THANATOPHORIC DYSPLASIA TYPE I ASSOCIATED WITH INCREASED NUCHAL TRANSLUCENCY IN THE FIRST TRIMESTER: Early Prenatal Diagnosis Using Combined Ultrasonography and Molecular Biology

A case of thanatophoric dysplasia (TD) type I associated with severely increased nuchal translucency at first trimester screening for Down syndrome is reported. A 38-year-old woman, G2P1, with previous uneventful pregnancy, was referred for amniocentesis at 16 weeks due to positive first trimester integrated test. Amniocentesis revealed a 46, XX fetus. At 16 weeks gestation, the ultrasound examination of the fetus revealed a narrow chest, short ribs, and a generalized severe shortening of the long bones. The patient underwent a follow-up scan at 19 weeks which demonstrated ultrasound findings consistent with severe rhizomelic micromelia. A wide prenatal panel of gene mutations related with skeletal dysplasia was performed. Nucleotidic sequence using QF-PCR on exons 7,10, 15, 19 of the fibroblast growth factor receptor 3 (FGFR3) demonstrated a 742 C>T (R248C) mutation, which resulted in an Arg248Cys substitution in heterozygous state, leading to a prenatal diagnosis of thanatophoric dysplasia type I. The early diagnosis of this lethal form of skeletal dysplasia directed the prenatal counseling and allowed appropriate obstetric management. Necropsy, post-mortem x-ray, and histologic analysis of the growth plate might aid the diagnosis of TD type I.