George J. Feldman

Opitz G/BBB syndrome, a defect of midline development, is due to mutations in a new RING finger gene on Xp22

Opitz syndrome (OS) is an inherited disorder characterized by midline defects including hypertelorism, hypospadias, lip-palate-laryngotracheal clefts and imperforate anus. We have identified a new gene on Xp22f MIDI (Midline 1), which is disrupted in an OS patient carrying an X-chromosome inversion and is also mutated in several OS families. MID1 encodes a member of the B-box family of proteins, which contain protein–protein interaction domains, including a RING finger, and are implicated in fundamental processes such as body axis patterning and control of cell proliferation. The association of MID1 with OS suggests an important role for this gene in midline development.

Transcriptional control of human diploid fibroblast collagen synthesis by γ-interferon

Abstract Recombinant γ-interferon (rec γ-IFN) caused potent inhibition of collagen synthesis by cultured confluent human diploid fibroblasts in a dose-dependent manner. Gel electrophoresis of the newly synthesized proteins from the culture media of rec γ-IFN-treated fibroblasts demonstrated a selective depression of procollagen without a significant change in non-collagenous proteins. Dot blot hybridization to a Type I procollagen cDNA probe showed that the inhibition of collagen production was accompanied by a decrease in the levels of collagen mRNA. These results indicate that rec γ-IFN is capable of exerting transcriptional modulation of collagen biosynthesis and suggest that it may play an important role in regulation of normal and pathologic fibrogenesis.

The genetics of fibrodysplasia ossificans progressiva

Fibrodysplasia ossificans progressiva (FOP) is a rare, heritable disorder with infrequent genetic transmission of the condition owing to low reproductive, fitness. The recent identification of several small, additional families with inheritance of classic features of FOP has provided the opportunity to expand positional cloning efforts to identify the mutated gene in FOP through whole-genome linkage nnalyses. Candidate gene studies using both genetic (linkage), and molecular (gene expression) approaches also are contributing to information about the genetic and cellular, causes of FOP.

Fibrodysplasia Ossificans Progressiva, a Heritable Disorder of Severe Heterotopic Ossification, Maps to Human Chromosome 4q27-31

Fibrodysplasia ossificans progressiva (FOP) is a severely disabling, autosomal-dominant disorder of connective tissue and is characterized by postnatal progressive heterotopic ossification of muscle, tendon, ligament, and fascia and by congenital malformation of the great toes. To identify the chromosomal location of the FOP gene, we conducted a genomewide linkage analysis, using four affected families with a total of 14 informative meioses. Male-to-male transmission of the FOP phenotype excluded X-linked inheritance. Highly polymorphic microsatellite markers covering all human autosomes were amplified by use of PCR. The FOP phenotype is linked to markers located in the 4q27-31 region (LOD score 3.10 at recombination fraction 0). Crossover events localize the putative FOP gene within a 36-cM interval bordered proximally by D4S1625 and distally by D4S2417. This interval contains at least one gene involved in the bone morphogenetic protein-signaling pathway.

Opitz G/BBB Syndrome in Xp22: Mutations in the MID1 Gene Cluster in the Carboxy-Terminal Domain

The MID1 gene in Xp22 codes for a novel member of proteins containing a RING finger, B-box, coiled-coil and a conserved C-terminal domain. Initially, three mutations in the C-terminal region were found in patients with Opitz G/BBB syndrome, a defect of midline development. Here we have determined the complete gene structure of the MID1 gene and have analyzed all nine exons for mutations in a set of 40 unrelated Opitz G/BBB patients. We now report six additional mutations all clustered in the carboxy-terminal domain of the MID1 protein. These data suggest that this conserved domain of the B-box proteins may play a fundamental role in the pathogenesis of Opitz syndrome and in morphogenetic events at the midline during blastogenesis.

Linkage exclusion and mutational analysis of the noggin gene in patients with fibrodysplasia ossificans progressiva (FOP)

Fibrodysplasia ossificans progressiva (FOP) is an extremely rare and disabling genetic disorder characterized by congenital malformation of the great toes and by progressive heterotopic endochondral ossification in predictable anatomical patterns. Although elevated levels of bone morphogenetic protein 4 (BMP4) occur in lymphoblastoid cells and in lesional cells of patients with FOP, mutations have not been identified in the BMP4 gene, suggesting that the mutation in FOP may reside in a BMP4‐interacting factor or in another component of the BMP4 pathway. A powerful antagonist of BMP4 is the secreted polypeptide noggin. A recent case report described a heterozygous 42‐bp deletion in the protein‐coding region of the noggin gene of a patient with FOP. In order to determine if noggin mutations are a widespread finding in FOP, we examined 31 families with 1 or more FOP patients. Linkage analysis with an array of highly polymorphic microsatellite markers closely linked to the noggin gene was performed in four classically‐affected multigenerational FOP families and excluded linkage of the noggin locus to FOP (the multipoint lod score was −2 or less throughout the entire range of markers). We sequenced the noggin gene in affected members of all four families, as well as in 18 patients with sporadic FOP, and failed to detect any mutations. Single‐strand conformation polymorphism (SSCP) analysis of 4 of these patients plus an additional 9 patients also failed to reveal any mutations. Among the samples analyzed by SSCP and DNA sequencing was an independently obtained DNA sample from the identical FOP patient previously described with the 42‐bp noggin deletion; no mutation was detected. Examination of the DNA sequences of 20 cloned noggin PCR products, undertaken to evaluate the possibility of a somatic mutation in the noggin gene which could be carried by a small subset of white blood cells, also failed to detect the presence of the reported 42‐bp deletion. We conclude that mutations in the coding region of noggin are not associated with FOP.

Developmental Dysplasia of the Hip: Linkage Mapping and Whole Exome Sequencing Identify a Shared Variant in CX3CR1 in All Affected Members of a Large Multigeneration Family

Developmental dysplasia of the hip (DDH) is a debilitating condition characterized by incomplete formation of the acetabulum leading to dislocation of the femur, suboptimal joint function, and accelerated wear of the articular cartilage resulting in arthritis. DDH affects 1 in 1000 newborns in the United States; there are well‐defined “pockets” of high prevalence in Japan, and in Italy and other Mediterranean countries. Although reasonably accurate for detecting gross forms of hip dysplasia, existing techniques fail to find milder forms of dysplasia. Undetected hip dysplasia is the leading cause of osteoarthritis of the hip in young individuals, causing over 40% of cases in this age group. A sensitive and specific test for DDH has remained a desirable yet elusive goal in orthopedics for a long time. A 72‐member, four‐generation affected family has been recruited, and DNA from its members retrieved. Genomewide linkage analysis revealed a 2.61‐Mb candidate region (38.7–41.31 Mb from the p term of chromosome 3) co‐inherited by all affected members with a maximum logarithm (base 10) of odds (LOD) score of 3.31. Whole exome sequencing and analysis of this candidate region in four severely affected family members revealed one shared variant, rs3732378, that causes a threonine (polar) to methionine (non‐polar) alteration at position 280 in the transmembrane domain of CX3CR1. This mutation is predicted to have a deleterious effect on its encoded protein, which functions as a receptor for the ligand fractalkine. By Sanger sequencing this variant was found to be present in the DNA of all affected individuals and obligate heterozygotes. CX3CR1 mediates cellular adhesive and migratory functions and is known to be expressed in mesenchymal stem cells destined to become chondrocytes. A genetic risk factor that might be among the etiologic factors for the family in this study has been identified, along with other possible aggravating mutations shared by four severely affected family members. These findings might illuminate the molecular pathways affecting chondrocyte maturation and bone formation.

Over‐expression of BMP4 and BMP5 in a child with axial skeletal malformations and heterotopic ossification: A new syndrome

Bone morphogenetic proteins (BMPs) are a highly conserved class of signaling molecules that induce ectopic cartilage and bone formation in vivo. Dysregulated expression of bone morphogenetic protein 4 (BMP4) is found in the cells of patients who have fibrodysplasia ossificans progressiva (FOP), a genetic disorder of axial and appendicular skeletal malformation and progressive heterotopic ossification. Loss of function mutations in the bone morphogenetic protein 5 (bmp5) gene leading to under‐expression of BMP5 cause the murine short ear syndrome, characterized by small malformed ears and a broad range of axial skeletal malformations. We found features reminiscent of both the short ear mouse and FOP in a child with malformed external ears, multiple malformations of the axial skeleton, and progressive heterotopic ossification in the neck and back. We examined BMP mRNA expression in transformed lymphocytes by semi‐quantitative RT‐PCR and protein expression by ELISA assays and immunohistochemistry. Elevated levels of BMP4 and BMP5 mRNA and protein were detected in the patients cells while levels of BMP2 mRNA were unchanged. Our data suggest that dysregulated expression of BMP4 and BMP5 genes is associated with an array of human axial skeletal abnormalities similar to the short ear mouse and FOP.

Variable expression and incomplete penetrance of developmental dysplasia of the hip: clinical challenge in a 71-member multigeneration family.

Developmental dysplasia of the hip is a crippling condition that affects children and adults. Identical twin studies support a strong causative genetic component. Although clinical tests for newborns can detect gross malformations, it is the subtle malformations that are often not detected, resulting in early onset osteoarthritis of the hip in adults. As a first step in identifying the causative mutation, we have recruited the largest documented affected family with 71 members spanning generations. Clinical and radiographic signs of developmental dysplasia of the hip are described, and the diagnostic challenge of identifying affected family members is discussed.Variable expression of disease allele is evident in several members of the family and greatly contributes to the diagnostic challenge facing clinicians.

Linkage Mapping and Whole Exome Sequencing Identify a Shared Variant in CX3CR1 in a Large Multi-Generation Family

Developmental dysplasia of the hip (DDH) is a crippling condition that affects children and adults, with an average incidence of 1-1.5 cases per 1000 live births. It results in disabling arthritis of the hip in up to 60% patients in the 20-40 year age group. There is no accurate diagnostic test available for newborns. The purpose of our study is to develop a sensitive and specific genetic test for DDH by identifying causative mutations. Linkage analysis and whole exome sequencing of 4 severely affected individuals of a 4 generation 71 member family was performed. The damaging rs3732378 variant in the CX3CR1 chemokine receptor was shared by all affected family members and by 15% of 28 sporadic dysplastics.