No abstract

Deficiency of the hepatic cytosolic enzyme tyrosine aminotransferase (TAT) causes marked hypertyrosinaemia leading to painful palmoplantar hyperkeratoses, pseudodendritic keratitis and variable mental retardation (oculocutaneous tyrosinaemia type II or Richner-Hanhart syndrome). Parents may therefore seek prenatal diagnosis, but this is not possible by biochemical assays as tyrosine does not accumulate in amniotic fluid and TAT is not expressed in chorionic villi or amniocytes. Molecular analysis is therefore the only possible approach for prenatal diagnosis and carrier detection. To this end, we sought TAT gene mutations in 9 tyrosinaemia II patients from three consanguineous Palestinian kindreds. In two kindreds (7 patients), the only potential abnormality identified after sequencing all 12 exons and exon-intron boundaries was homozygosity for a silent, single-nucleotide transversion c.1224G > T (p.T408T) at the last base of exon 11. This was predicted to disrupt the 5' donor splice site of exon 11 and result in missplicing. However, as TAT is expressed exclusively in liver, patient mRNA could not be obtained for splicing analysis. A minigene approach was therefore used to assess the effect of c.1224G > T on exon 11 splicing. Transfection experiments with wild-type and c.1224G > T mutant minigene constructs demonstrated that c.1224G > T results in complete exon 11 skipping, illustrating the utility of this approach for confirming a putative splicing defect when cDNA is unavailable. Homozygosity for a c.1249C > T (R417X) exon 12 nonsense mutation (previously reported in a French patient) was identified in both patients from the third kindred, enabling successful prenatal diagnosis of an unaffected fetus using chorionic villous tissue.

No abstract

Approximately ten percent of patients with malignant melanoma have family histories of the disease, suggesting a genetic predisposition. Germline mutations in tumour suppressor p16 gene have been implicated as disease causing mutations in some of the melanoma families. The frequency of families with p16 germline mutations among melanoma prone families varies from eight to fifty percent. The range of the variability is influenced apparently by the number of melanoma affected individuals within the family, as well as by other, yet unidentified factors. Ethnic background is known to determine both the frequency and the nature of germline alterations. Recently, specific mutations in tumour suppressor genes involved in breast cancer and in colon cancer were found at elevated frequency among Ashkenazi Jews. This report describes results of a screening for p16 germline alterations in a collection of Israeli melanoma families. We have analyzed genomic DNA from thirty one Ashkenazi and non-Ashkenazi Jewish melanoma families, as well as from thirty melanoma patients without an apparent family history of the disease. The entire coding region of the p16 gene was screened by single strand conformation polymorphism analysis and direct DNA sequencing. We have detected a number of carriers with the Ala148 Thr polymorphism at the end of the second exon and several instances of 500(G=>C) substitution at the 3' untranslated portion of the gene.