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Microdeletion Syndromes
Published in Merlin G. Butler, F. John Meaney, Genetics of Developmental Disabilities, 2019
Gopalrao V. N. Velagaleti, Nancy J. Carpenter
Most subjects with LGS are sporadic, although a few familial cases showing an autosomal dominant pattern of inheritance have been reported (66,67). Langer–Giedion syndrome is associated with deletions of the long arm of chromosome 8 which are usually visible by conventional cytogenetic analysis. Early reports of patients included those with terminal and interstitial deletions involving the 8q22–q24 region (68). In 1984, Buhler and Malik (69) reported the shortest region of overlap of the deletions as part of band q24.1. This finding was subsequently confirmed by reports of other patients with small interstitial deletions (70,71). Deletion maps were subsequently constructed for the 8q23-q24 region using polymorphic DNA markers (72,73). A study by Ludecke et al. (74) of chromosome abnormalities in TRPS1 patients using YAC cloning, Southern blotting, PCR analysis, and FISH analysis demonstrated that the TRPS1 gene was located about 1000 kb from a gene for HME. Because patients with LGS have deletions encompassing both genes, LGS is a true contiguous gene syndrome and is not due to the pleiotropic effects of a single gene. Subsequently, the genes EXT1 and TRPS1 were cloned (75,76), and mutations in these genes were reported in patients with HME and TRPS1 (77).
Molecular Genetics of Cleidocranial Dysplasia
Published in Fetal and Pediatric Pathology, 2021
Jamshid Motaei, Arash Salmaninejad, Ebrahim Jamali, Imaneh Khorsand, Mohammad Ahmadvand, Sasan Shabani, Farshid Karimi, Mohammad Sadegh Nazari, Golsa Ketabchi, Fatemeh Naqipour
Supernumerary teeth are usually associated with genetic syndromes. Several genes have been identified, including RUNX2, TRPS1, NHS, APC, and EVC [43]. However, the etiology of ST is not clear. The most common syndrome associated with supernumerary tooth is CCD [52], approximately 94% of CCD patients have dental anomalies, including ST. Dental abnormalities in CCD include delayed or failure of eruption of teeth, especially the permanent teeth, retention of primary teeth, crown and root abnormalities, high arched palate, underdevelopment of maxilla, delayed or no mandibular symphysis ossification, multiple impacted permanent teeth and also multiple supernumerary teeth [4,57]. Dentin formation (primary and permanent teeth) is normal, although there are problems in shedding of deciduous teeth and eruption of permanent teeth [44]. The reasons for delayed or failure eruption of permanent teeth in CCD are absence of cellular cementum at the root apex, decreased alkaline phosphatase levels and mechanical obstruction [57,58]. The presence of multiple ST in CCD may cause mechanical obstruction and may be a major factor for the impaction of permanent teeth [59].