Periodontal Ehlers-Danlos Syndrome Is Caused by Mutations in C1R and C1S, which Encode Subcomponents C1r and C1s of Complement.

Periodontal Ehlers-Danlos syndrome (pEDS) is an autosomal-dominant disorder characterized by early-onset periodontitis leading to premature loss of teeth, joint hypermobility, and mild skin findings. A locus was mapped to an approximately 5.8 Mb region at 12p13.1 but no candidate gene was identified. In an international consortium we recruited 19 independent families comprising 107 individuals with pEDS to identify the locus, characterize the clinical details in those with defined genetic causes, and try to understand the physiological basis of the condition. In 17 of these families, we identified heterozygous missense or in-frame insertion/deletion mutations in C1R (15 families) or C1S (2 families), contiguous genes in the mapped locus that encode subunits C1r and C1s of the first component of the classical complement pathway. These two proteins form a heterotetramer that then combines with six C1q subunits. Pathogenic variants involve the subunit interfaces or inter-domain hinges of C1r and C1s and are associated with intracellular retention and mild endoplasmic reticulum enlargement. Clinical features of affected individuals in these families include rapidly progressing periodontitis with onset in the teens or childhood, a previously unrecognized lack of attached gingiva, pretibial hyperpigmentation, skin and vascular fragility, easy bruising, and variable musculoskeletal symptoms. Our findings open a connection between the inflammatory classical complement pathway and connective tissue homeostasis.

What every clinical geneticist should know about testing for osteogenesis imperfecta in suspected child abuse cases.

Non-accidental injury (NAI) is a major medical concern in the United States. One of the challenges in evaluation of children with unexplained fractures is that genetic forms of bone fragility are one of the differential diagnoses. Infants who present with fractures with mild forms of osteogenesis imperfecta (OI) (OI type I or OI type IV), the most common genetic form of bone disease leading to fractures might be missed if clinical evaluation alone is used to make the diagnosis. Diagnostic clinical features (blue sclera, dentinogenesis imperfecta, Wormian bones on X-rays or positive family history) may not be present or apparent at the age of evaluation. The evaluating clinician faces the decision about whether genetic testing is necessary in certain NAI cases. In this review, we outline clinical presentations of mild OI and review the history of genetic testing for OI in the NAI versus OI setting. We summarize our data of molecular testing in the Collagen Diagnostic Laboratory (CDL) from 2008 to 2014 where NAI was noted on the request for DNA sequencing of COL1A1 and COL1A2. We provide recommendations for molecular testing in the NAI versus OI setting. First, DNA sequencing of COL1A1, COL1A2, and IFITM5 simultaneously and duplication/deletion testing is recommended. If a causative variant is not identified, in the absence of a pathologic clinical phenotype, no additional gene testing is indicated. If a VUS is found, parental segregation studies are recommended.

Homozygosity for a missense mutation in SERPINH1, which encodes the collagen chaperone protein HSP47, results in severe recessive osteogenesis imperfecta.

Osteogenesis imperfecta (OI) is characterized by bone fragility and fractures that may be accompanied by bone deformity, dentinogenesis imperfecta, short stature, and shortened life span. About 90% of individuals with OI have dominant mutations in the type I collagen genes COL1A1 and COL1A2. Recessive forms of OI resulting from mutations in collagen-modifying enzymes and chaperones CRTAP, LEPRE1, PPIB, and FKBP10 have recently been identified. We have identified an autosomal-recessive missense mutation (c.233T>C, p.Leu78Pro) in SERPINH1, which encodes the collagen chaperone-like protein HSP47, that leads to a severe OI phenotype. The mutation results in degradation of the endoplasmic reticulum resident HSP47 via the proteasome. Type I procollagen accumulates in the Golgi of fibroblasts from the affected individual and a population of the secreted type I procollagen is protease sensitive. These findings suggest that HSP47 monitors the integrity of the triple helix of type I procollagen at the ER/cis-Golgi boundary and, when absent, the rate of transit from the ER to the Golgi is increased and helical structure is compromised. The normal 3-hydroxylation of the prolyl residue at position 986 of the triple helical domain of proalpha1(I) chains places the role of HSP47 downstream from the CRTAP/P3H1/CyPB complex that is involved in prolyl 3-hydroxylation. Identification of this mutation in SERPINH1 gives further insight into critical steps of the collagen biosynthetic pathway and the molecular pathogenesis of OI.

Genetic evaluation of suspected osteogenesis imperfecta (OI).

Osteogenesis imperfecta (OI) is probably the most common genetic form of fracture predisposition. The term OI encompasses a broad range of clinical presentations that may be first apparent from early in pregnancies to late in life, reflecting the extent of bone deformity and fracture predisposition at different stages of development or postnatal ages. Depending on the age of presentation, OI can be difficult to distinguish from some other genetic and nongenetic causes of fractures, including nonaccidental injury (abuse). The strategies for evaluation and the testing discussed here provide guidelines for evaluation that should help to distinguish among causes for fracture and bone deformity.