Peining Li

A translocation causing increased alpha-klotho level results in hypophosphatemic rickets and hyperparathyroidism.

Phosphate homeostasis is central to diverse physiologic processes including energy homeostasis, formation of lipid bilayers, and bone formation. Reduced phosphate levels due to excessive renal loss cause hypophosphatemic rickets, a disease characterized by prominent bone defects; conversely, hyperphosphatemia, a major complication of renal failure, is accompanied by parathyroid hyperplasia, hyperparathyroidism, and osteodystrophy. Here, we define a syndrome featuring both hypophosphatemic rickets and hyperparathyroidism due to parathyroid hyperplasia as well as other skeletal abnormalities. We show that this disease is due to a de novo translocation with a breakpoint adjacent to α-Klotho, which encodes a β-glucuronidase, and is implicated in aging and regulation of FGF signaling. Plasma α-Klotho levels and β-glucuronidase activity are markedly increased in the affected patient; unexpectedly, the circulating FGF23 level is also markedly elevated. These findings suggest that the elevated α-Klotho level mimics aspects of the normal response to hyperphosphatemia and implicate α-Klotho in the selective regulation of phosphate levels and in the regulation of parathyroid mass and function; they also have implications for the pathogenesis and treatment of renal osteodystrophy in patients with kidney failure.

Genome-Wide Oligonucleotide Array Comparative Genomic Hybridization for Etiological Diagnosis of Mental Retardation: A Multicenter Experience of 1499 Clinical Cases

To assess the clinical utility of genome-wide oligonucleotide arrays in diagnosis of mental retardation and to address issues relating to interpretation of copy number changes (CNCs), we collected results on a total of 1499 proband patients from five academic diagnostic laboratories where the same 44K array platform has been used. Three of the five laboratories achieved a diagnostic yield of 14% and the other two had a yield of 11 and 7%, respectively. Approximately 80% of the abnormal cases had a single segment deletion or duplication, whereas the remaining 20% had a compound genomic imbalance involving two or more DNA segments. Deletion of 16p11.2 is a common microdeletion syndrome associated with mental retardation. We classified pathogenic CNCs into six groups according to the structural changes. Our data have demonstrated that the 44K platform provides a reasonable resolution for clinical use and a size of 300 kb can be used as a practical cutoff for further investigations of the clinical relevance of a CNC detected with this platform. We have discussed in depth the issues associated with the clinical use of array CGH and provided guidance for interpretation, reporting, and counseling of test results based on our experience.

Analytical and Clinical Validity of Whole-Genome Oligonucleotide Array Comparative Genomic Hybridization for Pediatric Patients With Mental Retardation and Developmental Delay

We performed a pilot study to establish the analytical and clinical validity of whole genome oligonucleotide array comparative genomic hybridization (oaCGH) using the 44,000 oligonucleotide array from Agilent Technologies. DNA specimens from 10 patients with different chromosomal abnormalities were used as the test group and sex mismatched normal male or female DNA as references. A series of DNA mixtures containing 50%, 33%, and 25% of a known deletion was generated to evaluate the analytical capacity of oaCGH on detecting mosaic pattern. Receiver operating characteristic (ROC) curves were computed to evaluate sensitivity, specificity, and analytical resolution for detecting deletions, duplications, and mosaic patterns. The oaCGH detected the chromosomally recognized deletions, duplications, and additional genomic aberrations. Flurorescent in situ hybridization (FISH) assays using targeted BAC clone probes confirmed oaCGH findings. Failure in detecting marker chromosomes, a polymorphic inversion, and a Robertsonian translocation was also noted. The oaCGH achieved 99% sensitivity and 99% specificity with a resolution of 300–500 Kb. It also demonstrated 85% sensitivity and 95% specificity in detecting 50% mosaicism; however, increased test‐to‐test variations and reduced sensitivity were noted as the mosaic percentage decreased. Chromosome and oaCGH analyses on 50 pediatric patients with mental retardation (MR) and developmental delay (DD) delineated the genomic content of chromosomal abnormalities in nine cases, pathogenic genomic disorders in three cases and benign genomic variants in six cases. These results affirmed the analytical and clinical validity of oaCGH and prompted a cytogenomic algorithm to integrate oaCGH, chromosome and FISH analyses for genetic diagnosis.

The Distribution and Most Recent Common Ancestor of the 17q21 Inversion in Humans

The polymorphic inversion on 17q21, sometimes called the microtubular associated protein tau (MAPT) inversion, is an approximately 900 kb inversion found primarily in Europeans and Southwest Asians. We have identified 21 SNPs that act as markers of the inverted, i.e., H2, haplotype. The inversion is found at the highest frequencies in Southwest Asia and Southern Europe (frequencies of approximately 30%); elsewhere in Europe, frequencies vary from < 5%, in Finns, to 28%, in Orcadians. The H2 inversion haplotype also occurs at low frequencies in Africa, Central Asia, East Asia, and the Americas, though the East Asian and Amerindian alleles may be due to recent gene flow from Europe. Molecular evolution analyses indicate that the H2 haplotype originally arose in Africa or Southwest Asia. Though the H2 inversion has many fixed differences across the approximately 900 kb, short tandem repeat polymorphism data indicate a very recent date for the most recent common ancestor, with dates ranging from 13,600 to 108,400 years, depending on assumptions and estimation methods. This estimate range is much more recent than the 3 million year age estimated by Stefansson et al. in 2005.

Clinical and Genomic Characterization of Distal Duplications and Deletions of Chromosome 4q: Study of Two Cases and Review of the Literature

Variable clinical presentations of patients with chromosomally detected deletions in the distal long arm (q) of chromosome 4 have been reported. The lack of molecular characterization of the deletion sizes and deleted genes hinders further genotype–phenotype correlation. Using a validated oligonucleotide array comparative genomic hybridization (oaCGH) analysis, we examined two patients with apparent chromosomal deletions in the distal 4q region. In the first, oaCGH identified a 2.441 megabase (Mb) duplication and a 12.651 Mb deletion at 4q34.1 in a pregnant female who transmitted this aberration to her son. This mother has only learning disabilities while her son had both renal and cardiac anomalies in the newborn period. Unrecognized paternal genetic factors may contribute to the variable expression. The second patient is a 17‐year‐old female with a history of Pierre Robin sequence, cardiac abnormalities and learning disabilities. She was diagnosed prenatally with a de novo 4q deletion, and oaCGH defined a 16.435 Mb deletion of 4q34.1–4q35.2. Phenotypic comparison and subtractive genomic mapping between these two cases suggested a 4 Mb region possibly harboring a candidate gene for Pierre Robin sequence. Our cases and review of reported cases with genomic findings indicated the presence of familial variants with variable expressivity as well as de novo or inherited pathogenic simple deletion, duplication and complex deletion and duplication in the distal 4q region.

Karyotype–phenotype insights from 11q14.1-q23.2 interstitial deletions: FZD4 haploinsufficiency and exudative vitreoretinopathy in a patient with a complex chromosome rearrangement†

We detected a unique de novo complex chromosome rearrangement (CCR) in a patient with multiple abnormalities including growth retardation, facial anomalies, exudative vitreoretinopathy (EVR), cleft palate, and minor digital anomalies. Cytogenetic analysis, fluorescent in situ hybridization, and microsatellite genotyping showed a reciprocal translocation between chromosomes 5 and 8, and a complex translocation‐deletion‐inversion process in the formation of derivative chromosomes 11 and 16. High‐density whole‐genome oligonucleotide array comparative genomic hybridization (oaCGH) defined a 35‐megabase interstitial deletion of 11q14.1‐q23.2 and a 1 megabase deletion of 16q22.3‐q23.1. The Frizzled‐4 (FZD4) gene is located within this 11q deletion. Parental studies and sequencing analysis confirmed that the patient was hemizygous for FZD4 due to the loss of a paternal allele on the derivative chromosome 11. Mutations in FZD4 are known to cause autosomal dominant exudative vitreoretinopathy (EVR1). Our patients findings suggest that haploinsufficiency of the FZD4 gene product can also be a disease‐causing mechanism for EVR1. We reviewed the clinical manifestations of 23 cases with 11q14‐q23 interstitial deletions, with particular scrutiny of the present case and four reported cases characterized by molecular cytogenetics. These findings were used to construct a regional deletion map consisting of a haplosufficient segment at 11q14.3, a flanking centromeric segment at 11q14.1‐q14.2, and a flanking telomeric segment at 11q21‐q23.3. We propose that deletions of the FZD4 gene located within the centromeric segment cause retinal dysgenesis, while deletions within the telomeric segment account for dysmorphic craniofacial features, growth and mental retardation, and mild digital anomalies. These results provide insight into karyotype–phenotype correlations and prompt a rational analytic approach to cases with interstitial deletions of the 11q14‐q23 region.

Evidence-based genomic diagnosis characterized chromosomal and cryptic imbalances in 30 elderly patients with myelodysplastic syndrome and acute myeloid leukemia

BackgroundTo evaluate the clinical validity of genome-wide oligonucleotide array comparative genomic hybridization (aCGH) for detecting somatic abnormalities, we have applied this genomic analysis to 30 cases (13 MDS and 17 AML) with clonal chromosomal abnormalities detected in more than 50% of analyzed metaphase cells.ResultsThe aCGH detected all numerical chromosomal gains and losses from the mainline clones and 113 copy number alterations (CNAs) ranging from 0.257 to 102.519 megabases (Mb). Clinically significant recurrent deletions of 5q (involving the RPS14 gene), 12p12.3 (ETV6 gene), 17p13 (TP53 gene), 17q11.2 (NF1 gene) and 20q, double minutes containing the MYC gene and segmental amplification involving the MLL gene were further characterized with defined breakpoints and gene contents. Genomic features of microdeletions at 17q11.2 were confirmed by FISH using targeted BAC clones. The aCGH also defined break points in a derivative chromosome 6, der(6)t(3;6)(q21.3;p22.2), and an isodicentric X chromosome. However, chromosomally observed sideline clonal abnormalities in five cases were not detected by aCGH.ConclusionsOur data indicated that an integrated cytogenomic analysis will be a better diagnostic scheme to delineate genomic contents of chromosomal and cryptic abnormalities in patients with MDS and AML. An evidence-based approach to interpret somatic genomic findings was proposed.

Genomic Characterization of Prenatally Detected Chromosomal Structural Abnormalities Using Oligonucleotide Array Comparative Genomic Hybridization

Detection of chromosomal structural abnormalities using conventional cytogenetic methods poses a challenge for prenatal genetic counseling due to unpredictable clinical outcomes and risk of recurrence. Of the 1,726 prenatal cases in a 3‐year period, we performed oligonucleotide array comparative genomic hybridization (aCGH) analysis on 11 cases detected with various structural chromosomal abnormalities. In nine cases, genomic aberrations and gene contents involving a 3p distal deletion, a marker chromosome from chromosome 4, a derivative chromosome 5 from a 5p/7q translocation, a de novo distal 6q deletion, a recombinant chromosome 8 comprised of an 8p duplication and an 8q deletion, an extra derivative chromosome 9 from an 8p/9q translocation, mosaicism for chromosome 12q with added material of initially unknown origin, an unbalanced 13q/15q rearrangement, and a distal 18q duplication and deletion were delineated. An absence of pathogenic copy number changes was noted in one case with a de novo 11q/14q translocation and in another with a familial insertion of 21q into a 19q. Genomic characterization of the structural abnormalities aided in the prediction of clinical outcomes. These results demonstrated the value of aCGH analysis in prenatal cases with subtle or complex chromosomal rearrangements. Furthermore, a retrospective analysis of clinical indications of our prenatal cases showed that approximately 20% of them had abnormal ultrasound findings and should be considered as high risk pregnancies for a combined chromosome and aCGH analysis.

Double-minute MYC amplification and deletion of MTAP, CDKN2A, CDKN2B, and ELAVL2 in an acute myeloid leukemia characterized by oligonucleotide-array comparative genomic hybridization

Chromosomal analysis and fluorescence in situ hybridization (FISH) have been routinely used in detecting recurrent chromosomal abnormalities in patients with various hematological malignancies. However, the genomic imbalances underlying many recurrent abnormalities could not be delineated due to the low resolution of chromosome analysis. We have performed oligonucleotide-array comparative genomic hybridization (oaCGH) in an AML case with a 15p/17p translocation, a suspected 9p21 deletion, monosomies of chromosomes X and 9, and 2 to 60 double minutes. The oaCGH findings confirmed the chromosomal observations and further characterized a 21.338-Mb 17p deletion, a 3.916-Mb deletion at 9p21.3 containing the MTAP, CDKN2A, CDKN2B, and ELAVL2 genes, and a 3.981-Mb 8q24 double minute containing the TRIB1, FAM84B, MYC, and PVT1 genes, with an average of 30 double minutes in each cell. FISH using MYC probes and bacterial artificial chromosome clone probes confirmed the genomic findings and revealed a progressional pattern for the 9p21.3 deletion. These results demonstrate the potential of oaCGH as a powerful diagnostic tool for characterizing genomic imbalances for patients with hematological malignancies.

Fluorescence In situ Hybridization: Cell-Based Genetic Diagnostic and Research Applications

Fluorescence in situ hybridization (FISH) is a macromolecule recognition technology based on the complementary nature of DNA or DNA/RNA double strands. Selected DNA strands incorporated with fluorophore-coupled nucleotides can be used as probes to hybridize onto the complementary sequences in tested cells and tissues and then visualized through a fluorescence microscope or an imaging system. This technology was initially developed as a physical mapping tool to delineate genes within chromosomes. Its high analytical resolution to a single gene level and high sensitivity and specificity enabled an immediate application for genetic diagnosis of constitutional common aneuploidies, microdeletion/microduplication syndromes, and subtelomeric rearrangements. FISH tests using panels of gene-specific probes for somatic recurrent losses, gains, and translocations have been routinely applied for hematologic and solid tumors and are one of the fastest-growing areas in cancer diagnosis. FISH has also been used to detect infectious microbias and parasites like malaria in human blood cells. Recent advances in FISH technology involve various methods for improving probe labeling efficiency and the use of super resolution imaging systems for direct visualization of intra-nuclear chromosomal organization and profiling of RNA transcription in single cells. Cas9-mediated FISH (CASFISH) allowed in situ labeling of repetitive sequences and single-copy sequences without the disruption of nuclear genomic organization in fixed or living cells. Using oligopaint-FISH and super-resolution imaging enabled in situ visualization of chromosome haplotypes from differentially specified single-nucleotide polymorphism loci. Single molecule RNA FISH (smRNA-FISH) using combinatorial labeling or sequential barcoding by multiple round of hybridization were applied to measure mRNA expression of multiple genes within single cells. Research applications of these single molecule single cells DNA and RNA FISH techniques have visualized intra-nuclear genomic structure and sub-cellular transcriptional dynamics of many genes and revealed their functions in various biological processes.