The pathogenesis of retinal and subdural haemorrhage in non-accidental head injury in infancy: Assessment using Bradford Hill criteria

Macrocephaly in the Primary Care Provider's Office

Macrocephaly is commonly encountered in the primary care provider's office. It is defined as an occipitofrontal circumference that is greater than 2 standard deviations above the mean for the child's given age. Macrocephaly is a nonspecific clinical finding that may be benign or require further evaluation. An algorithmic approach is useful for aiding in the clinical decision-making process to determine if further evaluation with neuroimaging is warranted. Abnormal findings may signify a harmful underlying cause, requiring referral to a genetic specialist or neurosurgeon.

The genomic load of deleterious mutations: relevance to death in infancy and childhood

The human diploid genome has approximately 40,000 functioning conserved genes distributed within 6 billion base pairs of DNA. Most individuals carry a few heterozygous deleterious mutations and this leads to an increased risk of recessive disease in the offspring of cousin unions. Rare recessive disease is more common in the children of cousin marriages than in the general population, even though <1% of marriages in the Western World are between first cousins. But more than 90% of the children of cousin marriages do not have recessive disease and are as healthy as the rest of the population. A mathematical model based on these observations generates simultaneous equations linking the mean number of deleterious mutations in the genome of adults (M), the mean number of new deleterious mutations arising in gametogenesis and passed to the next generation (N) and the number of genes in the human diploid genome (L). The best estimates are that M is <7 and N is approximately 1. The nature of meiosis indicates that deleterious mutations in zygotes will have a Poisson distribution with a mean of M + N. There must be strong selective pressure against zygotes at the upper end of the Poisson distribution otherwise the value of M would rise with each generation. It is suggested that this selection is based on synergistic interaction of heterozygous deleterious mutations acting in large complex highly redundant and robust genetic networks. To maintain the value of M in single figures over many thousands of generations means that the zygote loss must be of the order of 30%. Most of this loss will occur soon after conception but some will occur later; during fetal development, in infancy and even in childhood. Selection means genetic death and this is caused by disease to which the deleterious mutations predispose. In view of this genome sequencing should be undertaken in all infant deaths in which the cause of death is not ascertained by standard techniques.