Genetic control of the number of lumbar vertebrae in humans

The number of vertebrae in mammals is roughly constant within single species.
The number of cervical vertebrae is 7 in all mammals, while the number of
thoracic and lumbar vertebrae varies from 17 to 24. For instance humans usually
have 17 thoracic and lumbar vertebrae while pigs usually have 19. Approximately
10000 years ago man switched from a hunter-gatherer society to a farming
society. Animals were domesticated and the genes of these domesticated species
were modified by selective breeding. This had an effect on the number of lumbar
vertebrae of pigs. In the domesticated European pig 6 lumbar vertebrae are
found, while only 5 are found in Asian pigs and in European wild pigs. Similar
variations in number of vertebrae occur naturally in many species. By selecting
animals with a large number of vertebrae, European farmers changed the
population into a uniform group with 6 lumbar vertebrae. In pigs, the variation
in number of lumbar vertebrae is controlled by a specific group of genes.
In humans the same natural variation in the number of vertebrae occurs. A
majority of 88% of the population has 5 vertebrae, while 4% of the population
has 6 vertebrae and 8% of the population has 4. Furthermore, apes (chimpanzee,
gorilla, orang-utan and gibbon) usually have only 4 lumbar vertebrae. This
suggests that there is a genetic advantage for humans to have 5 lumbar
vertebrae. Since humans are the only one to have bipedal locomotion this could
be linked to motion. More specifically, the higher number of vertebrae might
allow more rotation between pelvis and thorax which facilitates bipedal gait.
Like all mammals, pigs and humans share a common history. Approximately 85
million years ago, both groups separated into different lineages. The traces of
their common past can still be found in the genes of both species. Large part
of the DNA of both species is the same, especially the genes that belong to the
basic mammalian heritage. Since the variation in number of vertebrae in pigs is
controlled by a specific group of genes, it can be hypothesized that the number
of lumbar vertebrae in humans is controlled by these same group of genes.

Primary Objective: to investigate whether the variation of the number of lumbar
vertebrae in humans is coded by the same genes which are responsible for this
as well as in other mammals.

observational study. The patient is selected by the physician on the basis of
the number of vertebrae. Twenty five unrelated consecutive patients with 4 and
25 unrelated consecutive patients with 6 lumbar vertebrae will be recruited. In
addition, 25 unrelated patients with 5 vertebrae will be recruited to obtain
three groups of 25 subjects. From each of the 75 participants a 5 ml blood
sample will be taken for the present study. Each patient will be assigned a
unique number, which will allow the researchers to combine CT-images with blood
samples. The tube, containing the blood will be labeled with M for male, F for
female, a number describing the number of vertebrae and the assigned subject
number. Blood samples will be taken according to the standard protocol at the
*VU-medisch centrum prikpoli*.

burden and risks are low.