Homozygous disruption of PDZD7 by reciprocal translocation in a consanguineous family: a new member of the Usher syndrome protein interactome causing congenital hearing impairment.

A homozygous reciprocal translocation, 46,XY,t(10;11),t(10;11), was detected in a boy with non-syndromic congenital sensorineural hearing impairment. Both parents and their four other children were heterozygous translocation carriers, 46,XX,t(10;11) and 46,XY,t(10;11), respectively. Fluorescence in situ hybridization of region-specific clones to patient chromosomes was used to localize the breakpoints within bacterial artificial chromosome (BAC) RP11-108L7 on chromosome 10q24.3 and within BAC CTD-2527F12 on chromosome 11q23.3. Junction fragments were cloned by vector ligation and sequenced. The chromosome 10 breakpoint was identified within the PDZ domain containing 7 (PDZD7) gene, disrupting the open reading frame of transcript PDZD7-C (without PDZ domain) and the 5'-untranslated region of transcript PDZD7-D (with one PDZ and two prolin-rich domains). The chromosome 11 breakpoint was localized in an intergenic segment. Reverse transcriptase-polymerase chain reaction analysis revealed PDZD7 expression in the human inner ear. A murine Pdzd7 transcript that is most similar in structure to human PDZD7-D is known to be expressed in the adult inner ear and retina. PDZD7 shares sequence homology with the PDZ domain-containing genes, USH1C (harmonin) and DFNB31 (whirlin). Allelic mutations in harmonin and whirlin can cause both Usher syndrome (USH1C and USH2D, respectively) and congenital hearing impairment (DFNB18 and DFNB31, respectively). Protein-protein interaction assays revealed the integration of PDZD7 in the protein network related to the human Usher syndrome. Collectively, our data provide strong evidence that PDZD7 is a new autosomal-recessive deafness-causing gene and also a prime candidate gene for Usher syndrome.

De novo t(12;17)(p13.3;q21.3) translocation with a breakpoint near the 5' end of the HOXB gene cluster in a patient with developmental delay and skeletal malformations.

A boy with severe mental retardation, funnel chest, bell-shaped thorax, and hexadactyly of both feet was found to have a balanced de novo t(12;17)(p13.3;q21.3) translocation. FISH with BAC clones and long-range PCR products assessed in the human genome sequence localized the breakpoint on chromosome 17q21.3 to a 21-kb segment that lies <30 kb upstream of the HOXB gene cluster and immediately adjacent to the 3' end of the TTLL6 gene. The breakpoint on chromosome 12 occurred within telomeric hexamer repeats and, therefore, is not likely to affect gene function directly. We propose that juxtaposition of the HOXB cluster to a repetitive DNA domain and/or separation from required cis-regulatory elements gave rise to a position effect.

Outcome of intracytoplasmic sperm injection with and without polar body diagnosis of oocytes.

OBJECTIVE: To compare the reproductive outcome of women undergoing intracytoplasmic sperm injection (ICSI) with or without polar body diagnosis of oocytes. DESIGN: Nonrandomized retrospective study. SETTING: University-based human genetic institute in collaboration with a private fertility center. PATIENT(S): Six hundred seven women undergoing ICSI with polar body diagnosis and 591 women undergoing ICSI without polar body diagnosis at the same time in the same fertility center. INTERVENTION(S): Polar body testing of ICSI oocytes by five-color fluorescence in situ hybridization. MAIN OUTCOME MEASURE(S): Pregnancy rate (positive fetal heartbeats) and live-birth rate (of at least one child). RESULT(S): The pregnancy and live-birth rates were significantly lower in women undergoing ICSI with polar body diagnosis than in women without polar body diagnosis. The negative effects of polar body diagnosis were evident in all analyzed subgroups, that is, women of different age groups, with one ICSI cycle, with transfer of a high-quality embryo, and with male factor infertility as indication for ICSI. CONCLUSION(S): Within the legal restrictions of the German embryo protection law aneuploidy testing of oocytes may not improve reproductive outcome.

A high oocyte yield for intracytoplasmic sperm injection treatment is associated with an increased chromosome error rate.

OBJECTIVE: To compare the chromosome error rate among oocytes from stimulated ovaries after retrieval of 1-5 oocytes, 6-10 oocytes, and >10 oocytes. DESIGN: Retrospective cohort study. SETTING: A university-based human genetic institute in collaboration with a private fertility center. PATIENT(S): Nine hundred thirty-three women undergoing intracytoplasmic sperm injection (ICSI) with a poor prognosis. INTERVENTION(S): Oocyte collection with ovarian stimulation. Polar body testing of ICSI oocytes for common chromosome errors. MAIN OUTCOME MEASURE(S): Chromosome error rate in oocytes, as determined by five-color fluorescence in situ hybridization. RESULT(S): In women less than 35 years and women between 35 and 40 years undergoing the first ICSI cycle, oocytes from the high-yield group had an increased likelihood for detectable chromosome errors (50.9% and 54.6%, respectively), compared to the intermediate-yield group (34.9% and 43.8%) and the low-yield group (23.3% and 41.2%). The overall high rate (>or=50%) of chromosomally abnormal oocytes in women more than 40 years appeared to be mainly due to the maternal age effect and increased only slightly with oocyte yield. CONCLUSION(S): Oocyte yield may be considered as an indicator of ovarian response to hormone stimulation. In women up to 40 years a high yield of oocytes after superovulation is associated with an increased chromosome error rate.

Isolation and differential expression of two isoforms of the ROBO2/Robo2 axon guidance receptor gene in humans and mice.

Expression of Robo receptor molecules is important for axon guidance across the midline of the mammalian central nervous system. Here we describe novel isoform a of human ROBO2, which is initially strongly expressed in the fetal human brain but thereafter only weakly expressed in adult brain and a few other tissues. The known isoform b of ROBO2 shows a more or less ubiquitous expression pattern, suggesting diverse functional roles. The genomic structure and distinct expression patterns of Robo2a and Robo2b have been conserved in the mouse, but in contrast to human ROBO2a mouse Robo2a is also abundant in adult brain. Exons 1 and 2 of human ROBO2a lie in an inherently unstable DNA segment at human chromosome 3p12.3 that is associated with segmental duplications, independent chromosome rearrangements during primate evolution, and homozygous deletion and loss of heterozygosity in various human cancers. The 5' end of mouse Robo2a lies in a <150-kb DNA segment of break in synteny between mouse chromosome 16C3.1 and the human genome.

Comparative cytogenetics of human chromosome 3q21.3 reveals a hot spot for ectopic recombination in hominoid evolution.

Fluorescence in situ hybridization mapping of fully integrated human BAC clones to primate chromosomes, combined with precise breakpoint localization by PCR analysis of flow-sorted chromosomes, was used to analyze the evolutionary rearrangements of the human 3q21.3-syntenic region in orangutan, siamang gibbon, and silvered-leaf monkey. Three independent evolutionary breakpoints were localized within a 230-kb segment contained in BACs RP11-93K22 and RP11-77P16. Approximately 200 kb of the human 3q21.3 sequence was not present on the homologous orangutan, siamang, and Old World monkey chromosomes, suggesting a genomic DNA insertion into the breakpoint region in the lineage leading to humans and African great apes. The breakpoints in the orangutan and siamang genomes were narrowed down to 12- and 20-kb DNA segments, respectively, which are enriched with endogenous retrovirus long terminal repeats and other repetitive elements. The inserted DNA segment represents part of an ancestral duplication. Paralogous sequence blocks were found at human 3q21, approximately 4 Mb proximal to the evolutionary breakpoint cluster region; at human 3p12.3, which contains an independent orangutan-specific breakpoint; and at the subtelomeric and pericentromeric regions of multiple human and orangutan chromosomes. The evolutionary breakpoint regions between human chromosome 3 and orangutan 2 as well their paralogous segments in the human genome coincide with breaks of chromosomal synteny in the mouse, rat, and/or chicken genomes. Collectively our data reveal reuse of the same short recombinogenic DNA segments in primate and vertebrate evolution, supporting a nonrandom breakage model of genome evolution.

Plasticity of human chromosome 3 during primate evolution.

Comparative mapping of more than 100 region-specific clones from human chromosome 3 in Bornean and Sumatran orangutans, siamang gibbon, and Old and New World monkeys allowed us to reconstruct ancestral simian and hominoid chromosomes. A single paracentric inversion derives chromosome 1 of the Old World monkey Presbytis cristata from the simian ancestor. In the New World monkey Callithrix geoffroyi and siamang, the ancestor diverged on multiple chromosomes, through utilizing different breakpoints. One shared and two independent inversions derive Bornean orangutan 2 and human 3, implying that neither Bornean orangutans nor humans have conserved the ancestral chromosome form. The inversions, fissions, and translocations in the five species analyzed involve at least 14 different evolutionary breakpoints along the entire length of human 3; however, particular regions appear to be more susceptible to chromosome reshuffling. The ancestral pericentromeric region has promoted both large-scale and micro-rearrangements. Small segments homologous to human 3q11.2 and 3q21.2 were repositioned intrachromosomally independent of the surrounding markers in the orangutan lineage. Breakage and rearrangement of the human 3p12.3 region were associated with extensive intragenomic duplications at multiple orangutan and gibbon subtelomeric sites. We propose that new chromosomes and genomes arise through large-scale rearrangements of evolutionarily conserved genomic building blocks and additional duplication, amplification, and/or repositioning of inherently unstable smaller DNA segments contained within them.