Massive gingival hyperplasia preceding dental eruption in I-cell disease

Mannose 6-phosphate-dependent targeting of lysosomal enzymes is required for normal craniofacial and dental development

Mucolipidosis II (MLII) is a severe systemic genetic disorder caused by defects in mannose 6-phosphate-dependent targeting of multiple lysosomal hydrolases and subsequent lysosomal accumulation of non-degraded material. MLII patients exhibit marked facial coarseness and gingival overgrowth soon after birth, accompanied with delayed tooth eruption and dental infections. To examine the pathomechanisms of early craniofacial and dental abnormalities, we analyzed mice with an MLII patient mutation that mimic the clinical and biochemical symptoms of MLII patients. The mouse data were compared with clinical and histological data of gingiva and teeth from MLII patients. Here, we report that progressive thickening and porosity of calvarial and mandibular bones, accompanied by elevated bone loss due to 2-fold higher number of osteoclasts cause the characteristic craniofacial phenotype in MLII. The analysis of postnatal tooth development by microcomputed tomography imaging and histology revealed normal dentin and enamel formation, and increased cementum thickness accompanied with accumulation of storage material in cementoblasts of MLII mice. Massive accumulation of storage material in subepithelial cells as well as disorganization of collagen fibrils led to gingival hypertrophy. Electron and immunofluorescence microscopy, together with (35)S-sulfate incorporation experiments revealed the accumulation of non-degraded material, non-esterified cholesterol and glycosaminoglycans in gingival fibroblasts, which was accompanied by missorting of various lysosomal proteins (α-fucosidase 1, cathepsin L and Z, Npc2, α-l-iduronidase). Our study shows that MLII mice closely mimic the craniofacial and dental phenotype of MLII patients and reveals the critical role of mannose 6-phosphate-dependent targeting of lysosomal proteins for alveolar bone, cementum and gingiva homeostasis.

Severe gingival hyperplasia in a child with I-cell disease

I-cell disease (mucolipidosis II) is a rare metabolic disorder resulting from the deficiency of a specific lysosomal enzyme, N-acetylglucosamine-1-phosphotransferease. The disease presents as a mental and motor developmental delay with oral manifestations that include severe gingival hyperplasia usually seen before one year of age. The life expectancy of children with this condition is poor, with death usually occurring around the fifth year. A case report of a 3-year-old Pakistani male, with I-cell disease, is presented. The chief dental concerns of the parents were his swollen gums and delayed tooth eruption. Supportive treatment only was initiated. Differential diagnosis for severe gingival overgrowth in young patients should take account of this rare metabolic disorder in addition to hereditary and idiopathic fibromatosis and drug associated gingival overgrowth.

Evidence of genetic heterogeneity for hereditary gingival fibromatosis

Hereditary Gingival Fibromatosis (HGF) is the most common genetic form of gingival fibromatosis. The condition is most frequently reported to be transmitted as an autosomal-dominant trait, but autosomal-recessive inheritance has also been reported. The clinical presentation of HGF is variable, both in the distribution (number of teeth involved) and in the degree (severity) of expression. It is unknown if the variable clinical expression of HGF in different families is due to variable expression of a common gene mutation, allelic mutations, or non-allelic mutations. The apparently different modes of Mendelian inheritance of HGF suggest genetic heterogeneity. A gene locus for HGF has been localized to a 37-cM genetic interval on chromosome 2p21-p22 (D2S1352, Zmax = 5.10, theta = 0.00) flanked by D2S1788 and D2S441. To evaluate the generality of this linkage, we tested linkage with 9 markers from this candidate region in another large family, segregating for an autosomal-dominant form of generalized HGF, and found no support for linkage with any of these markers. Furthermore, statistical tests of this apparent heterogeneity were highly significant. Analysis of these data provides direct evidence that at least two genetically distinct loci are responsible for autosomal-dominant hereditary gingival fibromatosis.

Heterogeneity in the gingival fibromatoses

Forty-nine cases of isolated familial and idiopathic gingival fibromatoses, consisting of 12 cases from six families and 37 cases of idiopathic gingival fibromatosis, were reviewed. Pedigrees of five families revealed various penetrances and genetic heterogeneity as suggested by the presence of both autosomal dominant and autosomal recessive inheritances. Ultrastructurally, the lesions were composed of fibroblast-like cells and myofibroblast-like cells, with the former being the predominant cell type. The 267 cases of familial and idiopathic gingival fibromatoses were analyzed, and they with or without hypertrichosis, mental retardation, and/or epilepsy. These included 49 cases seen by the authors, 50 cases from the Japanese literature, and 168 cases from non-Japanese literature. Isolated gingival fibromatosis occurred more frequently after age of 12 years (P less than 0.0074). There was no significant difference in age of onset between generalized and localized forms of the idiopathic gingival fibromatosis. Gingival fibromatosis with hypertrichosis and mental retardation and/or epilepsy occurred frequently before 12 years (P less than 0.069). It has been shown that heterogeneity of the gingival fibromatosis is a result of either histologic heterogeneity, genetic heterogeneity, or a combination with other systemic disorders.

Mannosidosis: isolation and comparison of mannose-containing oligosaccharides from gingiva and urine

Excessive gingival hyperplasia with storage of mannose-rich oligosaccharides appears to be a unique feature present in a 31-year-old mannosidosis patient. Fractionation and analysis of the gingiva established the presence of (Man)2GlcNAc (2.2 mumol/g), (Man)3GlcNAc (3.5 mumol/g), (Man)4GlcNAc (2.8 mumol/g) and higher oligomers (Man)5GlcNAc--(Man)8GlcNAc (0.5 mumol/g); (Man, mannose; GlcNAc, N-acetylglucosamine). Eight characteristic oligosaccharides were isolated from the patient's urine by thin-layer chromatography. The most abundant was (Man)2GlcNAc (161--558 mumol/l); decreasing amounts of higher homologues up to a dekasaccharide, (Man)9GlcNAc (1--4 mumol/l) were also present. In contrast to urine, in which the trisaccharide was predominant, tetrasaccharides and pentasaccharides were more abundant in gingiva.