The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


A re-evaluation of the Down syndrome diagnosis for LB1 (Homo floresiensis)

KAREN L. BAAB1, DEAN FALK2,3, PETER BROWN4, JOAN T. RICHTSMEIER5, KIERAN MCNULTY5,6, CHARLES F. HILDEBOLT7, FRED W. PRIOR7, KIRK E. SMITH7 and WILLIAM JUNGERS8.

1Department of Anatomy, Midwestern University, 2Department of Anthropology, Florida State University, 3Senior Scholar, School for Advanced Research, Santa Fe, 4School of Archaeology and Anthropology, Australian National University, 5Department of Anthropology, The Pennsylvania State University, 6Department of Anthropology, University of Minnesota, 7Department of Radiology, Washington University School of Medicine, 8Anatomical Sciences, Stony Brook University

March 27, 2015 3:30, Grand Ballroom E/F/G Add to calendar

The type specimen of Homo floresiensis (LB1), a small-bodied species with its roots in Plio-Pleistocene Homo, was recently diagnosed with Down syndrome (DS). In the absence of cytogenetic data for LB1, the diagnosis was based on 17 of the >80 clinical signs of DS argued to be present in the LB1 skeleton.

We re-evaluated these claims using comparative data from the Liang Bua hominins, modern humans with DS, and unaffected modern humans. Many of the putative signs were not present in LB1 (e.g., LB1 has a frontal sinus), or differed significantly in their anatomical presentation from that seen in DS individuals (e.g., flat feet, flaring ilia). Moreover, estimated stature and brain size of LB1 are outside the range of values reported for adults with DS, and LB1’s body shape is not typical of DS. We identified additional signs of DS not addressed in the initial diagnosis that are also absent in LB1, including thin cranial bones, midfacial hypoplasia, and a posteriorly flattened occiput.

Down syndrome is best viewed as a complex genetic disorder, where the specific phenotypic manifestations in a given individual are products of genetic, environmental and stochastic influences. As any particular DS individual will present only a subset of the >80 clinical signs of this disorder, trait-by-trait enumeration cannot provide a competent diagnosis of DS, and the absence of individual features does not rule out a diagnosis of this disease. Nevertheless, the existing evidence does not support this diagnosis, and LB1 remains the type specimen of Homo floresiensis.