Surprisingly, 1 in 2,000 people inherit a pair of chromosomes from one parent

Some people have incredibly long runs of homozygosity with no clear deleterious effect.

Sohini Ramachandran

You inherit half of your DNA from mother and half from father. That’s the theory. In practice, more than 3 million people worldwide inherited more DNA from one of the parents – many of them healthy and unaware of the legacy.

Unequal inheritance was discovered in the advent of in vitro procedures. Geneticists found that, on rare occasions, the egg and the sperm had differed in the number of chromosomes and still produced an embryo with the standard number of chromosomes. They called it uniparental disomy – from one-parent addition of a chromosome. In the following decades, clinicians diagnosed a few thousand patients with various disorders caused by uniparental disomy.

The condition – associated with health problems – was thought to be present in 1 of 3,500 individuals. New research shows that much higher prevalence – 1 in 2,000 – was overlooked because of many healthy cases.

The study made use of large genomic datasets gathered by private 23andMe and public UK Biobank. Looking through 4.9 million individuals, the team analyzed 214,915 trios of parent-parent-child. Across them, 105 cases of uniparental disomy accounted for 1 in 2,000 frequency.

Inheritance of chromosomes 1, 4, 16, 21, 22, and X was disrupted most often. Maternal DNA dominated most of the cases – three times as prevalent as the paternal origin.

Source: Nakka, P., Smith, S. P., O’Donnell-Luria, A. H., McManus, K. F., Mountain, J. L., Ramachandran, S., … & 23andMe Research Team. (2019). Characterization of prevalence and health consequences of uniparental disomy in four million individuals from the general population. Doi:10.1016/j.ajhg.2019.09.016.
Photo: Hesed Padilla-Nash and Thomas Ried, NIH.

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