2023-06-15 05:06:06
Humans have skin patterns that are not visible, due to an anomaly in how the epidermis is formed.
And contrary to some internet rumors, animals can’t see them (no, your cat can’t see your secret lines). But these spots and lines can appear with various skin conditions, including eczema and vitiligo.
By the turn of the 20th century, German dermatologist Alfred Blaschko had studied the skin of more than 150 patients. He noticed the patterns of moles, birthmarks and other skin conditions across their bodies and discovered that they seemed to follow specific lines.
It appears that the lines were present at birth and did not follow any other known body system such as blood vessels or nerves. Instead, she creates sweeping arches for the chest, mountain shapes across the back, and rounded butt rings.
More details, including scalp spirals and waving, were added to the map 100 years later by the physician Rudolf Hubble.
It is now believed that these Blaschko lines follow the movements our cells made as they divided and grew in the skin we are in now, during embryonic development. Specifically, they are drawn by the pathways of keratinocytes – the main cell in superficial skin – and melanocytes – the cells deep in the epidermis responsible for our skin’s pigment.
The melanocytes form in the neural crest of the fetus while it is still just a speck of a few hundred cells. Around this point in female development, cells start randomly choosing which X chromosome to switch off, as we only need one active X chromosome per cell, yet we inherit two, one from the mother and one from the father.
Therefore, some of the embryonic cells that give rise to our skin cells will have a paternal X chromosome, while others will have a maternal X chromosome. All cells that divide from those early cells will maintain the same epigenetic X chromosome setup, which means that the entire Blaschko line will also share this version of DNA, while the line next to it may be the same, or it may have the other X.
This is how some patterns appear as streaks, while others appear as larger spots. These patches of genotyping are called mosaicism, and they can occur with mutations that occur early in development as well, not just X-linked traits.
And because human pigmentation color is determined by more than just a gene in our X chromosome, you can’t usually see this effect in humans. However, in other animals, genes for coat color are linked exclusively to their X chromosome.
Their patches of color clearly identify where the two different types of cells are located, one set with the mother’s X chromosome and the other with the father. But some conditions can also make these lines visible in humans.
Mutations involving color-producing cells can result in pigment mosaics in the form of stripes and swirls that follow Blaschko’s lines.
And while it’s fun to speculate what your unique set of Blaschko stripes might look like, understanding these patterns can help doctors diagnose skin conditions, too.
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