of TH01 with human longevity revisited

von Wurmb-Schwark1, Amke Caliebe2, Thorsten Schwark1, Rabea Kleindorp3, Micaela Poetsch4, Schreiber3,5 and Almut Nebel*,3

The gene tyrosine hydroxylase 1 (TH01) has been suggested as a candidate for human longevity. A previous study has shown an association between longevity and specific alleles of the TH01 short tandem repeat (STR) polymorphism in an Italian population. This STR locus is also widely used in forensic genetics. If the TH01–longevity association could be confirmed in independent samples, this finding would have important ramifications for the use of this polymorphism in a forensic context. In the present study, we sought to replicate the previous association result by investigating 471 long-lived individuals years) and 462 younger controls (19–75 years) from Germany. In the analyzed samples, the association between TH01 and longevity was not replicated. However, the obtained TH01 allele frequencies were consistent with published data. We observed considerable differences in the allele distribution between Germans and Italians, in particular with regard to allele 9.3, which displayed a previously undetected decreasing West–East and North–South cline across Europe. The discrepant TH01–longevity association results in Germans and Italians could therefore be due to population-specific effects. This finding highlights the need to take into consideration population genetic data when dealing with association studies.

Keywords: TH01; human longevity; forensic; STR; allele 9.3

INTRODUCTION

arterial hypertension8,9 or smoking,10–13 albeit with conflicting results. As a forensically employed genetic polymorphism – at least in Germany – must not reveal information about phenotype, personality or disease susceptibility of the tested individual,14 a confirmed association between TH01 alleles and longevity could result in the exclusion of this marker from forensic investigations.

The gene tyrosine hydroxylase 1 (TH01) has been suggested as a candidate for human longevity. Given its role in stress response, it is conceivable that allelic variation in this gene influences survival into old age. A previous study investigated a possible association of the short tandem repeat (STR) polymorphism in intron 1 of TH01 (localization: 11p15.5–p15, motif: TCAT) with longevity in Italians.1 The authors reported a statistically significant reduction in the frequency of homozygotes of long TH01 tetranucleotide repeats (Z9) in male centenarians compared with younger men. There was no association in females. Subsequent TH01–longevity studies, which differed from the original investigation1 in terms of study design, the analysis approaches and examined markers, described contradictory findings.2–4 For instance, Tan et al3 observed an increase in carriers of the long allele 9.3 in Italian centenarians versus younger individuals. In summary, the involvement of TH01 variation in human longevity still remains unresolved. However, if this association could be confirmed, this would have important ramifications for the use of this locus in forensic genetics.

In view of the important role of the TH01 locus in legal medicine and the implications a genuine association would have, we sought to replicate, as primary end point, the initial finding in Italians1 in our collection of 471 long-lived individuals (LLI) and 462 younger controls from Germany. Furthermore, we investigated whether allele 9.3 exerts a role as a modulator of longevity as suggested by Tan et al.3

MATERIALS AND METHODS

Study population

Four hundred seventy-one unrelated German LLI between 96 and 110 years of age at recruitment (median age: 101 years) were studied. Three hundred fifty- four (75%) of the LLI were centenarians. The sample of younger German controls was obtained from the popgen biobank15 and comprised 462 living subjects aged between 19 and 75 years (median age: 59 years). The controls were matched to the LLI in terms of ancestry and gender, thus minimizing any systematic genetic differences between these samples that might arise due to very low levels of undetected population structure. Based on current predic- tions only 1.5% of all 60-year-old and 1.8% of all 75-year-old German females will live up to 100 years. For males, the probability is even lower (Human Mortality Database; http://www.demogr.mpg.de). Thus, fewer than eight of the younger controls are estimated to become centenarians themselves, a negligible proportion that does not affect power. The recruitment procedures for LLI and

The TH01-STR is one of the most widely used markers in forensic casework. It is a mandatory locus in many forensic databases (eg, CODIS in the US, DAD in Germany, UK Forensic Database in Great Britain) and has therefore been included in most commercially available STR multiplex PCR kits.5 However, in recent years, TH01 has not only been linked to human longevity but was also described to be associated with psychiatric disorders6 and sudden infant death syndrome.7 Other studies investigated a possible role of TH01 in

1Institute of Legal Medicine, Christian-Albrechts-University and the University Hospital Schleswig-Holstein, Kiel, Germany; 2Institute of Medical Informatics and Statistics, Christian-Albrechts-University and the University Hospital Schleswig-Holstein, Kiel, Germany; 3Institute of Clinical Molecular Biology, Christian-Albrechts-University and the University Hospital Schleswig-Holstein, Kiel, Germany; 4Institute of Legal Medicine, University Hospital Essen, Essen, Germany; 5Popgen Biobank, Christian-Albrechts- University and the University Hospital Schleswig-Holstein, Kiel, Germany *Correspondence: Dr A Nebel, Institute of Clinical Molecular Biology, Christian-Albrechts-University, Schittenhelmstrasse 12, 24105 Kiel, Germany. Tel: +49 431 597 1373; Fax: +49 431 597 2196; E-mail: a.nebel@mucosa.de Received 17 September 2010; revised 20 January 2011; accepted 9 February 2011