Refining the phenotype associated with biallelic DNAJC21 mutations.

Inherited bone marrow failure syndromes (IBMFS) are caused by mutations in genes involved in genomic stability. Although they may be recognized by the association of typical clinical features, variable penetrance and expressivity are common, and clinical diagnosis is often challenging. DNAJC21, which is involved in ribosome biogenesis, was recently linked to bone marrow failure. However, the specific phenotype and natural history remain to be defined. We correlate molecular data, phenotype, and clinical history of 5 unreported affected children and all individuals reported in the literature. All patients present features consistent with IBMFS: bone marrow failure, growth retardation, failure to thrive, developmental delay, recurrent infections, and skin, teeth or hair abnormalities. Additional features present in some individuals include retinal abnormalities, pancreatic insufficiency, liver cirrhosis, skeletal abnormalities, congenital hip dysplasia, joint hypermobility, and cryptorchidism. We suggest that DNAJC21-related diseases constitute a distinct IBMFS, with features overlapping Shwachman-Diamond syndrome and Dyskeratosis congenita, and additional characteristics that are specific to DNAJC21 mutations. The full phenotypic spectrum, natural history, and optimal management will require more reports. Considering the aplastic anemia, the possible increased risk for leukemia, and the multisystemic features, we provide a checklist for clinical evaluation at diagnosis and regular follow-up.

Whole-genome array CGH identifies pathogenic copy number variations in fetuses with major malformations and a normal karyotype.

Despite a wide range of clinical tools, the etiology of mental retardation and multiple congenital malformations remains unknown for many patients. Array-based comparative genomic hybridization (aCGH) has proven to be a valuable tool in these cases, as its pangenomic coverage allows the identification of chromosomal aberrations that are undetectable by other genetic methods targeting specific genomic regions. Therefore, aCGH is increasingly used in clinical genetics, both in the postnatal and the prenatal settings. While the diagnostic yield in the postnatal population has been established at 10-12%, studies investigating fetuses have reported variable results. We used whole-genome aCGH to investigate fetuses presenting at least one major malformation detected on ultrasound, but for whom standard genetic analyses (including karyotype) failed to provide a diagnosis. We identified a clinically significant chromosomal aberration in 8.2% of tested fetuses (4/49), and a result of unclear clinical significance in 12.2% of tested fetuses (6/49). Our results document the value of whole-genome aCGH as a prenatal diagnostic tool and highlight the interpretation difficulties associated with copy number variations of unclear significance.

Identification of new susceptibility regions for X;Y translocations in patients with testicular disorder of sex development.

Testicular disorder of sex development in the presence of a 46,XX karyotype is a rare condition. In most instances, it is caused by an X;Y translocation in the paternal gametes, causing SRY to be transferred on the X chromosome. An abnormal recombination event between homologous genes PRKX and PRKY is implicated in approximately one third of the cases. In this study, we report the characterization by fluorescence in situ hybridization of four patients with a 46,X,der(X)t(X;Y) constitution: two monozygotic adult twins, one adult male and a young boy. Molecular cytogenetic analyses using BAC clones specific to the X and Y chromosomes revealed that the translocation is not mediated by an abnormal PRKX-PRKY recombination event in any of our patients. On the other hand, the twins and the adult male have similar breakpoints, having almost the entire short arm of the Y chromosome translocated on their der(X). On their der(X) chromosome, breakpoints are located close to PRKX, in an interval of less than 200 kb. As for the young boy, his breakpoints are located approximately 300 kb proximal to SRY, in Yp11.31, and at the beginning of the pseudoautosomal region in Xp22.33. Our data suggest that some regions are prone to breakage on the sex chromosomes and that these regions represent possible hot spots for X;Y translocations that are not mediated by abnormal recombination.

Molecular studies of a patient with complete androgen insensitivity and a 47,XXY karyotype.

A phenotypic female with complete androgen insensitivity from a maternally inherited mutation in the androgen receptor had a 47,XXY karyotype. Partial maternal X isodisomy explained the expression of androgen insensitivity despite the presence of 2 X chromosomes.

Defining the phenotype in an autosomal recessive cutis laxa syndrome with a combined congenital defect of glycosylation.

Autosomal recessive cutis laxa is a genetically heterogeneous condition. Its molecular basis is largely unknown. Recently, a combined disorder of N- and O-linked glycosylation was described in children with congenital cutis laxa in association with severe central nervous system involvement, brain migration defects, seizures and hearing loss. We report on seven additional patients with similar clinical features in combination with congenital disorder of glycosylation type IIx. On the basis of phenotype in 10 patients, we define an autosomal recessive cutis laxa syndrome. The patients have a complex phenotype of neonatal cutis laxa, transient feeding intolerance, late closure of the fontanel, characteristic facial features including down-slanting palpebral fissures, short nose and small mouth, and developmental delay. There is a variable degree of the central nervous system involvement and variable systemic presentation. The biochemical analysis using transferrin isoelectric focusing gives false negative results in some of the youngest patients. Analysis of the apolipoprotein C-III isoelectric focusing, however, is diagnostic in all cases.

Specific language impairment as the prominent feature in a patient with a low-level trisomy 21 mosaicism.

BACKGROUND: The extent and severity of the disabilities is variable among individuals with Down syndrome, although generally characterized by a range of physical and intellectual conditions, including language impairment. Whether the language deficit is due to the intellectual disability (ID) or associated to the supernumerary or portion of chromosome 21 is still debated. METHODS: Karyotyping was performed on blood lymphocyte and skin fibroblasts. Fluorescence in situ hybridization analysis was performed on cultured lymphocytes and buccal smear cells. RESULTS: The trisomy 21 (T21) mosaicism was characterized by 0.7-10% of mosaic cells in the different tissues, in a 14-year-old girl presenting an intellectual development within the normal range and specific language impairment (SLI) as the only prominent feature. CONCLUSION: This case illustrates the wide range of phenotypical abnormalities possibly associated with T21 mosaicism. We propose that SLI is indeed a phenotypic trait specific to Down syndrome rather than subsequent to the ID most often associated to the syndrome.

Dynamic increase of a 45,X cell line in a patient with multicentric ring Y chromosomes.

Because ring Y chromosomes are unstable during cell division most reported patients are mosaics, usually including a 45,X cell line. The phenotype varies from normal males or females with streak gonads to sexual ambiguities. We present here the case of a 23-year-old man who was referred at 11 years for growth delay. The GTG-banded karyotypes of lymphocytes revealed two cell lines: 46,X,dic r(Y) seen in 76% of the metaphases analyzed and 45,X (24%). Karyotypes and FISH were performed eight years later with the following probes: DYZ3 (Y centromere), SRY (sex-region of the Y), DYZ1 (Yq heterochromatin), CEPX/Y (X centromere and Yq heterochromatin), TelVysion Xp/Yp, Xq/Yq (X and Y subtelomeres), pan-telomeric, cosmid clones LLycos130G04 and LLycos37C09 (PARII), and BAC clone RP11-5C5 (Yq11.223). The results showed an increase in the 45,X cell line (60%) and a reduction in the 46,X,dic r(Y) cell line (36.4%). The use of Yq probes showed that the ring Y chromosome was dicentric. In addition, other ring Y structures were observed. The breakpoints occurred in proximal Yp11.32 or in Yp11.31 distal to SRY and in Yq12 distal to the PARII region. Therefore, most of the Y remained intact and all genes, with the exception of those in PARI, are present in double dosage in the dic r(Y). The level of mosaicism was important in defining the phenotype.

Phenotypic variability in isodicentric Y patients: study of nine cases.

Isodicentric chromosomes are the most commonly reported aberrations of the human Y chromosome. As they are unstable during cell division and can generate various types of cell lines, most reported patients are chromosomal mosaics, generally including a 45,X cell line. Phenotypes depend on the location of the breakpoints as well as on the proportion of each cell line and vary from male to abnormal female or individual with ambiguous genitalia. Although phenotypic variability is known to also depend on the degree of mosaicism in the various tissues, gonads are rarely studied. We report nine cases of isodicentric Y chromosomes studied by conventional and molecular cytogenetic: three males, five females, and one individual with sexual ambiguity. Two males had a non-mosaic karyotype, while the third male was a mosaic with a predominant 46,XY cell line. Three of the females had a major 45,X cell line, while the last two females and the patient with ambiguous genitalia had a major 46,X,idic(Y) cell line. Analyses of gonadal tissues from the individual with sexual ambiguity and of three of the five female patients gave results concordant with their phenotype, allowing us to better understand the sexual differentiation of these patients.

Complex mosaicism in sex reversed SRY+ male twins.

Sex reversal is characterized by discordance between genetic and phenotypic sex. Most XX males result from an unequal interchange between X and Y chromosomes during paternal meiosis, therefore transferring SRY to the X chromosome, which explains the male development in the presence of an otherwise normal female karyotype. We present here the case of sex reversed SRY+ male twins with several cell lines. They consulted for infertility. The presence of SRY on an X chromosome was demonstrated by FISH. Their respective karyotypes were: 46,X,der(X)t(X;Y)(p22.3;p11.2)[249]/45,X [12]/45,der(X)t(X;Y)(p22.3;p11.2)[11]/47,XX,der(X)t(X;Y) (p22.3;p11.2)[1]/47,X,der(X)t(X;Y)(p22.3;p11.2)x2[1]/50, XX,der(X)t(X;Y)(p22.3;p11.2)x4[1]/46,XX[1] for the first twin (SH-1) and 46,X,der(X)t(X;Y)(p22.3;p11.2)[108]/45,X [3]/47,XX,der(X)t(X;Y)(p22.3;p11.2)[2]/45,der(X)t(X;Y) (p22.3;p11.2)[1]/47,X,der(X)t(X;Y)(p22.3;p11.2)x2[1] for the second twin (SH-2). There are three different types of XX males: 1) with normal genitalia, 2) with genital ambiguity, and 3) XX true hermaphrodites. The phenotype of the twins presented in this report is consistent with what is generally seen in XX SRY+ males: they have normal genitalia.

Population history and its impact on medical genetics in Quebec.

Knowledge of the genetic demography of Quebec is useful for gene mapping, diagnosis, treatment, community genetics and public health. The French-Canadian population of Quebec, currently about 6 million people, descends from about 8500 French settlers who arrived in Nouvelle-France between 1608 and 1759. The migrations of those settlers and their descendants led to a series of regional founder effects, reflected in the geographical distribution of genetic diseases in Quebec. This review describes elements of population history and clinical genetics pertinent to the treatment of French Canadians and other population groups from Quebec and summarizes the cardinal features of over 30 conditions reported in French Canadians. Some were discovered in French Canadians, such as autosomal recessive ataxia of the Charlevoix-Saguenay (MIM 270550), agenesis of corpus callosum and peripheral neuropathy (MIM 218000) and French-Canadian-type Leigh syndrome (MIM 220111). Other conditions are particularly frequent or have special genetic characteristics in French Canadians, including oculopharyngeal muscular dystrophy, hepatorenal tyrosinaemia, cystic fibrosis, Leber hereditary optic neuropathy and familial hypercholesterolaemia. Three genetic diseases of Quebec First Nations children are also discussed: Cree encephalitis (MIM 608505), Cree leukoencephalopathy (MIM 603896) and North American Indian childhood cirrhosis (MIM 604901).

Deletions involving long-range conserved nongenic sequences upstream and downstream of FOXL2 as a novel disease-causing mechanism in blepharophimosis syndrome.

The expression of a gene requires not only a normal coding sequence but also intact regulatory regions, which can be located at large distances from the target genes, as demonstrated for an increasing number of developmental genes. In previous mutation studies of the role of FOXL2 in blepharophimosis syndrome (BPES), we identified intragenic mutations in 70% of our patients. Three translocation breakpoints upstream of FOXL2 in patients with BPES suggested a position effect. Here, we identified novel microdeletions outside of FOXL2 in cases of sporadic and familial BPES. Specifically, four rearrangements, with an overlap of 126 kb, are located 230 kb upstream of FOXL2, telomeric to the reported translocation breakpoints. Moreover, the shortest region of deletion overlap (SRO) contains several conserved nongenic sequences (CNGs) harboring putative transcription-factor binding sites and representing potential long-range cis-regulatory elements. Interestingly, the human region orthologous to the 12-kb sequence deleted in the polled intersex syndrome in goat, which is an animal model for BPES, is contained in this SRO, providing evidence of human-goat conservation of FOXL2 expression and of the mutational mechanism. Surprisingly, in a fifth family with BPES, one rearrangement was found downstream of FOXL2. In addition, we report nine novel rearrangements encompassing FOXL2 that range from partial gene deletions to submicroscopic deletions. Overall, genomic rearrangements encompassing or outside of FOXL2 account for 16% of all molecular defects found in our families with BPES. In summary, this is the first report of extragenic deletions in BPES, providing further evidence of potential long-range cis-regulatory elements regulating FOXL2 expression. It contributes to the enlarging group of developmental diseases caused by defective distant regulation of gene expression. Finally, we demonstrate that CNGs are candidate regions for genomic rearrangements in developmental genes.

Complex chromosome rearrangement and recombinant balanced translocation in a mother and a daughter with the same phenotypic abnormalities.

We report on the diagnosis of a complex chromosome rearrangement in a mother and the transmission of a simplified translocation in her fetus. The mother had mental retardation, short stature, facial dysmorphism, and hydronephrosis, but was never investigated before she was pregnant. A blood sample was taken for karyotyping at the time of amniocentesis for advanced maternal age. The mother's karyotype revealed two translocations involving chromosome 5, chromosome 16 twice, and chromosome 20 as follow: 46,XX,t(5;16;20)(5pter-->5q11.2::16q12.1-->16q23::20p11.2-->20pter;16pter-->16q12.1::5q11.2-->5qter;16qter-->16q23::20p11.2-->20qter). The amniocentesis revealed a female karyotype with an apparently balanced translocation: 46,XX,t(16;20)(q23;p11.2). The translocation of the fetus probably resulted from a meiotic recombination between the derived 5 and the normal 16 in the mother. The baby was born and presented the same facial dysmorphism and hydronephrosis. The simplification of a complex rearrangement through recombination into a balanced product has only been rarely described and it is to our knowledge the first time that both the carrier of the complex rearrangement and her descendant with a simplified rearrangement share phenotypic abnormalities.

Multicolor fluorescence in situ hybridization in clinical cytogenetic diagnostics.

Multicolor fluorescence in situ hybridization is a technology that has vastly expanded the diagnostic repertoire of the clinical cytogenetics laboratory. The limitations of conventional chromosome banding analysis can often be overcome by the high sensitivity and specificity of multicolor fluorescence in situ hybridization tests. This article reviews the latest multicolor fluorescence in situ hybridization tests (including multiplex fluorescence in situ hybridization, spectral karyotyping, cross-species color banding, and comparative genomic hybridization) that are currently limited to a few select clinical cytogenetic laboratories, but may soon have more dominant roles in clinical cytogenetic practice.

LDL receptor-related protein 5 (LRP5) affects bone accrual and eye development.

In humans, low peak bone mass is a significant risk factor for osteoporosis. We report that LRP5, encoding the low-density lipoprotein receptor-related protein 5, affects bone mass accrual during growth. Mutations in LRP5 cause the autosomal recessive disorder osteoporosis-pseudoglioma syndrome (OPPG). We find that OPPG carriers have reduced bone mass when compared to age- and gender-matched controls. We demonstrate LRP5 expression by osteoblasts in situ and show that LRP5 can transduce Wnt signaling in vitro via the canonical pathway. We further show that a mutant-secreted form of LRP5 can reduce bone thickness in mouse calvarial explant cultures. These data indicate that Wnt-mediated signaling via LRP5 affects bone accrual during growth and is important for the establishment of peak bone mass.

Prenatal diagnosis and molecular cytogenetics in a case of partial trisomy 14 and monosomy 21.

We report an unbalanced translocation involving chromosomes 14 and 21 which presented as fetal ventriculomegaly at 33 weeks gestation. Second trimester ultrasound had indicated normal fetal anatomy, including normal intracranial structures. Parental karyotypes showed a paternal balanced translocation: 46,XY,t(14;21)(q12;q21). The unbalanced translocation in the fetus resulted in trisomy for 14pter-->q12 and monosomy for 21pter-->q21. Postnatal examination showed that the male infant had a cleft palate, but no cleft lip, and mild dysmorphic features. Postnatal MRI revealed bilateral and symmetric dilatation of the occipital horns, atria, and temporal horns of the lateral ventricles. Molecular cytogenetic techniques were used to delineate further the breakpoint on chromosome 14 to a site distal of the D14S1071 locus and the breakpoint on chromosome 21 to a region between D21S1918 and D21S1902. More precise definitions of chromosomal breakpoints in such clinical cases should provide more accurate prognosis for individuals with unbalanced karyotypes and assist in the identification of putative developmentally important genes.

Integration of cytogenetic landmarks into the draft sequence of the human genome.

We have placed 7,600 cytogenetically defined landmarks on the draft sequence of the human genome to help with the characterization of genes altered by gross chromosomal aberrations that cause human disease. The landmarks are large-insert clones mapped to chromosome bands by fluorescence in situ hybridization. Each clone contains a sequence tag that is positioned on the genomic sequence. This genome-wide set of sequence-anchored clones allows structural and functional analyses of the genome. This resource represents the first comprehensive integration of cytogenetic, radiation hybrid, linkage and sequence maps of the human genome; provides an independent validation of the sequence map and framework for contig order and orientation; surveys the genome for large-scale duplications, which are likely to require special attention during sequence assembly; and allows a stringent assessment of sequence differences between the dark and light bands of chromosomes. It also provides insight into large-scale chromatin structure and the evolution of chromosomes and gene families and will accelerate our understanding of the molecular bases of human disease and cancer.

Phenotype of a patient with pure partial trisomy 2p(p23-->pter).

We present the case of a 7-month-old girl with the karyotype 46,XX, der(13) t(2;13)(p23;p11.2).ish der(13)(wcp2+) de novo. Painting confirmed that the additional segment on 13p was of chromosome 2 origin, resulting in trisomy 2p23 -->2pter. The child had a prominent forehead with a flat hemangioma, depressed nasal bridge, protruding tongue, posteriorly angulated ears, esotropia with poor abduction of the right eye, bilateral severe myopia (-5.5 D), retinal hypopigmentation, foveal hypoplasia, and striking left optic nerve hypoplasia. She also had pectus excavatum, a protruding abdomen with diastasis recti, generalized hypotonia, delayed fine and gross motor development, grade II reflux on the left side, and grade III-IV reflux on the right side. An EEG showed epileptiform discharges. Computed tomographic scan of the brain showed decreased white matter, but magnetic resonance imaging showed normal results.