After further investigation, there are two forms of pathological dwarfism that are relevant to the LB1 specimen. I am providing links here to the online descriptions of the disorders at
Online Mendelian Inheritance in Man (OMIM), which is the main phenotypic association database run by the
National Library of Medicine.
The first of these is
primary autosomal recessive microcephaly, caused by the MCPH1 gene, which codes for a protein called microcephalin. The normal action of the gene product is not well characterized. There are other forms, caused by mutations in different genes. The typical effects are very short stature and reduced head circumference. Apparently there may or may not be profound mental retardation or other skeletal effects.
I find the second more persuasive.
Seckel syndrome is an autosomal recessive disorder sometimes called "bird-headed disorder" because it results in a facial morphology featuring a prominent "beaked" nose and facial projection. LB1 lacks the beaked nose; indeed its nasal bones are apparently small and do not project from the face. But other symptoms of the disorder include the profoundly small body size and head size found in the specimen, the incidence of missing or malformed teeth (LB1 has missing right M
Both of these disorders include many symptoms that are not known or not found in the specimen, and that is one reason that I am hesitant to accept the hypothesis of pathology. But it is clear that some pathologies could explain the small brain size and small body size of LB1. The question is whether other symptoms might allow a diagnosis.
