOS2 and obstructive sleep apnea syndrome: Though not associated with asthma morbidity, asthmatics with OSA had higher serum levels of NOS inhibitor ADMA, reduced L-arginine availability for NOS (lower L-arginine to ornithine ratio), and increased arginase activity (elevated L-ornithine and proline) compared to those without OSA, though notably only L-ornithine and proline levels remained statistically significant after adjustment for BMI.