* Fetal medicine unit, Cairo University, Egypt;
** Radiology department, Kasr Alainy hospitals, Cairo University, Egypt;

Homozygous mutation in DTDST gene (diastrophic dysplasia sulfate transporter gene) results in diastrophic dysplasia which is inherited in an autosomal recessive pattern^{1, 2}. Mutation in this gene results in a spectrum of skeletal dysplasias which are variable in severity and consists of achondrogenesis type 1, atelosteogenesis type 2 and recessive multiple epiphyseal dysplasia in addition to diastrophic dysplasia ³.The ultrasonic features of diastrophic dysplasia are characteristic and include micromelia sometimes with curvature , hitchhiker thumb (proximal insertion with fixed abduction) with other digital malformations , limitation in mobility of joints,  talipes, scoliosis, abnormal "cauliflower" ears and cleft palate in some occasions ^1,2. The hitchhiker thumb is the pathognomonic feature of diastrophic dysplasia ². The highest incidence of this rare skeletal dysplasia is present among Finss ^{1, 2}. Diastrophic dysplasia is not lethal with neonatal mortality rate estimated to be about 25% due to laryngotracheomalacia and stenosis ^{1, 2}. Volumetric ultrasound technique is superior to usual two-dimensional studies in depicting limb anomalies and specifically facial dysmorphism².

Case report

A 21-year old woman without consanguinity or family history of any genetic disorders was referred to Cairo University Fetal Medicine Unit because of suspicion of lethal skeletal dysplasia raised in a scan one week prior to our scan. Our ultrasound examination revealed:

Images 2 and 3: micromelia with all the long bones are far below the 5^th centile for GA.

Image 4 and video 1: although thoracic hypoplasia is suggested on axial scan, the degree of thoracic hypoplasia does not seem to be lethal with absence of any dip or deformity on the thoracoabdominal junction.

Images 5, 6 and videos 2, 3: show micrognathia both by inferior facial angle measurement and volumetric surface rendering; note also the hypoplastic mandible in video 3 viewed in axial section.

Videos 4 and 5: visualization of the fetal anatomy at this stage may be beneficial and help in narrowing the differential diagnosis. The anatomy scan in the visualized systems is normal.

Video 6: axial scan of the fetal face depicting normal lips and palate (which is of a particular importance in diastrophic dysplasia due to the associated cleft palate in nearly one third of the reported cases).

Images 7, 8 and video 7: show the talipes both in 2D and volumetric modes.

Image 9 and videos 8, 9: show the hitchhiker thumb which is pathognomonic for diastrophic dysplasia.

Images 10, 11, and 12: show the hitchhiker thumb and the clinodactyly with postnatal correlation.

Image 13, 14 and video 10: show the swollen malformed external ear.

Image 15 and 16: show the square face.

Images 17, 18 and 19: The postnatal documentation and confirmation of the diagnosis.

References:

1. Honorio JC, Bruns RF, Grundtner LF, Raskin S, Ferrari LP, Araujo Junior E, Nardozza LM. Diastrophic dysplasia: prenatal diagnosis and review of the literature. Sao Paulo Med J. 2013; 131(2):127-32.

2. Sepulveda W, Sepulveda-Swatson E, Sanchez J.  Diastrophic dysplasia: prenatal three-dimensional ultrasound findings. Ultrasound Obstet Gynecol 2004; 23:312-14.

3. Rossi A, Superti-Furga A. Mutations in the diastrophic dysplasia sulfate transporter (DTDST) gene (SLC26A2): 22 novel mutations, mutation review, associated skeletal phenotypes, and diagnostic relevance. Hum Mutat 2001; 17(3):159-71