Familial adenomatous polyposis in two Black South African families.

The apparent low incidence of colon cancer in the Black population of South Africa has been ascribed to a non-Western diet. The present authors report the identification of two common 5-bp deletions at codons 1309 and 1061 of the adenomatous polyposis coli (APC) gene in a Xhosa and Zulu patient, respectively. The in vitro transcription/translation test (PTT) and a non-radioactive heteroduplex method, which facilitates resolution of enzymatically amplified DNA by agarose gel electrophoresis, were used for mutation detection. This study represents the first report of APC mutations in indigenous Black individuals clinically diagnosed with familial adenomatous polyposis coli (FAP). The two deletion mutations are responsible for FAP in 35% of affected South Africans, a frequency similar to that described in several other non-African populations. The apparently low incidence of colon cancer in the African population may be ascribed either to the rare occurrence of the 'second hit' needed for polyp formation or to a lower incidence of mutations in the APC gene.

Adult extrarenal Wilms tumor occurring in the uterus.

Five previous cases of extrarenal Wilms tumor (EWT) occurring in the uterus have been reported. The oldest patient was 22 years. We report a case of uterine EWT occurring in a 42-year-old woman. Histologically, there was typical triphasic differentiation, including epithelial, blastemal, and mesenchymal elements. The important differential diagnosis in this age group, the malignant mixed mullerian tumor, is excluded by the absence of glomeruloid structures and primitive tubules. The exact histogenesis of EWT is unknown but most likely relates to the presence of nephrogenic rests occurring in the female genital tract.

Analysis of the NRAMP1 gene implicated in iron transport: association with multiple sclerosis and age effects.

Multiple sclerosis (MS) is believed to be an autoimmune process occurring in genetically susceptible individuals after an appropriate environmental exposure. We have exploited the homogeneous Afrikaner population of European ancestry to investigate the likelihood that iron dysregulation, in association with infectious and/or autoimmune disease susceptibility, may underlie the MS phenotype in a subgroup of patients. The functional Z-DNA forming repeat polymorphism of the natural resistance-associated macrophage protein-1 (NRAMP1) gene was analyzed in 104 patients diagnosed with MS and 522 Caucasian controls. A family-based control group consisting of 32 parental alleles not transmitted to MS offspring was additionally studied to exclude the likelihood of population substructures. Statistically significant differences in allelic distribution were observed between the patient and control samples drawn from the same population (P < 0.01). Evidence is furthermore provided that alleles considered to be detrimental in relation to autoimmune disease susceptibility may be maintained in the population as a consequence of improved survival to reproductive age following infectious disease challenge. Although it remains to be determined whether the disease phenotype in MS patients with allele 5 of the NRAMP1 promoter polymorphism is directly related to dysregulation of iron or modified susceptibility to viral infection and/or autoimmunity, a combination of these processes most likely underlies the disease phenotype in these patients. In view of the emerging role of polymorphic variants in complex diseases and minimizing of possible confounding factors in this association study, we conclude that allelic variation in the NRAMP1 promoter may contribute significantly to MS susceptibility in the South African Caucasian population.

Familial adenomatous polyposis coli in South Africa--molecular basis and diagnosis.

OBJECTIVE: To determine the molecular basis and establish a routine molecular diagnostic service for familial adenomatous polyposis coli (FAP) families in South Africa. DESIGN: The coding region of the adenomatous polyposis coli (APC) gene in affected FAP kindreds was screened using heteroduplex analysis, single-strand conformation polymorphism analysis and the protein truncation test. SETTING: Department of Human Genetics, University of Stellenbosch, and the Cancer Research Campaign Laboratories, Department of Pathology, University of Edinburgh and Molecular Medicine Centre, Western General Hospital, Edinburgh, Scotland (academic visit of 6 months). SUBJECTS: FAP-affected individuals and at-risk family members in 28 apparently unrelated South African families. RESULTS: A total of nine different APC mutations was identified, allowing DNA-based diagnosis in 20 families. Three of these mutations have not been described previously in other populations. CONCLUSION: Pre-symptomatic diagnosis using direct mutation detection is cost-effective and surgical intervention has the potential to prevent cancer in at-risk individuals from FAP families.

Somatic mutations of the APC, KRAS, and TP53 genes in nonpolypoid colorectal adenomas.

Colorectal adenomas are macroscopically visible morphological changes of the mucosa that can develop focal carcinoma in the absence of surgical intervention. The successive molecular changes proposed to occur at different stages in the adenoma-carcinoma sequence were primarily based on DNA studies of exophytic, polypoid-type adenomas. Not all colorectal lesions, however, display an exophytic phenotype and a presumed distinct colorectal neoplasm, the nonpolypoid adenoma, was subsequently described as a precursor of colorectal cancer. The low incidence of KRAS mutations in nonpolypoid colorectal adenomas reported previously suggested a different genetic basis for the transformation process in these lesions. We have pursued the identification of genetic changes in benign sporadic nonpolypoid colorectal adenomas in a selected Swedish patient group with no family history of colorectal cancer. Mutation screening of the adenomatous polyposis coli (APC), KRAS, and TP53 genes was conducted using the protein truncation test, heteroduplex-single-strand conformation polymorphism analysis, and denaturing gradient gel electrophoresis on PCR-amplified fragments. Fourteen mutations in the APC gene were characterized in 10/20 samples. Mutations in the KRAS and TP53 genes were identified in 3/57 and 4/51 adenomas, respectively. The mutation frequencies and distribution of mutations in APC correlate with published data on exophytic adenomas. The low mutation frequency of the TP53 gene is consistent with the benign nature of the research material. KRAS activation (an early event in polypoid colorectal adenomas) apparently does not play a significant role in nonpolypoid adenoma development but may result in the development of a polypoid configuration. Genes Chromosomes Cancer 27:202-208, 2000.

Multiple APC mutations in sporadic flat colorectal adenomas.

Adenomas are established pre-malignant lesions in colorectal carcinogenesis. To date the adenoma-carcinoma sequence for the development of colorectal carcinoma (CRC) has been based largely on molecular data of exophytic, polypoid-type adenomas. Subsequently, a different type of adenoma has been identified: the flat adenoma, so called for its flat, non-exophytic appearance, making it less likely to be detected during conventional endoscopy. However, due to technological advances in endoscopic methods, flat-type adenomas can now frequently be detected and are no longer considered rare colorectal lesions. The phenotype of flat colorectal adenomas differs macroscopically and histologically from exophytic adenomas. Flat colorectal adenomas, as a rule, are tubular structures often revealing high-grade dysplasia, irrespective of the size or villous component. Flat adenomas have also been recognised as pre-cancerous lesions in gastric cancer. Unlike the wealth of clinical and molecular information available for polypoid (exophytic) adenomas, molecular profiles of flat-type lesions have not yet been characterised systematically and the full clinical significance hereto realised. Previous molecular investigation of the K-ras gene in flat colorectal adenomas suggests a distinct pathway in their development. In this study, mutation analysis of the adenomatous polyposis coli (APC) gene using the protein truncation test (PTT) in 20 flat colorectal adenomas in a selected group of 16 patients without hereditary predisposition to colorectal cancer, revealed double truncations of the APC gene in four adenomas. In one of these adenomas a third mutation was detected by DNA sequence analysis.

A novel deletion at codon 441 of the APC gene associated with ophthalmic lesions (CHRPE) in a South African family.

A novel mutation at codon 441 in exon 10 of the adenomatous polyposis coli (APC) gene was identified in a South African family of mixed ancestry, using a convenient, non-radioactive, heteroduplex-SSCP screening assay. This single thymidine deletion after nucleotide position 1322 creates a frameshift resulting in a downstream stop codon at amino acid residue 453 of the APC gene. Genotypes of nine family members were subsequently correlated with the presence or absence of congenital hypertrophy of the retinal pigment epithelium (CHRPE), since expression of this common extracolonic manifestation of FAP is largely determined by the length of the truncated protein. CHRPE was absent in the five unaffected family members analysed, while four mutation positive subjects showed these ophthalmic lesions. Correlation between the molecular analysis and ophthalmic examinations, performed without knowledge of clinical and genetic status respectively, provided additional evidence in favour of the view that the range of phenotypic expression in FAP may result from different allelic manifestations of APC mutations.

Presymptomatic diagnosis of familial adenomatous polyposis using intragenic polymorphisms and CA repeats flanking the APC gene.

To assess the value of DNA markers for the diagnosis of familial adenomatous polyposis (FAP) in South Africa, two highly informative CA-repeat polymorphisms (LNS CA-repeat in D5S346 and YN5.64c CA-repeat in D5S82) flanking the adenomatous polyposis coli (APC) gene, and three intragenic restriction fragment length polymorphisms (RFLPs) (exon 11/RsaI, exon 15.11/MspI, 3'UTR/SspI), were used for haplotype analysis in 13 South African families with the disease. The combination of these polymorphic markers proved to be highly informative and allowed an accurate diagnosis of FAP in 34/35 of the at-risk individuals analysed. Indirect molecular screening can therefore provide a comprehensive pre-clinical diagnostic test for FAP in South Africa. No predominant haplotype was found to be associated with FAP within the South African population. This suggests the absence of founder-type mutations in affected families and therefore marker studies remain important for the pre-clinical diagnosis of FAP in South Africa.

The use of DNA markers in the pre-clinical diagnosis of familial adenomatous polyposis in families in South Africa.

Haplotype association studies were performed in 10 unrelated South African families and 1 German immigrant family with familial adenomatous polyposis (FAP). Three DNA probes, recognising five restriction fragment length polymorphisms (RFLPs) around the gene locus for FAP on chromosome 5q, were used. The RFLP analysis was informative or partially informative in all the families studied. Five haplotypes were found to segregate with the disease locus. The predominant association of two of these haplotypes with FAP in the South African families suggests that two mutations may cause the disease in about 70% of families in this population. Meiotic recombination events were detected between the FAP gene and probe M4 (D5S6), but not probes Pi227 (D5S37) and C11p11 (D5S71). Haplotype analysis allowed the preclinical diagnosis of FAP in 5 subjects.

Screening South African familial adenomatous polyposis families for the five-nucleotide deletion at codon 1309 of the APC gene.

We report the occurrence of a common five-nucleotide deletion at codon 1309 of the adenomatous polyposis coli (APC) gene in four different South African population groups. The mutation causes familial adenomatous polyposis (FAP) in 18% (4/22 unrelated patients screened) of affected South Africans, which is similar to the frequency described in several other populations. Knowledge of the gene mutation underlying FAP enabled conclusive genetic testing of at-risk family members of four index patients in which this specific mutation has been characterized. The non-radioactive heteroduplex method described in this study allowed cost-effective molecular diagnosis directly after electrophoresis of enzymatically-amplified DNA in agarose gels. The resulting reduction of uncertainty for at-risk relatives is an important benefit of diagnosis at the DNA level.

Haplotype associations of three DNA polymorphisms at the human low density lipoprotein receptor gene locus in familial hypercholesterolaemia.

The frequency and inheritance of three restriction fragment length polymorphisms (RFLPs) of the low density lipoprotein (LDL) receptor gene were investigated in 27 South African families with familial hypercholesterolaemia. Four haplotypes, defined by the enzymes PvuII, StuI, and NcoI, were found to segregate in this population. The frequency of the rare allele detected by NcoI was found to be 0.53 in 45 unrelated familial hypercholesterolaemic (FH) patients compared to 0.33 in 60 normal controls (p less than 0.005). In 71% of the families studied, a haplotype with common alleles for PvuII and StuI and the rare allele for NcoI cosegregated with the defective gene. In 20% of the families, a second haplotype with rare alleles for PvuII and StuI and common allele for NcoI segregated with FH. In these families the haplotypes unambiguously cosegregate with the disease and can therefore be used for early diagnosis of FH.

Balanced chromosome translocations and abnormal phenotypes. A report of 5 cases.

Five cases in which phenotypic abnormalities were found in association with apparent balanced chromosomal translocations are described. In 3 patients, one of the parents was found to be a carrier of the same translocation. In a further patient, the translocation was shown to be de novo and in the remaining patient the father was not available for chromosome studies. In a review of the literature the breakpoints in 36 familial balanced translocations were compared with 40 de novo translocations (including the present cases) all associated with phenotypic abnormalities. No common translocation was found in these groups, but it was observed that chromosomes 4 and 5 were significantly more involved in de novo translocations than in familial translocations. The possible aetiology and implications for prenatal diagnoses are discussed.