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Sri Lanka Dental Journal , 2011 April (Vol:41 No:1)

Author(s): E.M.U.C.K. Herath, P.R. Jayasooriya, I.R. Perera
Other formats: Abstract , PDF
Published on: Wed, 15 Aug 2012 15:05:40 +0530
Last updated on: Wed, 15 Aug 2012 15:05:40 +0530
Sri Lanka Dental Journal, 2011 April (Vol:41 No:1)
1391-07280

Descriptive analysis of subtypes of amelogenesis imperfecta

ABSTRACT

Objective
Amelogenesis imperfecta (AI) is defined as clinically and genetically diverse group of conditions that are caused by mutations in genes. The present study aims to describe the different clinical presentations, patterns of inheritance and syndromic forms observed in a group of children with AI in Sri Lanka, in order to create awareness among Dental Surgeons, regarding this complicated group of disorders.

Study sample
The study sample comprised of 12 females and 8 males belonging to sixteen families.

Results
Hypoplastic type (Type I) of AI was the commonest form affecting 45% of the children. Thirty percent of children showed features of hypomaturation type (Type II) while 15% and 10% showed features of hypocalcification (Type III), hypoplastic/hypomaturation (Type IV) form of disease respectively. Sub typing performed with Witkop and Sauk classification as a guidline revealed all sub types except for IE (hypoplastic diffuse smooth type), IIC and D (hypomaturationsnow capped type) and IIIB (hypocalcified-diffuse type). Children who may have Kohlschutter syndrome, Cone rod dystrophy and Tricho-dentoosseous syndrome were identified and are undergoing further investigations to confirm the diagnoses.

Conclusion
By describing the different forms f AI, we expect to improve the awareness of this complicated group of conditions among Sri Lankan Dental Surgeons. In addition, the importance of identifying the syndromic forms of AI is highlighted.

Key words
Amelogenesis imperfect, pattern of inheritance.


Dr. E.M.U.C.K. Herath
BDS, MS (Restorative Dentistry), Senior Lecturer and Consultant Paedodontist, Div of Paedodontics, Department of Community Dentistry, Faculty of Dental Sciences, University of Peradeniya, Sri Lanka.

Dr. P.R. Jayasooriya (Correspondence)
BDS, PhD (Japan), Senior Lecturer in Oral Pathology Department of Oral Pathology, Faculty of Dental
Sciences, University of Peradeniya, Sri Lanka.
Tel: +94-81-2397435 Fax: +94-81-2388948
E-mail:primalij@yahoo.com

Dr. I.R. Perera
BDS, MSc, MD (Community Dentistry), Dental Public Health Specialist, Community Dental Unit,
Dental Institute, Colombo, Sri Lanka

FULLTEXT

Introduction

Amelogenesis Imperfecta (AI) is a developmental disorder of genomic origin, associated with abnormal enamel formation. Although AI is considered as a single disease entity, it actually represents a group of heterogeneous conditions, with diverse structural defects of enamel resulting in a range of clinical phenotypes.1,2,3 The structural defects of AI may occur at the time of formation of the organic matrix, mineralization of the matrix or maturation of enamel giving rise respectively to either hypoplastic, hypocalcification or hypomaturation type of AI. However, within each of the afore mentioned categories, sub types with different patterns of inheritance and wide variety of clinical manifestations exists resulting in at least 15 subtypes of AI. Hence it is essential to use a classification to characterize the different sub types of AI. The most widely used classification by Witkop and Sauk (Table 1) is based on phenotype and pedigree analysis.4 Although an ideal classification should also include genomic analysis to identify the mutations associated with the sub types, it is not used routinely for diagnostic purposes.2,3 At present, AI is diagnosed based on the family history, pedigree plotting and clinical observation. Furthermore, the diagnosis involves exclusion of other enamel defects such as fluorosis and chronological hypoplasia, prior to establishment of likely inheritance patterns and clinical phenotype using Witkop and Sauk classification as a guideline.

The prevalence of AI varies from 1:700 to 1:14,000 depending on the population studied.3 Although, AI is not a very common disorder that the Dental Surgeons would encounter in their dayto-day practices, they may see a few patients over the years. As the correct identification is essential to provide the best management, which should not only include restorative treatment, but also genetic counseling as well as reassurance of both parents and patients, thorough knowledge of this complicated group of conditions are essential.

Therefore, the present study aims to describe the different clinical presentations, inheritance patterns and syndromic forms observed in a group of children with AI in Sri Lanka, in order to create awareness among Dental Surgeons, regarding this complicated group of disorders.

Method

Patient Selection
Children presenting to the Division of Paedodontics, Faculty of Dental Sciences, University of Peradeniya over a period of two years from 2008 to 2010, with the aim of seeking treatment for discoloured/ sensitive or abnormal appearance of teeth were first screened to identify patients suffering from AI. AI was diagnosed by evaluating the history, pedigree analysis, clinical and radiological appearance of teeth, and histopathological specimens when available. Sub typing of AI was performed using the findings afore mentioned with Witkop and Sauks classification as a guideline (Table 1).

The study sample thus obtained included twenty children with AI, belonging to 16 families with four families contributing two children with AI each.

Table 1: Classification of Amelogenesis Imperfecta

Type

Pattern

Specific Features

Inheritance

IA
IB
IC
ID
IE
IF
IG

Hypoplastic
Hypoplastic
Hypoplastic
Hypoplastic
Hypoplastic
Hypoplastic
Hypoplastic

Generalized pitted
Localized pitted
Localized pitted
Diffuse smooth
Diffuse smooth
Diffuse rough
Enamel agenesis

Autosomal dominant
Autosomal dominant
Autosomal recessive
Autosomal dominant
X-linked dominant
Autosomal dominant
Autosomal recessive

IIA
IIB
IIC
IID

Hypomaturation
Hypomaturation
Hypomaturation
Hypomaturation

Diffuse pigmented
Diffuse
Snow capped
Snow capped

Autosomal recessive
X-linked recessive
X-linked
Autosomal dominant?

IIIA
IIIB

Hypocalcification
Hypocalcification

Diffuse
Diffuse

Autosomal dominant
Autosomal recessive

IVA
IVB

Hypomaturation-hupoplastic
Hypoplastic-hypomaturation

Taurodontism present
Taurodontism present

Autosomal dominant
Autosomal dominant

Results

The demographic data with the diagnosis including type and sub type of AI achieved for each child is shown in Table 2.

In the present study sample, the mean age of the children affected with AI was 12 years and ranged from 3-17 years. Female predilection (12/20) with male to female ratio of 2:3 was also noted. With reference to racial distribution, majority of the affected children were Sinhalese 65 %( 13/20) followed by15 %( 3/20) Tamils and 20 %( 4/20) Muslims.

Out of the twenty patients with AI, 45 %( 9/20) had hypoplastic (Type I) (Fig 1) form of disease while 30 %( 6/20), 15 %( 3/20), 10 %( 2/20) respectively had hypomaturation (Type II)(Fig 2), hypocalcification (TypeIII) (Fig 3), hypoplastic/hypomaturation (Type IV) form of disease.

Table 2: Demographic data with diagnosis of the study population (click to enlarge)
Table 2

With reference to identification of patterns of inheritance and pedigree plotting, a positive family history could be identified in 50% (8/16) of the families having children with AI. With pedigree plotting, positive identification of pattern of inheritance as either autosomal dominant or x-linked pattern was possible in 7 families (8 children) and one family (one child) respectively. In addition, in the group of children without positive family history, 8 had parents who were related to each other leading to consanguinity in the family. These 8 children were considered to show autosomal recessive pattern of inheritance, as consanguinity is known to give rise to diseases showing aforementioned pattern of inheritance. The remaining 3 children without identifiable pattern of inheritance were considered as sporadic cases of AI. The clinical presentation of AI to some extent depends on the type and in the present study out of the 9 children showing hypoplastic pattern, two children in one family presented with generalized pitted sub type (IA) where teeth had enamel which contrasted well with underlying dentine radiologically. Clinically pits were seen arranged in to horizontal and vertical lines in areas with other areas showing a more haphazard distribution. These pits were more common on the buccal surfaces of teeth compared to other surfaces. As, no other family member was affected; these children were considered to have a sporadic form of AI (Patient no 16 and 17, Table 2). Three children belonging to two families had localized pitted sub types (IB and IC) where the pits were seen on buccal surfaces mainly with incisial edges showing regular enamel, which contrasted well with dentine radiologically. Out of the three children one child (Patient no 9, Table 2) had IB sub type with autosomal dominant type of inheritance, while in the remaining two children both dentitions were affected, in addition the parents of these children were related allowing the condition to be classified as IC with autosomal recessive type of inheritance (Patient no 4 and 5, Table 2). None of the children included in the study had diffuse smooth type (IE); hence it was not possible to demonstrate the lionization effect, which is observed in females. Two children in one family showed diffuse rough pattern (IF), with teeth shaped as crown preparations and containing open contact points, exhibiting a very thin layer of enamel (Patient no 13 and 14, Table 2). Two children had teeth with exposed rough dentine without any enamel and anterior open bite, which was categorized as enamel agenesis type (IG) (Patient no 15 and 20, Table 2).

Four and two children belonging to three and two families respectively showed hypomaturation type diffuse pigmented (IIA) (Patient no 7, 10, 18 and 19, Table 2) and diffuse pigmented (IIB) (Patient no 1 and 11, Table 2) pattern of AI. These children had enamel, which showed a similar radio density to dentine. Clinically the shapes of the teeth were normal while colour ranged from mottled to yellow brown. With reference to patient no 11, both mother and sister of the patient showed less severe form of slight irregularly arranged vertical bands of opaque enamel alternating with normal enamel under transillumination. In our study sample no children had snow capped pattern of hypomaturation type of AI.

Three children presented with hypocalcification type of AI, where the parents said that the children had brown, yellow colored teeth, which were appropriately shaped on eruption. On examination, most of the teeth did not show any enamel on occlusal surfaces, while except for the cervical portion other areas had exposed dentine (Patient no 2, 3 and 6, Table 2). Two children also exhibited rapid calculus deposition. The study sample included children with hypocalcified type of AI showing only autosomal dominant inheritance pattern where the teeth are less severely affected (sub type IIIA). None of the children in the present sample had autosomal recessive inheritance pattern (sub type IIIB) with severely affected teeth.

Two children showed AI of Hypomaturation-Hypoplastic type with Taurodontism (AIHHT) (Type IV) where pits were evident on the buccal surfaces with other areas showing a yellowish brown colour (Patient no 8 and 12, Table 2). Radiological investigations revealed single rooted teeth with large pulp chambers and molars showing varying degrees of taurodontism. However, features of Tricho-dento-osseous syndrome (TDO) including curly hair and bone sclerosis in addition to AI were only observed in patient number 12.

Discussion

According to earlier definitions AI was considered as a specific enamel defect without the involvement of other structures.5 However, recent findings have led AI to be considered as a genetic disease that may exist in isolation or associated with other features in syndromes.3 Syndromes/conditions that have been associated with AI include Kohlschutter syndrome, TDO syndrome, Platyspondyly, Nephrocalcinosis and Cone- rod dystrophy.3 One child (Patient no 15-Table 2) included in the present study may have features of cone rod dystrophy that has been linked to a micro deletion at 2q11 with autosomal recessive type of inheritance.6,7 In our patient also, the autosomal recessive pattern of inheritance could be confirmed as she was from a family exhibiting consanguinity. At present the patient is undergoing further investigations to confirm the diagnosis. In addition, another child (Patient no 10-Table
2) coming from a consanguineous family had epilepsy and is undergoing further investigations to determine if he is suffering from less severe form of Kohlschutter syndrome.8,9 Although, patient no 8 and 12 both have AIHHT, patient number 8 did not show features of TDO syndrome, such as curly hair and skeletal changes including bone sclerosis, while patient no 12 showed features of TDO syndrome. According to a previous study taurodontism of the first mandibular molar has been shown to be useful to distinguish between TDO syndrome and AIHHT.10 Supporting the above conclusion, patient no 8 did not show taurodontism of mandibular first molar in contrast to patient number 12, who presented with severe form of taurodontism of mandibular first molar. According to literature, Nephrocalcinosis is thought affect children who have hypoplastic type of AI, which is inherited in autosomal recessive trait.11 Therefore, patients, no 4, 5 and 20 who have fulfilled above criteria will be investigated to identify whether they are suffering from Nephrocalcinosis.

AI is a complicated group of conditions resulting in different clinical phenotypes, which usually, correspond to the structural defect. As, diagnosis based purely on the clinical phenotype result in over/under diagnosis of the condition, clinicians recommend the use of both clinical observation and pedigree analysis when diagnosing AI. Following clues were used to identify the inheritance pattern of AI in the present study,

  1. Autosomal dominant inheritance: Male to male transmission with approximately half the offspring of an affected individual showing clinical features of disease and affected males and females showing similar clinical features.
  2. Autosomal recessive trait: Unaffected parents having affected offspring with parents in consanguineous marriages.
  3. X-linked inheritance: Recessive trait: No male-to-male transmission Dominant trait: Male offspring showing more severe presentation with some females in the family showing lionization.

However, in the present study several difficulties/problems were encountered in the pedigree analysis. With reference to patients exhibiting autosomal dominant type of inheritance, horizontal spread among the siblings of the affected parent's family was not observed except for three families. In addition, the disease was also not observed
among cousins (first degree relatives), even when a grandparent was affected. However, it is difficult to determine whether the information related to siblings and cousins are true as the authors were unable to examine all the individuals of the affected families and the information was gathered by speaking to the parents of the affected children only.

It was also not possible to sub classify the type of AI in affected parents as most were wearing prosthesis. However, a single parent (mother) (Patient no 11-Table 2) showed a less severe form than the child. It was correlated to the x-linked type of inheritance observed in the family. The less severe form observed in the mother can be contributed to the occurrence of the lionization (inactivation of one X chromosome, while the other X chromosome is active) phenomenon which gives rise to different clinical appearances in male and females.4

In the present study, patients without a positive family history or consanguinity in the family were considered as having sporadic form of AI. However, sporadic form may actually represent examples of new mutations or variable expression with or without incomplete penetrance of a dominant
gene. 3 Hence, although patients no 16 and 17 were considered to have the sporadic form, they may actually have autosomal dominant type of inheritance with variable expression in the parent (father). Supporting this fact, father and children, showed peg laterals which is also thought to be transmitted in an autosomal dominant form.4

Although, with available information authors attempted to identify the mode of inheritance in the present group of patients, speculative nature of the findings are acknowledged. Hence, in order to confirm the diagnosis and the nature of the mutations genetic analysis is recommended. According to previous studies, X-liked form of AI has been shown to be associated with mutations in AMLEX gene that codes for amelogenin. With reference to autosomal dominant forms of AI, mutations in enamelin coding gene ENAM has been identified to contribute to hypoplastic type, while the molecular aetiology of the hypocalcified type remains unknown to date.12 TDO syndrome is contributed to DLX3 mutations while molecular aetiology of AIHHT remains unknown.13 Autosomal recessive form of AI has been shown to be associated with mutations in genes coding proteinases, enamelysin (MMP-20) and kalikrein 4, responsible for processing the extra cellular matrix.12 However, it was not possible to perform genetic analysis for the present group of patients due to the cost involved.

By describing the different forms of AI, we expect to improve the awareness of this complicated group of conditions among Sri Lankan Dental Surgeons. In addition, the importance of identifying the syndromic forms of AI is highlighted. This baseline data could be used to emphasize the importance of early accurate diagnosis leading to better treatment outcomes contributing to improved quality of life among patients affected by AI.

Figure 1

Figure 1:
Amelogenesis imperfecta - Hypoplastic type

Figure 2

Figure 2:
Amelogenesis imperfecta - Hypomaturation type

Figure 3

Figure 3:
Amelogenesis imperfecta - Hypocalcification type

References

  1. Witkop CJ. Amelogenesis imperfecta, dentinogenesis imperfecta and dentine dysplasia revisited: problems in classification. J Oral Pathol 1988; 17:547-553.
  2. Aldred MJ, Savarirayan R, Crawford PJM. Amelogenesis imperfecta: a clssification and catalogue for 21st century. Oral Diseases 2003; 9: 19-23.
  3. Crawford PJM, Aldred MJ, Bloch-Zupan A. Amelogenesis imperfecta. Orphanet Journal of Rare Diseases. 2007; 2: 17
  4. Neville BW, Damm DD, Allen CM, Bouquot JE. Oral & Maxillofacial Pathology, WB Saunders Company USA, 2nd edition, 2002 Chapter 2 Abnormalities of teeth. pp 49-107.
  5. Witkop CJ, Kuhlmann W, Sauk JJ. Autosomal recessive hypomaturation amelogenesis imperfecta. Oral Surg 1973; 36: 367-382.
  6. Michaelides M, Bloch-Zupan A, Holder G, Hunt D, Moore A. Autosomal recessive cone-rod dystrophy associated with Amelogenesis imperfecta. J Med Genet. 2004; 4:468-473.
  7. Hamel CP. Cone rod dystrophies. Orphanet J Rare Dis. 2007; 2: 7. Published online 2007 February 1. doi: 10.1186/1750-1172-2-7.
  8. Christodoulou J, Hall RK, Menahem S, Hopkins IJ, Rogers JG. A syndrome of epilepsy, dementia and amelogenesis imperfecta: genetic and clinical features. J Med Genet. 25: 12: 827-830.
  9. Harberlandt E, Svejda C, Felber S, Baumgartner S, Gunter B, Utermann G, Kotozot D. Yellow teeth, Seizures and Mental retardation-A less severe case of Kohlschutter-Tonz syndrome. Am J Med Genet. 2006;140:281-283.
  10. Seow WK. Taurodontism of the mandibular first permanent molar distinguishes between tricho-dento-osseous (TDO) syndrome and amelogenesis imperfecta. Clin Genet 1993; 43: 240-6.
  11. Kirzioglu Z, Ulu KG, Sezer MT, Yuksel S. The relationship of amelogenesis imperfect and nephrocalcinosis syndrome. Med Oral Patol Oral Cir Bucal 2009;11:579-82.
  12. Wright JT. Molecular aetiologies and associated phenotypes of amelogenesis imperfecta. Am J Med Genet 2006; 140: 2547-2555.
  13. Price JA, Wright JT, Walker SJ, Crawford PJM, Aldred MJ, Hart TC. Tricho-dento-osseous syndrome and amelogenesis imperfecta with taurodontism are genetically distinct conditions. Clin Genet. 1999; 56: 35-40.
 

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