👤 Margharita Silengo

Tricho-rhino-phalangeal syndrome (TRPS) is characterized by craniofacial and skeletal abnormalities, and subdivided in TRPS I, caused by mutations in TRPS1, and TRPS II, caused by a contiguous gene deletion affecting (amongst others) TRPS1 and EXT1. We performed a collaborative international study to delineate phenotype, natural history, variability, and genotype-phenotype correlations in more detail. We gathered information on 103 cytogenetically or molecularly confirmed affected individuals. TRPS I was present in 85 individuals (22 missense mutations, 62 other mutations), TRPS II in 14, and in 5 it remained uncertain whether TRPS1 was partially or completely deleted. Main features defining the facial phenotype include fine and sparse hair, thick and broad eyebrows, especially the medial portion, a broad nasal ridge and tip, underdeveloped nasal alae, and a broad columella. The facial manifestations in patients with TRPS I and TRPS II do not show a significant difference. In the limbs the main findings are short hands and feet, hypermobility, and a tendency for isolated metacarpals and metatarsals to be shortened. Nails of fingers and toes are typically thin and dystrophic. The radiological hallmark are the cone-shaped epiphyses and in TRPS II multiple exostoses. Osteopenia is common in both, as is reduced linear growth, both prenatally and postnatally. Variability for all findings, also within a single family, can be marked. Morbidity mostly concerns joint problems, manifesting in increased or decreased mobility, pain and in a minority an increased fracture rate. The hips can be markedly affected at a (very) young age. Intellectual disability is uncommon in TRPS I and, if present, usually mild. In TRPS II intellectual disability is present in most but not all, and again typically mild to moderate in severity. Missense mutations are located exclusively in exon 6 and 7 of TRPS1. Other mutations are located anywhere in exons 4-7. Whole gene deletions are common but have variable breakpoints. Most of the phenotype in patients with TRPS II is explained by the deletion of TRPS1 and EXT1, but haploinsufficiency of RAD21 is also likely to contribute. Genotype-phenotype studies showed that mutations located in exon 6 may have somewhat more pronounced facial characteristics and more marked shortening of hands and feet compared to mutations located elsewhere in TRPS1, but numbers are too small to allow firm conclusions. Show less

Hereditary multiple exostosis represents the most frequent bone tumor disease in humans. It consists of cartilage deformities affecting the juxta-ephyseal region of long bones. Usually benign, exostosis could degenerate in malignant chondrosarcoma form in less than 5% of the cases. Being caused by mutations in the predicted tumor suppressor genes, EXT1 (chr 8q23-q24) and EXT2 (chr 11p11-p12) genes, HMEs are usually inherited with an autosomal dominant pattern, although "de novo" cases are not infrequent. Here we present our genetic diagnostic report on the largest Southern Italy cohort of HME patients consisting of 90 subjects recruited over the last 5years. Molecular screening performed by direct sequencing of both EXT1 and EXT2 genes, by MLPA and Array CGH analyses led to the identification of 66 mutations (56 different occurrences) and one large EXT2 deletion out of 90 patients (74.4%). The total of 21 mutations (20 different occurrences, 33.3%) and the EXT2 gene deletion were novel. In agreement with literature data, EXT1 gene mutations were scattered along all the protein sequence, while EXT2 lesions fell in the first part of the protein. Conservation, damaging prediction and 3-D modeling, in-silico, analyses, performed on three novel missense variants, confirmed that at least in two cases the novel aminoacidic changes could alter the structure stability causing a strong protein misfolding. Here we present 20 novel EXT1/EXT2 mutations and one large EXT2 deletion identified in the largest Southern Italy cohort of patients affected by hereditary multiple exostosis. Show less