Objective      To investigate the types of mutation and genotypic frequency of surfactant protein B (SP-B) in neonatal respiratory distress syndrome (RDS).       Methods      Unrelated 40 cases with neonatal RDS of Han ethnic group in Beijing region in our department from August 2006 to April 2011 were selected as RDS group

while unrelated 40 other cases of Han ethnic group in same period were selected as control group. Two groups matched with gestational age. Expression of SP-B in lung cells was tested with immunohistochemical assay. Expression of SP-B in lung tissue and bronchoalveolar lavage fluid (BALF) was determined with Western blotting. Types of genetic mutations in SP-B +1 580 locus were screened with polymerase chain reaction (PCR) and gene sequencing.       Results      The number of SP-B positive cells were less in RDS group than in control group（t=10.191，P0.01）. Eight cases in RDS group simultaneously had lower expression level of mature SP-B in lung tissue and BALF

while 7 cases in the same group had lower level of mature SP-B only in BALF. Genetic mutations including homozygous and heterozygous mutation existed in SP-B exon 4 of both 2 groups

which located in +1 580 site of SP-B gene. Twenty cases had gene mutation of SP-B in RDS group

including 12 homozygous mutations with C/C genotypes and 8 heterozygous mutations with C/T genetic types. Eight cases had gene mutations of SP-B +1 580 in control group including 1 homozygous mutation with C/C genotype and 7 heterozygous mutations with C/T genotypes. Genotypic frequency of homozygous mutation(C/C) of SP-B +1 580 in RDS group was 30.0% while that of heterozygous mutation (C/T) was 20.0%. Genotypic frequency of homozygous mutation(C/C) of SP-B +1 580 in control group was 2.5% while that of heterozygous mutation(C/T) was 1.75%. Genotypic frequency of heterozygous mutation(C/C) in RDS group had higher level than that in control group （Chi square=11.114

P0.01）.       Conclusion      Genetic mutations including homozygous and heterozygous mutation exist in SP-B gene +1 580 in neonatal RDS

and the homozygous mutation (C/C) at the SP-B+1 580 site is associated with occurrence of RDS.