Twin zygosity studies with the formula from DNA-View's Kinship Module after molecular analyses by polymorphic markers
Introduction
Human Monozygotic (MZ) twins originate from the cleavage of a single fertilised zygote into two separate zygotes, during the early embryogenesis. Human MZ twins estimated to occur once in 250 live births. Their genome is considered identical. Discordance for well-defined syndrome, or isolated birth defects, or chromosomal abnormalities in MZ twins as well as for complex multifactorial traits and diseases, was described in several instances, in the literature. Environmental factors, but also the origin, development, genetic and epigenetic factors possibly involved in the reduced concordance, must be considered in future studies on MZ twins. A skewed or non-random X-inactivation was also assumed as possible event for discordance in intrapair MZ female twins.
The reduced concordance between MZ twins remains in fact poorly understood, and we need now to compare the genome sequence of MZ twins carefully, in the light of modern molecular insight of the human genome, to reveal any possible variation and difference between a set of human MZ twins.
Section snippets
Materials and methods
We report the preliminary results of a study we are performing in a series of MZ twins referred to the Genetics and Molecular Medicine Unit for different reasons.
In all cases, we performed the zygosity test by using the CODIS polymorphic markers (TPOX, D3S1358, FGA, CSF1PO, D7S820, D8S1179, THO1, D13S317, D16S359, D18S51, D21S11) typed as previously described [1].
In three cases, the MZ twins were concordant for the same genetic disorder: Rett syndrome with the same MECP2 mutation, the same,
Results
The molecular analysis of zygosity, performed on the basis of a different number of DNA polymorphic markers of CODIS, confirmed that in all set of twins included in the study, the subjects were MZ twins. The application of the formula from the Kinship Module of the DNA-View program gave us the following results: the likelihood ratio (LR) for MZ for the twins with different mosaicism for 46,XX/45,X was 36,800 (11 markers analysed).
The twins discordant for the cardiac congenital defects were MZ
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