Mild phenotype in two siblings with distal monosomy 12p13.31 → pter

We report two sibs with trisomy for the region 2p25.1 --> pter and monosomy for the region 12p13.31-->pter, due to adjacent-1 segregation of a maternal balanced reciprocal translocation, 46,XX,t(2;12)(p25.1,p13.31). These sibs presented with a mild phenotype, but nevertheless showed features of each of the contributing aneusomies. Monosomy 12p has previously been considered to have a variable and indistinct phenotype. Comparison of these patients with previous reports showed that many features, including microcephaly, facial dysmorphia, developmental and growth delay and dental and digital anomalies are frequently associated with monosomy for 12p. Many of these features are common to other aneusomies, thereby mitigating against a distinct 12p monosomy syndrome at this time. However, the combination of digital and dental anomalies may suggest the presence of this particular monosomy. The proband and his sister had some of the more non-specific features of 2p trisomy syndrome, and comparison with previous reports suggested that the characteristic 2p trisomy syndrome is more usually associated with larger or more proximal trisomies of 2p.