TeachableMedicalNews article 03132020

Teachable moment in classrooms:

  1. chemical basis of life chapter – concept of one gene, one protein
  2. cellular basis of life chapter – gene mutation leading to protein  malfunction
  3. tissue chapter – junctional structures, hemidesmosomes
  4. integumentary system chapter – functions of epidermis

The news item:  Recently an article appeared about a newborn who was missing a good part of his skin:

Baby born without skin puzzles doctors, but mom says ‘we have faith, that’s all that matters’

Houston doctors are running tests to diagnose a baby born with most of his skin missing. Mom’s only been able to hold baby twice in three months.

The article mentioned the disorder epidermolysis bullosa, genetic testing for diagnosis, and the low frequency of this disorder.

So, Why Do I Care??  While the combination of the aplasia cutis and epidermolysis bullosa disorder has a very low frequency (20 cases for every million childbirth), this means 80 newborns every year in the USA alone.  The disorder comes to light after birth, and it is very traumatic for the parents, because they can’t hold their own kids.  This disorder costs the life of many newborns (15-50% mortality), because the epidermis part of the skin peels away from the skin.

Plain English, Please!!!  First, let’s talk about the skin.  The skin has two main layers.  The epidermis is the top layer, and the dermis is the lower layer.  In between there is a thin connecting layer called the basement membrane.  It all looks like layers of a carpeted floor.  The concrete floor is the dermis; the padding is the basement membrane, and the carpet on top is the epidermis.  The carpet epidermis keeps water from escaping from our bodies, and prevents the entry of pathogens. The concrete floor dermis gives strength to our skin, and the padding basement membrane connects the epidermis and dermis together.

Second, let’s talk about what keeps the epidermis in place.  The epidermis has to be firmly linked to the basement membrane, so when skin is pulled or injured by abrasion, the epidermis doesn’t peel away from the dermis. The loss of epidermis would mean loss of water, and an open door for pathogens to invade our tissues.  The epidermis is linked to the basement membranes at patches called hemidesmosomes.  Within each patch imagine thousands of bolts made of proteins pointing downward, and anchoring nuts (also made of proteins) in the basement membrane are threaded onto those bolts.  Now we bolted the two layers together.

Third, let’s talk about the anchoring structures.  The protein bolts are called integrins, and the anchoring nuts are called anchoring fibers made of type 7 collagen protein.  The newborn in the article most likely has a type 7 collagen mutation, where there is a change in the DNA sequence of the type 7 collagen gene, so genetic testing would confirm that. The mutation changes the shape of the nuts, and they no longer fit the bolts.  The unbolted epidermis separates from the basement membrane, causing that layer of the skin to peel off the body. Clinically that is one form of epidermolysis bullosa.