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Strategies to dissect phenotypic and genetic heterogeneity of major depressive disorder (MDD) have mainly relied on subphenotypes, such as age at onset (AAO) and recurrence/episodicity. Yet, evidence on whether these subphenotypes are familial or heritable is scarce. The aims of this study are to investigate the familiality of AAO and episode frequency in MDD and to assess the proportion of their variance explained by common single nucleotide polymorphisms (SNP heritability).
For investigating familiality, we used 691 families with 2–5 full siblings with recurrent MDD from the DeNt study. We fitted (square root) AAO and episode count in a linear and a negative binomial mixed model, respectively, with family as random effect and adjusting for sex, age and center. The strength of familiality was assessed with intraclass correlation coefficients (ICC). For estimating SNP heritabilities, we used 3468 unrelated MDD cases from the RADIANT and GSK Munich studies. After similarly adjusting for covariates, derived residuals were used with the GREML method in GCTA (genome-wide complex trait analysis) software.
Significant familial clustering was found for both AAO (ICC = 0.28) and episodicity (ICC = 0.07). We calculated from respective ICC estimates the maximal additive heritability of AAO (0.56) and episodicity (0.15). SNP heritability of AAO was 0.17 (p = 0.04); analysis was underpowered for calculating SNP heritability of episodicity.
AAO and episodicity aggregate in families to a moderate and small degree, respectively. AAO is under stronger additive genetic control than episodicity. Larger samples are needed to calculate the SNP heritability of episodicity. The described statistical framework could be useful in future analyses.
Although usually thought of as external environmental stressors, a significant heritable component has been reported for measures of stressful life events (SLEs) in twin studies.
We examined the variance in SLEs captured by common genetic variants from a genome-wide association study (GWAS) of 2578 individuals. Genome-wide complex trait analysis (GCTA) was used to estimate the phenotypic variance tagged by single nucleotide polymorphisms (SNPs). We also performed a GWAS on the number of SLEs, and looked at correlations between siblings.
A significant proportion of variance in SLEs was captured by SNPs (30%, p = 0.04). When events were divided into those considered to be dependent or independent, an equal amount of variance was explained for both. This ‘heritability’ was in part confounded by personality measures of neuroticism and psychoticism. A GWAS for the total number of SLEs revealed one SNP that reached genome-wide significance (p = 4 × 10−8), although this association was not replicated in separate samples. Using available sibling data for 744 individuals, we also found a significant positive correlation of R2 = 0.08 in SLEs (p = 0.03).
These results provide independent validation from molecular data for the heritability of reporting environmental measures, and show that this heritability is in part due to both common variants and the confounding effect of personality.
Traditionally, a 1-cm surgical resection margin is used for early oral tongue tumours.
All tumour stage one (n = 65) and stage two (n = 13) oral tongue cancers treated between January 1999 and January 2009 were followed for a median of 38 months (minimum 12 months). The sites of close and involved margins were histologically reviewed.
Involved and close margins occurred in 14 and 55 per cent of cases, respectively. The number of involved vs clear or close margins was equivalent in tumour stage one (90 vs 82 per cent), node-negative (100 vs 84 per cent) and perineural or lymphovascular invasion (20 vs 21 per cent) cases. Close or involved margins were similarly likely to be posterior (59 per cent) as anterior (41 per cent, p = 0.22), lateral (57 per cent) as medial (43 per cent, p = 0.34), and mucosal (59 per cent) as deep (41 per cent, p = 0.22). Local recurrence occurred in 28 per cent of cases at a median of 12 months, and was more likely in cases with involved (50 per cent) than clear or close margins (25 per cent, p = 0.10). Disease-free survival was worse in involved margins cases (p = 0.002).
Involved margins are common in early tongue tumours, and are associated with increased local recurrence and worse survival. Close or involved margins occur in all directions and all tumour types. A wider margin may be justified.
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