Neuronal NO synthase (NOS1) is a major candidate gene for asthma

Asthma is a common, but heterogeneous disease, characterized by reversible airway obstruction, bronchial hyperresponsiveness (BHR); and is commonly as sociated with atopy. The messenger molecule nitric oxide (NO), that is form ed by neuronal NO synthase (NOS1), is known to have a key role in bronchomo tor control in animals. In humans the gene for NOS1 is located on chromosom e 12q24, in a region that had been shown in family studies to be linked to the diagnosis of asthma. We identified variants of the NOS1 gene, and asses sed whether there was a genetic association between these variants of NOS1 and the diagnosis asthma. A total of 410 Caucasian asthma patients and 238 Caucasian controls were screened for three bi-allelic polymorphisms in the NOS1 gene that had been detected by single-stranded conformational polymorp hism (SSCP) analysis and confirmed by sequencing. Allele frequencies of a p olymorphism in exon 29 of the NOS1 gene were significantly different betwee n asthmatics and controls (P < 0.05). These findings suggest that variants of the NOS1 gene may be one sourer of genetic risk for asthma.