Failure to diagnose hypochondroplasia by prenatal diagnosis: a case report

BACKGROUND: Hypochondroplasia (HCH) is a common nonlethal skeletal dysplasia caused by pathogenic variations in the fibroblast growth factor receptor 3 (FGFR3) gene, and HCH has similar clinical manifestations with achondroplasia (ACH), which can be screened during the fetal period by prenatal ultrasound testing and diagnosed by genetic testing. CASE PRESENTATION: we report the special case of a patient with obvious growth retardation and rhizomelic disproportionate short stature, accompanied by other manifestations, including an enlarged head and short hands at 1 year old. However, several multiple color ultrasound exams identified shortened limbs (< 3rd percentile), an increased biparietal diameter (> 95th percentile) and a low nasal bridge in the fetal period. Due to the high incidence rate of ACH, genetic testing for the hotspot FGFR3 gene c.1138 g > A pathogenic variations was performed immediately in the third trimester. Unfortunately, the definitive diagnosis could not be made before birth due to the negative result of hotspot gene exam. Whole exome sequencing (WES) was performed at 1 year identified FGFR3 gene c.1620C > A variations positivity, and the patient was finally diagnosed as HCH. CONCLUSION: Our report extends the understanding of the limitations of prenatal genetic diagnostic testing, especially the hot spot pathogenic variations test should be not the only clinical diagnostic basis. Moreover, this case also emphasizes that further gene analysis for patients with significant conflict between the clinical manifestation and the prenatal genetic panel examination findings should be reconducted timely to spare the family from a delayed diagnosis or a misdiagnosis.