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Amelogenesis imperfecta in the dentition of a wild chimpanzee

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Amelogenesis imperfecta in the dentition of a wild chimpanzee

Abstract

This report describes a case of amelogenesis imperfecta in the dentition of a female chimpanzee. Amelogenesis imperfecta is a group of rare genetic conditions that create severe enamel defects, which, although well researched in humans, has not yet been investigated in wild non-human primates.
J Med Primatol. 2017;1–3. wileyonlinelibrary.com/journal/jmp  
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© 2017 John Wiley & Sons A/S.
Published by John Wiley & Sons Ltd
Accepted: 3 October 2017
DOI: 10.1111/jmp.12323
CASE REPORT
Amelogenesis imperfecta in the dentition of a wild chimpanzee
Ian Towle1| Joel D. Irish1,2 | Isabelle De Groote1
1Research Centre in Evolutionary
Anthropology and Palaeoecology, School of
Natural Sciences and Psychology, Liverpool
John Moores University, Liverpool, UK
2Evolutionary Studies Institute and Centre for
Excellence in PaleoSciences, University of the
Witwatersrand, Johannesburg, South Africa
Correspondence
Ian Towle, Research Centre in Evolutionary
Anthropology and Palaeoecology, School
of Natural Sciences and Psychology, John
Moores University, Liverpool, UK.
Email: ianetowle@hotmail.co.uk
Funding information
Liverpool John Moores University
Abstract
This report describes a case of amelogenesis imperfecta in the dentition of a female
chimpanzee. Amelogenesis imperfecta is a group of rare genetic conditions that create
severe enamel defects, which, although well researched in humans, has not yet been
investigated in wild non- human primates.
KEYWORDS
dental defects, enamel hypoplasia, hereditary disease
1 | INTRODUCTION
Amelogenesis imperfecta (AI) refers to a group of genetic conditions
that create enamel defects, affecting one in every 700 to 14 000 hu-
mans.1,2 A variety of different genetic mutations can be responsible
for these heritable diseases.3-6 Pitting- and plane- form enamel hypo-
plasia are common, but abnormal enamel density, thickness and dis-
coloration are also associated with different forms.7-16 To differentiate
between different types of AI, clinical, histological and radiographic
methods have been used.2,5,10
Amelogenesis imperfecta has yet to be implicitly stated as present
in a non- human primate dentition; however, research has implicated
genetic factors in the formation of severe defects, and descriptions of
specimens have been reported that may fit with what is now classified as
AI.17-19 Given the large number of mutations that can cause these herita-
ble conditions in humans, it is perhaps surprising that more examples of
similar defects in primates have not been described. This deficiency likely
reflects much larger sample sizes and the proportionally greater amount
of research, that is carried out on humans. In this study, the dentitions of
gorillas, chimpanzees and baboons were examined for signs of AI.
2 | MATERIALS AND METHODS
A total of 119 chimpanzee, 93 gorilla and 43 baboon dentitions were
analysed, with both permanent (n = 5740) and deciduous (n = 1353)
teeth studied. This material is curated at the Powell- Cotton Museum
in Kent, UK. The primates were wild shot and collected in the first half
of the 20th century.20,21 Like most of the chimpanzee sample, the indi-
vidual discussed below originated from the Batouri district, Cameroon.
All teeth were examined macroscopically with a 10 × hand lens
also used to confirm defects. The presence and position of pitting- ,
plane- and linear- form of hypoplasia were recorded for each tooth.
Other enamel defects such as discoloration, porosity and reduction in
size were recorded, along with congenitally missing and supernumer-
ary teeth. As well, dental pathologies and unusual wear data were col-
lected, including caries, calculus, periodontal disease and abscesses,
for a separate study.
3 | RESULTS
Although many specimens in the samples display enamel defects, with
multiple types of hypoplasia, only one displays defects consistent
with a diagnosis of AI—specimen M 299, an adult female chimpanzee.
Pitting enamel hypoplasia is visible on all anterior teeth as well as the
maxillary first premolars and both sets of lower premolars (Figure 1).
No defects are visible on the molars. Apart from the defects them-
selves, the teeth appear normal in size and morphology.
The pitting is irregular in both shape and size, but small circular de-
pressions are most common (Figure 1A,B), with some larger irregular
defects that resemble plane- form defects (Figure 1C). Hypoplasia is
most defined on the labial/buccal surface and the cervical half of the
crown. All anterior teeth are equally affected, with roughly the same
2 
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   TOWLE ET aL.
position and severity of defects (Figure 1A,D). A “mottled” or “wavy”
appearance to the enamel is also evident on these teeth. The colour of
the enamel appears normal, but dark post- mortem discoloration may
mask defects. The mandibular left first premolar is congenitally absent
(Figure 1D). There are no caries, antemortem enamel fractures, peri-
odontal disease or severe occlusal attrition. Small amounts of calculus
are visible on the posterior mandibular teeth.
4 | DISCUSSION
The pattern of defects and the teeth affected support a diagnosis of
AI for M 299. The uniform pattern on anterior teeth, and lack of same
on the molars, strongly suggests the defects are not related to physi-
ological stress during development.2,22,23 Further, the defects do not
resemble those caused by congenital viruses, vitamin deficiencies,
malnutrition, fluorosis or other mineral contaminants in humans.24-26
A congenitally missing tooth may further support an AI diagnosis be-
cause these conditions often co- occur.10
Of the four main AI types common in humans, the features in this
chimpanzee’s dentition most closely match those of the Hypoplastic
(Type 1) variety.9,10,27 In line with this suggestion is little or no dis-
coloration, and no obvious reduction in size or unusual interproximal
spacing. As well, there is clear enamel pitting and plane- form de-
fects across large areas of the crown in multiple teeth. Specifically,
the defects appear indistinguishable from those recorded in hu-
mans as Type 1A,28,29 characterized by enamel pitting that varies
from pinpoint to pinhead in size on the buccal/labial surfaces of
permanent teeth.30 It is also common with this condition for some
teeth to show no visible defects,28 to explain why the chimpanzee’s
molars seem unaffected; that said, post- mortem discoloration and
antemortem wear may mask defects. This AI type creates the fewest
dental problems in humans,29 which may explain the otherwise good
dental health of this individual.
Although other potential cases of AI in primates must be con-
firmed, it is suggestive that the range of defects exhibited in non-
human primates may be as diverse as in humans [eg,17,19]. It is also
likely that many examples have been overlooked in primate skeletal
collections, particularly in the light of recent DNA advancement show-
ing just how diverse AI defects can be in humans. DNA analysis of this
individual as well as additional observations of AI in the dentitions of
other primates would further our understanding of these enamel ge-
netic disorders in primates as a whole.
ACKNOWLEDGMENTS
We thank I. Livne from the Powell- Cotton museum for access to the
primate collection. This research was supported by a studentship to
the first author from Liverpool John Moores University.
ORCID
Ian Towle http://orcid.org/0000-0001-8099-6220
Joel D. Irish http://orcid.org/0000-0001-7857-8847
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FIGURE1 Female chimpanzee showing
enamel defects and a congenital missing
tooth. A, Buccal/labial view of enamel
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How to cite this article: Towle I, Irish JD, De Groote I.
Amelogenesis imperfecta in the dentition of a wild
chimpanzee. J Med Primatol. 2017;00:1–3.
https://doi.org/10.1111/jmp.12323
... Defects are often characterised into four broad categories, pit-form (PEH), plane-form, linear-form (LEH), and localised hypoplasia (Guatelli-Steinberg, 2015;Pindborg, 1970;Seow, 1990;Hillson and Bond, 1997;Skinner et al., 2016). However, splitting defects into these categories can sometimes be difficult (e.g., Ogden et al., 2007;Towle et al., 2018;Ioannou et al., 2016). ...
... Hillson (2014) described these defects as extreme linear defects, with one perikymata significantly widened. Similarly, plane-form hypoplasia is often reported in the literature as part of other types of defects, in particular PEH or localised defects (Guatelli-Steinberg, 2003;Littleton and Townsend, 2005;Skinner et al., 2016;Towle et al., 2018). These defects are often found alongside other severe enamel defects, including those associated with conditions such as congenital syphilis or amelogenesis imperfecta (e.g., Ioannou et al., 2016;Towle et al., 2017). ...
... No plane-form defects were recorded in any of the hominin samples. A specific example of plane-form hypoplasia was found in the chimpanzee sample and has been published as a case study (Towle et al., 2018). When individuals with and without localised hypoplasia are analysed separately, there is more PEH in the group with no localised enamel lesions for both gorillas and chimpanzees. ...
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