Autosomal recessive cystinuria caused by genome-wide paternal uniparental isodisomy in a patient with Beckwith-Wiedemann syndrome.

Approximately 20% of Beckwith-Wiedemann syndrome (BWS) cases are caused by mosaic paternal uniparental disomy of chromosome 11 (pUPD11). Although pUPD11 is usually limited to the short arm of chromosome 11, a small minority of BWS cases show genome-wide mosaic pUPD (GWpUPD). These patients show variable clinical features depending on mosaic ratio, imprinting status of other chromosomes, and paternally inherited recessive mutations. To date, there have been no reports of a mosaic GWpUPD patient with an autosomal recessive disease caused by a paternally inherited recessive mutation. Here, we describe a patient concurrently showing the clinical features of BWS and autosomal recessive cystinuria. Genetic analyses revealed that the patient has mosaic GWpUPD and an inherited paternal homozygous mutation in SLC7A9. This is the first report indicating that a paternally inherited recessive mutation can cause an autosomal recessive disease in cases of GWpUPD mosaicism. Investigation into recessive mutations and the dysregulation of imprinting domains is critical in understanding precise clinical conditions of patients with mosaic GWpUPD.

A novel de novo point mutation of the OCT-binding site in the IGF2/H19-imprinting control region in a Beckwith-Wiedemann syndrome patient.

The IGF2/H19-imprinting control region (ICR1) functions as an insulator to methylation-sensitive binding of CTCF protein, and regulates imprinted expression of IGF2 and H19 in a parental origin-specific manner. ICR1 methylation defects cause abnormal expression of imprinted genes, leading to Beckwith-Wiedemann syndrome (BWS) or Silver-Russell syndrome (SRS). Not only ICR1 microdeletions involving the CTCF-binding site, but also point mutations and a small deletion of the OCT-binding site have been shown to trigger methylation defects in BWS. Here, mutational analysis of ICR1 in 11 BWS and 12 SRS patients with ICR1 methylation defects revealed a novel de novo point mutation of the OCT-binding site on the maternal allele in one BWS patient. In BWS, all reported mutations and the small deletion of the OCT-binding site, including our case, have occurred within repeat A2. These findings indicate that the OCT-binding site is important for maintaining an unmethylated status of maternal ICR1 in early embryogenesis.

Genetic and epigenetic alterations on the short arm of chromosome 11 are involved in a majority of sporadic Wilms' tumours.

Wilms' tumour is one of the most common solid tumours of childhood. 11p13 (WT1 locus) and 11p15.5 (WT2 locus) are known to have genetic or epigenetic aberrations in these tumours. In Wilms' tumours, mutation of the Wilms tumour 1 (WT1) gene at the WT1 locus has been reported, and the WT2 locus, comprising the two independent imprinted domains IGF2/H19 and KIP2/LIT1, can undergo maternal deletion or alterations associated with imprinting. Although these alterations have been identified in many studies, it is still not clear how frequently combined genetic and epigenetic alterations of these loci are involved in Wilms' tumours or how these alterations occur. To answer both questions, we performed genetic and epigenetic analyses of these loci, together with an additional gene, CTNNB1, in 35 sporadic Wilms' tumours. Loss of heterozygosity of 11p15.5 and loss of imprinting of IGF2 were the most frequent genetic (29%) and epigenetic (40%) alterations in Wilms' tumours, respectively. In total, 83% of the tumours had at least one alteration at 11p15.5 and/or 11p13. One-third of the tumours had alterations at multiple loci. Our results suggest that chromosome 11p is not only genetically but also epigenetically critical for the majority of Wilms' tumours.

Imprinting disruption of the CDKN1C/KCNQ1OT1 domain: the molecular mechanisms causing Beckwith-Wiedemann syndrome and cancer.

Human chromosomal region 11p15.5, which is homologous to mouse chromosome region 7F5, is a well-known imprinted region. The CDKN1C/KCNQ1OT1 imprinted domain, which is one of two imprinted domains at 11p15.5, includes nine imprinted genes regulated by an imprinting center (IC). The CDKN1C/KCNQ1OT1 IC is a differentially methylated region of KCNQ1OT1(KCNQ1OT-DMR) with DNA methylation on the maternal allele and no methylation on the paternal allele. CDKN1C (alias p57KIP2), an imprinted gene with maternal expression, encoding a cyclin-dependent kinase inhibitor, is a critical gene within the CDKN1C/KCNQ1OT1 domain. In Beckwith-Wiedemann syndrome (BWS), approximately 50% of patients show loss of DNA methylation accompanied by loss of histone H3 Lys9 dimethylation on maternal KCNQ1OT-DMR, namely an imprinting disruption, leading to diminished expression of CDKN1C. In cancer, at least three molecular mechanisms--imprinting disruption, aberrant DNA methylations at the CDKN1C promoter, and loss of heterozygosity (LOH) of the maternal allele--are seen and all three result in diminished expression of CDKN1C. Imprinting disruption of the CDKN1C/KCNQ1OT1 domain is involved in the development of both BWS and cancer and it changes the maternal epigenotype to the paternal type, leading to diminished CDKN1C expression. In this review, we describe recent advances in epigenetic control of the CDKN1C/KCNQ1OT1 imprinted domain in both humans and mice.

A novel imprinted gene, KCNQ1DN, within the WT2 critical region of human chromosome 11p15.5 and its reduced expression in Wilms' tumors.

WT2 is defined by a maternal-specific loss of heterozygosity on human chromosome 11p15.5 in Wilms' and other embryonal tumors. Therefore, the imprinted genes in this region are candidates for involvement in Wilms' tumorigenesis. We now report a novel imprinted gene, KCNQ1DN (KCNQ1 downstream neighbor). This gene is located between p57(KIP2) and KvLQT1 (KCNQ1) of 11p15.5 within the WT2 critical region. KCNQ1DN is imprinted and expressed from the maternal allele. We examined the expression of KCNQ1DN in Wilms' tumors. Seven of eighteen (39%) samples showed no expression. In contrast, other maternal imprinted genes in this region, including p57(KIP2), IMPT1, and IPL exhibited almost normal expression in these samples, although some samples expressed IGF2 biallelically. These results suggest that KCNQ1DN existing far from the H19/IGF2 region may play some role in Wilms' tumorigenesis along with IGF2.

C11orf21, a novel gene within the Beckwith-Wiedemann syndrome region in human chromosome 11p15.5.

A novel gene, C11orf2, was identified by BLAST search in the human chromosome 11p15.5 region potentially responsible for Beckwith-Wiedemann Syndrome (BWS) and some cancers. Two cDNA clones with different sizes were obtained, which share a potential ORF of 399bp and are different in their 3' untranslated regions. This gene was revealed to be expressed exclusively in human heart and in almost no other tissues examined by northern blotting. Two transcripts of different sizes, 0.9 and 3.1kb, were identified in heart, consistent with the length of the two cDNA clones. The gene shows biallelic expression (non-imprinted) in fetal liver, although it is located in the imprinted domain of 11p15.5. C11orf21 codes a protein of 132 amino acids as proved by the expression of C11orf21-EGFP fusion protein in cultured cells. The EGFP-fusion protein expressed in cultured cells localized mainly in the cytoplasm.

Sequence-based structural features between Kvlqt1 and Tapa1 on mouse chromosome 7F4/F5 corresponding to the Beckwith-Wiedemann syndrome region on human 11p15.5: long-stretches of unusually well conserved intronic sequences of kvlqt1 between mouse and human.

Mouse chromosome 7F4/F5 is a syntenic locus of human 11p15.5 in which many imprinted genes are clustered. Transmission of aberrant human 11p15.5 or duplicated 11p causes Beckwith-Wiedemann syndrome (BWS) depending on which parent the chromosome is derived from. To analyze a syntenic mouse locus corresponding to human 11p15.5, mouse BAC contigs were constructed between Nap2 and Tapa1, in which 390 kb was sequenced between Kvlqt1 and Tapa1. An unexpected finding was that of highly conserved intronic sequences of Kvlqt1 between mouse and human, and their homologies came up to at least 160 kb because the length of this gene extended to 350 kb, suggesting the possibility of some functional constraint due to transcriptional and/or post-transcriptional regulation of this region. Many expressed sequence tags (ESTs) were mapped on this locus. Three genes, Lit1 (Kvlqt1-AS), Mtr1 and Tssc4, were identified and characterized. Lit1 is an antisense-transcript of Kvlqt1 and paternally expressed and maternally methylated throughout the developmental stage. The position where Lit1 exists corresponded to a highly conserved region between mouse and human. This transcript extends at least 60 kb from downstream to upstream of exon 10 in Kvlqt1. Tssc4 and Mtr1 carried putative open reading frames but neither was imprinted. Further characterization of this locus based on the sequence comparison between mouse and human will contribute valuable information towards resolving the mechanism of the occurrence of BWS and the associated childhood tumor.

Identification of a novel single nucleotide polymorphism (SNP) in the human organic cation transporter-like 2-antisense (ORCTL2S) gene.

We found a single nucleotide polymorphism (SNP) in exon 3 of the human organic cation transporter-like 2-antisense (ORCTL2S) gene: a base substitution A266G which was confirmed by direct sequencing. Heterozygosity of the polymorphic alleles was 0.45 in a Japanese population. This polymorphism will be useful in the allelic expression analysis of the ORCTL2S gene.

An NsiI RFLP in the human long QT intronic transcript 1 (LIT1).

An NsiI polymorphic site has been found in the human long QT intronic transcript 1 (LIT1). In this transcript, we found a C-to-T transition, which was located between exons 10 and 11 of KVLQT1, and was confirmed by sequencing analysis. The allelic frequency of this polymorphism, was 0.82: 0.18 in Japanese individuals. Our novel polymorphism, combined with other polymorphisms, could be very useful in helping to determine whether the imprinting of LIT1 is disrupted in Beckwith-Wiedemann syndrome (BWS) or in human cancers.

[A case of AIDS patient who was hard to diagnose from an initial symptom of interstitial pneumonitis].

A thirty-six year old male was admitted to the hospital because of fever and dyspnea. On the eighth day the patient turned out to be HIV positive. Although aggressive therapy was performed, the patient died of HIV related disease such as Pneumocystis carinii pneumonitis and CMV infection which led to multiple organ failure seventeen days after admission. We reported a case of AIDS patient who was hard to diagnose from an initial symptom of interstitial pneumonitis.