Discordance of oral-facial-digital syndrome type 1 in monozygotic twin girls

The oral-facial-digital syndrome type 1 (OFD1) includes limb, facial, intra oral malformations and the gene for the disorder was recently mapped to Xp2 2.3-p22.2. We report on monozygotic twin girls discordant for OFD1, Monozyg osity is supported by placental pathology (monochorionic diamniotic) and mo lecular studies with probability of dizygosity <1 x 10(-6). The affected tw in has oral cavity abnormalities including median cleft lip, cleft palate, lobulated hamartomatous tongue, aberrant hyperplastic oral frenula, alveola r notches, and absent lateral incisors. Facial manifestations include telec anthus, hypoplastic alae nasi, and transient neonatal facial milia, The pat ient also has short and deviated fingers with partial cutaneous syndactyly, At 10 years, she has not had central nervous system or kidney problems, X- inactivation study revealed similar X-inactivation patterns in the lymphobl asts of both twins. We conclude that skewed X-inactivation is an unlikely c ause for the discordance, which is more likely due to a postzygotic mutatio n in the affected twin. (C) 1999 Wiley-Liss, Inc.