Genetic analysis of seven pateints with Hereditary Multiple Osteochondromas (HMO)

Abstract

Background: HMO (Hereditary Multiple Osteochondroma), an uncommon autosomal dominant disorder, is characterized by the development of multiple osteochondromas, which are nonmalignant cartilage-capped bone tumors growing outwards from long bone metaphyses.

Methods: The present work retrospectively analyzed seven children with HMO who were enrolled for routine clinical diagnosis and treatment, including X-ray examination. Subsequent genetic detection was carried out using whole exome sequencing (WES). In addition, this work applied Sanger sequencing to be the validation approach. Moreover, this work also examined amino acid (AA) evolutionary conservatism under the influence of certain missense variants.

Results: The clinical indications of all seven patients and their family members were thoroughly indexed. WES identified diagnostic variants in the EXT1 or EXT2 gene in these patients. In these variants, four were reported for the first time, namely EXT1: c.1285-2A>T, EXT2: c.1139delT, EXT1: c.203G>A, and EXT1: c.1645_1673del. Familial validation revealed that three of the variants were hereditary, while the other four were de novo, which was consistent with the phenotype in each case.

Conclusion: Our results expanded HMO variation spectrum, and laid certain foundations for the precise counseling of those affected families.

Keywords: EXT1 gene; EXT2 gene; Hereditary multiple osteochondromas; Novel mutation; Whole-exome sequencing.

Figure 1

Clinical manifestations of the HMO patients (Part I). Case 1: the X-ray images of the patient’s hip (A), tibiofibulas (B), knees (C) and right forearm (D) showing multiple exostoses. Case 2: the X-ray images of the patient’s both humerus (E, F), knees (G), and left scapula (H) with multiple exostoses. (The red circle indicates rare lesion) Case 3: the X-ray images of the patient’s hip (I), tibiofibulas and knees (J), both arms (K, L) showing multiple exostoses at the metaphysis of long bones.

Figure 2

Clinical manifestations of the HMO patients (Part II). Case 4: the X-ray images of the patient’s hip (A), tibiofibulas and knees (B, front; C, side) with exostoses at the metaphysis regions. Case 5: the X-ray images of the patient’s stem (D, scoliosis), hip (E), knees (F), tibiofibulas (G) and left palm (H) showing multiple exostoses. (The red circle indicates rare lesion) Case 6: the X-ray images of the patient’s upper arms (I, J), tibiofibulas and knees (K) and knees (L, M) showing exostoses at the metaphysis regions. Case 7: the X-ray images of the patient’s hip (N), tibiofibulas (O), knees (P, backwards), left knee (Q, side) and left forearm (R) with multiple exostoses.

Figure 3

The pedigree diagrams, genetic variants, and the corresponding carrying status in each family. Case 1: the pedigree diagram (A), and the Sanger peak image of EXT1:c.1285-2A>T variant (B). Case 2: the pedigree diagram (C), and the Sanger peak image of EXT2: c.1139delT variant (D). Case 3: the pedigree diagram (E) and bam image of EXT1: c.1016G>A variant (F); (G) the evolutionary conservatism of the EXT1: G339 residue among species. Case 4: the pedigree diagram (H), and bam image of EXT1: c.203G>A variant (I). Case 5: the pedigree diagram (J), and Sanger peak image of EXT1: c.963-1G>T variant (K). Case 6: the pedigree diagram (L), and Sanger peak image of EXT1: c.1469delT variant (M). Case 7: the pedigree diagram (N), and Sanger peak image of EXT1: c.1645_1673del variant (O). Black arrows indicate probands, and red arrows or boxes indicate mutation sites.