Deactivating Germline Mutations in LEMD3 Cause Osteopoikilosis and Buschke-Ollendorff Syndrome, but Not Sporadic Melorheostosis

Abstract

Autosomal dominant OPK and BOS feature widespread foci of osteosclerotic trabeculae without or with skin lesions, respectively. Occasionally, a larger area of dense bone in OPK or BOS resembles MEL, a sporadic sclerosing disorder primarily involving cortical bone. Others, finding deactivating germline LEMD3 mutations in OPK or BOS, concluded such defects explain all three conditions. We found germline LEMD3 mutations in OPK and BOS but not in sporadic MEL. Introduction:In 2004, others discovered that heterozygous, loss-of-function, germline mutations in the LEMD3 gene (LEMD3 or MAN1) cause both osteopoikilosis (OPK) and Buschke-Ollendorff syndrome (BOS). OPK is an autosomal dominant, usually benign, skeletal dysplasia featuring multiple, small, especially metaphyseal, oval or round, dense trabecular foci distributed symmetrically throughout the skeleton. BOS combines OPK with connective tissue nevi comprised of collagen and elastin. In some OPK and BOS families, an individual may have relatively large, asymmetric areas of dense cortical bone interpreted as melorheostosis (MEL). MEL, however, classically refers to a sporadic, troublesome skeletal dysostosis featuring large, asymmetric, "flowing hyperostosis" of long bone cortices often with overlying, constricting soft tissue abnormalities. However, a heterozygous germline mutation in LEMD3 was offered to explain MEL. Materials and Methods: We studied 11 unrelated individuals with sclerosing bone disorders where LEMD3 mutation was a potential etiology: familial OPK (1), familial BOS (2), previously reported familial OPK with MEL (1), sporadic MEL (3), sporadic MEL with mixed-sclerosing-bone dystrophy (1), and patients with other unusual sclerosing bone disorders (3). All coding exons and adjacent mRNA splice sites for LEMD3 were amplified by PCR and sequenced using genomic DNA from leukocytes. We did not study lesional tissue from bone or skin. Results: In the OPK family, a heterozygous nonsense mutation (c.1433T>A, p.L478X) was discovered in exon 1. In the two BOS families, a heterozygous nonsense mutation (exon 1, c.1323C>A, p.Y441X) and a heterozygous frame-shift mutation (exon 1, c.332_333insTC) were identified. In the individual with MEL and familial OPK, a heterozygous nonsense mutation (c.1963C>T, p.R655X) was detected in exon 7. However, no LEMD3 mutation was found for any other patient, including all four with sporadic MEL. Conclusions: We confirm that OPK and BOS individuals, including those with MEL-like lesions, have heterozygous, deactivating, germline LEMD3 mutations. However, MEL remains of unknown etiology.

Case Report: Severe Melorheostosis Involving the Ipsilateral Extremities

“…However, another study did not find mutation in three patients with sporadic melorheostosis [12]. The exact causes remain unclear.…”

Elevated serum lactate dehydrogenase isoenzymes and aspartate transaminase distinguish Albers-Schönberg disease (Chloride Channel 7 Deficiency Osteopetrosis) among the sclerosing bone disorders

“…drome (22) (3), X-linked hypophosphatemia (5), juvenile Paget disease (23) (4), melorheostosis (3), fibrodysplasia ossificans progressiva (3), autosomal-dominant osteosclerosis with brittle teeth (24) (10), osteomesopyknosis (2), and undiagnosed (25) (1).…”

Melorheostosis: Case report of rare disease

“…Kim J-E demonstrated that there is down regulation of adhesion proteins those involved in osteoblastic regulation, specifically transforming growth factor β induced gene product, which helps in the development of hyperostosis and associated soft tissue abnormalities [9] . Another possible aetiology of melorheostosis is a loss of function mutation in the LEMD3 gene, a protein involved in bone morphogenic protein and tumor growth factor-β signalling [10] . Above mentioned both hypothesis support the genetic involvement of the disease so further work have to be done, to find out exact cause and role of gene therapy for this rare disease.…”