A molecular classification of moles and its use in filiation tests.

Pregnancies, including ones that follow sexual assaults, occasionally produce hydatidiform moles. The alleged fathers (AFs) of moles have been tested for paternity by identifying the mole's locus phenotype-the one or two visible paternal obligate alleles (POAs) per locus. The probability that the mole inherited the POAs from the AF was divided by the probability that the mole inherited the POAs from a random man. This likelihood ratio (LR) would increase if the mole's specific genotype was known. Moles are generated in five different ways that produce five distinct genotypes. Examining a mole's multilocus STR profile reveals a mole's pathogenesis, determines locus genotypes, and increases paternity LRs.

Parentage of Hydatidiform Moles.

We were presented with the STR (short tandem repeat) profiles from two separate paternity trios. Each trio consisted of a mother, an alleged father, and products of conception (POC) that contained a hydatidiform mole but no visible fetus. In both cases, antecedent pregnancies had followed alleged sexual assaults. Mole classification and pathogenesis are described in order to explain the analyses and statistical reasoning used in each case. One mole exhibited several loci with two different paternal alleles, indicating it was a dispermic (heterozygous) mole. Maternal decidua contaminated the POC, preventing the identification of paternal obligate alleles (POAs) at some loci. The other mole exhibited only one paternal allele/locus at all loci and no maternal alleles, indicating it was a diandric and diploid (homozygous) mole. In each case, traditional calculations were used to determine paternity indices (PIs) at loci that exhibited one paternal allele/locus. PIs at mole loci with two different paternal alleles/locus were calculated from formulas first used for child chimeras that are always dispermic. Combined paternity indices in both mole cases strongly supported the paternity of each suspect.

A review of the biology and classification of human chimeras.

BACKGROUND: Chimeras are organisms composed of cells derived from two or more zygotes. Clinicians, blood group serologists, and cytogeneticists have recognized natural human chimeras for more than 60 years and molecular biologists are now able to recognize them using more sensitive and definitive tests. STUDY DESIGN: Human chimeras are divided into two major classes, man-made and natural. Man-made chimeras include transplanted patients and several kinds of iatrogenic chimeras including those that develop after in vitro fertilization (IVF). Natural chimeras have historically included twin chimeras and fusion chimeras. Recently described microchimeras are primarily natural ones as well. Updated terminology and classification are suggested to account for information gleaned from natural and experimental animal chimeras. CONCLUSIONS: Many human chimeras remain undetected. The states of health and disease of human chimeras remain largely unknown. Of four ways to detect human chimeras, molecular typing is the most sensitive and specific. Before systematic and temporal studies can be undertaken, improved cell sampling and better analytical detection methods are necessary. Chimeras may be sought among dizygotic twins and children born after IVF procedures.

Pretense of parentage by siblings in immigration: Polesky's paradox reconsidered.

BACKGROUND: Older and younger siblings occasionally attempt to impersonate parent and child to expedite immigration under US family-based visa policies. The rate with which full siblings escape detection by current relationship tests is unknown. STUDY DESIGN AND METHODS: Retrospective study of full-sibling immigrant pairs was undertaken to determine the proportion that show insufficient genetic evidence to exclude parentage. Sibship and parentage indices (SI and PI) were compared/case in unexcluded sibling cases and true parent-child cases. Alleles shared per short-tandem-repeat locus were compared in sibling and parent-child pairs. The proportion of successful parentage fraud by siblings was estimated from the parentage exclusion rate among immigrants and the proportion of sibships without genetic inconsistencies (GIs). RESULTS: When 11 to 25 independent loci were tested per two-sibling case to verify or refute parentage, tests failed to demonstrate any GI in 9% and PI was greater than SI in seven of 10 of these cases. Another 29% of full-sibling pairs demonstrated insufficient evidence (fewer than two GIs) to exclude parentage. Thus, 0.4% of sibling pairs could falsely claim a parent-child relationship and show no GIs. Another 1.4% could make that false claim and not present sufficient evidence to be excluded. CONCLUSION: At present, with no evidence of parentage exclusion in a full-sibling pair, the relative magnitudes of PI and SI are misleading relationship indicators because too few loci are examined and rates of sharing one and two alleles/locus vary greatly in parentage and sibling pairs. Only evidence of exclusion ascertains false parentage claims by siblings. Nevertheless, the expected rate of successful fraud is quite low.

Empowering sibship analyses with reference pedigrees.

BACKGROUND: In sibship analysis, the usual comparison of an alleged (test) sibling's short tandem repeat (STR) types with those of a reference sibling may prove inconclusive. Increasing the number of examined STR loci may not change sibship probabilities very much. We increased the number of verified reference siblings to resolve problematic cases of alleged sibship. STUDY DESIGN AND METHODS: (A) Ten paternity cases were chosen in which there were three highly probable children of each alleged father. Pairs of the alleged father's children were analyzed for full sibship. The test sib with the lowest likelihood of sibship was reanalyzed by a comparison with two reference siblings combined. (B) Five problematic sibship cases are presented to demonstrate how two-person reference pedigrees can improve diagnosis over tests using one reference person. RESULTS: (A) Two-person pedigrees exponentially increased sibship probabilities of true siblings above those produced by one reference person. (B) In problem cases, reference pedigrees provided data that: (1) statistically verified some alleged sibships in which analyses using one reference person yielded inconclusive results, (2) allowed exclusion of some alleged sibships, or (3) suggested alternate blood relationships to the alleged one. CONCLUSIONS: Use of reference pedigrees often resolves sibship questions left unsettled by tests using reference individuals. Adding reference relatives is a far more powerful analytical strategy than adding test loci. Whenever possible, verified blood relatives should be incorporated into a reference pedigree to retest an alleged sibling whose initial results were unclear.

Detection of genotype recycling fraud in U.S. immigrants.

Relationship testing laboratories provide genetic evidence to support or refute claims of kinship between U.S. citizen petitioners and potential immigrant beneficiaries. One female beneficiary presented a male amelogenin type and alleles at 15 autosomal loci that were identical to an alleged brother's. Laboratory records showed that her alleged father had petitioned to have 15 children emigrate from Ghana. The petitioner's 15 paternity indices exceeded 105, but the children shared only four short tandem repeat (STR) profiles, suggesting fraudulent reuse of genotypes in this alleged pedigree (AP). To determine the extent of this "genotype recycling," I examined the laboratory's 555 APs from Ghana and 532 control APs from Nigeria. Seventeen Ghanaian APs (3.1%) but no Nigerian APs showed genotype recycling. Of 90 tested people in the 17 APs, 56 shared identical STR profiles with others in their AP. Of these 56 people, 10 were petitioners with unexpectedly high parentage indices. Seven of 56 had amelogenin types that disagreed with their declared genders. Database searches for identical multilocus genotypes in allegedly different people would best detect this fraud.

Dead man talking: sustained utility of data from archaic paternity tests.

BACKGROUND: Almost all relationship analysts now use molecular (DNA) tests to obtain necessary genetic information, yet older blood group tests remain valid. Circumstances may provide blood test results from old reports to avoid trying to sample DNA from inaccessible sources. CASE STUDY: A mother recently claimed that a deceased man (alleged father [AF]) sired her child. Insurance investigation recovered two paternity test reports from an AABB-accredited laboratory. The 16- and 18-year-old reports employed blood groups and protein polymorphisms to exonerate two different men. One report contained the multilocus phenotypes of the AF and the other contained the phenotypes of the mother and child at the same loci. A new case was synthesized from the old reports. RESULTS: Genetic inconsistencies (three direct and one indirect) were demonstrated among the nine loci that had been typed in both the AF and the mother-child pair. CONCLUSION: New relationship tests may be reconstructed from phenotypes reported before the molecular test era. This approach avoids exhumation and other problematic methods of specimen retrieval.

Two new hemoglobin variants: Hb Sinai-Greenspring [beta34(B16)Val-->Ile, GTC > ATC] and Hb Sinai-Bel Air [beta53(D4)Ala-->Asp, GCT > GAT].

Neonatal screening for hemoglobinopathies occasionally results in the detection of novel hemoglobin (Hb) variants. Two heterozygous infants were found with different beta chain mutations, neither of which produced obvious clinical or laboratory abnormalities on routine examinations. The variants were characterized by cation exchange high performance liquid chromatography (HPLC), reversed phase HPLC, and sequencing of amplified beta-globin genes. Functional studies could not be performed at this time.

Incest indices from microsatellite genotypes of mother-child pairs.

BACKGROUND: Suspected incestuous paternity is encountered infrequently and investigation may be complicated by absence of the suspected father. Incest indices (IIs) can be calculated from microsatellite (STR) types of only a mother and child, but could be misleading. Therefore, the method was evaluated. STUDY DESIGN AND METHODS: Combined incest indices (CIIs) of 50 randomly mated (RM) mothers and their children were compared with those of 50 simulated incestuous (SI) mothers and their children. Each CII was calculated from 18 individual locus IIs. Combined indices were categorized as "diagnostic" (<0.010 and >100 for RM and SI cases, respectively), "indicative" (CII was directionally correct but not erroneously diagnostic), and "misleading" (>1.0 in RM and <0.01 in SI). The relative importance was determined of each of the three variables contributing to the CII. RESULTS: In 41 cases (41%), CIIs attained diagnostic values. Fifty-two CIIs were indicative. CIIs were misleading in 3 RM cases and 4 SI cases. The number of mother-child (M-C) STR genotype similarities was the most important determinant of CIIs. Infrequent alleles in M-C similarities were important in raising CIIs in SI. The kind of M-C genotype similarity was the least important variable. CONCLUSIONS: Study of 18 STR loci produces diagnostic CIIs in only two of five suspected incest cases. Study of approximately 33 independent STRs would assure that greater than 97.5 percent of cases will have diagnostic CIIs if incest occurred. Study of loci that are more informative than typical STRs would be advantageous.

Maternal typing and test sufficiency in parentage analyses.

BACKGROUND: The contribution of maternal typing to paternity analysis was evaluated to determine how many additional loci to study in one-parent cases. STUDY DESIGN AND METHODS: Four groups underwent paternity analyses with an eight-locus test battery. Files of 25 case trios were retrieved, in which alleged fathers had achieved paternity indices of greater than 100 ("included trios"). Maternal types were omitted and the cases were reanalyzed ("included duos"). Mother-child pairs of the cases were then coupled with unrelated men ("excluded trios"), and the cases were analyzed. Maternal types were omitted from the excluded trios and cases were reanalyzed ("excluded duos"). RESULTS: Paternity indices of men in included duos were markedly reduced when compared to included trios; odds were sufficiently low in 9 of 25 men that paternity remained in doubt. After omission of maternal phenotypes, excluded duos exposed 33 percent fewer genetic inconsistencies than excluded trios; 5 of 25 men in excluded duos demonstrated less than two genetic inconsistencies and 1 man had none. The specific probabilities of paternity exclusion in motherless cases averaged 61 percent per locus of those in case trios. One random man in 52 duos was not excluded by the eight tests versus 1 in 417 trios. CONCLUSIONS: Omission of maternal typing from eight common microsatellite paternity tests reduced conclusive evidence for or against paternity by 30 to 40 percent. False inclusion of random men is an important failing of tests in motherless cases. Cases involving one parent and child (e.g., in immigration) would require examination of an additional five similar loci to compensate for absent maternal data. A change in standards is suggested.

The specific power of parentage exclusion in a child's blood relatives.

BACKGROUND: The impersonation of parent and child by two other blood relatives is an important problem in parentage analysis involving potential immigrants. STUDY DESIGN AND METHODS: A statistic (AR) is proposed, based on the specific power of exclusion of paternity, which describes the ability of a child's test results to demonstrate evidence of nonparentage under the hypothesis that an ostensible parent is actually an older sibling. A case illustrates the value of A(R): a woman and her two alleged children were typed at 3 variable number of tandem repeat (VNTR) loci after 18 short tandem repeat (STR) loci initially showed strong evidence of the woman's maternity of one child and her exclusion from parentage of the second. AR and 1 - AR were calculated from the STR types of the first child. RESULTS: The woman was excluded from maternity of both children with the additional VNTR tests. Given the 18 STR test findings of the first child, the probability was 12 percent that there would be no inconsistencies with parentage in a sibling pretending to be a parent. CONCLUSION: The value 1 - AR, siblings not excluded from parentage, explains how a seemingly large number of examined loci can fail to reveal even one genetic inconsistency if two siblings have posed as parent and child. Approximately 25 STR loci appear necessary to achieve 95 percent confidence of detecting at least one genetic inconsistency indicative of nonparentage.

Testing for parentage and kinship.

PURPOSE OF REVIEW: Parentage analyses are of interest to workers in health care, law enforcement, immigration and other fields. This review describes recent applications, technical advances, and quality improvements. RECENT FINDINGS: Mutations at short tandem repeat sequence loci confound interpretations of genetic data used to assess all blood relationships. Rates of the usual mutation type (change in repeat number) are probably related to specific alleles at each locus as well as to allele length, locus, and gender. Short tandem repeat sequences have relatively limited information content per locus. Intermediate tandem repeat sequence loci may be better. In immigration proceedings, probabilities can be calculated for excluding parentage in blood relatives who might impersonate the biologic parent. Unrelated immigrants from a subpopulation may appear to be related, but it is now possible to statistically determine the effect of population substructure on kinship determinations. In forensic analyses, sex chromosomal (X and Y) short tandem repeat sequences and mitochondrial DNA sequence variations have helped identify the parental lineages of human remains. Recent laboratory quality improvements include a way to estimate the frequency of common mother-child specimen mislabeling in routine paternity cases. In prenatal testing there are now methods for avoiding erroneous assignment of contaminant maternal alleles to the fetus. False paternity exclusions can be avoided by adhering to a standard of the American Association of Blood Banks requiring duplicate DNA isolation and retesting of excluded men. SUMMARY: Laboratory technology and quality have advanced, but genetic tests with greater information content are needed. Better communication is highly desirable between persons requesting tests and parentage laboratories.

Molecular evidence of Munchausen syndrome by proxy.

Many perpetrators of Munchausen syndrome by proxy present bloodstained materials as counterfeit evidence of proxy hemorrhage. Although blood grouping may show that the blood is not the proxy's, DNA typing may specifically identify the blood's source. A mother claimed that she alone had witnessed gastrointestinal bleeding of her son and presented bloodstained towels as evidence. Several clinical investigations had failed to reveal a bleeding source. I compared the DNA types of the bloodstains and the child's buccal cells. The bloodstain and epithelial cells differed at 4 of 8 microsatellite loci and at the amelogenin locus. The blood and buccal cells shared 1 allele at every locus, suggesting that their sources were closely related. The probability that the source of the blood was maternal was 0.9915 (prior probability, 0.5). I recommend DNA matching in suspected cases of Munchausen syndrome by proxy whenever blood is presented as evidence.