Meiotic segregation of Robertsonian translocations ascertained in cleavage-stage embryos--implications for preimplantation genetic diagnosis.

BACKGROUND: The aim of this study was to ascertain the prevalence of meiotic segregation products in embryos from carriers of 13/14 and 14/21 Robertsonian translocations and to estimate the predictive value of testing single cells using the fluorescence in situ hybridization (FISH) technique, to provide more information for decision-making about PGD. METHODS: In this prospective cohort study, the copy number of translocation chromosomes in nuclei from lysed blastomeres of cleavage-stage embryos was ascertained using locus-specific FISH probes. Logistic regression analysis, controlling for translocation type, female age and fertility status, was used to calculate the odds ratio (OR) of unbalanced segregation products for female and male heterozygotes. The primary diagnostic measure was the predictive value of the test result. The primary outcome measure was the live birth rate per couple. RESULTS: Female carriers were four times more likely than male carriers to produce embryos with an unbalanced translocation product (OR 3.8, 95% confidence interval 2.0-7.2, P < 0.001). The prevalence of abnormality for the chromosomes tested in embryos from female or male heterozygotes was estimated to be 43 or 28%, respectively, while estimates of the predictive value were 93-100 or 96-100% for a normal test result and 79 or 57% for an abnormal test result. The live birth rate per couple was 58% for female carriers and 50% for male carriers. CONCLUSIONS: For female carriers, PGD using FISH could reduce the risk of miscarriage from either translocation or the risk of Down syndrome from the 14/21 Robertsonian translocation. PGD using FISH for male carriers is unlikely to be indicated given the relatively low prevalence of chromosome imbalance and low predictive value.

Terminal deletion of chromosome 5p in a patient with phenotypical features of Lujan-Fryns syndrome.

We report a young man with phenotypical features suggestive of Lujan-Fryns syndrome and behaviour of an autistic spectrum disorder, who has a subtle terminal deletion of the short arm of chromosome 5. Individuals reported previously with a similar chromosomal abnormality have had developmental delay and a 'breathy, raspy' voice. It may be appropriate to consider screening patients with a phenotype suggestive of Lujan-Fryns syndrome by fluorescence in situ hybridisation (FISH) using a probe for the subtelomeric region of the short arm of chromosome 5.

Robertsonian translocations--reproductive risks and indications for preimplantation genetic diagnosis.

BACKGROUND: Robertsonian translocations carry reproductive risks that are dependent on the chromosomes involved and the sex of the carrier. We describe five couples that presented for preimplantation genetic diagnosis (PGD). METHODS: PGD was carried out using cleavage-stage (day 3) embryo biopsy, fluorescence in-situ hybridization (FISH) with locus-specific probes, and day 4 embryo transfer. RESULTS: Couple A (45,XX,der(14;21)(q10;q10)) had two previous pregnancies, one with translocation trisomy 21. A successful singleton pregnancy followed two cycles of PGD. Couple B (45,XX,der(13;14)(q10;q10)) had four miscarriages, two with translocation trisomy 14. One cycle of PGD resulted in triplets. Couple C (45,XX,der(13;14)(q10;q10)) had four years of infertility; two cycles were unsuccessful. Couple D (45,XY,der(13;14)(q10;q10)) presented with oligozoospermia. A singleton pregnancy followed two cycles of PGD. Couple E (45,XY,der(13;14)(q10;q10)) had a sperm count within the normal range and low levels of aneuploid spermatozoa. PGD was therefore not recommended. No evidence for a high incidence of embryos with chaotic or mosaic chromosome complements was found. CONCLUSIONS: For fertile couples, careful risk assessment and genetic counselling should precede consideration for PGD. Where translocation couples need assisted conception for subfertility, PGD is a valuable screen for imbalance, even when the risk of viable chromosome abnormality is low.

Renal cancer and malformations in relatives of patients with Bardet-Biedl syndrome.

BACKGROUND: Bardet-Biedl syndrome (BBS) is an autosomal recessive disorder with five loci identified thus far. The spectrum of disease includes diverse malformations of the kidney and lower urinary tract. The incidence of BBS is approximately 1/100,000 with a predicted heterozygote frequency of 1/160, and it has been suggested that heterozygotes are at increased risk of obesity and hypertension. METHODS: We describe renal disease in relatives of 109 UK BBS patients. Using PCR with fluorescent microsatellite markers we amplified DNA derived from renal tumours of affected parents to determine whether there was loss of heterozygosity at any of four BBS loci and two other gene loci associated with clear cell renal cell carcinoma (CC-RCC). RESULTS: CC-RCC was diagnosed in three of 180 BBS parents and there was loss of heterozygosity at BBS1 (11q13) in the tumour tissue of one of these subjects. In addition, there was a high incidence of renal agenesis in siblings of BBS patients and two BBS families were identified with apparently dominant inheritance of renal malformations. In one family we were able to demonstrate that renal malformations segregated with the BBS2 locus (16q21). CONCLUSIONS: Since all parents and two-thirds of siblings of BBS patients must be heterozygous for BBS mutations, our observations may implicate BBS genes in the pathogenesis of both renal cancer and malformations, both disorders of precursor cell growth and differentiation. We suggest these observations may have important implications for screening potential BBS carriers for kidney disease and may lead to a greater understanding of the aetiology of renal disease in the general population.

Primary, nonsyndromic vesicoureteric reflux and its nephropathy is genetically heterogeneous, with a locus on chromosome 1.

Primary vesicoureteric reflux (VUR) affects 1%-2% of whites, and reflux nephropathy (RN) causes up to 15% of end-stage renal failure in children and adults. There is a 30-50-fold increased incidence of VUR in first-degree relatives of probands, compared with the general population. We report the results of the first genomewide search of VUR and RN; we studied seven European families whose members exhibit apparently dominant inheritance. We initially typed 387 polymorphic markers spaced, on average, at 10 cM throughout the genome; we used the GENEHUNTER program to provide parametric and nonparametric linkage analyses of affected individuals. The most positive locus spanned 20 cM on 1p13 between GATA176C01 and D1S1653 and had a nonparametric LOD score (NPL) of 5.76 (P=.0002) and a parametric LOD score of 3.16. Saturation with markers at 1-cM intervals increased the NPL to 5.94 (P=.00009). Hence, VUR maps to a locus on chromosome 1. There was evidence of genetic heterogeneity at the chromosome 1 locus, and 12 additional loci were identified genomewide, with P<.05. No significant linkage was found to 6p, where a renal and ureteric malformation locus has been reported, or to PAX2, mutations of which cause VUR in renal-coloboma syndrome. Our results support the hypothesis that VUR is a genetic disorder.

Renal chloride channel, CLCN5, mutations in Dent's disease.

Dent's disease is an X-linked renal tubular disorder characterized by low-molecular-weight proteinuria, hypercalciuria, nephrocalcinosis, nephrolithiasis, and renal failure. Patients with Dent's disease may also suffer from rickets and other features of the renal Fanconi Syndrome. Patients may have mutations in the X-linked renal chloride channel gene, CLCN5, which encodes a 746-amino-acid protein with 12-13 transmembrane domains. We have investigated the 11 coding exons of CLCN5 for mutations in eight unrelated patients with Dent's disease. Leukocyte DNA was used for the polymerase chain reaction amplification of CLCN5 and the products analyzed for single-stranded conformational polymorphisms (SSCPs). Abnormal SSCPs were sequenced and revealed eight mutations. These consisted of three nonsense mutations (Arg34Stop, Arg648Stop, Arg704Stop), four deletions involving codons 40, 86, 157, and 241, and one acceptor splice consensus sequence mutation tgcag --> tgaag. The mutations were confirmed either by restriction endonuclease or sequence-specific oligonucleotide hybridization analysis. In addition, an analysis of 110 alleles from 74 unrelated normal individuals demonstrated that the DNA sequence changes were not common polymorphisms. All of the mutations predict truncated chloride channels that are likely to result in a functional loss. Thus, our findings expand the spectrum of CLCN5 mutations associated with Dent's disease and the results will help to elucidate further the functional domains of this novel chloride channel.

Detection of mutations in COL4A5 in patients with Alport syndrome.

Alport syndrome (AS) can be caused by mutations in COL4A5, one of the six type IV collagen genes. For the purposes of confirming diagnoses, carrier screening and correlating genotype to phenotype, we have screened all 51 exons of this gene by SSCP analysis in 153 families with suspected AS. Mutations were identified in 77 families (of which 20 have previously been reported) and are reported with all available clinical information. All types of mutation were found (missense, nonsense, splicing, small and large deletions and insertions), with the commonest type being those affecting glycine residues in the collagen triple helix. Our 50% detection rate is similar to that of other groups and may imply the presence of mutations outside of the COL4A5 coding region or the existence of a second X-linked AS gene.

New criteria for improved diagnosis of Bardet-Biedl syndrome: results of a population survey.

Bardet-Biedl syndrome (BBS) is an autosomal recessive condition characterised by rod-cone dystrophy, postaxial polydactyly, central obesity, mental retardation, hypogonadism, and renal dysfunction. BBS expression varies both within and between families and diagnosis is often difficult. We sought to define the condition more clearly by studying 109 BBS patients and their families, the largest population surveyed to date. The average age at diagnosis was 9 years, which is late for such a debilitating condition, but the slow development of the clinical features of BBS probably accounts for this. Postaxial polydactyly had been present in 69% of patients at birth, but obesity had only begun to develop at around 2-3 years, and retinal degeneration had not become apparent until a mean age of 8.5 years. Our study identified some novel clinical features, including neurological, speech, and language deficits, behavioural traits, facial dysmorphism, and dental anomalies. In the light of these features we propose a revision of the diagnostic criteria, which may facilitate earlier diagnosis of this disorder. We present evidence for an overlapping phenotype with the Laurence-Moon syndrome and propose a unifying, descriptive label be adopted (polydactyly-obesity-kidney-eye syndrome). We report an increased prevalence of renal malformations and renal cell carcinoma in the unaffected relatives of BBS patients and suggest that these may be a consequence of heterozygosity for BBS genes. Our findings have important implications for the care of BBS patients and their unaffected relatives.

Bardet-Biedl syndrome: a molecular and phenotypic study of 18 families.

The autosomal recessive disorder Bardet-Biedl syndrome is characterised by retinal degeneration, polydactyly, obesity, mental retardation, hypogenitalism, renal dysplasia, and short stature. It is heterogeneous with at least four gene loci (BBS1-4) having been mapped to date. We have studied 18 multiply affected families noting the presence of both major and minor manifestations. Using a fluorescently based PCR technique, we genotyped each family member and assigned linkage to one of the four loci. Given this degree of heterogeneity we hoped to find phenotypic differences between linkage categories. We found 44% of families linked to 11q13 (BBS1) and 17% linked to 16q21 (BBS2). Only one family was linked to 15q22 (BBS4) and none to 3p12. We conclude that BBS1 is the major locus among white Bardet-Biedl patients and that BBS3 is extremely rare. Only subtle phenotypic differences were observed, the most striking of which was a finding of taller affected offspring compared with their parents in the BBS1 category. Affected subjects in the BBS2 and 4 groups were significantly shorter than their parents. Twenty eight percent of pedigrees did not show linkage to any known locus, evidence for at least a fifth gene. We conclude that the different genes responsible for Bardet-Biedl syndrome may influence growth characteristics such as height.

Phenotypic diversity in the Smith-Lemli-Opitz syndrome.

The phenotype of four cases of Smith-Lemli-Opitz syndrome (SLO) with proven defects in cholesterol biosynthesis are compared, and shown to be markedly disparate even between sibs, and demonstrate the dilemma for the clinician. The advent of a biochemical test for SLO has been enormously valuable in determining which patients are truly affected by the condition, but because of the wide phenotypic variation, a diagnosis on clinical features alone remains problematic.

Two sibs with anophthalmia and pulmonary hypoplasia (the Matthew-Wood syndrome).

We describe two sibs with pulmonary hypoplasia and anophthalmia; one also had a number of other malformations. Only one other broadly similar case could be found in the literature, and it was an isolated occurrence. The condition is named the Matthew-Wood syndrome.

Probable de novo 17q duplication (q11.2-->q21.1): a newly recognised chromosomal syndrome in a child with Klinefelter's syndrome.

A child is described with a previously unreported probable trisomy for a segment of the long arm of chromosome 17 responsible for some distinct clinical features. These include craniofacial and skin abnormalities, failure to thrive, partial malrotation of the gut, malabsorption, gastro-oesophageal reflux, neurodevelopmental delay, autonomic disturbance, and cardiac and CNS abnormalities. The coexistence of Klinefelter's syndrome (47,XXY) is of minor significance in relation to this child's phenotype.