Biparental Inheritance Research Articles

Gonadal mosaicism as a rare cause of autosomal recessive inheritance

Autosomal recessive diseases are typically caused by the biparental inheritance of familial mutant alleles. Unusual mechanisms by which the recessiveness of a mutant allele is unmasked include uniparental isodisomy and the occurrence of a de novo chromosomal rearrangement that disrupts the other allele. Gonadal mosaicism is a condition in which a postfertilization mutation is confined to the gamete precursors and is not detected in somatic tissues. Gonadal mosaicism is known to give the impression of autosomal recessive inheritance when recurrence of an autosomal-dominant condition among offspring of phenotypically normal parents is observed. Here, we report an extremely rare event in which maternal gonadal mosaicism for a recessive mutation in COL4A4 caused the recurrence of Alport syndrome within a consanguineous family. Such rare occurrence should be taken into account when analyzing pedigrees both for clinical and research purposes.

Maternal inheritance of mitochondrial genomes and complex inheritance of chloroplast genomes in Actinidia Lind.: evidences from interspecific crosses

The inheritance pattern of chloroplast and mitochondria is a critical determinant in studying plant phylogenetics, biogeography and hybridization. To better understand chloroplast and mitochondrial inheritance patterns in Actinidia (traditionally called kiwifruit), we performed 11 artificial interspecific crosses and studied the ploidy levels, morphology, and sequence polymorphisms of chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) of parents and progenies. Sequence analysis showed that the mtDNA haplotypes of F1 hybrids entirely matched those of the female parents, indicating strictly maternal inheritance of Actinidia mtDNA. However, the cpDNA haplotypes of F1 hybrids, which were predominantly derived from the male parent (9 crosses), could also originate from the mother (1 cross) or both parents (1 cross), demonstrating paternal, maternal, and biparental inheritance of Actinidia cpDNA. The inheritance patterns of the cpDNA in Actinidia hybrids differed according to the species and genotypes chosen to be the parents, rather than the ploidy levels of the parent selected. The multiple inheritance modes of Actinidia cpDNA contradicted the strictly paternal inheritance patterns observed in previous studies, and provided new insights into the use of cpDNA markers in studies of phylogenetics, biogeography and introgression in Actinidia and other angiosperms.

Segmental paternal UPD14 – SNP array saves the day?

<h3>Background</h3> A baby in neonatal intensive care with respiratory insufficiency, skeletal dysplasia and dysmorphism was clinically suspected to have paternal uniparental disomy of chromosome 14 (UPD14). Molecular testing for UPD14 was requested. <h3>Methods</h3> Microsatellite markers on chromosome 14 were geno-typed in the affected child and both parents. Standard karyotype and interphase FISH using probes that map to 14qter were performed on the proband. SNP microarray (Illumina HumanCytoS-NP-12) was performed on the parent-child trio. <h3>Results</h3> Single nucleotide polymorphism (SNP) microarray detected a copy number neutral segment showing loss of heterozy-gosity (LOH) of approximately 12 Mb in size at the 14q terminus in the proband, encompassing the UPD14 critical imprinted region at 14q32. A SNP trio analysis showed that this segment was of paternal origin only in the proband, while the remainder of chromosome 14 showed biparental inheritance. The results of microsatel-lite and cytogenetic analyses were consistent with SNP microarray results. <h3>Conclusions</h3> A diagnosis of segmental paternal isoUPD14 was confirmed, consistent with the clinical presentation. SNP micro-array fully characterised the molecular abnormality in this case and may be an efficient replacement for traditional microsatellite-based UPD analyses.

Authors’ response: polarization microscopy and rescue ICSI

1 h We thank Dr Coticchio for his commentary on our article ‘Spindle examination in unfertilized eggs using the polarization microscope can assist rescue ICS’. His view on some key points in our study harmonize with ideas and issues we have discussed and debated over and over. Therefore, we are pleased to be able to highlight answers for issues he has raised. First, we know the issue of whether to perform rescue intracytoplasmic sperm injection (ICSI) or to cancel the current cycle is still under debate. The goal of assisted reproductive technology is to help infertile couples have a healthy baby, not increase the number of transferable embryos of compromised quality. The biological and clinical implications of oocyte ageing are well reported in numerous articles, including cytogenetic abnormalities in the resulting embryo following rescue ICSI (Morton et al., 1997; Pehlivan et al., 2004) as well as congenital abnormalities (Tarin et al., 2002). However, we should also consider that routine ICSI and IVF might also cause an increased risk of major congenital anomalies compared with natural conception (Wen et al., 2012). To our knowledge, there have been reports of successful births following rescue ICSI (Yuzpe et al., 2000; Shalom-PAZ et al., 2011). As previously shown from data in our centre (Shalom-PAZ et al., 2011), out of 20 pregnancies, only one was diagnosed with trisomy 21 and was terminated, while the other children were found to be

The Mitochondrial LSU rRNA Group II Intron of Ustilago maydis Encodes an Active Homing Endonuclease Likely Involved in Intron Mobility

BackgroundThe a2 mating type locus gene lga2 is critical for uniparental mitochondrial DNA inheritance during sexual development of Ustilago maydis. Specifically, the absence of lga2 results in biparental inheritance, along with efficient transfer of intronic regions in the large subunit rRNA gene between parental molecules. However, the underlying role of the predicted LAGLIDADG homing endonuclease gene I-UmaI located within the group II intron LRII1 has remained unresolved.Methodology/Principal FindingsWe have investigated the enzymatic activity of I-UmaI in vitro based on expression of a tagged full-length and a naturally occurring mutant derivative, which harbors only the N-terminal LAGLIDADG domain. This confirmed Mg2+-dependent endonuclease activity and cleavage at the LRII1 insertion site to generate four base pair extensions with 3′ overhangs. Specifically, I-UmaI recognizes an asymmetric DNA sequence with a minimum length of 14 base pairs (5′-GACGGGAAGACCCT-3′) and tolerates subtle base pair substitutions within the homing site. Enzymatic analysis of the mutant variant indicated a correlation between the activity in vitro and intron homing. Bioinformatic analyses revealed that putatively functional or former functional I-UmaI homologs are confined to a few members within the Ustilaginales and Agaricales, including the phylogenetically distant species Lentinula edodes, and are linked to group II introns inserted into homologous positions in the LSU rDNA.Conclusions/SignificanceThe present data provide strong evidence that intron homing efficiently operates under conditions of biparental inheritance in U. maydis. Conversely, uniparental inheritance may be critical to restrict the transmission of mobile introns. Bioinformatic analyses suggest that I-UmaI-associated introns have been acquired independently in distant taxa and are more widespread than anticipated from available genomic data.

Biparental inheritance of organelles in Pelargonium: evidence for intergenomic recombination of mitochondrial DNA

While uniparental transmission of mtDNA is widespread and dominating in eukaryotes leaving mutation as the major source of genotypic diversity, recently, biparental inheritance of mitochondrial genes has been demonstrated in reciprocal crosses of Pelargonium zonale and P. inquinans. The thereby arising heteroplasmy carries the potential for recombination between mtDNAs of different descent, i.e. between the parental mitochondrial genomes. We have analyzed these Pelargonium hybrids for mitochondrial intergenomic recombination events by examining differences in DNA blot hybridization patterns of the mitochondrial genes atp1 and cob. Further investigation of these genes and their flanking regions using nucleotide sequence polymorphisms and PCR revealed DNA segments in the progeny, which contained both P. zonale and P. inquinans sequences suggesting an intergenomic recombination in hybrids of Pelargonium. This turns Pelargonium into an interesting subject for studies of recombination and evolutionary dynamics of mitochondrial genomes.

A homozygous balanced reciprocal translocation suggests LINC00237 as a candidate gene for MOMO (macrosomia, obesity, macrocephaly, and ocular abnormalities) syndrome

Macrosomia, obesity, macrocephaly, and ocular abnormalities syndrome (MOMO syndrome) has been reported in only four patients to date. In these sporadic cases, no chromosomal or molecular abnormality has been identified thus far. Here, we report on the clinical, cytogenetic, and molecular findings in a child of healthy consanguineous parents suffering from MOMO syndrome. Conventional karyotyping revealed an inherited homozygous balanced reciprocal translocation (16;20)(q21;p11.2). Uniparental disomy testing showed bi-parental inheritance for both derivative chromosomes 16 and 20. The patient's oligonucleotide array-comparative genomic hybridization profile revealed no abnormality. From the homozygous balanced reciprocal translocation (16;20)(q21;p11.2), a positional cloning strategy, designed to narrow 16q21 and 20p11.2 breakpoints, revealed the disruption of a novel gene located at 20p11.23. This gene is now named LINC00237, according to the HUGO (Human Genome Organization) nomenclature. The gene apparently leads to the production of a non-coding RNA. We established that LINC00237 was expressed in lymphocytes of control individuals while normal transcripts were absent in lymphocytes of our MOMO patient. LINC00237 was not ubiquitously expressed in control tissues, but it was notably highly expressed in the brain. Our results suggested autosomal recessive inheritance of MOMO syndrome. LINC00237 could play a role in the pathogenesis of this syndrome and could provide new insights into hyperphagia-related obesity and intellectual disability.

Discovery of Rare Homozygous Mutations from Studies of Consanguineous Pedigrees

The unmasking of recessive mutations by virtue of biparental inheritance of the same ancestral haplotype on which they reside (autozygosity) has provided human geneticists with one of their most powerful tools in unraveling the genetic basis of autosomal recessive disorders. This has historically been achieved by tracking the blocks of homozygosity as surrogates of autozygosity using polymorphic microsatellite markers. Mapping the entire set of autozygous blocks per individual (autozygome) at high resolution became possible with the advent of high-density SNP arrays. The more recent availability of next-generation sequencing has markedly accelerated the rate at which rare recessive mutations are identified by obviating the need to prioritize genes for sequencing within candidate autozygous loci. This unit will review the individual and combined use of these techniques in the context of mapping novel recessive disease genes, as well as potential pitfalls and recommended solutions.

Paternal transmission of mitochondrial DNA as an integral part of mitochondrial inheritance in metapopulations of Drosophila simulans

Maternal inheritance is one of the hallmarks of animal mitochondrial DNA (mtDNA) and central to its success as a molecular marker. This mode of inheritance and subsequent lack of heterologous recombination allows us to retrace evolutionary relationships unambiguously down the matriline and without the confounding effects of recombinant genetic information. Accumulating evidence of biparental inheritance of mtDNA (paternal leakage), however, challenges our current understanding of how this molecule is inherited. Here, using Drosophila simulans collected from an East African metapopulation exhibiting recurring mitochondrial heteroplasmy, we conducted single fly matings and screened F1 offspring for the presence of paternal mtDNA using allele-specific PCR assays (AS-PCR). In all, 27 out of 4092 offspring were identified as harboring paternal mtDNA, suggesting a frequency of 0.66% paternal leakage in this species. Our findings strongly suggest that recurring mtDNA heteroplasmy as observed in natural populations of Drosophila simulans is most likely caused by repeated paternal leakage. Our findings further suggest that this phenomenon to potentially be an integral part of mtDNA inheritance in these populations and consequently of significance for mtDNA as a molecular marker.

Biparental Inheritance Through Uniparental Transmission: The Doubly Uniparental Inheritance (DUI) of Mitochondrial DNA

Many bivalvian mollusks have a sperm-transmitted mitochondrial genome (M), along with the standard egg-transmitted one (F). The phenomenon, known as doubly uniparental inheritance (DUI) of mtDNA, is the only known case in which biparental inheritance of a cytoplasmic genome is the rule rather than the exception. In the mussel Mytilus sperm mitochondria disperse randomly among blastomeres in female embryos, but form an aggregate and stay in the same blastomere in male embryos. In adults, somatic tissues of both sexes are dominated by the F genome. Sperm contains only the M genome and eggs the F (and perhaps traces of M). A female produces mostly daughters, mostly sons, or both sexes in about equal numbers, irrespective of its mate. Thus maleness and M mtDNA fate are tightly linked and under maternal control. Hybridization and triploidization affect the former but not the latter, which suggests that the two are not causally linked. Gene content and arrangement are the same in conspecific F and M genomes, but primary sequence has diverged from 20 % to 40 %, depending on species. The two genomes differ at the control region (CR). Synonymous substitutions accumulate faster in the M than the F genome and non-synonymous even faster. Expression studies indicate that the M genome is active only at spermatogenesis. These observations suggest that the M genome is under a more relaxed selective constraint than the F. Some mytilid species carry, in low frequencies, sperm-transmitted mtDNAs whose primary sequence is of the F type and the CR is an F/M mosaic (“masculinized” genomes). In venerids sperm mitochondria behavior, M genome fate and sex determination are as in mytilids. In unionids the M genome also evolves faster than the F and F/M sequence divergence reaches 50 %. The identification of F-specific and M-specific open reading frames in non-coding regions of unionids and mytilids, in conjunction with the CR’s mosaic structure of masculinized genomes, suggest that the mitochondrial genomes of species with DUI carry sequences that affect their transmission route. A model that incorporates these findings is presented in this review.

Highly conserved low‐copy nuclear genes as effective markers for phylogenetic analyses in angiosperms

Organismal phylogeny provides a crucial evolutionary framework for many studies and the angiosperm phylogeny has been greatly improved recently, largely using organellar and rDNA genes. However, low-copy protein-coding nuclear genes have not been widely used on a large scale in spite of the advantages of their biparental inheritance and vast number of choices. Here, we identified 1083 highly conserved low-copy nuclear genes by genome comparison. Furthermore, we demonstrated the use of five nuclear genes in 91 angiosperms representing 46 orders (73% of orders) and three gymnosperms as outgroups for a highly resolved phylogeny. These nuclear genes are easy to clone and align, and more phylogenetically informative than widely used organellar genes. The angiosperm phylogeny reconstructed using these genes was largely congruent with previous ones mainly inferred from organellar genes. Intriguingly, several new placements were uncovered for some groups, including those among the rosids, the asterids, and between the eudicots and several basal angiosperm groups. These conserved universal nuclear genes have several inherent qualities enabling them to be good markers for reconstructing angiosperm phylogeny, even eukaryotic relationships, further providing new insights into the evolutionary history of angiosperms.

Hybridization between an invasive and a native species of the crayfish genus Orconectes in north-central Ohio

Hybridization between native and invasive species is an important but little-studied factor in crayfish invasions, with few documented natural cases. Here, we report genetic evidence of hybridization between invasive O. rusticus (Girard, 1852) and native O. sanbornii (Girard, 1852) in the Huron River in north-central Ohio based on a combination of molecular markers: nuclear DNA, mitochondrial DNA, and allozymes. Although we found no fixed differences between the species at nuclear DNA loci, fixed differences in mtDNA and allozyme loci confirmed the presence of individuals of hybrid ancestry. We also found preliminary evidence of possible mitochondrial recombination and biparental inheritance (though the existence of rare haplotypes cannot be excluded at the present time). We examined morphological features of both species in sympatry and allopatry and confirmed species-diagnostic morphological features including gonopod traits and shape of the annulus ventralis. This study is the second to detect hybridization between O. rusticus and a congener, which suggests that this may be an important mechanism of invasion by O. rusticus when closely related species are present. Further study of this system, including more extensive sampling and additional molecular markers, is necessary to understand the extent and implications of hybridization for the native species.

The mitochondrial genome of the white-rot fungus Flammulina velutipes

Mitochondria are important cellular organelles in eu-karyotic cells and play a crucial role in the generation of adenosine triphosphate (ATP) for biological energy through oxidative phosphorylation. As with chloro-plasts, mitochondria have their own DNA and are self-replicating organelles (Alberts et al., 2002). In animal cells, mitochondrial DNA (mtDNA) is maternally inher-ited. However, mtDNA in fungi is inherited by one of two types of mechanisms: uniparental inheritance (UPI) or biparental inheritance (BPI) (Basse, 2010; Birky, 1975, 2001; Fukuda et al., 1995; Matsumoto and Fukumasa-Nakai, 1996). Fungal mtDNA, which has various sizes ranging from 19 to 121 kb, tends to have a faster evolutionary rate than nuclear DNA (Brown et al., 1982; Bruns and Szaro, 1992). Mitochondrial cyto-chrome

Paternally inherited alleles in male body parts of an ant (Diacamma sp.) sex mosaic: implication for androgenetic male production in the Hymenoptera

Sex mosaicism, also called gynandromorphism, refers to an accidental phenomenon in dioecious organisms (mainly animals) in which an individual phenotype includes both female and male characteristics. Despite the rarity of this phenomenon, elucidating the mechanisms of naturally occurring sex mosaicism should deepen our understanding of diverse sex determination and differentiation systems in nature. We report the results of a genetic study of a sex mosaic individual of the ant Diacamma sp. from Japan’s Okinawa Island. Parentage analysis using microsatellite markers revealed that the female and male parts of the sex mosaic showed different inheritance patterns: female parts had alleles consistent with their biparental inheritance, whereas most of the male parts had alleles consistent with their paternal inheritance (i.e., androgenesis). We discuss plausible cytogenetic mechanisms that gave rise to the male parts of this individual: polyspermy and the subsequent independent cleavage by a surplus sperm pronucleus, and maternal genome elimination after fertilization of an ovule. Moreover, we hypothesize that the androgenetically produced males found in some Hymenoptera might share the same underlying cytogenetic mechanism with hymenopteran sex mosaicism.

Obesity in pycnodysostosis due to UPD1: Possible effect of an imprinted gene on chromosome 1

Pycnodysostosis is a rare autosomal recessive bone disorder that results from loss-of-function mutations in the CTSK gene. This gene is located at chromosome band 1q21 and codes for a lysosomal cysteine protease that functions in bone resorption and remodeling [Gelb et al., 1996]. In the last 40 years, an atypical mode of inheritance (uniparental disomy—UPD) has been recognized as a mechanism responsible for certain genetic disorders. Abnormal genomic imprinting has been detected in several syndromes, including Prader–Willi, Angelman (both in chromosome region 15q11–q13), and Wiedemann–Beckwith (11p15). In addition, the presence of two chromosomes derived from a single parent in an affected individual may be responsible for the homozygosity of autosomal recessive disorders [Kotzot and Utermann, 2005]. Not long after the identification of the CTSK gene in pycnodysostosis, a case of paternal UPD of chromosome 1 (UPD1) was described in a patient with typical pycnodysostosis who was homozygous for a missense mutation present only in the father. Polymorphic DNA markers from chromosome 1 demonstrated that the error occurred due to a meiosis II non-disjunction event [Gelb et al., 1998]. As in this particular case of UPD and pycnodysostosis, all other reported patients with UPD1 do not show unexpected phenotypes aside from the specific condition, suggesting that chromosome 1 is not involved in imprinting disorders [Nimmo et al., 2010]. In further molecular analyses of patients presenting with pycnodysostosis and craniosynosotosis described by Bertola et al. [2010], we determined that one out of six individuals showed paternal UPD1 (case 4). The proposita is an 11-year-old girl, the first child of nonconsanguineous parents, with typical pycnodysostosis, including delayed anterior fontanel closure, multiple bone fractures, short stature, obtuse angle of the mandible, bone sclerosis, and acroosteolysis. She was previously described by Bertola et al. [2010] along with five other patients, all of whom presented with craniosynostosis, previously considered a rare finding in this skeletal dysplasia. Contrary to the others, this patient developed obesity at the age of 8. Endocrine and biochemical analyses showed normal levels of insulin/glycemia, IGFI and IGFBP3, a normal GH response to provocative tests, and moderately elevated levels of leptin. Bidirectional sequencing of the CTSK gene showed a novel homozygous missense mutation, p.Cys318Tyr. The father, but not the mother, was heterozygous for this gene alteration. As UPD1 had already been linked to pycnodysostosis, we performed a microsatellite analysis to investigate whether this mechanism could explain the skeletal dysplasia of our patient. It showed homozygosity for all studied loci in the patient (Fig. 1). Polymorphic markers on chromosome 2 detected biparental inheritance of some markers, thus excluding non-maternity. In autosomal recessive disorders, the parents of affected individuals generally are obligate heterozygotes. This situation can be attributed to consanguinity, especially in rare disorders, to high frequency of the mutant gene in certain populations, or to chance alone. Nevertheless, in the last three decades, UPD has emerged as an alternate mechanism responsible for abnormal phenotypes resulting from homozygosity for autosomal recessive loci. However, the overall importance of this mechanism is not clear. Twentythree cases of UPD for chromosome 1 have been reported, mainly in

Biparental inheritance of chromosomal abnormalities in male twins with non-syndromic mental retardation

In a monozygotic twin couple with mental retardation (MR), we identified a maternally inherited inversion and a paternally inherited translocation: 46,XY,inv(10)(p11.2q21.2)mat,t(9;18)(p22;q21.1)pat. The maternally inherited inv(10) was a benign variant without any apparent phenotypical implications. The translocation breakpoint at 9p was within a cluster of interferon α genes and the 18q21 breakpoint truncated ZBTB7C (zinc finger and BTB containing 7C gene). In addition, analyses with array-CGH revealed a 931 kb maternally inherited deletion on chromosome 8q22 as well as an 875 kb maternally inherited duplication on 5p14. The deletion encompasses the RIM2 (Rab3A-interacting molecule 2), FZD6 (Frizzled homolog 6) and BAALC (Brain and Acute Leukemia Gene, Cytoplasmic) genes and the duplication includes the 5′ end of the CDH9 (cadherin 9) gene. Exome sequencing did not reveal any additional mutations that could explain the MR phenotype. The protein products of the above mentioned genes are involved in different aspects of brain development and/or maintenance of the neurons which suggest that accumulation of genetic defects segregating from both parents might be the basis of MR in the twins. This hypothesis was further supported by protein interaction analysis.

Internal transcribed spacer 2 (nu ITS2 rRNA) sequence-structure phylogenetics: towards an automated reconstruction of the green algal tree of life.

BackgroundChloroplast-encoded genes (matK and rbcL) have been formally proposed for use in DNA barcoding efforts targeting embryophytes. Extending such a protocol to chlorophytan green algae, though, is fraught with problems including non homology (matK) and heterogeneity that prevents the creation of a universal PCR toolkit (rbcL). Some have advocated the use of the nuclear-encoded, internal transcribed spacer two (ITS2) as an alternative to the traditional chloroplast markers. However, the ITS2 is broadly perceived to be insufficiently conserved or to be confounded by introgression or biparental inheritance patterns, precluding its broad use in phylogenetic reconstruction or as a DNA barcode. A growing body of evidence has shown that simultaneous analysis of nucleotide data with secondary structure information can overcome at least some of the limitations of ITS2. The goal of this investigation was to assess the feasibility of an automated, sequence-structure approach for analysis of IT2 data from a large sampling of phylum Chlorophyta.Methodology/Principal FindingsSequences and secondary structures from 591 chlorophycean, 741 trebouxiophycean and 938 ulvophycean algae, all obtained from the ITS2 Database, were aligned using a sequence structure-specific scoring matrix. Phylogenetic relationships were reconstructed by Profile Neighbor-Joining coupled with a sequence structure-specific, general time reversible substitution model. Results from analyses of the ITS2 data were robust at multiple nodes and showed considerable congruence with results from published phylogenetic analyses.Conclusions/SignificanceOur observations on the power of automated, sequence-structure analyses of ITS2 to reconstruct phylum-level phylogenies of the green algae validate this approach to assessing diversity for large sets of chlorophytan taxa. Moreover, our results indicate that objections to the use of ITS2 for DNA barcoding should be weighed against the utility of an automated, data analysis approach with demonstrated power to reconstruct evolutionary patterns for highly divergent lineages.

Albinism does not correlate with biparental inheritance of plastid DNA in interspecific hybrids in Cicer species

Cultivated chickpea ( Cicer arietinum) was crossed with its wild relatives from the genus Cicer to transfer favorable genes from the wider gene pool into the cultivar. Post-hybridization barriers led to yellowing and subsequent senescence from as early as 5 days after fertilization, however, the ovules of hybrid embryos could be rescued in vitro. Hybrids were classified as green, partially green or albino. The hybrid status of regenerated plantlets in vitro was confirmed by amplification of nuclear DNA markers. To check whether chloroplast development correlated with plastid DNA inheritance in these crosses, primers were designed using conserved plastid gene sequences from wild and cultivated species. All three possible plastid inheritance patterns were observed: paternal, maternal and biparental. This is the first report of biparental inheritance of plastid DNA in Cicer. No correlation was observed between parental origin of the plastid genome and degree of albinism, indicating that chloroplast development in hybrid genotypes was mostly influenced by nuclear factors.

Partial paternal uniparental disomy of chromosome 6 in monozygotic twins with transient neonatal diabetes mellitus and macroglossia

Transient neonatal diabetes mellitus (TNDM) usually develops within the first few weeks of life and resolves at a median age of 3 months. In most of the cases, TNDM is caused by the over-expression of a paternally expressed imprinted PLAGL1 locus on chromosome 6q24. The most frequent manifestation other than TNDM is intrauterine growth retardation (IUGR), and in some cases macroglossia. We investigated monozygotic twins who had macroglossia without IUGR. Both of the twins developed insulin-dependent hyperglycemia within the first week of life, which subsequently resolved. DNA profiling with polymerase chain reaction amplification was performed for polymorphic microsatellite markers of chromosome 6. The six informative markers, located between 6p24 and 6q15, showed normal biparental inheritance. However, the six distal informative markers, located between 6q23.2 and the 6q telomeric region, showed the absence of a maternal allele and the presence of a single paternal allele. The monosomy of the 6q telomeric region was not confirmed by chromosome banding showing 46, XX. These findings provide further evidence that partial paternal uniparental disomy of chromosome 6 (pUPD6) causes TNDM. The phenotypes other than diabetes observed in patients with partial pUPD6 may differ from those observed in patients with complete pUPD6.

Mosaic Trisomy 9 at Amniocentesis: Prenatal Diagnosis and Molecular Genetic Analyses

To present prenatal diagnosis and molecular genetic analyses of mosaic trisomy 9. A 35-year-old woman, gravida 3, para 1, underwent amniocentesis at 17 weeks of gestation because of her advanced maternal age. Amniocentesis revealed a karyotype of 47,XX,+9[3]/46,XX[6]. Repeat amniocentesis at 19 weeks of gestation revealed a karyotype of 47,XX,+9[6]/46,XX[19]. At 22 weeks of gestation, she was referred to a tertiary medical center for genetic counseling, and amniocentesis revealed a karyotype of 47,XX,+9[2]/46,XX[22]. Array comparative genomic hybridization analysis of uncultured amniocytes revealed no genomic imbalance in chromosome 9. However, interphase fluorescence in situ hybridization analysis of uncultured amniocytes showed that nine (18%) of 50 cells were trisomic for chromosome 9. Polymorphic DNA marker analyses also revealed a diallelic pattern with unequal biparental inheritance of chromosome 9 and a dosage ratio of 1:18 (paternal allele:maternal allele) in the uncultured amniocytes and a dosage ratio of 1:36 in the cultured amniocytes, indicating that the euploid cell line had maternal uniparental isodisomy for chromosome 9. Level II ultrasound demonstrated bilateral ventriculomegaly. The pregnancy was subsequently terminated, and a malformed fetus was delivered. Postnatal cytogenetic and polymorphic DNA marker analyses of the fetal and extraembryonic tissues confirmed the prenatal diagnosis. Mosaic trisomy 9 carries a high risk of fetal abnormalities warranting detailed sonographic investigation of congenital malformations. Mosaic trisomy 9 can be associated with maternal uniparental disomy for chromosome 9 in euploid cell lines. Array comparative genomic hybridization is limited for the detection of low-level mosaicism.