HX10 The history of birthmarks: from maternal impressions to genetic discovery

Abstract Birthmarks have held diverse cultural, historical and scientific significance throughout time. In Chinese and Indian traditions, they were considered karmic imprints, symbolizing deeds or experiences from past lives. Similarly, European folklore connected birthmarks to maternal impressions, the belief that a mother’s emotional or physical experiences during pregnancy – such as consuming certain foods or witnessing traumatic events – could imprint marks on the unborn child. This belief persisted for centuries, with European philosophers like Galen and Descartes suggesting that maternal imagination or exposure to specific stimuli influenced fetal development. From the 16th century, maternal impressions were widely accepted, with advice warning pregnant women against viewing accidents or slaughter. The association of vascular birthmarks with facial areas was attributed to maternal gestures of fright, such as touching the face. Pregnant women were urged to satisfy food cravings to avoid marking their child and to touch hidden body parts to ensure any birthmark remained concealed. However, in the 18th century, scepticism began to grow. British obstetrician William Smellie and other physicians questioned this theory, emphasizing the lack of consistent evidence linking maternal experiences to birthmarks. By the late 19th century, the concept waned, although further cases continued to be documented. In 1875, for example, family practitioner James Clapperton published four cases of maternal impressions in the British Medical Journal, including the following: ‘Mrs. H, aged 30, a healthy woman, went to the flour-bin; and when she put her hand into the bin, a mouse ran across her arm. The child was born with a mark on its arm, which now distinctly resembles a mouse’ (Clapperton J. Maternal impressions. BMJ 1875; 1: 169–70). ‘Birthmarks’ encompass a wide range of congenital cutaneous conditions from vascular anomalies to congenital melanocytic naevi. Over the past century our knowledge of the genetic events that cause birthmarks has developed significantly, particularly our understanding of mosaicism. In 1901, having studied over 150 patients with segmental cutaneous conditions, Blaschko produced illustrations of cutaneous linear patterns, now thought to represent pathways of ectodermal cell development. In 1976, Jackson proposed that Blaschko’s lines may be due to mosaicism, a concept further developed by Happle, who expanded the classification of cutaneous mosaic patterns. Early mosaic molecular discoveries included Paller’s identification in 1994 of keratin 10 mutations in epidermal naevi of epidermolytic hyperkeratotic type. In the last decade, next-generation sequencing has accelerated the discovery of mosaic variants in a multitude of cutaneous phenotypes, enabling genetic diagnosis for patients and families, improving genetic counselling and opening the door to potential future targeted therapies.