Genetic anticipation: fact or artifact, genetics or epigenetics?

TSC22D2 identified as a candidate susceptibility gene of multi-cancer pedigree using genome-wide linkage analysis and whole-exome sequencing

Cancer is a complex disease, which may involve multiple tumor susceptibility genes that mediate the occurrence and development of tumor molecular events. This study aimed to identify new genetic loci using genome-wide linkage analysis and whole-exome sequencing in a rare, large multi-cancer pedigree recently found in China. We performed high-throughput single-nucleotide polymorphism (SNP) array and linkage analyses of 24 core members of this pedigree and found that the disease susceptibility locus in the multi-cancer pedigree was mapped to chromosome 3q24-26. We also used microsatellites to further validate the results of the SNP locus linkage analysis. Furthermore, we sequenced the whole exome of three members in this pedigree and identified a novel mutant of transforming growth factor β stimulated clone 22 domain family, member 2 (TSC22D2, c.-91T-C) cosegregated with the cancer phenotype. This change was at a highly conserved position, and the exome results were validated using linkage analysis. Moreover, we found the histone H4 transcription factor (HINFP) binds to the promoter region of TSC22D2 and may regulate its transcription. In conclusion, our findings are of great significance to the early pathogenesis of tumors and contribute to the search for molecular targets for the early prevention and treatment of tumors.

Overcoming artefact: anticipation in 284 Portuguese kindreds with familial amyloid polyneuropathy (FAP) ATTRV30M

BACKGROUND

Early-onset (≤40 years) and later-onset (≥50 years) cases of familial amyloid polyneuropathy (FAP) ATTRV30M are not different entities, often coexisting in the same family, and showing anticipation (earlier age-at-onset (AO) in younger generations, usually associated with more severe phenotype). Historically, anticipation has been ascribed to ascertainment biases. Our aim was to study anticipation in a very large number of FAP kindreds, removing possible biases, and gain further insight into parent-of-origin effects.

METHODS

We analysed 926 parent-offspring pairs (from the Unidade Clínica de Paramiloidose roster, collected in 70 years), both clinically observed and had well-established AO, correcting for intrafamilial correlations.

RESULTS

Women had a significantly higher AO, either for daughters (mean: 33.70, SD: 6.84) vs sons (29.43, 6.08); or mothers (39.57, 11.75) vs. fathers (35.62, 11.62). Also, 291 pairs showed marked anticipation (≥10 years); the transmitting parent was the mother in 203 pairs. Mother-son pairs showed larger anticipation (10.43, 9.34), while father-daughter pairs showed only a residual anticipation (1.23, 9.77). Gender of offspring and parents was highly significant (with no interaction). To remove possible biases, we repeated analyses: (1) excluding the proband; (2) removing pairs with simultaneous onset; and (3) excluding offspring born after 1960. Anticipation was found in all subsamples, with the same trend for a parent-of-origin effect. Noteworthy, parents with AO ≤40 years never had offspring with AO ≥50.

CONCLUSIONS

These findings confirm anticipation as a true biological phenomenon, also in FAP ATTRV30M. Acknowledgment of anticipation may have important clinical implications in genetic counselling of offspring and in follow-up of mutation carriers.

Epigenetics as a unifying principle in the aetiology of complex traits and diseases

Epigenetic modifications of DNA and histones might be crucial for understanding the molecular basis of complex phenotypes. One reason for this is that epigenetic factors are sometimes malleable and plastic enough to react to cues from the external and internal environments. Such induced epigenetic changes can be solidified and propagated during cell division, resulting in permanent maintenance of the acquired phenotype. In addition, the finding that there is partial epigenetic stability in somatic and germline cells allows insight into the molecular mechanisms of heritability. Epigenetics can provide a new framework for the search of aetiological factors in complex traits and diseases.

Genetic alteration associated with chronic lymphocytic leukemia

The genetics of B-cell chronic lymphocytic leukemia (B-CLL) differ considerably from most other forms of hematologic malignancy which are usually characterized by chromosome translocations. B-CLL typically contains chromosomal deletions and chromosomes 13q14 and 11q22-->q23 are the most common. These two regions appear to share a common ancestral origin (Auer et al., 2007b). Overall, chromosomal abnormalities can be found in the majority of patients with B-CLL when using sensitive techniques (Dohneret al., 2000) and possibly reflects an underlying predisposition, with a small but significant number of familial cases. Although single and consistent abnormalities are most common, multiple rearrangements can occur, often with disease progression (Feganetal., 1995; Dohner et al., 2000). Regions of recurrent deletion suggest the presence of tumor suppressor genes if following Knudson's theoretical 2-hit model. However, despite extensive sequencing analysis over the last decade and lack of pathogenic mutations identified, there has been a move away from this suggested hypothesis and alternative mechanisms of gene inactivation involving epigenetic silencing or haploinsufficiency may be considered as more likely in this disease. This review focuses on the common genetic abnormalities in B-CLL and relates them to some of the more recent hypotheses on inactivation of genes within these regions of deletion.

No evidence for anticipation in lymphoproliferative tumors in population-based samples

Genetic anticipation in familial non-Hodgkin's lymphoma, Hodgkin's lymphoma, and chronic lymphocytic leukemia (CLL) has been consistently reported in the literature. However, most of these findings were based on data from families ascertained for genetic studies. Fecundity bias, right censoring bias, and secular trends can lead to erroneous conclusions regarding the presence of anticipation. Our report investigates anticipation in four lymphoproliferative cancers, non-Hodgkin's lymphoma, Hodgkin's lymphoma, CLL, and multiple myeloma, drawn from Swedish and Danish population-based registries. We used marginal survival methods to test for a relative difference in age at diagnosis between parents and offspring and to account for other risk factors, staggered entries, censored data, and correlations among relatives. Changes in incidence rates of lymphoproliferative tumors were accommodated in the models by using time-varying covariates for different periods of diagnosis. Whereas no anticipation was observed for Hodgkin's lymphoma, CLL, and multiple myeloma, our initial model, which controlled for gender and country, suggested a significant difference (hazard ratio, 0.5; 95% confidence interval, 0.33-0.75) in age at diagnosis between the parents and offspring in the non-Hodgkin's lymphoma sample. However, once we accounted for the significant change in non-Hodgkin's lymphoma incidence over time, the statistical difference between parents and offspring disappeared (hazard ratio, 0.99; 95% confidence interval, 0.56-1.76). Our results emphasize the importance of considering secular trends when evaluating the possibility of anticipation in lymphoproliferative cancers. This is the first study to consider the changes of incidence over time as a source of bias when evaluating anticipation in lymphoproliferative cancers.