F syndrome (acropectorovertebral syndrome) is a dominantly inherited skeletal dysplasia affecting the hands, feet, sternum, and lumbosacral spine, which has previously been described in only two families. Here we report a six generation Turkish family with a related but distinct dominantly inherited acropectoral syndrome. All 22 affected subjects have soft tissue syndactyly of all fingers and all toes and 14 also have preaxial polydactyly of the hands and/or feet. In addition, 14 have a prominent upper sternum and/or a blind ending, inverted U shaped sinus in the anterior chest wall. Linkage studies and haplotype analysis carried out in 16 affected and nine unaffected members of this family showed that the underlying locus maps to a 6.4 cM interval on chromosome 7q36, between EN2 and D7S2423, a region to which a locus for preaxial polydactyly and triphalangeal thumb-polysyndactyly has previously been mapped. Our findings expand the range of phenotypes associated with this locus to include total soft tissue sy ndactyly and sternal deformity, and suggest that F syndrome may be another manifestation of the same genetic entity. In mice, ectopic expression of the gene Sonic hedgehog (Shh) in limb buds and lateral plate mesoderm during development causes preaxial polydactyly and sternal defects respectively, suggesting that misregulation of SHH may underlie the unusual combination of abnormalities in this family. A recently proposed candidate gene for 7q36 linked preaxial polydactyly is LMBR1, encoding a novel transmembrane receptor which may be an upstream regulator of SHH.
(F Med Genet 2001;38:304-309)
Keywords: preaxial polydactyly; sternal deformity; F syndrome; chromosome 7q36
F syndrome or acropectorovertebral syndrome (OMIM 102510) is a rare, dominantly inherited skeletal dysplasia affecting the distal limbs, sternum, and lumbosacral spine. It was first described in 1969 in eight members of a four generation American family whose surname began with the letter F  and has only once been reported since, in an Italian father and daughter.  In the hands, the malformation primarily involves the thumbs and index fingers, which are short, deformed, often partially duplicated, and joined by soft tissue webbing and sometimes a bony bridge. The capitate and hamate are invariably fused and other carpals are frequently fused as well. In the feet, there is soft tissue webbing between the toes, especially the first and second, occasional postaxial polydactyly, and hypoplasia, deformity, and fusion of the metatarsals, especially the first and second and the fourth and fifth. The talus and navicular are invariably fused, and there are also extensive fusions of most other tarsals. In the che st, there is characteristically a prominent upper sternum, with pectus excavatum of the lower sternum, while in the spine there is often spina bifida occulta of L5 and/or S1. The minor craniofacial anomalies and mild intellectual impairment observed in some affected members of the original family probably do not form part of the syndrome.
Here we report a large six generation Turkish family (fig 1) with a related but distinct combination of distal limb and sternal abnormalities, also inherited in an autosomal dominant...
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