Haas (Type IV) Polysyndactyly Presenting Prenatally with Bilateral Tibial Aplasia. E.W. McPherson1,2, W.A. Hogge1,3. 1) Dept Genetics, Magee Womens Hosp, Pittsburgh, PA; 2) Dept Human Genetics, Univ of Pittsburgh, GSPH, Pittsburgh, PA; 3) Dept of ObGyn, Univ of Pittsburgh, School of Medicine.
A 34 yo primigravida presented at 20 weeks because of fetal limb anomalies discovered on routine ultrasound. The fetus was appropriate for gestational age and the anomalies, which were confined to the limbs, included polydactylous severely clubbed feet, bilateral tibial aplasia, bilateral mild radial hypoplasia and cupped hands. The father had a history of bilateral cutaneous syndactyly of the third, fourth and fifth fingers with polyphalangism and polydactyly of the left thumb. Following surgery his hand function was excellent. His feet were unaffected. The fetal karyotype was normal. Due to the severity of the limb defects, the couple decided to terminate the pregnancy.
The 350 gr fetus had severe limb anomalies but no facial dysmorphism and no internal malformations. The wrists were in mild radial deviation. The hands were cupped with complete cutaneous syndactyly of all digits and fusion of the nails. There were six digits including a duplicated hypoplastic thumb on the right and five digits but no recognizable thumb on the left. There were bilateral severe equinovarus feet due to tibial aplasia. Both feet showed polysyndactyly with fusion of the nails.
The fetal hands and feet were typical for Haas (type IV) polysyndactyly which is an autosomal dominant with marked intrafamilial variability. Several typically affected patients have had a parent with partial syndactyly similar to the father of our patient. One previously reported patient had unilateral tibial aplasia. Because the frequency of Haas polysyndactyly is estimated at 1/300,000 and that for tibial aplasia is 1/1,000,000 coincidental occurrence of these anomalies in a second patient is extremely unlikely. Despite thumb involvement, radial hypoplasia has not been previously reported in Haas polysyndactyly. Our case extends the phenotypic spectrum of Haas polysyndactyly to include bilateral tibial aplasia and radial hypoplasia.