Pure proximal deletion of chromosome 21 and kyphosis

We report on two unrelated patients with a proximal deletion of the long arm of chromosome 21. The deletion encompassed 14.5Mb of DNA. Molecular studies showed that the two telomeric breakpoints were within the same DNA clone (BAC RP11-56D12). The centromeric breakpoints, however, were separated by only 250kb of DNA (BAC RP11-645E14 and RP11-324B9). The phenotype observed in the two patients was very different, as patient 2, who had the largest deletion, had severe kyphosis not observed in patient 1. Previous studies have identified a 6Mb region of chromosome 21 associated with severe kyphosis. Interestingly, this region overlaps the 250kb segment deleted in patient 2. We suggest that one gene (NT011512.4) located in this small overlapping region might be responsible for severe kyphosis.

Cytogenetic investigation of a child with a mosaic isochromosome 18q and ring 18q

We report on a baby girl from non-consanguineous Palestinian parents with intrauterine growth retardation, low birth weight, and developmental delay. She had a short stature, microcephaly, a prominent metopic suture, a glabellar haemangioma, exophthalmos, hypertelorism, upslanting palpebral fissures, horizontal nystagmus, flat nose, cleft lip and palate, a short neck, widely spaced nipples, umbilical hernia, flexion deformity of the wrist, ulnar deviation of fingers, and right club foot. Cortical atrophy, enlarged ventricles, a thin corpus callosum, thoracic hemivertebrae, and a ventricular septal defect were detected as well. High resolution chromosome analysis identified in 92% of cells an isochromosome 18 and in 8% of cells a ring 18. Molecular cytogenetic investigations confirmed that it was an i(18q) and a r(18q). The hypothesis to account for this anomaly and its corresponding phenotype are discussed.

Pleiotropic effects of CEP290 (NPHP6) mutations extend to Meckel syndrome

Meckel syndrome (MKS) is a rare autosomal recessive lethal condition characterized by central nervous system malformations, polydactyly, multicystic kidney dysplasia, and ductal changes of the liver. Three loci have been mapped (MKS1-MKS3), and two genes have been identified (MKS1/FLJ20345 and MKS3/TMEM67), whereas the gene at the MKS2 locus remains unknown. To identify new MKS loci, a genomewide linkage scan was performed using 10-cM-resolution microsatellite markers in eight families. The highest heterogeneity LOD score was obtained for chromosome 12, in an interval containing CEP290, a gene recently identified as causative of Joubert syndrome (JS) and isolated Leber congenital amaurosis. In view of our recent findings of allelism, at the MKS3 locus, between these two disorders, CEP290 was considered a candidate, and homozygous or compound heterozygous truncating mutations were identified in four families. Sequencing of additional cases identified CEP290 mutations in two fetuses with MKS and in four families presenting a cerebro-reno-digital syndrome, with a phenotype overlapping MKS and JS, further demonstrating that MKS and JS can be variable expressions of the same ciliopathy. These data identify a fourth locus for MKS (MKS4) and the CEP290 gene as responsible for MKS.

Spectrum of MKS1 and MKS3 mutations in Meckel syndrome: a genotype-phenotype correlation. Mutation in brief #960. Online

Meckel syndrome (MKS) is a rare autosomal recessive lethal condition characterized by central nervous system malformations (typically occipital meningoencephalocele), postaxial polydactyly, multicystic kidney dysplasia, and ductal proliferation in the portal area of the liver. MKS is genetically heterogeneous and three loci have been mapped respectively on 17q23 (MKS1), 11q13 (MKS2), and 8q24 (MKS3). Very recently, two genes have been identified: MKS1/FLJ20345 on 17q in Finnish kindreds, carrying the same intronic deletion, c.1408-35_c.1408-7del29, and MKS3/TMEM67 on 8q in families from Pakistan and Oman. Here we report the genotyping of the MKS1 and MKS3 genes in a large, multiethnic cohort of 120 independent cases of MKS. Our first results indicate that the MKS1 and MKS3 genes are each responsible for about 7% of MKS cases with various mutations in different populations. A strong phenotype-genotype correlation, depending on the mutated gene, was observed regarding the type of central nervous system malformation, the frequency of polydactyly, bone dysplasia, and situs inversus. The MKS1 c.1408-35_1408-7del29 intronic mutation was identified in three cases from French or English origin and dated back to 162 generations (approx. 4050 years) ago. We also identified a common MKS3 splice-site mutation, c.1575+1G>A, in five Pakistani sibships of three unrelated families of Mirpuri origin, with an estimated age-of-mutation of 5 generations (125 years).

Low Mannose-Binding Lectin Concentration Is Associated with Severe Infection in Patients with Hematological Cancer Who Are Undergoing Chemotherapy

BACKGROUND

Mannose-binding lectin (MBL) is a serum lectin involved in innate immune response. Low serum MBL concentration may constitute a risk factor for infection in patients receiving myelosuppressive chemotherapy.

METHODS

We conducted a prospective, observational study that assessed MBL concentration as a risk factor for infection in patients with hematological malignancy who were hospitalized to undergo at least 1 chemotherapy cycle. MBL deficiency was defined using an algorithm that considered the serum MBL concentration and the MBL genotype. The primary end point was the ratio of duration of febrile neutropenia to the duration of neutropenia. Secondary end points included the incidence of severe infection (e.g., sepsis, pneumonia, bacteremia, and invasive fungal infection). Logistic regression analysis was conducted, and Fisher's exact test was used to analyze binary outcomes, and Kaplan-Meier estimates and log rank tests were used for time-to-event variables.

RESULTS

We analyzed 255 patients who received 569 cycles of chemotherapy. The median duration of neutropenia per cycle was 7 days (interquartile range, 0-13 days). Sixty-two patients (24%) were found to have MBL deficiency. Febrile neutropenia occurred at least once in 200 patients. No difference in the primary outcome was seen. The incidence of severe infection was higher among MBL-deficient patients than among non-MBL-deficient patients (1.96 vs. 1.34 cases per 100 days for analysis of all patients [P=.008] and 1.85 vs. 0.94 cases per 100 days excluding patients with acute leukemia [P<.001]).

CONCLUSIONS

MBL deficiency does not predispose adults with hematological cancer to more-frequent or more-prolonged febrile episodes during myelosuppressive chemotherapy, but MBL-deficient patients have a greater number of severe infections and experience their first severe infection earlier, compared with nondeficient patients.

The ciliary gene RPGRIP1L is mutated in cerebello-oculo-renal syndrome (Joubert syndrome type B) and Meckel syndrome

Cerebello-oculo-renal syndrome (CORS), also called Joubert syndrome type B, and Meckel (MKS) syndrome belong to the group of developmental autosomal recessive disorders that are associated with primary cilium dysfunction. Using SNP mapping, we identified missense and truncating mutations in RPGRIP1L (KIAA1005) in both CORS and MKS, and we show that inactivation of the mouse ortholog Rpgrip1l (Ftm) recapitulates the cerebral, renal and hepatic defects of CORS and MKS. In addition, we show that RPGRIP1L colocalizes at the basal body and centrosomes with the protein products of both NPHP6 and NPHP4, known genes associated with MKS, CORS and nephronophthisis (a related renal disorder and ciliopathy). In addition, the RPGRIP1L missense mutations found in CORS individuals diminishes the interaction between RPGRIP1L and nephrocystin-4. Our findings show that mutations in RPGRIP1L can cause the multiorgan phenotypic abnormalities found in CORS or MKS, which therefore represent a continuum of the same underlying disorder.

Matthew-Wood syndrome is caused by truncating mutations in the retinol-binding protein receptor gene STRA6

Retinoic acid (RA) is a potent teratogen in all vertebrates when tight homeostatic controls on its endogenous dose, location, or timing are perturbed during early embryogenesis. STRA6 encodes an integral cell-membrane protein that favors RA uptake from soluble retinol-binding protein; its transcription is directly regulated by RA levels. Molecular analysis of STRA6 was undertaken in two human fetuses from consanguineous families we previously described with Matthew-Wood syndrome in a context of severe microphthalmia, pulmonary agenesis, bilateral diaphragmatic eventration, duodenal stenosis, pancreatic malformations, and intrauterine growth retardation. The fetuses had either a homozygous insertion/deletion in exon 2 or a homozygous insertion in exon 7 predicting a premature stop codon in STRA6 transcripts. Five other fetuses presenting at least one of the two major signs of clinical anophthalmia or pulmonary hypoplasia with at least one of the two associated signs of diaphragmatic closure defect or cardiopathy had no STRA6 mutations. These findings suggest a molecular basis for the prenatal manifestations of Matthew-Wood syndrome and suggest that phenotypic overlap with other associations may be due to genetic heterogeneity of elements common to the RA- and fibroblast growth factor-signaling cascades.

Genotype phenotype correlation of 30 patients with Smith-Magenis syndrome (SMS) using comparative genome hybridisation array: cleft palate in SMS is associated with larger deletions

BACKGROUND

Smith-Magenis syndrome (SMS) is rare (prevalence 1 in 25 000) and is associated with psychomotor delay, a particular behavioural pattern and congenital anomalies. SMS is often due to a chromosomal deletion of <4 Mb at the 17p11.2 locus, leading to haploinsufficiency of numerous genes. Mutations of one of these gemes, RAI1, seems to be responsible for the main features found with heterozygous 17p11.2 deletions.

METHODS

We studied DNA from 30 patients with SMS using a 300 bp amplimers comparative genome hybridisation array encompassing 75 loci from a 22 Mb section from the short arm of chromosome 17.

RESULTS

Three patients had large deletions (10%). Genotype-phenotype correlation showed that two of them had cleft palate, which was not found in any of the other patients with SMS (p<0.007, Fisher's exact test). The smallest extra-deleted region associated with cleft palate in SMS is 1.4 Mb, contains <16 genes and is located at 17p11.2-17p12. Gene expression array data showed that the ubiquitin B precursor (UBB) is significantly expressed in the first branchial arch in the fourth and fifth weeks of human development.

CONCLUSION

These data support UBB as a good candidate gene for isolated cleft palate.

Unusual clinical severity of complement membrane cofactor protein-associated hemolytic-uremic syndrome and uniparental isodisomy

Atypical hemolytic-uremic syndrome (aHUS; OMIM 235400) is genetically and clinically heterogeneous. Mutations in membrane cofactor protein (MCP; CD46), a widely expressed complement regulator, predispose to recurrent forms of the disease. Patients carrying MCP mutations have a favorable clinical outcome in comparison to those with factor H (CFH) or factor I (IF) mutations, which lead in most cases to end-stage renal failure. We identified 1 patient who presented at 1 year of age with a first episode of aHUS requiring dialysis therapy. After 2 recurrences of the disease, the patient developed end-stage renal failure. No mutation in the CFH and IF genes was found. A novel homozygous mutation (IVS10+2 T-->C) in the splice-donor of exon 10 encoding the transmembrane region of the MCP gene was associated with dramatically decreased cell-surface expression of MCP. Because the nucleotide substitution was inherited from the patient's father, but not her mother, a large deletion or uniparental disomy was suspected. Both karyotyping and cytogenetic analysis of chromosome 1q32 were performed, for which MCP maps showed no abnormalities. Subsequent genotype analysis using microsatellite markers spanning chromosome 1 showed that the affected child was homozygous for the entire series of markers tested and that all alleles originated from the father. Complete paternal uniparental isodisomy of chromosome 1 is a novel mechanism resulting in severe deficiency of MCP expression. The outcome of the disease reported here indicates that MCP mutation and complete paternal uniparental disomy of chromosome 1 could have an additive effect in determining the severity of the HUS phenotype.

Cytogenetic and histological features of a human embryo with homogeneous chromosome 8 trisomy

BACKGROUND

Homogeneous and complete trisomy 8 is extremely rare. With one recent neonatal exception, all reported cases have been mosaic, due to mitotic non-disjunction during early zygotic development. We report a case of chromosome 8 trisomy in a human embryo examined at Carnegie stage 11 (25 days post-fertilization). It presented severe cardiovascular and central nervous system malformations.

METHODS

The unusual bifid heart in this embryo spurred a detailed histological examination, karyotyping of a chorionic villus sample and subsequent FISH on inter-phase nuclei of intra-embryonic sections.

RESULTS

Trophoblast cells had a karyotype of 47,XX, +8. Within the embryo proper, FISH demonstrated that the trisomy 8 was homogeneous in embryonic as well as extra-embryonic tissues. FQ-PCR supports a meiosis I origin of non-disjunction. In sections, the pharyngeal arches (including cardiac outflow tract), forebrain, mesonephros and liver were absent. Somites and yolk sac blood vessels were irregularly shaped.

CONCLUSION

We show that homogeneous, intra-embryonic trisomy 8 is compatible with implantation and early human development. Molecular pathways that may be compromised and their impact on organogenesis are discussed.

Prenatal diagnosis and normal outcome of a 46,XX/46,XY chimera: A Case Report

The phenotypic spectrum of 46,XX/46,XY chimeric patients is variable. It ranges from normal male or female genitalia to different degrees of ambiguous genitalia. Chimerism results from the amalgamation of two different zygotes in a single embryo, whereas mosaicism results from a mitotic error in a single zygote. Several other mechanisms resulting in a chimera have been discussed in the literature. Here, we report on a new case of chimerism (46,XX/46,XY) diagnosed at 17 weeks' gestation on amniocentesis performed because of advanced maternal age. Ultrasound examination revealed normal female external genitalia, and a healthy baby girl was delivered at term. We used polymorphic markers spanning the X chromosome and several autosomes in order to identify the genetic mechanism involved. Mosaicism was excluded because of the presence of 3 alleles at 11 autosomal and 4 X chromosome loci. On autosomes, the origin of this third allele was maternal for two pericentromeric markers (located on 2p11.2 band and 8p11.2 band), paternal for six markers and paternal or maternal for the other three markers. On the X chromosome, the origin of the third allele was maternal for all four markers. Thus, two different paternal and maternal haploid sets were observed. These results are compatible with a tetragametic chimera.

Matthew-Wood syndrome: Report of two new cases supporting autosomal recessive inheritance and exclusion ofFGF10 andFGFR2

We describe two fetal cases of microphthalmia/anophthalmia, pulmonary agenesis, and diaphragmatic defect. This rare association is known as Matthew-Wood syndrome (MWS; MIM 601186) or by the acronym "PMD" (Pulmonary agenesis, Microphthalmia, Diaphragmatic defect). Fewer than ten pre- and perinatal diagnoses of Matthew-Wood syndrome have been described to date. The cause is unknown, and the mode of transmission remains unclear. Most cases have been reported as isolated and sporadic, although recurrence among sibs has been observed once. Our two cases both occurred in consanguineous families, further supporting autosomal recessive transmission. In addition, in one family at least one of the elder sibs presented an evocatively similar phenotype. The spatiotemporal expression pattern of the FGF10 and FGFR2 genes in human embryos and the reported phenotypes of knockout mice for these genes spurred us to examine their coding sequences in our two cases of MWS. While in our patients, no causative sequence variations were identified in FGF10 or FGFR2, this cognate ligand-receptor pair and its downstream effectors remain functional candidates for MWS and similar associations of congenital ocular, diaphragmatic and pulmonary malformations.

The Meckel-Gruber syndrome gene, MKS3, is mutated in Joubert syndrome

Joubert syndrome (JS) is an autosomal recessive disorder characterized by cerebellar vermis hypoplasia associated with hypotonia, developmental delay, abnormal respiratory patterns, and abnormal eye movements. The association of retinal dystrophy and renal anomalies defines JS type B. JS is a genetically heterogeneous condition with mutations in two genes, AHI1 and CEP290, identified to date. In addition, NPHP1 deletions identical to those that cause juvenile nephronophthisis have been identified in a subset of patients with a mild form of cerebellar and brainstem anomaly. Occipital encephalocele and/or polydactyly have occasionally been reported in some patients with JS, and these phenotypic features can also be observed in Meckel-Gruber syndrome (MKS). MKS is a rare, autosomal recessive lethal condition characterized by central nervous system malformations (typically, occipital meningoencephalocele), postaxial polydactyly, multicystic kidney dysplasia, and ductal proliferation in the portal area of the liver. Since there is obvious phenotypic overlap between JS and MKS, we hypothesized that mutations in the recently identified MKS genes, MKS1 on chromosome 17q and MKS3 on 8q, may be a cause of JS. After mutation analysis of MKS1 and MKS3 in a series of patients with JS (n=22), we identified MKS3 mutations in four patients with JS, thus defining MKS3 as the sixth JS locus (JBTS6). No MKS1 mutations were identified in this series, suggesting that the allelism is restricted to MKS3.

Sodium/iodide symporter (NIS) gene expression is the limiting step for the onset of thyroid function in the human fetus

CONTEXT

Terminal differentiation of the human thyroid is characterized by the onset of follicle formation and thyroid hormone synthesis at 11 gestational weeks (GW).

OBJECTIVE

This study aimed to investigate the ontogeny of thyroglobulin (Tg), thyroid peroxidase (TPO), sodium/iodide symporter (NIS), pendrin (PDS), dual oxidase 2 (DUOX2), thyroid-stimulating hormone receptor (TSHR), and thyroid transcription factor 1 (TITF1), forkhead box E1 (FOXE1), and paired box gene 8 (PAX8) in the developing human thyroid.

DESIGN

Thyroid tissues from human embryos and fetuses (7-33 GW; n = 45) were analyzed by quantitative PCR to monitor mRNA expression for each gene and by immunohistochemistry to determine the cellular distribution of TITF1, TSHR, Tg, TPO, NIS, and the onset of T4 production. A broken line regression model was fitted for each gene to compare the loglinear increase in expression before and after the onset of T4 synthesis.

RESULTS

TITF1, FOXE1, PAX8, TSHR, and DUOX2 were stably expressed from 7 to 33 GW. Tg, TPO, and PDS expression was detectable as early as 7 GW and was correlated with gestational age (all, P < 0.01), and the slope of the regression line was significantly different before and after the onset of T4 synthesis at 11 GW (all, P < 0.01). NIS expression appeared last and showed the highest fit by the broken line regression model of all genes (correlation age P < 0.0001, broken line regression P < 0.0001). Immunohistochemical studies detected TITF1, TSHR, and Tg in unpolarized thyrocytes before follicle formation. T(4) and NIS labeling were only found in developing follicles from 11 GW on.

CONCLUSION

These results imply a key role of NIS for the onset of human thyroid function.

Chimera and other fertilization errors

The finding of a mixture of 46,XX and 46,XY cells in an individual has been rarely reported in literature. It usually results in individuals with ambiguous genitalia. Approximately 10% of true human hermaphrodites show this type of karyotype. However, the underlying mechanisms are poorly understood. It may be the result of mosaicism or chimerism. By definition, a chimera is produced by the fusion of two different zygotes in a single embryo, while a mosaic contains genetically different cells issued from a single zygote. Several mechanisms are involved in the production of chimera. Stricto sensu, chimerism occurs from the post-zygotic fusion of two distinct embryos leading to a tetragametic chimera. In addition, there are other entities, which are also referred to as chimera: parthenogenetic chimera and chimera resulting from fertilization of the second polar body. Furthermore, a particular type of chimera called 'androgenetic chimera' recently described in fetuses with placental mesenchymal dysplasia and in rare patients with Beckwith-Wiedemann syndrome is discussed. Strategies to study mechanisms leading to the production of chimera and mosaics are also proposed.

NUP98 rearrangements in hematopoietic malignancies: a study of the Groupe Francophone de Cytogénétique Hématologique

The NUP98 gene is fused with 19 different partner genes in various human hematopoietic malignancies. In order to gain additional clinico-hematological data and to identify new partners of NUP98, the Groupe Francophone de Cytogénétique Hématologique (GFCH) collected cases of hematological malignancies where a 11p15 rearrangement was detected. Fluorescence in situ hybridization (FISH) analysis showed that 35% of these patients (23/66) carried a rearrangement of the NUP98 locus. Genes of the HOXA cluster and the nuclear-receptor set domain (NSD) genes were frequently fused to NUP98, mainly in de novo myeloid malignancies whereas the DDX10 and TOP1 genes were equally rearranged in de novo and in therapy-related myeloid proliferations. Involvement of ADD3 and C6ORF80 genes were detected, respectively, in myeloid disorders and in T-cell acute lymphoblastic leukemia (T-ALL), whereas the RAP1GDS1 gene was fused to NUP98 in T-ALL. Three new chromosomal breakpoints: 3q22.1, 7p15 (in a localization distinct from the HOXA locus) and Xq28 were detected in rearrangements with the NUP98 gene locus. The present study as well as a review of the 73 cases previously reported in the literature allowed us to delineate some chromosomal, clinical and molecular features of patients carrying a NUP98 gene rearrangements.