So first we start with an art lesson.
The painting from 1656 by Diego Velasquez is entitled "Las Meninas" (The Maids of Honour). It is one of the most influential works in Western art history. The two figures to the far right have achondroplasia.
Achondroplasia (pronounced Ay-kondro-play-zha) is a genetic disorder that occurs in about 1/25,000 people. It's caused by a malfunctioning gene (FGFR3) that's needed in normal bone growth.
In order to have the condition, you need to have one gene. Having two genes is not compatible with life; babies that inherit two genes usually die in utero or after birth. Those that inherit one gene get the condition.
So if two parents both have achrondroplasia, then if they get pregnant, they have a 25% chance of having a child that will die; a 50% chance of having a child with the condition; and a 25% chance of having a totally normal child with no gene at all.
If only one parent has achrondroplasia, then the children have a 50% chance of being normal, and 50% chance of having achrondroplasia. None will die from inheriting two genes.
What if two parents were closely related, like brother and sister? In this case, their chances of having a child with the same disorder is the same if they were unrelated parents with achondroplasia.
Also, almost 80% of cases occur spontaneously because of a new genetic defect that happens for no reason. But those people can pass on the gene to their children.
So what kinds of traits do people with achondroplasia have? On average, men grow to about 4 ft 3 inches; the women 4 feet. The usually have bowed legs, large skulls for their size and facial features that are very similar. Just like in the painting above. Their arms and legs are short in proportion to their torso. Their fingers are usually short. Intelligence wise, they are completely normal. They have a life expectancy that's pretty long, although about 10 years less than an average adult.
Please keep in mind this post is for writing purposes only and is not to be construed as medical advice!
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