Medical Genetics Index	Glossary

	DNA to the Rescue for an Immigrant's Child

One of the first demonstrations of the power of DNA testing involved its use to resolve a rather complex immigration dispute. (Jeffreys AJ, Brookfield JFY, Semeonoff R: Positive identification of an immigration test-case using human DNA fingerprints. Nature 317:818, 1985.) A Ghanaian boy born in England emigrated to Ghana to join his father, then later returned alone to his mother. However, evidence existed to suggest that the boy that returned was a substitute - either an unrelated individual or the son of one of the mother's sisters, all of whom lived in Ghana. Conventional blood and HLA typing indicated that the boy was almost certainly related to the woman in question (probability that he was not related = 0.01), but those data could not be used to determine whether the woman was the boy's mother or his aunt, and the boy was denied entrance to England. The task then was to use DNA testing to determine whether the women - hereafter referred to as the mother - was indeed the mother of the boy. Several factors affected this case: neither the father nor the mother's sisters were available for testing the mother was certain that the boy was her son, but was not sure about who was his father the mother had two daughters and another son (each at least half-sibs of the boy) available for testing DNA was obtained from the mother, the boy, the brother and both sisters, digested with Hinf1, blotted and hybridized to each of two minisatellite probes (i.e. multilocus fingerprinting to detect hypervariable VNTR loci). Analyses of these fingerprints was conducted in two steps: The first step in testing was to establish the DNA fingerprint of the unavailable father. His fingerprint could largely be reconstructed by identifying paternal-specific bands in the bands in the collective fingerprints of the three undisputed children of the mother (i.e. bands absent in the mother's fingerprint). A total of 39 paternal fragments were identified, of which roughly half were present in the boy's fingerprint, strongly supporting the contention that he was a sibling of the three other children. Subtracting the paternal fragments from the boy's fingerprint left 40 maternal fragments. Each of these was present in the fingerprint of the mother, providing strong evidence to support her claim that the boy was her son. DNA testing provides quantitative estimates or probabilities of relationships, which were outlined in detail for this case. Briefly, the following probabilities were estimated (based on the conservative probability of band sharing between unrelated individuals being 0.26): Probability that the boy was unrelated to the family = 7 x 10-23 (based on 61 of his bands being present in either the mother's or father's fingerprint) Probability that the boy is unrelated to the mother even though they share 25 fragments = 0.2625 or 2 x 10-15 Probability that the mother is actually a sister of the boy's true mother, even though she has all 25 of the boy's maternal-specific fragments = 6 x 10-6 These probabilities were beyond argument, and the boy was admitted to the country.

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Last updated on March 24, 1996

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