Longevity and Patau syndrome: what determines survival?

The authors report of an 8-year-old girl with non-mosaic Patau syndrome. The median life expectancy of Patau syndrome is 7-10 days, and 90% die in the first year of life. Survival is often attributed to mosaicism and the severity of associated malformations. We delineate the developing phenotype and review the literature discussing potential contributory factors to longevity.

A computer modelling study of the uptake, structure and distribution of carbonate defects in hydroxy-apatite.

Computer modelling techniques have been employed to qualitatively and quantitatively investigate the uptake and distribution of carbonate groups in the hydroxyapatite lattice. Two substitutional defects are considered: the type-A defect, where the carbonate group is located in the hydroxy channel, and the type-B defect, where the carbonate group is located at the position of a phosphate group. A combined type A-B defect is also considered and different charge compensations have been taken into account. The lowest energy configuration of the A-type carbonate has the O-C-O axis aligned with the channel in the c-direction of the apatite lattice and the third oxygen atom lying in the a/b plane. The orientation of the carbonate of the B-type defect is strongly affected by the composition of the apatite material, varying from a position (almost) flat in the a/b plane to being orientated with its plane in the b/c plane. However, Ca-O interactions are always maximised and charge compensating ions are located near the carbonate ion. When we make a direct comparison of the energies per substitutional carbonate group, the results of the different defect simulations show that the type-A defect where two hydroxy groups are replaced by one carbonate group is energetically preferred (DeltaH = -404 kJ mol(-1)), followed by the combined A-B defect, where both a phosphate and a hydroxy group are replaced by two carbonate groups (DeltaH = -259 kJ mol(-1)). The type-B defect, where we have replaced a phosphate group by both a carbonate group and another hydroxy group in the same location is energetically neutral (DeltaH = -1 kJ mol(-1)), but when the replacement of the phosphate group by a carbonate is charge compensated by the substitution of a sodium or potassium ion for a calcium ion, the resulting type-B defect is energetically favourable (DeltaH(Na) = -71 kJ mol(-1),DeltaH(K) = -6 kJ mol(-1)) and its formation is also promoted by A-type defects present in the lattice. Our simulations suggest that it is energetically possible for all substitutions to occur, which are calculated as ion-exchange reactions from aqueous solution. Carbonate defects are widely found in biological hydroxy-apatite and our simulations, showing that incorporation of carbonate from solution into the hydroxyapatite lattice is thermodynamically feasible, hence agree with experiment.