Case records of the Massachusetts General Hospital. Case 24-2014. A 27-year-old man with severe osteoporosis and multiple bone fractures

Osteogenesis Imperfecta and Split Foot Malformation due to 7q21.2q21.3 Deletion Including COL1A2, DLX5/6 Genes: Review of the Literature

Copy number variation in loss of 7q21 is a genetic disorder characterized by split hand/foot malformation, hearing loss, developmental delay, myoclonus, dystonia, joint laxity, and psychiatric disorders. Osteogenesis imperfecta caused by whole gene deletions of COL1A2 is a very rare condition. We report a Turkish girl with ectrodactyly, joint laxity, multiple bone fractures, blue sclera, early teeth decay, mild learning disability, and depression. A copy number variant in loss of 4.8 Mb at chromosome 7 (q21.2q21.3) included the 58 genes including DLX5, DLX6, DYNC1I1, SLC25A13, SGCE, and COL1A2 . They were identified by chromosomal microarray analysis. We compared the findings in our patients with those previously reported. This case report highlights the importance of using microarray to identify the genetic etiology in patients with ectrodactyly and osteogenesis imperfecta.

Hajdu-Cheney Syndrome: A Systematic Review of the Literature

Hajdu–Cheney syndrome (HCS) is a rare genetic disease that causes acroosteolysis and generalized osteoporosis, accompanied by a series of developmental skeletal disorders and multiple clinical and radiological manifestations. It has an autosomal dominant inheritance, although there are several sporadic non-hereditary cases. The gene that has been associated with Hajdu-Cheney syndrome is NOTCH2. The described phenotype and clinical signs and symptoms are many, varied, and evolve over time. As few as 50 cases of this disease, for which there is currently no curative treatment, have been reported to date. The main objective of this systematic review was to evaluate the results obtained in research regarding Hajdu–Cheney Syndrome. The findings are reported in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines and were registered on the web PROSPERO under the registration number CRD42020164377. A bibliographic search was carried out using the online databases Orphanet, PubMed, and Scielo; articles from other open access sources were also considered. Finally, 76 articles were included, and after their analysis, we have obtained a series of hypotheses as results that will support further studies on this matter.

Osteogenesis Imperfecta Type I Caused by COL1A1 Deletions

Osteogenesis imperfecta (OI) type I is usually caused by COL1A1 stop or frameshift mutations, leading to COL1A1 haploinsufficiency. Here we report on 12 individuals from 5 families who had OI type I due to an unusual cause—heterozygous deletions of the entire COL1A1 gene. The deletions were initially detected by semiconductor-based sequencing of genomic DNA and confirmed by quantitative PCR. Array comparative genomic hybridization in DNA of the index patient in each family showed that deletion size varied from 18.5 kb to 2.23 Mb between families, encompassing between 1 and 47 genes (COL1A1 included). The skeletal phenotype of the affected individuals was similar to that of patients with haploinsufficiency caused by COL1A1 stop or frameshift mutations. However, one individual with a deletion that included also DLX3 and DLX4 had tooth discoloration and bone fragility. Three individuals from 2 families had deletions that included also CACNA1G, and these individuals had learning disabilities. These features are not usually observed in COL1A1 haploinsufficiency, but are in accordance with previously described individuals in whom deletions included the same genes. In summary, we found deletions of COL1A1 in 5 out of 161 families (3 %) with OI type I that were evaluated. Deletions encompassing not only COL1A1 but also neighboring genes can lead to contiguous gene syndromes that may include dental involvement and learning disability.

Hajdu-Cheney syndrome: a review

Hajdu Cheney Syndrome (HCS), Orpha 955, is a rare disease characterized by acroosteolysis, severe osteoporosis, short stature, specific craniofacial features, wormian bones, neurological symptoms, cardiovascular defects and polycystic kidneys. HCS is rare and is inherited as autosomal dominant although many sporadic cases have been reported. HCS is associated with mutations in exon 34 of NOTCH2 upstream the PEST domain that lead to the creation of a truncated and stable NOTCH2 protein with enhanced NOTCH2 signaling activity. Although the number of cases with NOTCH2 mutations reported are limited, it would seem that the diagnosis of HCS can be established by sequence analysis of exon 34 of NOTCH2. Notch receptors are single-pass transmembrane proteins that determine cell fate, and play a critical role in skeletal development and homeostasis. Dysregulation of Notch signaling is associated with skeletal developmental disorders. There is limited information about the mechanisms of the bone loss and acroosteolysis in HCS making decisions regarding therapeutic intervention difficult. Bone antiresorptive and anabolic agents have been tried to treat the osteoporosis, but their benefit has not been established. In conclusion, Notch regulates skeletal development and bone remodeling, and gain-of-function mutations of NOTCH2 are associated with HCS.