Volume 12 Issue 1, January 1996

Human personality traits which can be reliably measured by any of a number of rating scales, show a considerable heritable component^1,2. The tridimensional personality questionnaire (TPQ) is one such instrument and was designed by Cloninger to measure four distinct domains of temperament — Novelty Seeking, Harm Avoidance, Reward Dependence and Persistence — that are hypothesized to be based on distinct neurochemical and genetic substrates. Cloninger proposed that individual variations in the Novelty Seeking trait are mediated by genetic variability in dopamine transmission². Individuals who score higher than average on the TPQ Novelty Seeking scale are characterized as impulsive, exploratory, fickle, excitable, quick-tempered and extravagant, whereas those who score lower than average tend to be reflective, rigid, loyal, stoic, slow-tempered and frugal. We now show that higher than average Novelty Seeking test scores in a group of 124 unrelated Israeli subjects are significantly associated with a particular exonic polymorphism, the 7 repeat allele in the locus for the D4 dopamine receptor gene (D4DR). The association of high Novelty Seeking and the 7-repeat allele was independent of ethnicity, sex or age of the subjects. This work, together with the accompanying confirmations in this issue³, provides the first replicated association between a specific genetic locus involved in neuro-transmission and a normal personality trait.

Twin and adoption studies suggest that 30 to 60% of the variance in many personality traits is due to inherited factors. However, there is little knowledge of the number or identity of the responsible genes, how they differ between individuals, or how their gene products interact with the developing brain and with environmental and experiential factors to generate the complex blend of attitudes and actions that comprise human temperament¹. In the accompanying paper, Ebstein et al.² have found a population association between a long allele of polymorphic exon III repeat sequence of the D4 dopamine receptor gene (DADR) and the normal personality trait of Novelty Seeking. The possibility of a causal relationship between DADR and Novelty Seeking is further supported by studies showing that the number of exon III repeats can affect the binding of ligands to the receptor^3,4; that DADR is expressed in lim-bic areas involved in cognition and emotion^5,6; that dopamine mediates exploratory behaviour in experimental animals^7–12; that the rewarding effects of amphetamines and cocaine are related to dopamine release¹³; and that Novelty Seeking is low in dopamine-deficient patients with Parkinson's disease¹⁴. We investigated the relationship between DADR exon III sequence variants and personality test scores in a population of 315 mostly male siblings, other family members and individuals from the United States. The association between long alleles of exon III and personality traits related to Novelty Seeking was confirmed. Moreover, family studies showed that this association is the result of genetic transmission rather than of population stratification.

Protein complexes consisting of a cyclin-dependent kinase (CDK4 or CDK6) and cyclin D control passage through the G1 checkpoint of the cell cycle by phosphorylating the retinoblastoma (RB) protein¹. The ability of these complexes to phosphorylate RB is inhibited by a family of low molecular weight proteins including p16^INK4a (refs 2,3), p15^iNK4B (ref 4)? and p18 (ref 5) Germline mutations in the p16^INK4a gene have been identified in approximately half of families with hereditary melanoma^6–12. In this report, we describe an Arg24Cys mutation in CDK4 in two unrelated melanoma families which do not carry germline p16^INK4a mutations6. This mutation was detected in 11/11 melanoma patients, 2/17 unaffecteds and 0/5 spouses. The CDK4-Arg24Cys substitution has previously been identified as a somatic mutation in a melanoma that gives rise to a tumour-specific antigen recognized by autologous cytolytic T lymphocytes¹³. This mutation has a specific effect on the p16^INK4a binding domain of CDK4, but has no effect on its ability to bind cyclin D and form a functional kinase¹³. Therefore, the germline Arg24Cys mutation in CDK4 generates a dominant oncogene that is resistant to normal physiological inhibition by p16^INK4a. The only previous example of a dominant oncogene transmitted in the human germline is the RET gene that gives rise to MEN2A^14,15 and MEN2B¹⁶.