Clinical, Genetic and Orthopedic Characteristics of Desbuquois Dysplasia

Introduction. Desbuquois dysplasia is a rare skeletal dysplasia with an autosomal recessive inheritance, resembling to the group of multiple joint dislocations. The disease is caused by mutations in the CANT1 and XYLT1 genes, the protein products of which are involved in the degradation of proteoglycans, which play an important role in endochondral ossification. The polymorphism of clinical and radiological characteristics and the genetic heterogeneity of Desbuquois dysplasia necessitate the description of the phenotypic characteristics of patients with various types of mutations, which optimize diagnosis. Objective — description of the clinical and radiological characteristics of three Russian patients with Desbuquois dysplasia of types 1 and 2 with remarkable orthopedic manifestation, caused by mutations in the CANT1 and XYLT1 genes. Materials and Methods. Genealogical, clinical, radiographic and genetic data of three unrelated Russian patients aged 2 to 8 years was carried out. Genetic testing was carried out using clinical exome sequencing and methyl-sensitive PCR. Results. Two patients were diagnosed with type 1 disease due to a previously described homozygous mutation in the CANT1 gene: c.898C>T (p.Arg300Cys), and one — type 2 due to heterozygous mutations in the XYLT1 gene. One mutation: c.1651C>T (p.Arg551Cys) was detected during exome sequencing, and the second mutation: expansion of GGC repeats in the promoter region of the gene, revealed by methyl-sensitive PCR of the first exon of the gene. The main clinical signs of the disease were micromelic dwarfism, hypermobility in the joints and specific facial dysmorphisms, radiographic analysis revealed characteristic «monkey wrench» appearance of the proximal femur in all 3 patients, additional ossification center of the second metacarpal, advanced bone age and multiple dislocations in the joints. The patients also had extra-skeletal manifestations (congenital glaucoma, obstructive bronchitis, renal hypoplasia and congenital heart malformations). Conclusion. Genetic heterogeneity and the presence of polymorphism of clinical manifestations make it possible to consider sequencing of the clinical exome as the optimal method for diagnosing Desbuquois dysplasia types 1 and 2. Analysis of the literature and the results of our molecular genetic data indicate the possibility of expansion of the GGC repeat in the XYLT1 gene in patients with clinical manifestations of type 2 Desbuquois dysplasia.