Many people are aware of dwarfism, however, some people are not aware that dwarfism can be caused by many different conditions. One such condition is Acromesomelic dysplasia (AMD). So what exactly is AMD?
Acromesomelic dysplasia (AMD) is an extremely rare form of dwarfism. In fact, the condition is so rare that there have been less than one-hundred confirmed cases. AMD is a familial condition, inherited in an autosomal recessive pattern. The disorder is characterized by shortened forearms, forelegs, hands, and feet in comparison to the rest of the body. Other bones of the body may also have abnormalities. Abnormalities with cartilage as well as fingernails and toenails are also common. Other characteristics of AMD include a large head, a flat face, and a small nose. The condition is not always obvious at birth. As time passes, however, the disease becomes more progressive and much more obvious. There are three different types of AMD: Maroteaux Type (AMDM), Hunter-Thompson Type (AMDH), and Grebe Type (AMDG). All three forms of AMD are clinically and genetically distinct from one another.
Acromesomelic dysplasia Maroteaux Type (AMDM), in general, is the least severe form of AMD. It is caused by mutations of the NPR2 gene on chromosome 9. Although AMDM is considered an autosomal recessive trait (meaning that both copies of NPR2 must be mutated to cause disease), research has shown that a mild form of the disease results when only one copy of NPR2 is mutated. More research needs to be done to determine the wide range of clinical variability. As with other AMD disorders, babies with AMDM appear normal at birth. Signs of the disease do not appear until later in life. Characteristics of AMDM include shortening of the forearms and forelegs, fingers and toes that appear short and broad, spine abnormalities, enlarged head with a flat face and small nose, and delayed motor development. Individuals with AMDM have normal intelligence but there are significantly shorter than their peers. Outside of physical deformities, there are no complications from AMDM and individuals with the disease live relatively normal lives.
Acromesomelic dysplasia Hunter-Thompson Type (AMDH) is the rarest form of AMD. There have been less than ten confirmed cases. Although AMDH is generally more severe than AMDM, it is less severe than AMDG. The condition is caused by mutations of the CDMP-1 gene on chromosome 20. Unlike other forms of AMD, abnormally shortened bones seen with AMDH are limited to the limbs. Other characteristics of AMDH include frequent dislocation of the joints, missing or fused bones, normal intelligence, and normal facial appearance. Limited mobility is the main complication of AMDH. Most individuals with AMDH have severely limited mobility and some never walk.
Acromesomelic dysplasia Grebe Type (AMDG), in general, is the most severe form of AMD. The condition is caused by mutations of the CDMP-1 gene on chromosome 20, the same gene responsible for AMDH. AMDG is characterized by severe bone deformities of the limbs, feet, and hands; limited mobility of the elbows, wrists, fingers, knees, and ankles while other joints remain unaffected; missing thumb(s); normal facial appearance; and normal intelligence. Unlike other forms of AMD, AMDG can be fatal. Most fatalities occur before or slightly after birth. If a baby with AMDG makes it to his/her first birthday, then he/she is expected to live a normal life span. Research on AMDG is limited. In the few cases AMDG has been researched, it appears that individuals adapt remarkably well and live relatively normal lives despite their physical deformities.
Acromesomelic dysplasia (AMD) is an extremely rare form of dwarfism. It is an inherited condition marked by many characteristics. There are three forms of AMD, all of which are clinically and genetically distinct from one another. Aside from physical deformities, AMD rarely causes complications. Individuals with AMD live relatively normal lives.
