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Case Report: Exome Sequencing Identified a Novel Compound Heterozygous Variation in PLOD2 Causing Bruck Syndrome Type 2.

ABSTRACT: Bruck Syndrome (BRKS) is a rare type of recessive osteogenesis imperfecta (OI) and consists of two subtypes, BRKS1 and BRKS2, which are caused by variations in FKBP10 and PLOD2 genes, respectively. In this study, a family that had experienced multiple miscarriages and recurrent fetal skeletal dysplasia was recruited for the purpose of a multiplatform laboratory investigation. Prenatal genetic testing with whole-exome sequencing (WES) identified a compound heterozygous variation in the PLOD2 gene with two variants, namely c.2038C>T (p.R680^*) and c.191_201+3 delATACTGTGAAGGTA (p.Y64Cfs^*12). The amino acids affected by the two variants maintained conserved across species. And the result of immunohistochemistry (IHC) indicated that the expression of PLOD2 protein in the proband's osteochondral tissue was significantly decreased. These findings in our study expanded the variation spectrum of PLOD2 gene, provided solid evidence for the family's counseling in regard to future pregnancies, strongly supported the application of WES in prenatal diagnosis, and might give insight into the understanding of PLOD2 function.

SUBMITTER: Zhang J

PROVIDER: S-EPMC7921790 | biostudies-literature | 2021

REPOSITORIES: biostudies-literature

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Case Report: Exome Sequencing Identified a Novel Compound Heterozygous Variation in PLOD2 Causing Bruck Syndrome Type 2.

Zhang Jing J Hu Huaying H Mu Weihong W Yu Mei M Chen Wenqi W Mi Dongqing D Yang Kai K Guo Qing Q

Frontiers in genetics 20210216

Bruck Syndrome (BRKS) is a rare type of recessive osteogenesis imperfecta (OI) and consists of two subtypes, BRKS1 and BRKS2, which are caused by variations in FKBP10 and PLOD2 genes, respectively. In this study, a family that had experienced multiple miscarriages and recurrent fetal skeletal dysplasia was recruited for the purpose of a multiplatform laboratory investigation. Prenatal genetic testing with whole-exome sequencing (WES) identified a compound heterozygous variation in ...[more]

PMID: 33664768

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Project description:Bruck syndrome (BRKS) is the rare disorder that features congenital joint contractures often with pterygia and subsequent fractures, also known as osteogenesis imperfecta (OI) type XI (OMIM # 610968). Its two forms, BRKS1 (OMIM # 259450) and BRKS2 (OMIM # 609220), reflect autosomal recessive (AR) inheritance of FKBP10 and PLOD2 loss-of-function mutations, respectively. A 10-year-old girl was referred with blue sclera, osteopenia, poorly-healing fragility fractures, Wormian skull bones, cleft soft palate, congenital fusion of cervical vertebrae, progressive scoliosis, bell-shaped thorax, restrictive and reactive pulmonary disease, protrusio acetabuli, short stature, and additional dysmorphic features without joint contractures. Iliac crest biopsy after alendronate treatment that improved her bone density revealed low trabecular connectivity, abundant patchy osteoid, and active bone formation with widely-spaced tetracycline labels. Chromosome 22q11 deletion analysis for velocardiofacial syndrome, COL1A1 and COL1A2 sequencing for prevalent types of OI, and Sanger sequencing of LRP5, PPIB, FKBP10, and IFITM5 for rare pediatric osteoporoses were negative. Copy number microarray excluded a contiguous gene syndrome. Instead, exome sequencing revealed two missense variants in PLOD2 which encodes procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (lysyl hydroxylase 2, LH2); exon 8, c.797G>T, p.Gly266Val (paternal), and exon 12, c.1280A>G, p.Asn427Ser (maternal). In the Exome Aggregation Consortium (ExAC) database, low frequency (Gly266Val, 0.0000419) and absence (Asn427Ser) implicated both variants as mutations of PLOD2. The father, mother, and sister (who carried the exon 12 defect) were reportedly well with normal parental DXA findings. BRKS2, characterized by under-hydroxylation of type I collagen telopeptides compromising their crosslinking, has been reported in at least 16 probands/families. Most PLOD2 mutations involve exons 17-19 (of 20 total) encoding the C-terminal domain with LH activity. However, truncating defects (nonsense, frameshift, splice site mutations) are also found throughout PLOD2. In three reports, AR PLOD2 mutations are not associated with congenital contractures. Our patient's missense defects lie within the central domain of unknown function of PLOD2. In our patient, compound heterozygosity with PLOD2 mutations is associated with a clinical phenotype distinctive from classic BRKS2 indicating that when COL1A1 and COL1A2 mutation testing is negative for OI without congenital contractures or pterygia, atypical BRKS should be considered.

Project description:Bruck syndrome (BS) is a congenital disorder characterized by joint flexion contractures, skeletal dysplasia, and increased bone fragility, which overlaps clinically with osteogenesis imperfecta (OI). On a genetic level, BS is caused by biallelic mutations in either FKBP10 or PLOD2. PLOD2 encodes the lysyl hydroxylase 2 (LH2) enzyme, which is responsible for the hydroxylation of cross-linking lysine residues in fibrillar collagen telopeptide domains. This modification enables collagen to form chemically stable (permanent) intermolecular cross-links in the extracellular matrix. Normal bone collagen develops a unique mix of such stable and labile lysyl-oxidase-mediated cross-links, which contribute to bone strength, resistance to microdamage, and crack propagation, as well as the ordered deposition of mineral nanocrystals within the fibrillar collagen matrix. Bone from patients with BS caused by biallelic FKBP10 mutations has been shown to have abnormal collagen cross-linking; however, to date, no direct studies of human bone from BS caused by PLOD2 mutations have been reported. Here the results from a study of a 4-year-old boy with BS caused by compound heterozygous mutations in PLOD2 are discussed. Diminished hydroxylation of type I collagen telopeptide lysines but normal hydroxylation at triple-helical sites was found. Consequently, stable trivalent cross-links were essentially absent. Instead, allysine aldol dimeric cross-links dominated as in normal skin collagen. Furthermore, in contrast to the patient's bone collagen, telopeptide lysines in cartilage type II collagen cross-linked peptides from the patient's urine were normally hydroxylated. These findings shed light on the complex mechanisms that control the unique posttranslational chemistry and cross-linking of bone collagen, and how, when defective, they can cause brittle bones and related connective tissue problems. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Dataset Information

Case Report: Exome Sequencing Identified a Novel Compound Heterozygous Variation in PLOD2 Causing Bruck Syndrome Type 2.

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Case Report: Exome Sequencing Identified a Novel Compound Heterozygous Variation in <i>PLOD2</i> Causing Bruck Syndrome Type 2.

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