Dwarfism Awareness Month - SEDc

Rare Dwarfism Conditions Post #7 - Spondyloepiphyseal Dysplasia Congenita (SEDc) -(aka my condition!! 😊)

Spondyloepiphyseal dysplasia congenita (SEDc) is a genetic disability and a form of skeletal dysplasia.  “Spondylo” means spine, “epiphyseal” means the ends of the long bones, and “dysplasia” means a difference in growth/development, so spondyloepiphyseal dysplasia (SED) is a condition that affects the growth and development of the spine and long bones.  “Congenita” means present at birth.  SEDc is the most common form of SED, but there are other forms.  The other forms of SED are caused by changes in different genes, so are different than SEDc. 

Genetic Changes

SEDc is caused by changes in a gene COL2A1, which is located on the long arm of chromosome 12.  COL2A1 gives the body instructions for making a protein called type 2 collagen.  Type 2 collagen is one of the major building blocks of cartilage and the spinal “discs” between vertebrae, and is also important in the eyes and ears.  The type 2 collagen proteins have to come together and wrap around each other like a rope to give strength and flexibility to these tissues.  In people with SEDc, a single letter change in the gene gives the type 2 collagen protein a “kink”, so that it can’t form a strong, flexible rope.  

Spectrum of conditions

Changes, or mutations, in the gene COL2A1 cause a “spectrum” of skeletal dysplasias called the “type 2 collagenopathies.”  The most severe, achondrogenesis type II, is almost always lethal.  Hypochondrogenesis is still classified as “lethal” due to severe respiratory problems in infancy, but with medical advances including tracheostomies and ventilators, many babies are surviving and thriving - they just need some extra time for their lungs and airways to develop.  SEDc and spondyloepimetaphyseal-Strudwick-type (SEMD-Strudwick) are very similar conditions, that I’m not convinced are actually different from each other 😜.  Kniest syndrome is a related condition with some differences, that I’ll write about in a different post.  Milder conditions, usually classified as connective tissue disorders, include Stickler’s syndrome and premature arthritis.  I won’t be writing about these, since, unlike the other conditions listed above, people with them don’t usually have signs of skeletal dysplasia in childhood.  

Features

SEDc probably affects about 1 in 100,000 people, although we don’t have great data on this.  It is the 2nd-most common form of dwarfism among LPA members.  SEDc is a really variable condition, meaning that it affects every person differently.  Many people have short stature.  Most people with SEDc are between 3’3” and 5’3”, but people range from 2’5” to 5’8” (literally!!)  People with SEDc who are short statured usually have short-trunk dwarfism, meaning that the torso is shortened much more than the limbs.  I actually have average-length arms, even though my legs and torso are short! The reason many people haven’t met the “taller” people with SEDc is that they don’t come to LPA.  Even though many LPA members are inclusive of everyone with a skeletal dysplasia, people over 5” with SEDc and Kniest often don’t feel welcome. 

Because the cartilage is abnormal in people with SEDc, we tend to have a lot of joint problems.  When the human skeleton develops, it starts out as cartilage and turns to bone.  This process is known as “ossification.”  In people with SEDc, this ossification happens much later than in average-height folks.  Many joints form at odd angles.  The joints that are usually the most affected are the hips; people with SEDc rarely form an actual “ball” or “socket”, with the ball forming as a “squished mushroom cap” (thanks Lia for the analogy!) We often need joint reconstruction surgeries in childhood to help with mobility and pain.  Early arthritis and chronic joint pain is common, with many people needing hip replacements in their 20s, and knee replacements and ankle fusions in their 30s and 40s.  The shoulders, elbows, wrists, fingers, feet, neck, and back can also have pain.  

However, joint pain is highly variable among people with SEDc.  There are people with SEDc who are literally cheerleaders and bodybuilders and have almost no pain.  There are people like myself who struggle daily with pain in almost every joint.  People on the shorter end of the spectrum don’t necessarily have more pain than people on the taller end.  Many of us use scooters and other mobility aids to help get around.  

The spine is also affected in SEDc.  Many of us don’t form the 2nd vertebrae well, leading to instability in the neck.  This instability increases the risk of spinal cord injury and death with a minor accident, so many of us have fusions to stabilize this.  Spinal curvatures are very common, and many people have additional spinal surgeries to correct this, if the curvatures become problematic. 

Many, but not all, babies with SEDc are born with a cleft palate, or hole in the roof of the mouth.  This can make feeding difficult, so some children need a gastrostomy-tube (feeding tube).  Cleft palate can also cause some people to have a speech disorder in childhood and adulthood.  Some babies are born with club feet.  Some babies have breathing problems at birth due to “floppy airways” and underdeveloped lungs.  Myopia, or near-sightedness, is common, and we have an increased risk of retinal detachment, which is where the back of eye disconnects, causing vision loss.  Frequent ear infections and hearing loss are also common. 

Some, but not all, children with SEDc have delays in achieving motor milestones (ie. sitting and walking at the same time as average height kids).  Some children have speech delays due to cleft palate or hearing loss.  But most people with SEDc have typical or above-typical intelligence. My friends with SEDc are disability advocates, actresses, musicians, teachers, managers, computer technology wizzes, government-employees, doctors, medical students, writers, artists, engineers, entrepreneurs, wives, husbands, parents, soon-to-be-genetic counselors 😉.

Inheritance

SEDc is an autosomal dominant condition, meaning that only 1 copy of the gene COL2A1 has to be changed to have the condition (we each have two copies of this gene).  In many cases, SEDc is caused by a random genetic mutation at or before conception, in a child with no family history of the condition.  Once someone has SEDc, they have a 50% chance of passing it down to each child.  I know several people who are the 2nd or 3rd generation in their family to have SEDc.  

(Sources: MY BRAIN. Jk, I have sources for all of this, but didn’t feel like writing them all out.  If there’s something specific that you’d like to know where I got my info from, ask and I will gladly provide you with a reference 😊).