Summary of this article

Learn how to calculate likelihood ratios using SNPs. Learn the basics of increasing the probability of parent-child or blood relationship based on genetic data.

To find the likelihood ratio using SNPs, the probability of genotype match is calculated, which is then used to calculate the likelihood for a specific hypothesis (e.g. the hypothesis that a person has a specific parent-child relationship).Specifically, the following steps are performed.

SNP data collection: collect SNP data from the DNA of the parent-offspring candidates.
Match probability calculation: calculates the SNP match probability between parent-offspring candidates.
Likelihood ratio calculation: computes the likelihood ratio by comparing the likelihoods of the parent-offspring and non-parent-offspring relationship hypotheses.

For example, if the probability that the SNPs match is p and the probability that they do not match is q, the likelihood ratio (LR) is expressed as p/q.

Specific examples are given here.

Assumptions:
Allele of SNP A: parent ‘AA’, child ‘AA’.
Frequency of allele A in population:

1. likelihood in the presence of a parent-child relationship:

If the parent is ‘AA’, the probability that the child is also ‘AA’ is 1.

2. likelihood of no parent-child relationship:

The probability that a child is ‘AA’ depends on how common allele A is in the population.

3. calculation of the likelihood ratio (LR):

The likelihood ratio of 100 indicates that the hypothesis of a parent-child relationship is 100 times more favored than the hypothesis of no parent-child relationship.

If multiple SNPs are used, a similar calculation is performed for each SNP and their likelihood ratios are multiplied to obtain the final likelihood ratio.

医師監修監修日：2024年8月27日

岡博史（おかひろし）

医師・医学博士／ヒロクリニック統括院長

YouTubeチャンネルなどを通じて、遺伝子やNIPT（新型出生前診断）についてわかりやすく発信しています。

略歴

1996年慶應義塾大学医学部卒業
2004年慶應義塾大学医学博士号取得
2005年慶應義塾大学皮膚科学教室助手
2008年ヒロ皮フ形成クリニック開業
2009年医療法人社団福美会理事長
2015年医療法人社団福美会理事

資格・所属

CAPラボディレクター
日本皮膚科学会皮膚科専門医
日本医師会産業医
東京衛生検査所指導監督医

発信・関連リンク

この記事は、ヒロクリニックNIPTの編集・監修体制にもとづき、資格を持つ医師が内容を確認しています。

参考文献

Zimmermann B, Hill M, Gemelos G, Demko Z, Banjevic M, Baner J, et al. Noninvasive prenatal aneuploidy testing of chromosomes 13, 18, 21, X, and Y, using targeted sequencing of single-nucleotide polymorphisms. Prenat Diagn. 2012 Dec;32(13):1233-41.