The gene for pycnodysostosis maps to human chromosome 1cen-q21.

Pycnodysostosis (OMIM 265800) is an autosomal recessive skeletal disorder first described by Maroteaux and Lamy that is characterized by short stature, increased bone density, delayed closure of cranial sutures, loss of the mandibular angle, dysplastic clavicles, dissolution of the terminal phalanges of the hands and feet, dental abnormalities and increased bone fragility. Patients have a typical appearance secondary to prominence of the calvarium, smallness of the facial features, prominent nose and micrognathia. The French painter, Henri de Toulouse Lautrec (1864-1901), is believed to have had the disorder. Although more than 100 cases have been reported, we are aware of only two large consanguinous pedigrees in which the pycnodysostosis disorder segregates. We have studied the segregation of the pycnodysostosis phenotype in a large consanguinous Mexican pedigree, the clinical features of which are very similar to those described in the Arab pedigree studied by Edelson et al. Here, we report linkage for the pycnodysostosis phenotype in the 1cen-q21 region of human chromosome 1, and discuss candidate genes for this skeletal disorder.

Mutations in TWIST, a basic helix-loop-helix transcription factor, in Saethre-Chotzen syndrome.

Saethre-Chotzen syndrome is one of the most common autosomal dominant disorders of craniosynostosis in humans and is characterized by craniofacial and limb anomalies. The locus for Saethre-Chotzen syndrome maps to chromosome 7p21-p22. We have evaluated TWIST, a basic helix-loop-helix transcription factor, as a candidate gene for this condition because its expression pattern and mutant phenotypes in Drosophila and mouse are consistent with the Saethre-Chotzen phenotype. We mapped TWIST to human chromosome 7p21-p22 and mutational analysis reveals nonsense, missense, insertion and deletion mutations in patients. These mutations occur within the basic DNA binding, helix I and loop domains, or result in premature termination of the protein. Studies in Drosophila indicate that twist may affect the transcription of fibroblast growth factor receptors (FGFRs), another gene family implicated in human craniosynostosis. The emerging cascade of molecular components involved in craniofacial and limb development now includes TWIST, which may function as an upstream regulator of FGFRs.

Clinical delineation of a patient with trisomy 1q32.qter and monosomy 5p resulting from a familial translocation 1;5.

We describe a patient who had multiple malformations including ventriculomegaly, colpocephaly, corpus callosum, cerebellum and vermix hypoplasia, optic nerve hypoplasia, corneal opacity and congenital heart disease in whom a trisomy 1q32-qter and monosomy 5p derived from a t(1;5)mat was diagnosed by karyotype and FISH analysis. This trisomy/monosomy association has not been previously reported. The familial analysis of the translocation was carried out in four generations and its implications on the phenotype of the patient and genetic counseling are discussed.

Characterization of the human extracellular matrix protein 1 gene on chromosome 1q21.

Ecm1, the mouse gene encoding extracellular matrix protein 1, is highly expressed in bone and cartilage as well as in osteogenic, preosteoblastic and chondroblastic cell lines. Ecm1 was recently localized to a chromosomal region in mouse syntenic to human chromosome 1q21, establishing this gene as a prime candidate gene for pycnodysostosis, a rare, autosomal recessive sclerosing skeletal dysplasia. Shortly thereafter, it was determined that cathepsin K is the pycnodysostosis gene. We now report the radiation hybrid mapping of human ECM1 to 1q21, and the gene structure and coding sequence of human ECM1.

A fluorimetric method for red blood cell sorbitol dehydrogenase activity.

A new fluorimetric method for the quantification of red blood cell (RBC) sorbitol dehydrogenase is described. It is based on the oxidation of sorbitol to fructose, in presence of NAD+, catalysed by the RBC-sorbitol dehydrogenase. The quantity of NADH formed is then measured in a filter fluorimeter. Comparison with an indirect spectrophotometric assay yielded good correlation; however, the present method offers several advantages: it is more rapid, simple and inexpensive. It should be useful to screen for sorbitol dehydrogenase deficiency in large numbers of individuals, particularly patients with diabetes or cataracts.

Molecular detection or carriers of hemophilia A in Mexican families.

The genomic DNAs of carrier mothers from 20 hemophilia A unrelated Mexican families were analysed by polymerase chain reaction (PCR) amplification of the Bcl I polymorphic region at intron 18 of the factor VIII gene. Eleven women (55%) were found to be informative (Bcl I+/Bcl I-), eight (40%) were Bcl I- homozygotes and one (5%) was a Bcl I+ homozygote. In 18 daughters of the informative families we were able to establish carrier status for eight. The frequency of the Bcl I alleles in the 20 mothers was 0.675 for Bcl I- and 0.325 for Bcl I+ which give a frequency of 44% of heterozygous females in our sample.

Exclusion of the MSX1 homeobox gene as the gene for the Ellis van Creveld syndrome in the Amish.

Ellis van Creveld syndrome (EVC) is an autosomal recessive disorder which has previously been mapped to human chromosome 4p16.1. This disorder is characterized by disproportionate dwarfism, polydactyly, cleft palate, natal teeth, and congenital heart disease. The MSX1 homeobox gene also maps to the 4p16.1 region. Msx gene transcripts in the mouse embryo are known to be involved in pattern formation of the developing limb bud and craniofacial bones. Thus, on the basis of both map location and known gene function, MSX1 was an excellent candidate as the causative gene for EVC. Nonetheless, direct DNA sequencing of both exons of the MSX1 gene in five affected individuals segregating with the EVC phenotype, as well as those of two obligate carriers, revealed no mutations in the coding region of the gene.

A nonsense mutation in the cathepsin K gene observed in a family with pycnodysostosis.

Pycnodysostosis (MIM 265800) is a rare, autosomal recessive skeletal dysplasia characterized by short stature, wide cranial sutures, and increased bone density and fragility. Linkage analysis localized the disease gene to human chromosome 1q21, and subsequently the genetic interval was narrowed to between markers D1S2612 and D1S2345. Expressed sequence tagged markers corresponding to cathepsin K, a cysteine protease highly expressed in osteoclasts and thought to be important in bone resorption, were mapped previously in the candidate region. We have identified a cytosine to thymidine transition at nucleotide 862 (GenBank accession no. S79895) of the cathepsin K coding sequence in the DNA of an affected individual from a large, consanguinous Mexican family. This mutation results in an arginine to STOP alteration at amino acid 241, predicting premature termination of cathepsin K mRNA translation. All affected individuals in this family were homozygous for the mutation, suggesting that this alteration may lead to pycnodysostosis. Recognition of the role of cathepsin K in the etiology of pycnodysostosis should provide insights into the pathogenesis and treatment of other disorders of bone remodeling, including osteoporosis.

Achondroplasia is defined by recurrent G380R mutations of FGFR3.

Genomic DNA from 154 unrelated individuals with achondroplasia was evaluated for mutations in the fibroblast growth factor receptor 3 (FGFR3) transmembrane domain. All but one, an atypical case, were found to have a glycine-to-arginine substitution at codon 380. Of these, 150 had a G-to-A transition at nt 1138, and 3 had a G-to-C transversion at this same position. On the basis of estimates of the prevalence of achondroplasia, the mutation rate at the FGFR3 1138 guanosine nucleotide is two to three orders of magnitude higher than that previously reported for tranversions and transitions in CpG dinucleotides. To date, this represents the most mutable single nucleotide reported in the human genome. The homogeneity of mutations in achondroplasia is unprecedented for an autosomal dominant disorder and may explain the relative lack of heterogeneity in the achondroplasia phenotype.

Localization of the achondroplasia gene to the distal 2.5 Mb of human chromosome 4p.

Achondroplasia has been mapped to 4p16.3 using 18 multigenerational families with achondroplasia and 10 short tandem repeat polymorphic markers from this region. No evidence of genetic heterogeneity was found. Analysis of a recombinant family localizes the achondroplasia locus to the 2.5 Mb region between D4S43 and the telomere. Multipoint linkage analysis favors placement telomeric of D4S412. The establishment of closely linked markers will facilitate positional cloning of the achondroplasia gene and permit prenatal diagnosis of homozygous achondroplasia for at risk couples.

The gene for the Ellis-van Creveld syndrome is located on chromosome 4p16.

Ellis-van Creveld syndrome (EVC) is an autosomal recessive disorder characterized by disproportionate dwarfism, polydactyly, and congenital heart disease. This rare disorder is found with increased frequency among the Old Order Amish community in Lancaster County, Pennsylvania. We have used linkage analysis to localize the gene responsible for the EVC phenotype in nine interrelated Amish pedigrees and three unrelated families from Mexico, Ecuador, and Brazil. We now report the linkage for the Ellis-van Creveld syndrome gene to markers on the distal short arm of human chromosome 4, with Zmax = 6.91 at theta = 0.02 for marker HOX7, in a region proximal to the FGFR3 gene responsible for the achondroplasia phenotype.