Non-paternity event (NPE) is a term in genetic genealogy and clinical genetics to describe instances in which the biological father of a child is someone other than who it was presumed to be before testing. The presumption may be either on the part of the presumed father or by the physician. Non-paternity may result from a number of different scenarios: it may arise from sperm donation or when the mother had sexual intercourse with a man other than the presumed father. Other than the situations of gestational surrogacy and chimerism, the identity of a child's mother is seldom in doubt. Non-paternity (and non-maternity) may also result from hidden adoptions: that is, when a child is never told he or she was adopted. Where there is uncertainty, then the only definitive diagnosis of non-paternity is from DNA testing.
The discovery of previously unsuspected or undisclosed non-paternity may have both social and medical consequences. Non-paternity that is due to a previously undisclosed extra-marital relationship often has serious consequences for a marital relationship. Non-paternity is medically relevant when interpreting the results and utility of genetic screening for hereditary illnesses.
In genetic genealogy the term NPE is often used in a wider context to indicate a break in the link between the Y-chromosome and the surname. Such a breakage may occur because of formal or informal adoption, illegitimacy inside ("extramarital event"/infidelity or rape) or outside of marriage, child known by other surname (mother's maiden name, stepfather's name), the use of an alias or a deliberate change of surname.
Testing for non-paternity
The only definitive test for paternity is DNA testing. Requirements for consent and counselling for DNA testing vary by country. Sons can be tested by Y-DNA and atDNA, daughters by atDNA and X-DNA.
Rates of non-paternity
Rates of non-paternity in single births
However, a 2005 scientific review of international published studies of paternal discrepancy found a range in incidence from 0.8% to 30% (median 3.7%), suggesting that the widely quoted figure of 10% of non-paternal events is an overestimate. In situations where disputed parentage was the reason for the paternity testing, there were higher levels; an incidence of 17% to 33% (median of 26.9%). Most at risk of parental discrepancy were those born to younger parents, to unmarried couples and those of lower socio-economic status, or from certain cultural groups.
A 2006 study examined non-paternity rates from 67 published studies. Non-paternity rates for men who were judged to have high paternity confidence ranged from 1.9% in the U.S. and Canada, 1.6% in Europe, and 2.9% elsewhere. In contrast, men in studies of disputed paternity, considered to have low paternity confidence, the rates of non-paternity were higher – 29% in the U.S. and Canada, 29% in Europe, and 30% elsewhere.
The rates value varies according to the population studied:
- 1% in a sample of 971 children.
- United Kingdom:
- Mexico: 9.8% to 13.8% in a sample of 396 children
- Switzerland: 0.3 to 1.3% in a sample of 1,607 children
- United States:
- France: 2.8% in a sample of 362 children
Rates of non-paternity in one child of a pair of twins
Non-paternity of one child in a pair of twins, known as "heteropaternal superfecundation", is caused by the fertilization of one woman's eggs by the sperm from two separate fathers.
- One study has found that even in twins, non-paternity of one of the twins (heteropaternal superfecundation) "occurs in around 2.4% of tested twins", or approximately 1 pair of twins out of every 42 pairs of twins tested.[better source needed]
In one legal case in 2015, ruled on by New Jersey Superior Court Judge Sohail Mohammed, it was found that the twins at the centre of a paternity suit had been fathered by two different men. As a result of the genetic findings in that case, the male plaintiff who had been challenging the paternity of both twins, was ordered to pay support for just one of the twins.
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