A second autosomal split hand/split foot locus maps to chromosome 10q24-q25

Syndromic ectrodactyly with severe limb, ectodermal, urogenital, and palatal defects maps to chromosome 19

Congenital limb malformations rank behind only congenital heart disease as the most common birth defects observed in infants. Finding genes that cause defects in human limb patterning should be straightforward but has been limited, in part, by the bewildering spectrum of phenotypes, which are difficult to separate into etiologically distinct disorders. One approach to the identification of relevant genes is to take advantage of unique extended kindreds in which a defect in limb patterning is segregating. Recently, a large Dutch family with ectrodactyly, ectodermal dysplasia, cleft palate, and urogenital defects (EEC) was described by Maas et al. We have studied this kindred and localized a gene causing EEC to a locus on chromosome 19, in a region defined by D19S894 and D19S416. A second extended kindred with EEC does not map to this locus, indicating that EEC is a genetically heterogeneous disorder. Growth and patterning of the limbs, teeth, hair, and genitourinary system are mediated in part by epithelial-mesenchyme inductive interactions. The identification of both the gene causing EEC and its mutation may further elucidate the general signals mediating inductive mechanisms.

Pathogenesis of ectrodactyly in the Dactylaplasia mouse: aberrant cell death of the apical ectodermal ridge

Dactylaplasia, or Dac, was recently mapped to the distal portion of mouse chromosome 19 and shown to be inherited as an autosomal semi-dominant trait characterized by missing central digital rays. The most common locus for human split hand split foot malformation, also typically characterized by missing central digital rays, is 10q25, a region of synteny to the Dac locus. The Dac mouse appears to be an ideal genotypic and phenotypic model for this human malformation syndrome. Several genes lie in this region of synteny, however, only Fibroblast Growth Factor 8, or Fgf-8, has been implicated to have a role in limb development. We demonstrate that the developmental mechanism underlying loss of central rays in Dac limbs is dramatic cell death of the apical ectodermal ridge, or AER. This cell death pattern is apparent in E10.5-11.5 Dac limb buds stained with the supravital dye Nile Blue Sulfate. We demonstrate that Fgf8 expression in wild type limbs colocalizes spatially and temporally with AER cell death in Dac limbs. Furthermore, in our mapping panel, there is an absence of recombinants between Fgf-8 and the Dac locus in 133 backcross progeny with a median linkage estimate of approximately 0.5 cM. Thus, our results demonstrate that cell death of the AER in Dac limbs silences the role of the AER as key regulator of limb outgrowth, and that Fgf-8 is a strong candidate for the cause of the Dac phenotype.

Analysing human developmental abnormalities

About one in forty babies is born with a recognisable congenital anomaly at birth. Rapid progress is being made in recognising the genetic contribution to these defects. From over 2000 likely single gene malformation syndromes in humans the gene has been isolated or mapped in about 10%. Despite the availability of animal models, the study of malformations in humans continues to reveal novel genes and unpredicted functions for known genes. The importance of the study of clinical malformations to the understanding of embryological development in humans and other organisms is discussed and reviewed.

Refined mapping of a gene for split hand-split foot malformation (SHFM3) on chromosome 10q25

Split hand-split foot malformation (SHFM) is a genetically heterogeneous limb developmental defect characterised by the absence of digital rays and syndactyly of the remaining digits. Three disease loci have recently been mapped to chromosomes 7q21 (SHFM1), Xq26 (SHFM2), and 10q25 respectively (SHFM3). We report the mapping of SHFM3 to chromosome 10q25 in two large SHFM families of French ancestry (Zmax for the combined families = 6.62 at theta = 0 for marker AFM249wc5 at locus D10S222). Two recombinant events reduced the critical region to a 9 cM interval (D10S1709-D10S1663) encompassing several candidate genes including a paired box gene PAX2 (Zmax = 5.35 at theta = 0). The fibroblast growth factor 8 (FGF 8), the retinol binding protein (RBP4), the zinc finger protein (ZNF32), and the homeobox genes HMX2 and HOX11 are also good candidates by both their position and their function.

A split hand-split foot (SHFM3) gene is located at 10q24-->25

The split hand-split foot (SHSF) malformation affects the central rays of the upper and lower limbs. It presents either as an isolated defect or in association with other skeletal or non-skeletal abnormalities. An autosomal SHSF locus (SHFM1) was previously mapped to 7q22.1. We report the mapping of a second autosomal SHSF locus to 10q24-->25. A panel of families was tested with 17 marker loci mapped to the 10q24-->25 region. Maximum lod scores of 3.73, 4.33 and 4.33 at a recombination fraction of zero were obtained for the loci D10S198, PAX2 and D10S1239, respectively. An 19 cM critical region could be defined by haplotype analysis and several genes with a potential role in limb morphogenesis are located in this region. Heterogeneity testing indicates the existence of at least one additional autosomal SHSF locus.