Identification of a locus on chromosome 2q11 at which recessive amelogenesis imperfecta and cone-rod dystrophy cosegregate

Four different gene-related cone-rod dystrophy: clinical and genetic findings in six Chinese families with diverse modes of inheritance

Purpose: To investigate pathogenic variants in six families with cone-rod dystrophy (CORD) presenting various inheritance patterns by using whole-exome sequencing (WES) and analyzing phenotypic features. Methods: A total of six families with CORD were enrolled in Ningxia Eye Hospital for this study. The probands and their family members received comprehensive ophthalmic examinations, and DNA was abstracted from patients and family members. Whole-exome sequencing was performed on probands to screen the causative variants, and all suspected pathogenic variants were determined via Sanger sequencing. Furthermore, co-segregation analysis was performed on available family members. The pathogenicity of novel variants was predicted using in silico analysis and evaluated according to the American College of Medical Genetics and Genomics (ACMG) guidelines. Results: Of the six families, two families were assigned as X-linked recessive (XL), two families were assigned as autosomal recessive (AR), and two families were assigned as autosomal dominant (AD). Pathogenic variants were detected in CACNA1F in two X-linked recessive probands, among which family 1 had a hemizygous frameshift variant c.2201del (p.Val734Glyfs*17) and family 2 had a hemizygous missense variant c.245G>A (p.Arg82Gln). Both probands had high myopia, with fundus tessellation accompanied by abnormalities in the outer structure of the macular area. The homozygous splice variant c.2373 + 5G>T in PROM1 and the homozygous nonsense variant c.604C>T (p.Arg202Ter) in ADAM9 were detected in two autosomal recessive families of the probands. Both probands showed different degrees of atrophy in the macular area, and the lesions showed hypofluorescence changes in autofluorescence. The heterozygous variation in CRX c.682C>T (p.Gln228Ter) was detected in two autosomal dominant families. The onset age of the two probands was late, with better vision and severe macular atrophy. According to ACMG guidelines and the analysis of online in silico tools, all variations were labeled as potentially harmful or pathogenic. Conclusion: Pathogenic variants in CACNA1F, PROM1, ADAM9, and CRX genes were identified in six families affected by the diverse inheritance patterns of CORD. Furthermore, the potential impact of the nonsense-mediated decay (NMD) mechanism on the manifestation of CORD phenotypes was examined and addressed. Simultaneously, the spectrum of pathogenic variants and clinical phenotypes associated with the CORD gene was extended.

Tooth ultrastructure changes induced by a nonsense mutation in the FAM83H gene: insights into the diversity of amelogenesis imperfecta

OBJECTIVES

The current research on single-nucleotide polymorphism (SNP) mutation sites at different positions of the FAM83H gene and their phenotypic changes leading to amelogenesis imperfecta (AI) is inconsistent. We identified a previously reported heterozygous nonsense mutation c.1192C>T (p.Q398*) in the FAM83H gene and conducted a comprehensive analysis of the dental ultrastructure and chemical composition changes induced by this mutation. Additionally, we predicted the protein feature affected by this mutation site. The aim was to further deepen our understanding of the diversity of AI caused by different mutation sites in the FAM83H gene.

METHODS

Whole-exome sequencing (WES) and Sanger sequencing were used to confirm the mutation sites. Physical features of the patient's teeth were investigated using various methods including cone beam computer tomography (CBCT), scanning electron microscopy (SEM), contact profilometry (roughness measurement), and a nanomechanical tester (nanoindentation measurement). The protein features of wild-type and mutant FAM83H were predicted using bioinformatics methods.

RESULTS

One previously discovered FAM83H heterozygous nonsense mutation c.1192C>T (p.Q398*) was detected in the patient. SEM revealed inconsistent dentinal tubules, and EDS showed that calcium and phosphorus were lower in the patient's dentin but higher in the enamel compared to the control tooth. Roughness measurements showed that AI patients' teeth had rougher occlusal surfaces than those of the control tooth. Nanoindentation measurements showed that the enamel and dentin hardness values of the AI patients' teeth were both significantly reduced compared to those of the control tooth. Compared to the wild-type FAM83H protein, the mutant FAM83H protein shows alterations in stability, hydrophobicity, secondary structure, and tertiary structure. These changes could underlie functional differences and AI phenotype variations caused by this mutation site.

CONCLUSIONS

This study expands the understanding of the effects of FAM83H mutations on tooth structure.

CLINICAL RELEVANCE

Our study enhances our understanding of the genetic basis of AI and may contribute to improved diagnostics and personalized treatment strategies for patients with FAM83H-related AI.

Clear Aligners in Patients with Amelogenesis and Dentinogenesis Imperfecta

Dentinogenesis imperfecta (DI) and amelogenesis imperfecta (AI) are hereditary abnormalities of dental hard tissues. Dental abnormalities may also be accompanied by symptoms of disorders such as osteogenesis imperfecta. AI and DI have a significant burden on socializing, function, and comfort; therefore, frequent screening and accurate diagnosis is the cornerstone of managing such conditions. Both AI and DI could be treated with many strategies, including restorative, prosthetic, periodontal, surgical, and orthodontics treatment. The interdisciplinary combination of orthodontic, prosthodontic, and periodontic treatment has been proven to improve the prognosis of AI and DI. Regarding orthodontic treatment, the most difficult element of orthodontic therapy may be maintaining a high level of motivation for what might be a prolonged form of treatment spanning several years. There are many forms of orthodontic management for AI and DI, including removable appliances, functional appliances, and fixed appliances. Clear aligner therapy (CAT) contains a broad range of equipment that works in different ways, has different construction processes, and is compatible with different malocclusion procedures. The application of CAT in patients with AI and DI is favorable over the fixed applicants. However, the available evidence regarding the application of CAT in AI is weak and heterogeneous. In this review, we discussed the current evidence regarding the application of clear CAT in patients with AI and DI.

Features, genetics and their correlation in Jalili syndrome: a systematic review

Jalili syndrome is a rare genetic disorder first identified by Jalili in Gaza. Amelogenesis imperfecta and cone-rode dystrophy are simultaneously seen in Jalili syndrome patients as the main and primary manifestations. Molecular analysis has revealed that theCNNM4gene is responsible for this rare syndrome. Jalili syndrome has been observed in many countries around the world, especially in the Middle East and North Africa. In the current scoping systematic review we searched electronic databases to find studies related to Jalili syndrome. In this review we summarise the reported clinical symptoms,CNNM4gene and protein structure,CNNM4mutations, attempts to reach a genotype-phenotype correlation, the functional role ofCNNM4mutations, and epidemiological aspects of Jalili syndrome. In addition, we have analysed the reported mutations in mutation effect prediction databases in order to gain a better understanding of the mutation’s outcomes.

Jalili Syndrome: Cross-sectional and Longitudinal Features of Seven Patients With Cone-Rod Dystrophy and Amelogenesis Imperfecta

PURPOSE

To characterize a series of 7 patients with cone-rod dystrophy (CORD) and amelogenesis imperfecta (AI) owing to confirmed mutations in CNNM4, first described as "Jalili Syndrome."

DESIGN

Retrospective observational case series.

METHODS

Seven patients from 6 families with Jalili Syndrome were identified at 3 tertiary referral centers. We systematically reviewed their available medical records, spectral-domain optical coherence tomography (SD-OCT), fundus autofluorescence imaging (FAF), color fundus photography, and electrophysiological assessments.

RESULTS

The mean age at presentation was 6.7 years (range 3-16 years), with 6 male and 1 female patient. CNNM4 mutations were identified in all patients. The mean Snellen best-corrected visual acuity (BCVA) at presentation was 20/246 (range 20/98 to 20/399) in the right eye and 20/252 (range 20/98 to 20/480) in the left. Nystagmus was observed in all 7 patients, and photophobia was present in 6. Funduscopic findings at presentation were variable, ranging from only mild disc pallor to retinal vascular attenuation and macular atrophy. Multimodal imaging demonstrated disease progression in all 7 patients over time. Electroretinography uniformly revealed progressive cone-rod dysfunction.

CONCLUSIONS

Jalili Syndrome is a rare CORD associated with AI. We have further characterized its ocular phenotype, including describing SD-OCT, FAF, and electrophysiological features; and report several novel disease-causing sequence variants. Moreover, this study presents novel longitudinal data demonstrating structural and functional progression over time, allowing better informed advice on prognosis.

Novel splice site mutation in CNNM4 gene in a family with Jalili syndrome

Jalili syndrome is a rare autosomal recessive genetic disease characterized by the association of amelogenesis imperfecta and cone-rod retinal dystrophy. This syndrome is caused by mutations in the CNNM4 gene. Different types of CNNM4 mutations have been reported; missense, nonsense, large deletions, single base insertion, and duplication. We used Sanger sequencing to analyze a large consanguineous family with three siblings affected with Jalili syndrome, suspected clinically after dental and ophthalmological examination. These patients are carrying a novel homozygous mutation in the splice site acceptor of intron 3 (c.1682-1G > C) in the CNNM4 gene. We compare the findings of the present family to those from literature, in order to further delineate Jalili syndrome.

A new familial case of Jalili syndrome caused by a novel mutation in CNNM4

Jalili syndrome (JS) is a rare autosomal recessive disorder characterized by the combination of cone-rod dystrophy (CRD) and amelogenesis imperfecta. To date, 18 families with JS have been reported, 16 of which were found to have a mutation in CNNM4. We describe three siblings with clinical features of JS with a homozygous missense mutation in exon 4 of CNNM4, c.1781A>G (p.N594S). They demonstrated phenotypic variability in terms of ocular and dental findings. Although fundus examination and optical coherence tomography results were normal, the electroretinogram was compatible with CRD, supporting the diagnosis of JS. The dental phenotype severity also varied among the siblings.

Characterization of the nanoscratch, microstructure, and composition in hypoplastic amelogenesis imperfecta

Hypoplastic amelogenesis imperfecta is a widespread hereditary disease that causes the loss of enamel. The purpose of this study was to investigate the nanoscratch resistance of hypoplastic amelogenesis imperfecta for providing a reference for restorative treatment. Four unerupted third molars from a patient diagnosed with hypoplastic amelogenesis imperfecta and seven unerupted third molars from normal individuals were compared. Atomic force microscopy and energy-dispersive X-ray spectroscopy were used to observe the microstructure and composition of the teeth (enamel and dentin). The nanoscratch tests of teeth (enamel and dentin) were investigated using a nanoscratch tester, scanning electron microscopy, and a stylus profilometer. The results indicated that hypoplastic amelogenesis imperfecta teeth had different microstructures compared to normal teeth. Hypoplastic amelogenesis imperfecta demonstrated a higher composition of organic substance. Meanwhile, the friction coefficient of hypoplastic amelogenesis imperfecta was higher than that of normal teeth, and inferior frictional resistance of hypoplastic amelogenesis imperfecta teeth was observed. The main damaging mechanisms observed in hypoplastic amelogenesis imperfecta under nanoscratch were the combination of delamination, debris, and cracks in enamel with delamination, debris, and plastic deformation in dentin. Our findings suggested that new dental restorative materials should be selected to match the mechanical properties of hypoplastic amelogenesis imperfecta.

Dental phenotype in Jalili syndrome due to a c.1312 dupC homozygous mutation in the CNNM4 gene

Jalili syndrome denotes a recessively inherited combination of an eye disease (cone-rod dystrophy) and a dental disorder (amelogenesis imperfecta), which is caused by mutations in the CNNM4 gene. Whereas the ophthalmic consequences of these mutations have been studied comprehensively, the dental phenotype has obtained less attention. A defective transport of magnesium ions by the photoreceptors of the retina is assumed to account for the progressive visual impairment. Since magnesium is also incorporated in the mineral of dental hard tissues, we hypothesized that magnesium concentrations in defective enamel resulting from mutations in CNNM4 would be abnormal, if a similar deficiency of magnesium transport also accounted for the amelogenesis imperfecta. Thus, a detailed analysis of the dental hard tissues was performed in two boys of Kosovan origin affected by Jalili syndrome. Retinal dystrophy of the patients was diagnosed by a comprehensive eye examination and full-field electroretinography. A mutational analysis revealed a c.1312 dupC homozygous mutation in CNNM4, a genetic defect which had already been identified in other Kosovan families and putatively results in loss-of-function of the protein. The evaluation of six primary teeth using light and scanning electron microscopy as well as energy-dispersive X-ray spectroscopy showed that dental enamel was thin and deficient in mineral, suggesting a hypoplastic/hypomineralized type of amelogenesis imperfecta. The reduced mineral density of enamel was accompanied by decreased amounts of calcium, but significantly elevated levels of magnesium. In dentin, however, a similar mineral deficiency was associated with reduced magnesium and normal calcium levels. It is concluded that the c.1312 dupC mutation of CNNM4 results in mineralization defects of both enamel and dentin, which are associated with significantly abnormal magnesium concentrations. Thus, we could not disprove the hypothesis that a disrupted magnesium transport is involved in the development of the dental abnormalities observed in Jalili syndrome.

Molecular genetics of achromatopsia in Newfoundland reveal genetic heterogeneity, founder effects and the first cases of Jalili syndrome in North America

Achromatopsia (ACHM) is a severe retinal disorder characterized by an inability to distinguish colors, impaired visual acuity, photophobia and nystagmus. This rare autosomal recessive disorder of the cone photoreceptors is best known for its increased frequency due to founder effect in the Pingelapese population of the Pacific islands. Sixteen patients from Newfoundland, Canada were sequenced for mutations in the four known achromatopsia genes CNGA3, CNGB3, GNAT2, and PDE6C. The majority (n = 12) of patients were either homozygotes or compound heterozygotes for known achromatopsia alleles, two in CNGB3 (p.T383fsX and p.T296YfsX9) and three in CNGA3 (p.R283Q, p.R427C and p.L527R). Haplotype reconstruction showed that recurrent mutations p.T383fsX and p.L527R were due to a founder effect. Aggregate data from exome sequencing, segregation analysis and archived medical records support a rediagnosis of Jalili syndrome in affected siblings (n = 4) from Family 0094, which to our knowledge is the first family identified with Jalili Syndrome in North America.

Cone-rod dystrophy associated with amelogenesis imperfecta in a child with neurofibromatosis type 1

PURPOSE

To report a case of a 9-year-old child with neurofibromatosis type 1 (NF1) and Jalili syndrome, the latter denoting a rare combination of cone-rod dystrophy and amelogenesis imperfecta.

METHODS

Detailed ophthalmological and electrophysiological examinations were carried out and blood samples were taken from the patient and her father for molecular genetic analysis by direct DNA sequencing of the NF1 and the ancient conserved domain protein 4 (CNNM4) gene.

RESULTS

The diagnosis of neurofibromatosis type 1 (NF1) could be confirmed clinically and genetically. Furthermore, cone-rod dystrophy and amelogenesis imperfecta could be observed as typical features of a rare condition, acknowledged as Jalili syndrome. The diagnosis was assured on the basis of clinical examinations and molecular genetic analysis of the CNNM4 gene, which was previously shown to cause Jalili syndrome.

CONCLUSION

Our case shows a unique combination of NF1 and Jalili syndrome. The random association of two diseases is unusual and deserves attention. This case highlights the importance not only of detailed clinical examination, but also of molecular genetic analysis, which together provide a precise diagnosis.

Defining a new candidate gene for amelogenesis imperfecta: from molecular genetics to biochemistry

Amelogenesis imperfecta is a group of genetic conditions that affect the structure and clinical appearance of tooth enamel. The types (hypoplastic, hypocalcified, and hypomature) are correlated with defects in different stages of the process of enamel synthesis. Autosomal dominant, recessive, and X-linked types have been previously described. These disorders are considered clinically and genetically heterogeneous in etiology, involving a variety of genes, such as AMELX, ENAM, DLX3, FAM83H, MMP-20, KLK4, and WDR72. The mutations identified within these causal genes explain less than half of all cases of amelogenesis imperfecta. Most of the candidate and causal genes currently identified encode proteins involved in enamel synthesis. We think it is necessary to refocus the search for candidate genes using biochemical processes. This review provides theoretical evidence that the human SLC4A4 gene (sodium bicarbonate cotransporter) may be a new candidate gene.

Mutations in CNNM4 cause Jalili syndrome, consisting of autosomal-recessive cone-rod dystrophy and amelogenesis imperfecta

The combination of recessively inherited cone-rod dystrophy (CRD) and amelogenesis imperfecta (AI) was first reported by Jalili and Smith in 1988 in a family subsequently linked to a locus on chromosome 2q11, and it has since been reported in a second small family. We have identified five further ethnically diverse families cosegregating CRD and AI. Phenotypic characterization of teeth and visual function in the published and new families reveals a consistent syndrome in all seven families, and all link or are consistent with linkage to 2q11, confirming the existence of a genetically homogenous condition that we now propose to call Jalili syndrome. Using a positional-candidate approach, we have identified mutations in the CNNM4 gene, encoding a putative metal transporter, accounting for the condition in all seven families. Nine mutations are described in all, three missense, three terminations, two large deletions, and a single base insertion. We confirmed expression of Cnnm4 in the neural retina and in ameloblasts in the developing tooth, suggesting a hitherto unknown connection between tooth biomineralization and retinal function. The identification of CNNM4 as the causative gene for Jalili syndrome, characterized by syndromic CRD with AI, has the potential to provide new insights into the roles of metal transport in visual function and biomineralization.

Mutations in CNNM4 cause recessive cone-rod dystrophy with amelogenesis imperfecta

Cone-rod dystrophies are inherited dystrophies of the retina characterized by the accumulation of deposits mainly localized to the cone-rich macular region of the eye. Dystrophy can be limited to the retina or be part of a syndrome. Unlike nonsyndromic cone-rod dystrophies, syndromic cone-rod dystrophies are genetically heterogeneous with mutations in genes encoding structural, cell-adhesion, and transporter proteins. Using a genome-wide single-nucleotide polymorphism (SNP) haplotype analysis to fine map the locus and a gene-candidate approach, we identified homozygous mutations in the ancient conserved domain protein 4 gene (CNNM4) that either generate a truncated protein or occur in highly conserved regions of the protein. Given that CNNM4 is implicated in metal ion transport, cone-rod dystrophy and amelogenesis imperfecta may originate from abnormal ion homeostasis.

The genetic basis of inherited anomalies of the teeth. Part 2: syndromes with significant dental involvement

Teeth are specialized structural components of the craniofacial skeleton. Developmental defects occur either alone or in combination with other birth defects. In this paper, we review the dental anomalies in several multiple congenital anomaly (MCA) syndromes, in which the dental component is pivotal in the recognition of the phenotype and/or the molecular basis of the disorder is known. We will consider successively syndromic forms of amelogenesis imperfecta or enamel defects, dentinogenesis imperfecta (i.e. osteogenesis imperfecta) and other dentine anomalies. Focusing on dental aspects, we will review a selection of MCA syndromes associated with teeth number and/or shape anomalies. A better knowledge of the dental phenotype may contribute to an earlier diagnosis of some MCA syndromes involving teeth anomalies. They may serve as a diagnostic indicator or help confirm a syndrome diagnosis.

A novel autosomal-recessive mutation, whitish chalk-like teeth, resembling amelogenesis imperfecta, maps to rat chromosome 14 corresponding to human 4q21

A rat mutant, whitish chalk-like teeth (wct), with white, chalk-like abnormal incisors, was discovered and morphologically and genetically characterized. The mutant rats showed tooth enamel defects that were similar to those of human amelogenesis imperfecta. The wct mutation was found to disturb the morphological transition of ameloblasts from secretory to maturation stages and to induce cyst formation. This mutation also disturbs the transfer of iron into the enamel, resulting in the whitish chalk-like incisors. A genetic linkage study indicated that the wct locus maps to a specific interval of rat chromosome 14 between D14Got13 and D14Wox2. Interestingly, the human chromosomal region orthologous to wct, a 5.5-Mb interval in human chromosome 4q21, is a critical region for the locus of human amelogenesis imperfecta AIH2. These results strongly suggest that this wct mutant is a useful model for the identification of genes responsible for amelogenesis imperfecta and molecular mechanisms of tooth development.

Amelogenesis imperfecta

Amelogenesis imperfecta (AI) represents a group of developmental conditions, genomic in origin, which affect the structure and clinical appearance of enamel of all or nearly all the teeth in a more or less equal manner, and which may be associated with morphologic or biochemical changes elsewhere in the body. The prevalence varies from 1:700 to 1:14,000, according to the populations studied. The enamel may be hypoplastic, hypomineralised or both and teeth affected may be discoloured, sensitive or prone to disintegration. AI exists in isolation or associated with other abnormalities in syndromes. It may show autosomal dominant, autosomal recessive, sex-linked and sporadic inheritance patterns. In families with an X-linked form it has been shown that the disorder may result from mutations in the amelogenin gene, AMELX. The enamelin gene, ENAM, is implicated in the pathogenesis of the dominant forms of AI. Autosomal recessive AI has been reported in families with known consanguinity. Diagnosis is based on the family history, pedigree plotting and meticulous clinical observation. Genetic diagnosis is presently only a research tool. The condition presents problems of socialisation, function and discomfort but may be managed by early vigorous intervention, both preventively and restoratively, with treatment continued throughout childhood and into adult life. In infancy, the primary dentition may be protected by the use of preformed metal crowns on posterior teeth. The longer-term care involves either crowns or, more frequently these days, adhesive, plastic restorations.

Cone rod dystrophies

Cone rod dystrophies (CRDs) (prevalence 1/40,000) are inherited retinal dystrophies that belong to the group of pigmentary retinopathies. CRDs are characterized by retinal pigment deposits visible on fundus examination, predominantly localized to the macular region. In contrast to typical retinitis pigmentosa (RP), also called the rod cone dystrophies (RCDs) resulting from the primary loss in rod photoreceptors and later followed by the secondary loss in cone photoreceptors, CRDs reflect the opposite sequence of events. CRD is characterized by primary cone involvement, or, sometimes, by concomitant loss of both cones and rods that explains the predominant symptoms of CRDs: decreased visual acuity, color vision defects, photoaversion and decreased sensitivity in the central visual field, later followed by progressive loss in peripheral vision and night blindness. The clinical course of CRDs is generally more severe and rapid than that of RCDs, leading to earlier legal blindness and disability. At end stage, however, CRDs do not differ from RCDs. CRDs are most frequently non syndromic, but they may also be part of several syndromes, such as Bardet Biedl syndrome and Spinocerebellar Ataxia Type 7 (SCA7). Non syndromic CRDs are genetically heterogeneous (ten cloned genes and three loci have been identified so far). The four major causative genes involved in the pathogenesis of CRDs are ABCA4 (which causes Stargardt disease and also 30 to 60% of autosomal recessive CRDs), CRX and GUCY2D (which are responsible for many reported cases of autosomal dominant CRDs), and RPGR (which causes about 2/3 of X-linked RP and also an undetermined percentage of X-linked CRDs). It is likely that highly deleterious mutations in genes that otherwise cause RP or macular dystrophy may also lead to CRDs. The diagnosis of CRDs is based on clinical history, fundus examination and electroretinogram. Molecular diagnosis can be made for some genes, genetic counseling is always advised. Currently, there is no therapy that stops the evolution of the disease or restores the vision, and the visual prognosis is poor. Management aims at slowing down the degenerative process, treating the complications and helping patients to cope with the social and psychological impact of blindness.

Progressive cone and cone-rod dystrophies: phenotypes and underlying molecular genetic basis

The cone and cone-rod dystrophies form part of a heterogeneous group of retinal disorders that are an important cause of visual impairment in children and adults. There have been considerable advances made in recent years in our understanding of the pathogenesis of these retinal dystrophies, with many of the chromosomal loci and causative genes having now been identified. Mutations in 12 genes, including GUCA1A, peripherin/RDS, ABCA4 and RPGR, have been described to date; and in many cases detailed functional assessment of the effects of the encoded mutant proteins has been undertaken. This improved knowledge of disease mechanisms has raised the possibility of future treatments for these disorders, for which there are no specific therapies available at the present time.

A novel locus (RP33) for autosomal dominant retinitis pigmentosa mapping to chromosomal region 2cen-q12.1

Retinitis pigmentosa (RP) is a heterogeneous group of progressive degenerative disorders of the retina with a strong genetic component. Here, we report the clinical and genetic findings in a Chinese family in which autosomal dominant RP (adRP) was inherited by 13 affected members in four generations. Using a genome-wide linkage screening approach, a novel disease locus (RP33) was assigned to the long arm of chromosome 2. A maximum multi-point LOD score of 4.69 was reached at marker D2S2222 in 2q11.2. Meiotic recombination events in affected members placed RP33 in a 15.5 cM region between D2S329 and D2S2229. From meiotic recombinations in two unaffected members RP33 was further refined to a 4.8 cM (9.5 Mb) interval flanked by D2S2159 and D2S1343 in chromosomal region 2cen-q12.1. No disease-associated mutations were detected in the candidate genes SEMA4C, CNGA3 or HNK1ST from within the region. MERTK, a known disease gene for autosomal recessive RP located close to RP33 was similarly excluded. Clinically, the family presented relatively late onset of night blindness, gradually decreased visual acuity, progressive loss of peripheral visual field and typical RP fundus changes in the mid-periphery of the retina. In conclusion, a novel locus for adRP has been assigned to chromosomal region 2cen-q12.1, which in the present kindred was associated with a relatively late onset form of the disease.

Rat enamel contains RP59: a new context for a protein from osteogenic and haematopoietic precursor cells

We have recently identified a protein, RP59, in bone marrow cells and young osteoblasts, in cells involved in bone repair and in young erythroblasts and megakaryocytes. Here, we report immunohistochemical data at the light- and electron-microscope level indicating that RP59 is also present in newly secreted tooth enamel of the rat and in ameloblasts, the formative cells. In enamel matrix, RP59 was located proximal to secretory ameloblasts only, i.e. in newly secreted material. Distal enamel and enamel in association with maturation stage ameloblasts were unlabelled. Secretory ameloblasts contained RP59 in the matrix-proximal region including Tomes' processes, post-secretory ameloblasts in the cell-matrix interface. Western blotting of proteins from tooth germs identified RP59 as a band at 90 kD, co-migrating with RP59 from bone marrow and spleen. Antisera versus a chemically synthesised RP59 peptide and versus a bacteria-synthesised protein fragment reacted in the same manner. In situ hybridisation of tooth tissue revealed RP59 RNA specifically in ameloblasts. The reverse transcription/polymerase chain reaction method identified tooth RNA coding for RP59. Sequence analysis indicated that RP59 RNA from tooth and marrow had the same sequence. An internal sequence motif was found in rat RP59 resembling a signal implicated in secretion of the chicken "engrailed" gene product. The findings indicate that RP59 is a genuine product of ameloblasts and that it is secreted in the course of enamel formation together with other matrix components.

Evidence of amelogenesis imperfecta in an early African Homo erectus

The teeth of the Homo erectus child (Garba IV) recovered from Melka Kunture Ethiopia and dated to 1.5 Ma are characterized by generalized enamel dysplasia, reduced enamel radio-opacity, and severe attrition. This combination of features is found in a large group of hereditary, generalized enamel dysplasias known as amelogenesis imperfecta (AI). SEM studies carried out on epoxy replicas of teeth from the Garba IV child, confirmed that the defects noted were developmental and not due to diagenesis. The enamel prism arrangement is abnormal and there are deep vertical furrows lacking enamel on both buccal and lingual surfaces of all molars. The lesions differ from those characteristic of linear enamel hypoplasia that form discrete horizontal lesions or pits within otherwise normal enamel. We propose that the Garba IV child is the earliest example of AI and provides a link between palaeoanthropology and molecular biology in investigations of the evolutionary history of genetic disorders.

Phenotypic diversity and revision of the nomenclature for autosomal recessive amelogenesis imperfecta

PURPOSE

The purpose of this study was to characterize the phenotype in 9 families with autosomal recessive amelogenesis imperfecta (ARAI), and to propose a classification system allowing inclusion and delineation of diverse ARAI phenotypes.

STUDY DESIGN

Nine families with ARAI were evaluated clinically and radiographically. Exfoliated and extracted teeth were examined via light and scanning electron microscopy, with the enamel in one case evaluated by amino acid analysis.

RESULTS

The 9 families demonstrated diverse ARAI phenotypes including localized hypoplastic, generalized thin hypoplastic, hypocalcified and hypomaturation AI types.

CONCLUSIONS

Some ARAI phenotypes observed in this study and reported in the literature cannot be classified using currently accepted ARAI nomenclature. Therefore, we propose a revised nomenclature permitting both classification of all ARAI clinical forms and inclusion of anticipated molecular-based nomenclature, such as now exists for some X-linked and autosomal dominant AI subtypes.