Hereditary lymphedema is a developmental disorder characterized by chronic swelling of the extremities due to dysfunction of the lymphatic vessels. Two responsible genes have been identified: the vascular endothelial growth factor receptor 3 (VEGFR3) gene, implicated in congenital lymphedema, or Milroy disease, and the forkhead-related transcription factor gene FOXC2, causing lymphedema-distichiasis. We describe three families with an unusual association of hypotrichosis, lymphedema, and telangiectasia. Using microsatellite analysis, we first excluded both VEGFR3 and FOXC2 as causative genes; we then considered the murine ragged phenotype, caused by mutations in the Sox18 transcription factor, as a likely counterpart to the human disease, because it presents a combination of hair and cardiovascular anomalies, including symptoms of lymphatic dysfunction. Two of the families were consanguineous; in affected members of these families, we identified homozygous missense mutations in the SOX18 gene, located in 20q13. The two amino acid substitutions, W95R and A104P, affect conserved residues in the first alpha helix of the DNA-binding domain of the transcription factor. In the third family, the parents were nonconsanguineous, and both the affected child and his brother, who died in utero with hydrops fetalis, showed a heterozygous nonsense mutation that truncates the SOX18 protein in its transactivation domain; this substitution was not found in genomic DNA from either parent and hence constitutes a de novo germline mutation. Thus, we show that SOX18 mutations in humans cause both recessive and dominant hypotrichosis-lymphedema-telangiectasia, suggesting that, in addition to its established role in hair and blood vessel development, the SOX18 transcription factor plays a role in the development and/or maintenance of lymphatic vessels.
ICF syndrome is a rare autosomal recessive disease characterized by variable immunodeficiency, centromeric instability, and facial abnormalities. Mutations in the catalytic domain of DNMT3B, a gene encoding a de novo DNA methyltransferase, have been recognized in a subset of patients. ICF syndrome is a genetic disease directly related to a genomic methylation defect that mainly affects classical satellites 2 and 3, both components of constitutive heterochromatin. The variable incidence of DNMT3B mutations and the differential methylation defect of alpha satellites allow the identification of two types of patients, both showing an undermethylation of classical satellite DNA. This classification illustrates the specificity of the methylation process and raises questions about the genetic heterogeneity of the ICF syndrome.
Noonan syndrome (NS) is an autosomal dominant disorder caused by mutations in PTPN11, KRAS, SOS1, and RAF1. We performed SOS1, RAF1, BRAF, MEK1, and MEK2 mutation analysis in a cohort of 102 PTPN11- and KRAS-negative NS patients and found pathogenic SOS1 mutations in 10, RAF1 mutations in 4, and BRAF mutations in 2 patients. Three novel SOS1 mutations were found. One was classified as a rare benign variant and the other remains unclassified. We confirm a high prevalence of pulmonic stenosis and ectodermal abnormalities in SOS1-positive patients. Three patients with SOS1 mutations presented with tumors (embryonal rhabdomyosarcoma, Sertoli cell testis tumor, and granular cell tumors of the skin). One patient with a RAF1 mutation had a lesion suggestive for a giant cell tumor. This is the first report describing different tumor types in NS patients with germ line SOS1 mutations.
Objective Congenital diaphragmatic hernia (CDH) is a congenital birth defect affecting around 1/3000 births. We propose that a significant number of isolated CDH cases have an underlying genetic cause, and that a subset of these result from copy number variations (CNVs) identifiable by array CGH. MethodologyWe have designed a custom array targeted at genes and genomic loci associated with CDH. A total of 79 isolated CDH patients were screened using this targeted array. ResultsIn three patients, we detected genomic imbalances associated with the observed diaphragmatic hernia; a deletion of 8p22-p23.3, 14.2 Mb in size, a 340 kb duplication of Xq13.1 including the ephrin-B1 gene (EFNB1 ), and mosaicism for trisomy 2.Conclusion Using this approach, we detected genomic imbalances associated with CDH in 3/79 (4%) isolated CDH patients. Our findings further implicate 8p deletions as being associated with CDH. The duplication of EFNB1 further highlights this gene as a potential candidate involved in diaphragm development. Mosaicism for trisomy 2 is a rare event and unlikely to be a common cause of CDH. Further investigations of isolated CDH patients by array CGH will continue to identify novel submicroscopic loci and refine genomic regions associated with CDH.
Noonan syndrome (NS) is an autosomal dominant condition with facial dysmorphy, congenital cardiac defects and short stature. A gene for NS has previously been linked to a 14 cM region in 12q24. 2 We performed linkage analysis in a four generation Belgian family with NS in some individuals and cardio-facio-cutaneous (CFC) syndrome in others. Clinical data and linkage data in this family indicate that NS and CFC syndrome result from a variable expression of the same genetic defect. We report a maximum lod score of 4.43 at zero recombination for marker D12S84 in 12q24. A crossover in this pedigree narrows the candidate gene region for NS to a 5 cM interval between markers D12S84 and D12S1341.
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