Further delineation of the facial 13q14 deletion syndrome in 13 retinoblastoma patients

Thirteen years ago, Motegi and colleagues (J Med Genet 1987;24:696-697) summarized the specific facial phenotype of six Japanese retinoblastoma patients with interstitial 13q14 deletions. Among a series of 228 propositi with retinoblastoma referred to the Lausanne Retinoblastoma Clinic for treatment and genetic counseling between 1986 and 1997, 13 (5.7%) were diagnosed with a cytogenetic de-novo 13q14 deletion. We confirm the presence of the reported facial phenotype in our population of Caucasian patients and describe additional clinical traits, thus extending the facial phenotype associated with the 13q14 deletion. Del(13q14) comprises, among others, cranial anomalies, frontal bossing, deeply grooved and long philtrum, depressed and broad nasal bridge, bulbous tip of the nose, thick lower lip, thin upper lip, broad cheeks, and large ears and lobules. Recognition of this particular facial appearance was instrumental in the genetic diagnosis of 13q deletions and in the presymptomatic diagnosis of retinoblastoma in a significant number of our cases. Identification of this phenotype in a retinoblastoma patient allows for efficient diagnosis of recurrence in his progeny and/or sibship, while its ignorance will compromise genetic counseling due to the possible difficulties in detecting large deletions by standard molecular mutation analysis. Recognition of this syndrome in newborns without known familial risk for retinoblastoma is even more important as it is a clear warning sign that indicates immediate ophthalmic examination.

Molecular characterization of the deletion in retinoblastoma patients with 13q14 cytogenetic anomalies

We investigated the molecular deletions of twelve patients presenting with retinoblastoma and a cytogenetic abnormality including band 13q14. Dinucleotide markers spanning the complete chromosome 13 as well as two intragenic markers were analyzed in patients and their two parents. The deletion was considered confirmed when one heterozygous allele was missing, potential when a homozygous allele was observed in continuity with a clearly deleted allele, and noninformative when a homozygous allele was observed adjacent to a nondeleted region. The patients could be classified into three groups based on their cytogenetic abnormalities. In group 1, the cytogenetic deletion was restricted to band13q14 with confirmed or potential molecular deletions extending from D13S328 to D13S153. Although a possible common centromeric deletion breakpoint could exist for three of the patients and a common telomeric deletion breakpoint for two, the cytogenetic deletion was different for most of them. Group 2 included patients with a cytogenetic deletion extending up to 13q22. At the molecular level, the telomeric breakpoints were between the RB1 gene and D13S156. Here again, it is quite unlikely that a common telomeric breakpoint was responsible for the deletion. Group 3 consisted of special cases with either a paracentric inversion or a complex translocation. The cytogenetic abnormalities around 13q14 correlate with the molecular deletions that were observed in this study. Associated malformations cannot be easily predicted from the size of the deletions.

[Quick prenatal diagnosis using FISH in the analysis of non-cultured amniotic fluid cells]

We report our experience with fluorescence in situ hybridization (FISH) on uncultured amniocytes and standard cytogenetic analysis. The method have been suggested to 259 patients and performed for 199 amniotic fluid samples. Commercially available chromosome-specific DNA probes (Aneurysm) for chromosomes 13, 18, 21, X and Y were used. All full trisomy 18, 21 and monosomy X were detected by FISH analysis with exception of one case of mosaic monosomy X. No false-positive result was observed. The efficiency, practicability and acceptability of the FISH diagnosis are discussed.

[Assisted fertilization in azoospermic men: results of CHUV from 1994 to 1997]

In vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI) have revolutionised the treatment and prognosis of oligo-terato-asthenozoospermia (OTA). Sperm extraction in the vas deferens, the epididymis (MESA: with epididymal sperm aspiration) or the testicles (TESE: with testicular sperm extraction), associated with ICSI, can achieve pregnancy in cases of excretory or secretory azoospermia. We report the results of the use of MESA and TESE in 42 patients with an average age of 37 (age range 24 to 58). Of these, 26 have excretory azoospermia, 11 secretory azoospermia and 5 a problem linked to ejaculation. Of the 506 oocytes that were inseminated, 270 zygotes were obtained, giving a fertilisation rate of 53.4%. 85 embryo transfers were carried out (55 with fresh embryos and 30 with cryo-preserved embryos). Three spontaneous abortions and one extrauterine pregnancy were reported. Six pregnancies are developing normally. To date, 13 children have been born (9 boys and 4 girls) in 10 deliveries (7 single children and 3 sets of twins). The limits of male infertility need to be revised to take these new forms of therapy into account and patients should be advised on the new possibilities available.

A new mutation, 3905insT, accounts for 4.8% of 1173 CF chromosomes in Switzerland and causes a severe phenotype

We have analysed 1173 cystic fibrosis (CF) chromosomes from Switzerland for eight mutations in the CF transmembrane conductance regulator (CFTR) gene. This permitted the identification of 88.5% of all mutations present. A novel insertion mutation in exon 20 of the CFTR gene, 3905insT, was discovered. This mutation accounted for 4.8% of CFTR gene mutations in Switzerland and has since been identified in other populations of probable Swiss descent. It is associated with a highly variable clinical phenotype but always with pancreatic insufficiency. Haplotype analysis with three intragenic microsatellites in the CFTR gene showed that the mutation is associated with a haplotype rarely identified on other CFTR alleles and, therefore, that the frequency of the mutation in Switzerland is explained by a founder effect of a relatively recent mutation event.

Prognostic factors associated with loss of heterozygosity at the RB1 locus in retinoblastoma

The nature of the tumorigenic mutation was analyzed in 30 retinoblastoma (Rb) tumors (16 non-hereditary and 14 hereditary) and categorized into loss of heterozygosity (LOH) or retention of heterozygosity (non-LOH) at the RB1 locus. These genotypic characteristics were compared with the clinicopathological phenotype for possible correlation. The overall frequency of LOH was roughly 55%, in both hereditary and non-hereditary Rb. The presence of LOH was preferentially associated with differentiated tumors and absence of choroidal invasion. LOH was found in 82% of females versus 33% of males. Finally, LOH-initiated tumors were associated with a significantly younger age at diagnosis in hereditary Rb. In conclusion, the preferential association of LOH with absence of choroidal invasion, tumoral differentiation, and younger age at diagnosis may establish LOH as a prognostic marker in Rb patients.

[Retinoblastoma: clinical and molecular diagnostic aspects]

Retinoblastoma, a tumor of the immature retina concerns babies and young infants in particular. They make up for 14% of malignomas in the first years of life. There are two types of retinoblastoma: In the first two alleles of the gene Rb1 must be inactivated sequentially in the same retinoblast cell until this may escape control. In this case the retinoblastoma is always unilateral and unifocal. This is explained by the lower frequency of two mutations in one retinoblast. The other type, however, is inherited: One allele Rb1 is inactivated in all cells of the organism by mutation. The probability that a second mutation arrives in different retinoblasts is thus high. In this case bilateral multifocal tumors develop. Characterization of the Rb1 gene has permitted identification or at least determination of a haplotype in persons at risk. This knowledge is decisive for early recognition of babies at risk and for genetic counselling.

Sex mutation ratio in retinoblastoma and retinoma: relevance to genetic counseling

PURPOSE AND METHOD

The parental origin of initial somatic and germline mutations (M1) in the retinoblastoma gene (RB1) was explored in 36 retinoblastoma (Rb) and 5 retinoma patients, of which 16 were presumably non-hereditary and 25 were hereditary. By this approach the male:female mutation ratio was determined by the gender quotient of mutation origin.

RESULTS

The male to female mutation ratio in hereditary Rb was 19:2, which is consistent with a significant bias towards paternal origin of germline mutation. This ratio was of 5:2 in non-hereditary Rb which is not significant.

DISCUSSION

Together with the published data, these results support a preferential paternal mutagenesis in hereditary Rb, but appear to reject paternal genomic imprinting at the RB1 locus as previously proposed in non-hereditary Rb. Genetic counseling in sporadic Rb may be substantially improved by the identification of the parental origin of initial mutation.

[Clinical applications of molecular diagnosis of retinoblastoma ain 15 families]

PURPOSE

In 40% retinoblastoma (Rb) results from a hereditary mutation of the Rb susceptibility gene (RB1). In this study, we tested the usefulness of intragenic DNA analysis for ophthalmologic follow-up in affected families.

METHODS

Molecular analysis was performed on 103 DNA samples of 15 Rb families. We used 7 intragenic polymorphic markers and one within the ESD gene for mutation linkage analysis.

FINDINGS

DNA analysis was informative in 88% of relatives at risk of developing Rb. Among them, the presence of a mutated RB1 allele was excluded in 46%, while 29% were unaffected carriers and 25% had inherited the Rb predisposition.

CONCLUSION

In the majority of familial Rb, the DNA analysis allows the identification of children carrying a RB1 mutation and who will need a close ophthalmologic follow-up under general anesthesia. When the mutated gene is absent, ophthalmological examination under narcosis is unnecessary. Finally, identification of asymptomatic carriers improve the accuracy of genetic counselling.

Pseudo low penetrance in retinoblastoma. Fortuitous familial aggregation of sporadic cases caused by independently derived mutations in two large pedigrees

OBJECTIVE

The disparate occurrence of few cases of retinoblastoma in the same extended pedigree confronts us with the unsolved problem of a low-penetrant autosomal-dominant trait vs fortuitous familial aggregation of sporadic cases. Determination as to whether the disease arises from a common inherited mutation or sporadic mutations has important implications for genetic counseling. This is illustrated in this report of two presumed low-penetrant retinoblastoma pedigrees characterized by two distantly affected relatives connected through apparently healthy carriers.

DESIGN

We mathematically modeled the inheritance patterns and calculated the a priori relative probabilities of heredity with low penetrance vs chance occurrence of independent mutations for each pedigree. The derived odds clearly show that the disease, which occurred twice in each family, most likely resulted from unrelated mutations. To prove this, extensive DNA testing was conducted, including determination of intragenic RB1 DNA sequence polymorphisms and screening for mutation using the polymerase chain reaction coupled with single-strand conformation polymorphism analysis.

PATIENTS

All living key members from both pedigrees were included.

RESULTS

Consistent with our initial expectation, there was no common intragenic haplotype or common germ-line mutation that segregated with the disease phenotype in either of these two families.

CONCLUSIONS

We therefore conclude that collateral incidence of retinoblastoma in these two pedigrees occurred by chance and not according to autosomal-dominant inheritance with low penetrance. Furthermore, our data provide the first evidence, to our knowledge, that related individuals may have independent mutations involving an identical gene locus, giving rise to an artefactual inheritance pattern.

Paternal selection favoring mutant alleles of the retinoblastoma susceptibility gene

Penetrance and segregation rates of mutant Rb-1 alleles were assessed in all 51 members of eight kindreds with hereditary retinoblastoma by concomitant ophthalmologic examination and determination of seven intragenic restriction fragment length polymorphisms (RFLPs). Penetrance was in the range reported in the literature except for one family in which it was only 42.8%. However, the odds of transmitting a mutant Rb-1 allele from one generation to the next were 25:9 in this population, much above the Mendelian 1:1 ratio (P less than 0.025). This preferential transmission was discovered through the use of molecular information. Further analysis revealed that this distortion was due to preferential inheritance among children of male carriers (18:4, P less than 0.005). No difference from a 1:1 segregation ratio could be detected among the children of female carriers (7:5). These findings were consistent with a review of relevant data in the literature.

Association between haplotypes and specific mutations in Swiss cystic fibrosis families

Cystic fibrosis (CF) is the most common severe autosomal recessive genetic disorder in Caucasian populations, with an incidence of about 1 in 2000 live births, implying a carrier frequency of about 1 in 22. In 1989, the CF gene was isolated and characterized and the major mutation (delta F508), a 3-bp deletion that results in the loss of a phenylalanine residue at position 508, was detected. To determine the frequency of the delta F508 mutation and the predicted number of additional mutations in our population, we have undertaken a collaborative study of 215 CF patients and 175 CF parents in Switzerland. The delta F508 mutation in exon 10 has been found in 70% of the CF chromosomes, and the exon-11 mutation R553X seems to be the second most common CF mutation in our population, with a frequency of 5.3%, whereas the G551D mutation (also in exon 11) has not been detected at all. Haplotype determination of 430 CF and 175 normal chromosomes using XV-2c, KM19, MP6d-9, and J3.11 has been proven to be very helpful in providing additional carrier risk calculations: Haplotypes 1 (1221), 2 (1222), 6 (2111), and 7 (2221) increase the risk of being a carrier from 1 in 55 (haplotype 6) to 1 in 17 (haplotype 1), whereas haplotypes 3 (1122), 4 (1112), 8 (2222) and 10 (1111) lower the risk from 1 in 144 (haplotype 3) to 1 in 1678 (haplotype 10). Moreover, the mutation R553X shows strong correlation with haplotype 3, leading to the suggestion that haplotypes 1, 2, 5, and 6 may account for four additional mutations in Switzerland.(ABSTRACT TRUNCATED AT 250 WORDS)

[Lausanne study of retinoblastoma, 1986-90: deletion of esterase D locus in a collective of 128 patients]

Activity and phenotype of red blood cell esterase D were systematically determined in a population of 128 retinoblastoma patients from 99 families and compared to 158 controls, in order to detect a chromosome 13q14 deletion. Among these patients 12 were healthy carriers and 116 affected carriers of a mutant allele of the retinoblastoma susceptibility gene (110 retinoblastoma, 5 retinoma, 1 phtisis bulbi). 4 patients were found to have decreased ESD levels in connection with 13q14 deletion which was confirmed by chromosome analysis. The data presented here suggest that ESD quantification has a high specificity and sensitivity for the detection of homogenous chromosome 13 deletions in retinoblastoma patients.

Constitutional karyotype in retinoblastoma. Case report and review of literature

High resolution karyotype was performed in 13 retinoblastoma patients. A mosaic pattern for del(13)(q14.1;q14.3) was found in a girl with sporadic bilateral retinoblastoma and midface dysmorphism. In addition, 162 cases of 13q aberrations were reviewed, including 140 retinoblastoma patients and 22 non-penetrance 13q14 deletions. Some epidemiological and genetic involvements are discussed.