Genome wide study of maternal and parent-of-origin effects on the etiology of orofacial clefts

We performed a genome wide association analysis of maternally-mediated genetic effects and parent-of-origin (POO) effects on risk of orofacial clefting (OC) using over 2,000 case-parent triads collected through an international cleft consortium. We used log-linear regression models to test individual SNPs. For SNPs with a P-value <10(-5) for maternal genotypic effects, we also applied a haplotype-based method, TRIMM, to extract potential information from clusters of correlated SNPs. None of the SNPs were significant at the genome wide level. Our results suggest neither maternal genome nor POO effects play major roles in the etiology of OC in our sample. This finding is consistent with previous genetic studies and recent population-based cohort studies in Norway and Denmark, which showed no apparent difference between mother-to-offspring and father-to-offspring recurrence of clefting. We, however, cannot completely rule out maternal genome or POO effects as risk factors because very small effects might not be detectable with our sample size, they may influence risk through interactions with environmental exposures or may act through a more complex network of interacting genes. Thus, the most promising SNPs identified by this study may still be worth further investigation.

Evidence for gene-environment interaction in a genome wide study of nonsyndromic cleft palate

Nonsyndromic cleft palate (CP) is a common birth defect with a complex and heterogeneous etiology involving both genetic and environmental risk factors. We conducted a genome-wide association study (GWAS) using 550 case-parent trios, ascertained through a CP case collected in an international consortium. Family-based association tests of single nucleotide polymorphisms (SNP) and three common maternal exposures (maternal smoking, alcohol consumption, and multivitamin supplementation) were used in a combined 2 df test for gene (G) and gene-environment (G × E) interaction simultaneously, plus a separate 1 df test for G × E interaction alone. Conditional logistic regression models were used to estimate effects on risk to exposed and unexposed children. While no SNP achieved genome-wide significance when considered alone, markers in several genes attained or approached genome-wide significance when G × E interaction was included. Among these, MLLT3 and SMC2 on chromosome 9 showed multiple SNPs resulting in an increased risk if the mother consumed alcohol during the peri-conceptual period (3 months prior to conception through the first trimester). TBK1 on chr. 12 and ZNF236 on chr. 18 showed multiple SNPs associated with higher risk of CP in the presence of maternal smoking. Additional evidence of reduced risk due to G × E interaction in the presence of multivitamin supplementation was observed for SNPs in BAALC on chr. 8. These results emphasize the need to consider G × E interaction when searching for genes influencing risk to complex and heterogeneous disorders, such as nonsyndromic CP.

Association between genes on chromosome 4p16 and non-syndromic oral clefts in four populations

Isolated cleft lip with or without cleft palate and cleft palate are among the most common human birth defects. Several candidate gene studies on MSX1 have shown significant association between markers in MSX1 and risk of oral clefts, and re-sequencing studies have identified multiple mutations in MSX1 in a small minority of cases, which may account for 1-2% of all isolated oral clefts cases. We explored the 2-Mb region around MSX1, using a marker map of 393 single nucleotide polymorphisms (SNPs) in 297 cleft lip, with or without cleft palate, case-parent trios and 84 cleft palate trios from Maryland, Taiwan, Singapore, and Korea. Both individual markers and haplotypes of two to five SNPs showed several regions yielding statistical evidence for linkage and disequilibrium. Two genes (STK32B and EVC) yielded consistent evidence from cleft lip, with or without cleft palate, trios in all four populations. These two genes plus EVC2 also yielded suggestive evidence for linkage and disequilibrium among cleft palate trios. This analysis suggests that several genes, not just MSX1, in this region may influence risk of oral clefts.

Maternal transmission effects of the PAX genes among cleft case-parent trios from four populations

Isolated cleft lip with or without cleft palate (CL/P) is among the most common human birth defects, with a prevalence of 1 in 700 live births. The paired box (PAX) genes have been suggested as candidate genes for CL/P based largely on mouse models; however, few human studies have focused on this gene family. This study tests for association between markers in four PAX genes and CL/P using a case-parent trio design considering parent-of-origin effects. Trios from four populations (76 from Maryland, 146 from Taiwan, 35 from Singapore, and 40 from Korea) were genotyped for 34 single nucleotide polymorphisms (SNPs) in the PAX3, PAX6, PAX7, and PAX9 genes. We performed the transmission disequilibrium test (TDT) on individual SNPs. Parent-of-origin effects were assessed using the transmission asymmetry test (TAT) and the parent-of-origin likelihood ratio test (PO-LRT). TDT analysis showed one SNP (rs766325) in PAX7 yielding evidence of linkage and association when parent-of-origin was not considered, with an OR(transmission)=1.62 (P=0.003), and five SNPs in PAX6 (including two pairs in near perfect linkage disequilibrium). TAT analysis of all trios revealed two SNPs in PAX7 and four SNPs in PAX3 showing significant excess maternal transmission. For these six SNPs, the maternal OR(transmission) ranged between 1.74 and 2.40, and PO-LRT was also significant (P-values=0.035-0.012). When this analysis was limited to trios with male cases, SNPs in PAX7 showed higher maternal OR(transmission) and greater significance. PAX genes may influence the risk of CL/P through maternal effects, possibly imprinting, which seems to be stronger among male cases.

Differential parental transmission of markers in RUNX2 among cleft case-parent trios from four populations

Isolated cleft lip with or without cleft palate (CL/P) is among the most common human birth defects, with a prevalence around 1 in 700 live births. The Runt-related transcription factor 2 (RUNX2) gene has been suggested as a candidate gene for CL/P based largely on mouse models; however, no human studies have focused on RUNX2 as a risk factor for CL/P. This study examines the association between markers in RUNX2 and isolated, nonsyndromic CL/P using a case-parent trio design, while considering parent-of-origin effects. Case-parent trios from four populations (77 from Maryland, 146 from Taiwan, 35 from Singapore, and 40 from Korea) were genotyped for 24 single nucleotide polymorphisms (SNPs) in the RUNX2 gene. We performed the transmission disequilibrium test on individual SNPs. Parent-of-origin effects were assessed using the transmission asymmetry test and the parent-of-origin likelihood ratio test (PO-LRT). When all trios were combined, the transmission asymmetry test revealed a block of 11 SNPs showing excess maternal transmission significant at the P<0.01 level, plus one SNP (rs1934328) showing excess paternal transmission (P=0.002). For the 11 SNPs showing excess maternal transmission, odds ratios of being transmitted to the case from the mother ranged between 3.00 and 4.00. The parent-of-origin likelihood ratio tests for equality of maternal and paternal transmission were significant for three individual SNPs (rs910586, rs2819861, and rs1934328). Thus, RUNX2 appears to influence risk of CL/P through a parent-of-origin effect with excess maternal transmission.

Excess maternal transmission of markers in TCOF1 among cleft palate case-parent trios from three populations

Isolated cleft palate is among the most common human birth defects. The TCOF1 gene has been suggested as a candidate gene for cleft palate based on animal models. This study tests for association between markers in TCOF1 and isolated, nonsyndromic cleft palate using a case-parent trio design considering parent-of-origin effects. Case-parent trios from three populations (comprising a total of 81 case-parent trios) were genotyped for single nucleotide polymorphisms (SNPs) in the TCOF1 gene. We used the transmission disequilibrium test and the transmission asymmetry test on individual SNPs. When all trios were combined, the odds ratio for transmission of the minor allele, OR(transmission), was significant for SNP rs15251 (OR = 2.88, P = 0.007), as well as rs2255796 and rs2569062 (OR = 2.08, P = 0.03; OR = 2.43, P = 0.041; respectively) when parent of origin was not considered. The transmission asymmetry test also revealed one SNP (rs15251) showing excess maternal transmission significant at the P = 0.005 level (OR = 6.50). Parent-of-origin effects were assessed using the parent-of-origin likelihood ratio test on both SNPs and haplotypes. While the parent-of-origin likelihood ratio test was only marginally significant for this SNP (P = 0.136), analysis of haplotypes of rs2255796 and rs15251 suggested excess maternal transmission. Therefore, these data suggest TCOF1 may influence risk of cleft palate through a parent-of-origin effect.

Experience with sublabial transseptal transsphenoidal hypophysectomy at the Universiti Kebangsaan Malaysia

The transseptal transsphenoidal hypophysectomy has become a relatively frequent procedure in recent years. We performed 20 such procedures between January 1984 and December 1987 for various pituitary disorders. Significant complications such as CSF rhinorrhea, meningitis, diabetes insipidus, haemorrhage and septal perforation are discussed. The mortality rate for the series was 5%. In analysing the data, we feel that this technique of hypophysectomy is a safe procedure.

Antifibrinolytic treatment in subarachnoid hemorrhage

We enrolled 479 patients with subarachnoid hemorrhage in a multicenter, randomized, double-blind, placebo-controlled trial to determine whether treatment with the antifibrinolytic agent tranexamic acid improves outcome by preventing rebleeding. At three months there was no statistical difference between the outcomes in the tranexamic acid group and the control group. Of the 173 patients who died, 84 had received tranexamic acid and 89 placebo (95 per cent confidence interval for the difference in mortality rate, -6 to 11 per cent). Similarly, when analysis was restricted to patients with an angiographically demonstrated aneurysm, there was no significant difference between the groups. This absence of effect was not due to a lack of antifibrinolytic action, since the rate of rebleeding was reduced from 24 per cent in the control group to 9 per cent in the tranexamic acid-treated group (chi-square = 18.07, P less than 0.001), but resulted from a concurrent increase in the incidence of ischemic complications (15 per cent in the control group and 24 per cent in the tranexamic acid group; chi-square = 8.07, P less than 0.01). We conclude that until some method can be found to minimize ischemic complications, tranexamic acid is of no benefit in patients with subarachnoid hemorrhage.