A computerised method for calculating the probability of pedigrees from genetic data

On statistical analysis of forensic DNA: Theory, methods and computer programs

Statistics plays an important role in evaluating the evidential weight of forensic DNA. In this paper, general statistical principles for forensic DNA analysis are presented. We introduce the theory and methods for the statistical assessment in kinship determination and DNA mixture evaluation. In particular, analytical formulas for testing for biological relationship among three individuals and for assessing the DNA mixture evidence in the case of multiple subdivided ethnic groups are developed. Two user-friendly computer programs are demonstrated to exhibit their wide applicability in tackling with complex kinship/paternity and mixture problems. The EasyDNA program can solve a complicated paternity case in 1 min.

Arrhythmogenic right ventricular cardiomyopathy in two pairs of monozygotic twins

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inheritant disease with an autosomal dominant mode of transmission with incomplete penetrance and variable expression. Linkage analysis in affected families succeeds in identifying 9 loci determining 9 subtypes of the disease. Genotype phenotype correlation is unclear and the influence of various environmental factors is discussed.

OBJECTIVES

Genotype phenotype correlation in 2 pairs of monozygotic twins with ARVC and the role of environmental factors are analyzed.

PATIENTS AND METHODS

Among 40 pts with ARVC and their 195 relatives there were 2 pairs of monozygotic twins: brothers, age 47 y; and sisters, age 48 y. History, ECG, Holter monitoring, 2D and Doppler Echo, and MRI were analyzed.

RESULTS

Twin brothers: ARVC was diagnosed in the proband after the episode of VT with LBBB morphology (enlarged right ventricle, focal hypokinesia of apex, MR evidence of adipose tissue in RV wall). Identical morphology of RV was seen in asymptomatic twin brother. The patient presenting arrhythmia has been rowing for 4 years. Twin sisters: diagnosis was done during family screening. Both were asymptomatic. RV morphology typical for ARVC was found discrete in one of them (bulges adipose tissue in the RV apex); the latter showed changes suggesting RV abnormality (mild segmental dilatation of infundibulum, adipose tissue in a free wall of the RV). No differences in previous viral infections and sports involvement were observed.

CONCLUSIONS

1. Clinical picture of ARVC in monozygotic twins is not identical. 2. Strenuous effort may be a factor triggering the arrhythmia in pts with ARVC.

User-friendly programs for easy calculations in paternity testing and kinship determinations

Four computer programs are developed for easy calculations of likelihood ratios (LRs) for paternity testing and kinship determinations. The programs are constructed based on the concepts of Bayes Theorem, conditional probability and pedigree analysis. Computer enumeration is used for handling the calculations. The programs have wide applicability, and users can save and check the results easily. The programs employ the distinctive pull-down manual, making them very easy to use. In this paper, we explain the theory and describe various features of the software.

Deduction of paternity index from DNA mixture

Determination of individual genotypes in DNA mixture remains a challenge in forensic science. Using an approach of mixture of distributions, this article provides formula for calculation of paternity index (PI) in cases where only tissue mixture of the mother and alleged father, the genotypes of the mother and child, but not that of the alleged father are available. The formula has been used to solve a real case using mother's vaginal tissue contaminated with semen from alleged father.

Relatedness testing in subdivided populations

Assigning probabilities to alleged relationships, given DNA profiles, requires, among other things, calculation of a likelihood ratio (LR). Such calculations usually assume independence of genes: this assumption is not appropriate when the tested individuals share recent ancestry due to population substructure. Adjusted LR formulae, incorporating the coancestry coefficient F(ST), are presented here for various two-person relationships, and the issue of mutations in parentage testing is also addressed.

Beyond traditional paternity and identification cases. Selecting the most probable pedigree

The paper extends on the traditional methodology used to quantify DNA evidence in paternity or identification cases. By extending we imply that there are more than two alternatives to choose between. In a standard paternity case the two competing explanations H(1): "John Doe is the father of the child and H(2): "A random man is the father of the child, are typically considered. A paternity index of 100000 implies that the data is 100000 more likely assuming hypothesis H(1) rather than H(2). If H(2) is replaced by "A brother of John Doe is the father", the LR may change dramatically. The main topic of this paper is to determine the most probable pedigree given a certain set of data including DNA profiles. In the previous example this corresponds to determining the most likely relation between John Doe and the child. Based on DNA obtained from victims of a fire, bodies found in an ancient grave or from individuals seeking to confirm their anticipated family relations, we would like to determine the most probable pedigree. The approach we present provides the possibility to combine non-DNA evidence, say age of individuals, and DNA profiles. The program familias, obtainable as shareware from http://www.nr.no/familias, delivers the probabilities for the various family constellations. More precisely, the information (if any) prior to DNA is combined with the DNA-profiles in a Bayesian manner to deliver the posterior probabilities. We exemplify using the well published Romanov data where the accepted solution emerges among 4536 possibilities considered. Various other applications based on forensic case work are discussed. In addition we have simulated data to resemble an incest case. Since the true family relation is known in this case, we may evaluate the method.

Paternity probability when a relative of the father is an alleged father

When scientists use DNA evidence in court, coancestry effects such as population structure and relatedness are usually ignored. In paternity cases, only if a particular man has the child's paternal allele at a certain locus, can he not be excluded in the paternity dispute. However, it is certainly true that close relatives will be far more likely to have the child's paternal allele than will random members of the reference population. In particular, the probability that the true father's brother has the paternal allele is very much greater than that for any other relationship. In this paper, the authors describe a method for inference in a case where the true father may be a relative of the alleged father. This paper also reports that most current methods overstate the probability that the alleged father is the father.