Ageing, information and the magical number seven

How many deleterious mutations are there in the human genome?

An estimate of the number of deleterious mutations in the human genome is made using data on the frequency of rare recessive disease in cousin marriages and in the general population. Sexual reproduction ensures that deleterious mutations are distributed at random in zygotes with an approximate Poisson distribution. The mean of this distribution is the sum of the mean number of deleterious mutations in zygotes which contribute to the next generation (Y) and the mean number of new mutations which arise in each human generation (X). The estimates are that X is between 1 and 2.6 and Y is between 12 and 32. A mathematical model based on redundancy is then used to predict how zygote survival will vary with the number of deleterious mutations. The form of this relationship is the same as that seen in experiments on cell survival following radiation-induced mutational damage and this provides independent support for this theoretical approach. The zygotes that survive to contribute to the next generation have a skewed distribution with a mean of Y. It is argued that the number of deleterious mutations in the genome is an important variable in health and disease.

Fetal origin of maturity-onset diabetes mellitus: genetic or environmental cause?

Low birthweight is a risk factor for a number of diseases of adult life including non-insulin-dependent diabetes mellitus (NIDDM). This implies that either genetic constitution or factors operating during intrauterine development have a causal role in NIDDM. One reason for rejecting a genetic cause, however, is that there is a rapidly changing prevalence of NIDDM with the onset and establishment of affluence, which does not fit with conventional models of multifactorial genetic disease. But in this article a new model of genetic disease based on the concept of redundancy is explored. The idea is that mutant genes interact synergistically in highly redundant systems to degrade performance and increase the risk of disease. The mutational load is in turn determined by the pre-conceptual environment. This model can explain a rapidly changing prevalence of NIDDM.

Cranial suture closing in Homo sapiens: evidence for circaseptennian periodicity

In their classical study on cranial suture closing. Todd and Lyon (1924-25) expressed their belief that suture closure proceeds according to some periodic pattern. Spectral analysis applied to their data corroborates the opinion of Todd and Lyon. Closure of the cranial sutures in humans is pervaded by a circaseptennian periodicity. Pulses of accelerated closure occur at intervals of about 7 years, and are separated by periods of relative quiescence.

Schizophrenia, bacterial toxins and the genetics of redundancy

The hypothesis proposed is that episodes of bacterial toxaemia occurring early in life cause subtle brain damage which predisposes to schizophrenia. The damage is most likely to occur in individuals who have one or more mutations in a large set of genes controlling aspects of the immune response to infection. These genes, numbering several hundreds or even thousands, control a vital but highly redundant system. Schizophrenia, by reducing fertility, causes selective pressure against the mutations which would otherwise accumulate in the genome and degrade our ability to fight infection. This hypothesis is consistent with the key features of the disease which include a strong genetic component, neuroanatomical abnormalities, a seasonal influence, lack of association with HLA subtypes and the observation that the frequency of schizophrenia is similar in widely different populations. If bacterial toxins also have a role in precipitating acute psychosis, then the age incidence of schizophrenia can be explained.

Information and clonal concepts in ageing

A model based on information theory and one based on somatic mutation in an expanding pool of cells are combined to give a theory of ageing. A mathematical formula, based on concepts from information theory, gives a close fit to the age incidence of mortality and disease in middle and old age. The basic concept is that biological systems process information and make decisions to maintain their integrity. But the decision process is fallible and significant errors could lead to disease or death. Decay in the components of the system will lead to a rising error rate with age and the form of the curve will be influenced by redundancy which is a fundamental property of information systems. In addition it is suggested that an important part of the decay in the decision process is due to a subset of mutant stem cells which have a proliferative advantage and slowly expand in number throughout life. This idea is derived from application of a model of somatic mutation in expanding cells to data in cancer and on the increase of dominant mutations with paternal age. This composite view explains why ageing is less subject to the vagaries of the extrauterine environment than suggested by the simple information model and points to a significant role for the intrauterine environment in the ageing process.

The storage of energy as a cause of malignant transformation: a 7-phase model of carcinogenesis

Although many theories for the development of cancer exist, a new hypothesis for carcinogenesis is suggested and a new 7-phase model of malignant transformation described. Both the hypothesis and the model are based on the principle of a critical point in local energy (entropy?) storage, at a certain level of structural organisation within the cells. This principle has been previously formulated by the author from the rules of non-equilibrium thermodynamics. The model introduces a new terminology and explores the concepts of both high work value of energy and bifurcation. The ability (A) of cells is suggested to be the most important cellular feature in respect to cell survival. This ability implies that the cells follow the requirement Kir > 1, even in dangerous situations and under harmful environmental influence. But, when the cells have lost their ability (A) and all levels of the cell defence machine have been exhausted, then the local energy storage may provoke a cascade of harmful events within the cells. The S-stage is the most unstable state of the cell cycle. If such harmful events take place during DNA synthesis within the 'premalignant' cell, in the phase 'promotion' at the 4th bifurcation, they lead ultimately to carcinogenesis (i.e. malignant transformation). The 7-phase model of carcinogenesis is consistent and offers many advantages in comparison to the previous hypotheses. This model could help the design of experiments, development of new drugs and optimization of medical treatment. The new hypothesis could contribute to a better understanding of the processes of carcinogenesis and the uncontrolled division, growth and lability of tumour cells.