Single “texts” that are relevant in clarifying a disease or a developmental constitution can be amplified from a small number of cells (for example white blood cells) and subsequently read (i.e. sequenced). The molecular genetic analyses detect several types of misspellings in the genetic program of an individual. These comprise typing errors but also missing words or sentences that are too small to be detected by a chromosomal analysis. Such errors in the genetic text are the basis of many diseases as well as unexpected developmental constitutions.