Cyclopia and trisomy 13: ancient DNA reveals a 1,600-year-old Nasca infant

An extremely rare malformation

Cyclopia is the most severe form of a birth disorder in which the developing brain does not divide into two distinct hemispheres. It also affects the development of the face, which can result in a single orbit at the centre of the forehead and severe facial abnormalities. The term refers to the failure of the face to separate into two symmetrical halves, a defect affecting the body's midline in the first weeks of pregnancy.

Most babies born with this condition die before birth or shortly after. It occurs about once in every 100,000 births, which makes physical remains particularly rare, whether modern or ancient. It is precisely this rarity that gives the discovery its scientific interest: it offers an exceptional opportunity to link a malformation observed in bones to its genetic cause.

A double burial at the Jauranga site

Researchers excavated a tomb known as "Burial 25" at Jauranga, in the Palpa valley of southern Peru. It lay in a shallow soil layer, called Layer B, within a cemetery of the Middle Nasca culture, dated to around 325 to 440 CE. This cemetery had been built over an older settlement from the Paracas period, an Andean society that existed between roughly 800 and 100 BCE.

Two young girls, each in articulated skeletal form, were found in the same ceramic urn, one placed above the other. Articulated means the bones were preserved in their natural position and had not been scattered. The researchers named them JA13A and JA13B, and the study published in PNAS details the excavation and analysis.

What ancient DNA reveals

Sequencing of the ancient DNA established that both infants were female. JA13A carried an extra copy of chromosome 13, a condition called trisomy 13. The researchers suggest that this additional chromosome may explain her cyclopia. Trisomy means having three copies of a chromosome instead of two; it is also associated with Down syndrome and Edwards syndrome, but it is chromosome 13 that is at issue here.

Analyses of mitochondrial DNA, inherited from the mother, further show that the two babies were not linked through the maternal line: their DNA belonged to haplogroups D1 and C1. This detail reveals that the urn held two children with no direct maternal kinship, something archaeologists could not have determined from the bones alone.

An identical funerary treatment

JA13A's skeleton shows several anomalies: a skull lacking nasal bones and nostrils, an undivided upper jaw, fused optic nerve openings, unusually curved shoulder blades, and two malformed vertebrae. JA13B, by contrast, shows no skeletal anomalies. The difference between the two skeletons is therefore clear, even though they shared a burial.

Despite this difference, the two girls received the same funerary treatment as other children in the community. Children under six were often placed in ceramic pots after death, a practice recorded in about a quarter of documented child burials in the region. The authors stress that a congenital malformation alone does not indicate whether a person was considered disabled or treated differently, as ancient Andean societies held varied attitudes toward bodily differences.

A tool for biological archaeology

This study shows how ancient DNA complements what bones reveal. By combining genetic sequencing with the physical analysis of skeletal remains, researchers can link a rare condition to its precise genetic cause. This approach opens a path to studying other malformations in archaeological collections, which are often stored without their biological origin having been established.

It also provides a framework for understanding biological differences without automatically tying them to a person's social status. The Jauranga case shows that reading a tomb requires cross-referencing genetics, anatomy and funerary context, and that each of these levels can tell a different story.