Download The mystery of the tallest giants is revealed

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The mystery of the tallest giants is revealed
2/18/15
Until now, it has been possible to explain 35% of gigantism cases: an explanation still needed to be found for
the remaining 65% of cases. This has now been achieved for the most spectacular cases among this remaining
group following an international study which gathered data on 200 giants throughout the world. Professor Albert
Beckers who is a professor at the University of Liege and Head of the Department of Endocrinology at the
University Hospital of Liege has, together with his colleagues, succeeded in identifying the gene responsible
for the tallest giants known to mankind. They found that individuals affected by the condition known as the XLAG syndrome, carry a microduplication of 4 genes including the GPR101 gene on the X chromosome.
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"Where do giants live"? How would you answer a
child if they asked you this question? You would probably answer "in fairytales" or "in fantasy films" in order
to reassure the child or simply because you are unaware of the fact that there are giants living in our midst…
The tallest man ever recorded up to the present day was an American called Robert Wadlow (1918-1940). He
measured 2m72. The tallest man alive today is Sultan Kösen; he was born in Turkey and measures 2m51.
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Closer to home, Julius Koch (alias Constantin the giant) lived in Mons from 1872 to 1902 and measured 2m59
while a man currently living in France has grown to a height of 2m48.
Gigantism is characterised by excessive growth. There are different syndromes which are directly related to
excessive production of growth hormone. "When this overproduction occurs before the individual has finished
growing, this may result in gigantism. On the other hand, when this excessive production of growth hormone
occurs in the adult, acromegaly occurs, that is to say an abnormal increase in the size of hands, feet, the nose
and the soft tissues in general", explains Professor Albert Beckers, Head of the Endocrinology Department
at the Liege University Hospital Center (CHU). "Once growth has finished, growth hormone can no longer act
on the size of bones except the lower jaw but it also acts on the soft tissues".
Hypophyseal adenomas, benign tumors with collateral damage
The cause of this hyperproduction of growth hormone is situated in the pituitary gland, the part of the
brain where a large range of hormones are produced. In most cases of gigantism or acromegaly, a
pituitary adenoma is the cause of this hormonal imbalance. It is a benign tumor affecting this gland which
results in collateral damage such as the overproduction of hormones or the compression of adjoining brain
structures once the tumor has reached a significant size.
For more than 30 years Albert Beckers has been fascinated by giants and has studied the causes of gigantism.
He also discovered a new familial form of pituitary adenoma: FIPA (Familial Isolated Pituitary Adenomas).
The results of that study were published in 2006 in the Journal of Clinical Endocrinology and Metabolism
(JCEM) (1) (see article: Hypophyseal tumors, the search for the genes has begun!). "At the same time,
we also demonstrated the involvement of the AIP gene in this pathology because 15% of patients suffering
from this disease presented with mutations on this gene", continues the scientist (2). In-depth research has
also enabled Albert Beckers and his colleagues to establish that pituitary adenomas in patients presenting
with a mutation on the AIP gene (patients AIP +) was a lot more aggressive and early than in patients who
did not have a mutation on this gene (patients AIP -) (3). "AIP + patients have pituitary adenomas before the
age of 20 that are twice as big as those affecting AIP patients who tend to develop tumors at around the age
of forty", says Albert Beckers.
The genetic data of 200 giants under the microscope
Given the fact that giants develop following an imbalance in the production of the growth hormone during
childhood/adolescence and that AIP + patients develop hypophyseal adenomas at a younger age, it is not
surprising that researchers have observed a large number of giants among AIP+ patients. "This is where we
got the idea to begin a large international study on giants in 2011", indicates the endocrinology specialist.
"This study has made it possible to gather clinical and genetic data on 200 giants around the world. Up to
that point we could explain 35% of gigantism cases; we therefore wanted to discover the genetic causes for
the remaining 65% of cases". Among the research centers that participated in this international study is the
National Institute of Health (NIH) in the USA. "A colleague and friend of mine who works there had been trying
to find a genetic explanation for a form of gigantism but without success. We therefore decided to collaborate in
order to try to solve this mystery", explains Albert Beckers. "His research team had identified the duplication of
11 genes on the X chromosome but none of these genes was well-known or linked to the production of growth
hormone. In addition, they were working on a small which was not sufficient to demonstrate the existence of a
new syndrome or to confirm the involvement of these duplications in gigantism", the scientist continues. The
researchers at NIH therefore pointed out the location of the region of the X chromosome where the duplication
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of the 11 genes was observed to the researchers in Liege. "Using our gigantism database, three months later,
the problem was solved"! Albert Beckers explains.
When the noose tightened around the GPR101 gene
Having established beyond doubt that the region identified by the American researchers corresponded to a
locus of gigantism, the scientists defined a new gigantism syndrome: X-LAG (X-linked acrogigantism). "This
is a syndrome that begins in the cradle and which causes the tallest giants", points out Albert Beckers. "The
children are born normally and begin to grow abnormally even before they are one year old. They develop large
pituitary adenomas which do not respond well to traditional therapies. They secrete phenomenal quantities of
growth hormone as well as prolactin". Genetic studies have shown that these "little" giants (who are seen to
exhibit gigantism at a very young age) are carriers of the duplication of genes on the X chromosome.
In parallel, the scientists tasked themselves with determining which of the 11 duplicated genes were
responsible for this syndrome. Having reduced the number of genes potentially involved to 4 by cross-checking
between the patients, Albert Beckers and his colleagues looked at which of them were expressed in the
hypophyseal tumors of patients who had been operated upon. "Three of these genes were quite normally
expressed while the fourth was represented respectively between 600 and 100 times more in two distinct
tumors. This was undoubtedly the culprit!" reveals the specialist. The gene in question was GPR101 which
codes for a receptor whose function is unknown to this day.
A still unknown receptor in the spotlight
Published in The New England Journal of Medicine (4), the results of this study show the duplication of the
GPR101 gene which explains the development of the biggest giants in the world. "We cannot prove it, but we
would be prepared to bet that Robert Waldow, who measured 2m72, was affected by the X-LAG syndrome",
indicates Albert Beckers. "What we show in this study, is that the syndrome is related to the duplication of the
4 genes on the X chromosome, that GPR101 is probably the culprit and that this chromosomal aberration is
dominant and affects a slightly larger number of women than men. It is also the second genetic cause of FIPA,
because it can be transmitted by affected parents to their children", continues the researcher.
The receptor which is coded by the GPR101 gene is certainly actively involved in the regulation of the
growth hormone and its role is directly linked to GHRH - the hormone that releases the growth hormone and whose receptor is also over-expressed in patients affected by this condition. Up to now, chromosomal
aberrations involved in gigantism consisted of the mutation of genes and not the duplication of these same
genes. It is therefore a new genetic mechanism that causes growth problems that has been demonstrated
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in this study.
"This work opens up many and varied research
avenues", indicates Albert Beckers. "We have found the gene that codes for a receptor that is unknown to us.
We assume that it is used in the growth of the organism but extra research will be necessary to confirm this
theory. What is sure is that it is involved in a highly effective biological production of growth hormone! Perhaps
this receptor also plays a role in dwarfism…"?
Research which has yet to reveal all its findings…
The theories resulting from the researchers' discovery are many and are likely to keep scientists who are
interested in gigantism busy for a long time. "Whatever happens, we must first find the ligand of this receptor,
stimulate it and slow it down in order to observe the consequences of these manipulations and to see if this
receptor is involved in other diseases", continues the endocrinology specialist.
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Today, scientists are following different avenues of research to unveil the mystery surrounding giants with a
view to one day improving the quality of life of individuals affected by gigantism syndromes. This is because
of the fact that, apart from the obvious handicap caused by their great height, giants are subject to a number
of conditions and die relatively young.
At the present time, Professor Albert Beckers' team has three articles which are about to be published and
which will reveal new discoveries about the underlying mechanisms of gigantism. Among the research work
conducted by the team from Liege, is the analysis of bone samples taken from the Constantin giant of Mons
who measured 2m59…
(1) Clinical Characterization of Familial Isolated Pituitary Adenomas. The Journal of Clinical Endocrinology &
Metabolism Vol. 91, No. 9 3316-3323
(2) Aryl Hydrocarbon Receptor Interacting Protein Gene Mutations in Familial Isolated. Pituitary Adenomas :
Analysis in 73 families. J. Clin. Endocrinol. Metab, 92(5):1891-1896, 2007. Doi : 10.1210/ jc.2006-2513.
(3) Clinical Characteristics and Therapeutic Responses in Patients with Germ-Line AIP Mutations and
Pituitary Adenomas: An International Collaborative Study. The Journal of Clinical Endocrinology &
Metabolism Vol. 95, No. 11 E373-E383.
(4) Gigantism and Acromegaly Due to Xq26 Microduplications and GPR101 Mutation. N Engl J Med. 2014
Dec 18;371(25):2363-74. doi: 10.1056/NEJMoa1408028
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