2D/3D sonographic imaging of thanatophoric dysplasia type I at 19 weeks of gestation

Abstract

Thanatophoric dysplasia is a sporadic, lethal congenital skeletal dysplasia. There are two major subtypes: (1) a short, curved femur characterizes type I; and (2) a straighter femur with cloverleaf skull characterizes type II. We, here, present a case of type I disease. A 30‐year‐old pregnant woman was referred to the ultrasound unit due to fetal short extremities at 19 weeks and 4 days of gestation. Ultrasound revealed short limbs and a severely small thorax. Every limb bone was markedly short, and the femur, tibia, fibula and humerus were remarkably curved. 3D ultrasound demonstrated the abnormal appearance of extremities. Cranial and intracranial structures were normal. One week later, no growth of limb bones was seen. Thanatophoric dysplasia type I was strongly suspected and counseling of the couple was done. Pregnancy was terminated at 21 weeks of gestation and a female fetus was aborted. Short and curved limb bones were confirmed by postnatal X‐ray. Genomic DNA obtained by cord blood showed a point mutation in the fibroblast growth factor receptor 3 (FGFR3) gene; a C to T substitution at position 742 in the FGFR3 gene, resulting in a Arg248Cys substitution, known to be associated with type I disease. By ultrasound in the second trimester, prenatal diagnosis of skeletal dysplasia can be feasible. However, differentiating this lethal disease from non‐lethal skeletal disorders should be done prudently.