An Exploratory Study On Surfactant Protein B(SP-B) Hereditary Deficiency Of Neonatal Respiratory Distress Syndrome In Full Term Infant

Objective To provide scientific experimental evidence for further gene therapy,frequency of surfactant protein B (SP-B) hereditary deficiency and types of mutationwere evaluated and genetic pathogenesis was investigate in full term infants withneonatal respiratory distress syndrome (RDS).Methods Unrelated20cases with RDS of full term infants in Han ethnic populationwere selected as RDS group while unrelated20other cases in Han ethnic populationwere selected as control group. There was not significant difference between twogroups below items including gestational age, birth weight, gender, maternal age andmode of delivery. Levels of SP-B in bronchoalveolar lavage fluid (BAL) weredetermined with enzyme-linked immunosorbent assay while expression of SP-B inlung tissue was tested with immunohistochemical technique. Deoxyribonucleic acid(DNA) from human blood was extracted with routine technique for DNA. Mutationsof exon4in SP-B gene were analyzed with polymerase chain reaction (PCR) and genesequencing technology.Results Levels of BAL SP-B on day1(20.0±8.05ng/ml), day3(21.1±8.13ng/ml),and day7(20.1±7.88ng/ml) of RDS and within30min (19.4±8.02ng/ml) afterdeath in RDS group were significantly lower than that in control group with thecorresponding values (92.8±32.21,102.4±28.76,105.6±30.41,92.0±32.71ng/ml)(P <0.001). The numbers of positive cells (18.5±10.7) expressing SP-B protein inlung tissue of RDS group were also significantly lower than that (94.9±31.8) in control group （t＝10.191, P＜0.001). The less were levels of BAL SP-B protein andthe positive cells expressing SP-B protein in lung tissue, the more severe were typesof RDS on dependent of chest X-ray diagnostic criteria, that is, there was a goodcompliance among them. Two groups had eight cases with hereditary SP-B deficiencyincluding seven cases in RDS group and one case in control group. Point mutation ofgene existed in exon Ⅳ, which had three genotypes including C/T, C/C and T/T.Among gene mutation of SP-B in exon Ⅳ, seven cases had gene mutation of SP-B inRDS group including homozygous mutation with C/C genetic type of six cases andheterozygous mutation with C/T genetic type of one case while one case had genemutation of SP-B in control group including heterozygous mutation with C/T genetictype of one case and no case with homozygous mutation of C/C genetic type. Side ofeight parents had the same types. According to the comprehensive analysis of genestructurethe in SP-B exon Ⅳ of patients and their parents’, seven cases in RDS groupand one in control group were diagnosed finally as SP-B hereditary deficiency.Genetic mutation in exon IV located in1580site of SP-B gene, whose normal aminoacid codon was ACT, whereas amino acid codon after mutation was ATT or A(C/T)Twith the corresponding amino acids position for131. As result, original threonine wasreplaced by isoleucine (Thr131Ile). Frequency of genetic mutation of exon Ⅳ inRDS group was0.35(7/20) while that of control group was0.05(1/20). Frequency ofgenetic mutation of exon Ⅳ in RDS was higher than that in control group（2=3.906,P=0.048）. RDS group had six cases with C/C homozygous mutation and one withC/T heterozygous mutation, of which frequency of C/C homozygous mutation was0.3(6/20) and with C/T heterozygous mutation was0.05(1/20), respectively. Controlgroup had one case with C/T heterozygous mutation and no case with C/Chomozygous mutation, with the corresponding frequency of genetic mutation being0.05(1/20) and0(0/20), respectively. The homozygous mutation frequency (0.3) inRDS group was higher than that (0) of control group（2=4.902, P=0.027）, whichsuggesting relation between homozygous mutation located in1580site of exon Ⅳ ofSP-B gene and onset of neonatal RDS in full term infants in Han ethnic group in Beijing. However, there were no significant difference on frequency in heterozygousmutation between RDS group and control group, which suggesting no relationbetween heterozygous mutation located in1580site of exon IV in SP-B gene andonset of neonatal RDS in full term infants in Han ethnic group in Beijing.Conclusion (1) BAL SP-B protein deficiency was involved in pathogenesis ofneonatal RDS in full term infants in Han ethnic group.(2)The lower expression ofSP-B in lung tissue was involved in pathogenesis of neonatal RDS in full term infantsin Han ethnic group.(3)Gene mutations existed in exon Ⅳ of SP-B gene in full terminfants in Han ethnic group, and its frequency is0.35, including homozygousmutation frequency (0.3) and heterozygous mutation frequency (0.05). The frequencyof gene mutations in RDS group was higher than that of control group.(4)Thereexisted relation between homozygous mutation in1580site of SP-B gene and onset ofneonatal RDS in full term infants in Han ethnic group.