Mutations in NOTCH2 in patients with Hajdu–Cheney syndrome

Abstract

Summary The Hajdu–Cheney syndrome is a very rare disease that affects several organ system, leading to severe osteoporosis and other abnormalities. We describe clinical and genetic findings of nine patients with this disease. Introduction The Hajdu–Cheney syndrome (HCS) is a rare autosomal dominant disorder characterized by severe osteoporosis, acroosteolysis of the distal phalanges, renal cysts, and other abnormalities. Recently, heterozygous mutations in NOTCH2 were identified as the cause of HCS. Methods Nine patients with typical presentations of HCS took part in this study: five affected patients from two small families and four sporadic cases. Peripheral blood DNA was obtained and exome sequencing performed in one affected individual per family and in all four sporadic cases. Sanger sequencing confirmed mutations in all patients. Results One of the identified mutations was introduced in a plasmid encoding NOTCH2. Wild-type and mutant NOTCH2 were transiently expressed in HEK293 cells to assess intracellular localization after ligand activation. Deleterious heterozygous mutations in the last NOTCH2 exon were identified in all patients; five of the six mutations were novel. Conclusion Consistent with previous reports, all mutations are predicted to result in a loss of the proline/glutamic acid/serine/threonine sequence, which harbors signals for degradation, therefore suggesting activating mutations. One of the six mutations furthermore predicted disruption of the second nuclear localization signal of NOTCH2, but the mutant revealed normal nuclear localization after transfection, which is consistent with the proposed gain-of-function mechanism as the cause of this autosomal dominant disease. Our findings confirm that heterozygous NOTCH2 mutations are the cause of HCS and expand the mutational spectrum of this disorder.

Anabolic actions of Notch on mature bone

“…Mutations of Notch components are known to cause defects in axial skeletal development. For example, spondylocostal dysostosis results from mutations in human DLL3 (10,11,37,38), a Notch ligand, whereas NOTCH2 mutations alone cause Hagdu-Cheney syndrome, a rare disease characterized by facial abnormalities, acro-osteolysis and, interestingly, osteoporosis (39,40). Mutations of JAG1 and NOTCH2 in concert cause Alagille syndrome, marked by impaired craniofacial development due to somite segmentation defects.…”

The developmental biology of genetic Notch disorders

“…(B) Mutations in NOTCH2 lead to Alagille syndrome (black) or Hajdu-Cheney syndrome (red). Alagille NOTCH2 mutations generally abrogate cysteines in the ligand-binding EGF repeats, or arginines in the ankyrin repeats, while Hajdu-Cheney NOTCH2 mutations are generally frameshift or nonsense mutations that lead to absence of the PEST domain and thus gain of function of NOTCH2 activity (Descartes et al, 2014;Gray et al, 2012;Han et al, 2015;Isidor et al, 2011a,b;Majewski et al, 2011;Narumi et al, 2013;Simpson et al, 2011;Zhao et al, 2013). ANK, ankyrin repeats; DSL, Delta/Serrate/LAG-2 domain; EGF, epidermal growth factor; HD, heterodimerization domain; JSD, Jagged Serrate domain; LNR, Lin-Notch repeats; MNNL, Notch ligand N-terminal domain; NRR, negative regulatory region; PDZL, PDZ ligand domain [PDZ, post synaptic density protein (PSD95)]; PEST, proline (P), glutamic acid (E), serine (S) and threonine (T) degradation domain; RAM, Rbp-associated molecule domain; SP, signal peptide; TAD, transactivation domain; TM, transmembrane domain; vWFC, von Willebrand factor type C domain.…”

Hajdu-Cheney Syndrome, a Disease Associated with NOTCH2 Mutations

“…Exome-wide sequencing of families affected by HCS demonstrated the presence of mutations in exon 34 of NOTCH2 , upstream the PEST domain, which is necessary for the ubiquitination and degradation of NOTCH2. The nonsense mutations or short deletions create a stop codon and the premature termination of the protein product, which is stable and causes a gain-of-NOTCH2 function [52–55]. Because the mutation occurs in the terminal exon of NOTCH2 , there is a reduced capacity to activate the process of nonsense-mediated mRNA decay and NOTCH2 transcript levels are not affected.…”