DNA analysis of AHI1, NPHP1 and CYCLIN D1 in Joubert syndrome patients from the Netherlands.

Joubert syndrome (JBS) is a clinically variable and genetically heterogeneous developmental brain disorder with autosomal recessive inheritance. Five genes, AHI1, NPHP1, CEP290, MKS3, and RPGRIP1L, and two additional loci on chromosome 9 and 11 have been identified so far. The relative contributions of AHI1 mutations and NPHP1 deletions have not yet been determined in a population-based JBS patient cohort. We therefore undertook a nationwide survey of JBS in the Netherlands and performed DNA analysis of the AHI1 and NPHP1 genes, as well as a new candidate gene CYCLIN D1. We obtained clinical data and DNA samples of 25 Dutch JBS patients. DNA analysis of AHI1 revealed pathogenic homozygous or compound heterozygous AHI1 mutations in four patients (16%). Based on the birth prevalence of about 1 in 100,000 for JBS in the Netherlands, we estimated a carrier frequency of AHI1 mutations of approximately 1 in 400. In another two patients, the AHI1 mutation Arg830Trp was identified (homozygously and heterozygously), a possible low penetrance allele. No deletions of NPHP1 or CYCLIN D1 mutations were detected in these 25 patients. In the four patients with AHI1 mutations, retinal disease (Leber congenital amaurosis or retinal dystrophy) was present in two, whereas none had renal disease. Pooling our data and data from the literature, retinal disease seems to occur in 75% of AHI1-associated JBS patients. Renal disease is present in 10% at most. We conclude that AHI1 mutations are an important cause of JBS in Dutch patients, and should always be looked for in patients suspected of JBS, especially when retinal dystrophy is present. Patients with AHI1 mutations should be regularly checked for retinal and renal disease up until adolescence.

Discordant NIPT result in a viable trisomy-21 pregnancy due to prolonged contribution to cfDNA by a demised trisomy-14 cotwin.

One of the confounders in noninvasive prenatal testing (NIPT) is the vanishing twin phenomenon. Prolonged contribution to the maternal Cell-free DNA (cfDNA) pool by cytotrophoblasts representing a demised, aneuploid cotwin may lead to a false-positive outcome for a normal, viable twin. We show that a vanishing trisomy-14 twin contributes to cfDNA for more than 2 weeks after demise.

A DGGE system for comprehensive mutation screening of BRCA1 and BRCA2: application in a Dutch cancer clinic setting.

Rapid and reliable identification of deleterious changes in the breast cancer genes BRCA1 and BRCA2 has become one of the major issues in most DNA services laboratories. To rapidly detect all possible changes within the coding and splice site determining sequences of the breast cancer genes, we established a semiautomated denaturing gradient gel electrophoresis (DGGE) mutation scanning system. All exons of both genes are covered by the DGGE scan, comprising 120 amplicons. We use a semiautomated approach, amplifying all individual amplicons with the same PCR program, after which the amplicons are pooled. DGGE is performed using three slightly different gel conditions. Validation was performed using DNA samples with known sequence variants in 107 of the 120 amplicons; all variants were detected. This DGGE mutation scanning, in combination with a PCR test for two Dutch founder deletions in BRCA1 was then applied in 431 families in which 52 deleterious changes and 70 unclassified variants were found. Fifteen unclassified variants were not reported before. The system was easily adopted by five other laboratories, where in another 3,593 families both exons 11 were analyzed by the protein truncation test (PTT) and the remaining exons by DGGE. In total, a deleterious change (nonsense, frameshift, splice-site mutation, or large deletion) was found in 661 families (16.4%), 462 in BRCA1 (11.5%), 197 in BRCA2 (4.9%), and in two index cases a deleterious change in both BRCA1 and BRCA2 was identified. Eleven deleterious changes in BRCA1 and 36 in BRCA2 had not been reported before. In conclusion, this DGGE mutation screening method for BRCA1 and BRCA2 is proven to be highly sensitive and is easy to adopt, which makes screening of large numbers of patients feasible. The results of screening of BRCA1 and BRCA2 in more than 4,000 families present a valuable overview of mutations in the Dutch population.