Two large families with hereditary macular degeneration (HMD), one from central Sweden (116 cases), the other from northern Sweden (130 cases), were found to have a common origin. The disease was traced to a couple born in central Sweden (county of Kopparberg) in the 17th century. The disease was introduced to northern Sweden (county of Västerbotten) in the 18th century. Age of onset and severity of the disease varied widely in the 246 patients, 130 men and 116 women, carrying the same mutated gene. The distribution of age of onset was bimodal with one maximum before and one maximum after puberty. Women more often than men had their onset before puberty. The disease was inherited as an autosomal dominant trait with a high but not complete penetrance. At least one patient appeared to be homozygous.
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Nordström et al. (2009) studied this question.