Physical mapping of the t(12;22) translocation breakpoints in a family with a complex type of 3/3'/4 synpolydactyly

Cenani–Lenz syndactyly in a patient with features of Kabuki syndrome

We report a 5 9/12-year-old male with Cenani-Lenz syndactyly (CLS). He presented with three malformed digits on each hand and bilateral 2,3 partial cutaneous toe syndactyly. The expression of this presumed autosomal recessive disorder is variable and has been confused with split hand foot malformation (SHFM). Not all CLS patients show the typical 'spoon hand' configuration originally described. Affected CLS patients show a disorganized appearance of the phalanges with some degree of syndactyly/oligodactyly, in addition to metacarpal and carpal fusions. Radioulnar synostosis may be present. Cases lacking radioulnar synostosis may show proximal dislocation of the radial heads. The distal limb anomalies seen in our patient resemble other reported CLS patients. Radiographic evaluation showed a disorganized appearance of the phalanges, a 'kissing delta phalanx' of one proximal phalanx, metacarpal fusions, carpal coalitions and posterior subluxation of the radial heads. Clinical examination revealed features suggestive of Kabuki syndrome including large, prominent ears, sparse, medially flared and arched eyebrows, wide palpebral fissures, long eyelashes, and oligodontia with flat head 'screwdriver-shaped' incisors, in addition to persistent finger and thumb-tip pads. The faces of CLS patients are rarely shown or described. However, some patients in published reports have large, prominent ears. A recent report suggested midfacial dysmorphism in two patients with CLS (). Although the findings of CLS with features of Kabuki syndrome in our patient may be coincidental, the faces of CLS patients need to be carefully evaluated and described to determine if there is a distinctive accompanying facial phenotype.

Mild facial dysmorphism and quasidominant inheritance in Cenani-Lenz syndrome

Cenani-Lenz syndrome (CLS; MIM 212780) is a rare autosomal recessive syndactyly/synostosis syndrome. No facial dysmorphism was previously noted. We studied two families; in the first an affected female had a previously affected brother and her father was said to have been similarly affected. Extensive inbreeding in this family suggests quasidominant inheritance. In the second family there was a history of a similarly affected sib who, in addition, had genital anomalies and cleft palate. The parents were first cousins. Both probands had similar mild facial dysmorphism; a high broad, prominent forehead, hypertelorism, a depressed nasal bridge, downslanting palpebral fissures, a short nose, a short prominent philtrum and malar hypoplasia. The present report suggests mild facial dysmorphism and quasidominant inheritance in one family with Cenani-Lenz syndrome.

The fibulin-1 gene (FBLN1) is disrupted in a t(12;22) associated with a complex type of synpolydactyly

Molecular analysis of the reciprocal chromosomal translocation t(12;22)(p11.2;q13.3) cosegregating with a complex type of synpolydactyly showed involvement of an alternatively spliced exon of the fibulin-1 gene (FBLN1 located in 22q13.3) and the C12orf2 (HoJ-1) gene on the short arm of chromosome 12. Investigation of the possible functional involvement of the fibulin-1 protein (FBLN1) in the observed phenotype showed that FBLN1 is expressed in the extracellular matrix (ECM) in association with the digits in the developing limb. Furthermore, fibroblasts derived from patients with the complex type of synpolydactyly displayed alterations in the level of FBLN1-D splice variant incorporated into the ECM and secreted into the conditioned culture medium. By contrast, the expression of the FBLN1-C splice variant was not perturbed in the patient fibroblasts. Based on these findings, we propose that the t(12;22) results in haploinsufficiency of the FBLN1-D variant, which could lead to the observed limb malformations.

Molecular cloning and characterization of DEC2, a new member of basic helix-loop-helix proteins

DEC1 is a basic helix-loop-helix (bHLH) protein related to Drosophila Hairy, Enhancer of split and HES, and involved in the control of proliferation and/or differentiation of chondrocytes, neurons, etc. We report here the identification and characterization of human, mouse and rat DEC2, a novel member of the DEC subfamily. DEC2 had high (97%) and moderate (52%) similarities in the bHLH region and the Orange domain with DEC1, respectively. However, DEC2, but not DEC1, had alanine and glycine-rich regions in the C-terminal half. Unlike Hairy, Enhancer of split and HES, DEC2 lacked the WRPW motif for interaction with the corepressor Groucho. The DEC2 gene was mapped to human chromosome 12p11.23-p12.1, mouse chromosome 6 G2-G3 and rat chromosome 4q43 distal-q4, where the conserved linkage homology has been identified among these species. Unlike DEC1, which was broadly expressed in many tissues, DEC2 showed a more restricted pattern of mRNA expression. The DEC subfamily proteins may play an important role in tissue development.

A novel human processed gene, DAD-R, maps to 12p12 and is expressed in several organs

A cDNA of a processed gene of human DAD-1 (defender against apoptotic cell death) was cloned from the human neuroblastoma cell line SH-SY5Y. The genomic sequence of this novel processed gene, DAD-R, lacked introns and was flanked by 8 bp terminal repeats. RT-PCR showed that the transcript is expressed predominantly in testis, ovaries, pancreas, lung and skeletal muscle. DAD-R has several possible initiation codons, one of them producing an open reading frame comprising 75% of the DAD-1 gene. We determined the chromosomal localization of DAD-R as 12p11.2-12p12.1, an area linked to familial synpolydactyly and frequently amplified in a variety of cancers, including those of testis, ovaries, pancreas and lungs.