Table 4a.

FGFR3 Allelic Disorders to Consider in the Differential Diagnosis of Thanatophoric Dysplasia

DisorderCommentDistinguishing Clinical Features
Homozygous achondroplasia
  • Typically lethal in perinatal period
  • Clinical presentation similar to TD, w/short limbs & foramen magnum stenosis
  • Family history of achondroplasia in both parents
  • These conditions can be impossible to distinguish on clinical & radiographic grounds.
SADDAN (severe achondroplasia w/developmental delay & acanthosis nigricans) (OMIM 616482)
  • Rare disorder characterized by extremely short stature, severe tibial bowing, seizures, foramen magnum stenosis, hydrocephalus, structural brain malformations, developmental delay, & acanthosis nigricans
  • Caused by FGFR3 pathogenic variant p.Lys650Met 1
  • Tibial bowing
  • Clavicular bowing
  • Unlike TD, persons w/SADDAN dysplasia often survive beyond infancy w/o ventilatory support. However, respiratory support or ventilation may be required in neonatal period & neonatal death is reported.

From: Thanatophoric Dysplasia

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