Identical twins will have the same DNA, genetic material (genotype), but it may be expressed differently (phenotype).
This specific learning problem is referred to as Turner neurocognitive phenotype and appears to be due to loss of X chromosome genes important for selected aspects of nervous system development.
The pattern of familial aggregation suggests that in individual families, a small number of genes act together to cause the phenotype.
The barrier phenotype of the brain endothelium is induced and maintained by chemical factors released by brain cells, particularly perivascular astrocytic end feet.
Genetic syndromes with an associated dysmorphic facial phenotype are of particular interest.