What is thanatophoric dysplasia?
Thanatophoric dysplasia is a severe type of skeletal abnormality that causes extreme shortening of the limbs, a small ribcage with very short ribs, severely under-developed lungs, and abnormalities of the skull. Babies with thanatophoric dysplasia usually do not survive after birth because their lungs are too under-developed. There are two types of thanatophoic dysplasia (TD): type I and type II. There are several overlapping features that are seen in both TD type 1 and TD type 2, which include: a narrow ribcage, shortened ribs, a large head with distinctive facial features, poor muscle tone, shortened fingers and toes, and extra folds of skin along the limbs. Two major differentiators between TD type I and TD type 2 have to do with the shape of the femurs (thigh bones) and the shape of the skull. Babies with TD type I typically have bowing (curving) of the femurs and a large skull that has a relatively normal shape, while babies with TD type 2 typically have straight femurs and moderate-to-severe malformation of the skull called a cloverleaf deformity, ask the skull's shape resembles that of a three leaf clover when viewed from above.
The word "dysplasia" is Greek for "bad/difficult formation", referring the the abnormalities of the skeletal system. The word "thanatophoric" is Greek for "death-bearing" because most babies with TD are stillborn or die shortly after birth as a result of their severely under-developed lungs. With that said, there are a few individuals who have survived beyond the neonatal period with extensive medical assistance.
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What are some other names for thanatophoric dysplasia?
Other names for thanatophoric dysplasia type I include: thanatophoric dwarfism, platyspondylic lethal skeletal dysplasia (San Diego type), and lethal short-limbed platyspondylic dwarfism (San Diego type).
Other names for thanatophoric dysplasia type II include: thanatophoric dysplasia with straight femurs and cloverleaf sull, thanatophoric dysplasia with Kleeblattshaedel, and cloverleaf skull with thanatophoric dwarfism.
There are many different types of skeletal dysplasias, and sometimes it is not possible to know which specific skeletal dysplasia is present until after the baby's birth. For more information on skeletal dysplasias in general, see The Children's Hospital of Philadelphia's Skeletal Dysplasia website.
How common is thanatophoric dysplasia?
Thanatophoric dysplasia is estimated to occur in approximately 1/40,000 live births (estimates based on birth defects monitoring programs suggest a range of between 1/33,330 and 1/47,620 live births).
- Waller DK et al. The population-based prevalence of achondroplasia and thanatophoric dysplasia in selected regions of the US. Am J Med Genet A. 2008;146A(18):2385-89.