Further delineation of the phenotype caused by biallelic variants in the WDR4 gene.

Microcephalic primordial dwarfisms are a group of rare Mendelian disorders characterized by severe growth retardation and microcephaly. The molecular basis is heterogeneous, with disease-causing genes implicated in different cellular functions. Recently, 2 patients were reported with the same homozygous variant in the WDR4 gene, coding for an enzyme responsible for the m7 G46 post transcriptional modification of tRNA. We report here 2 sisters harboring compound heterozygous variants of WDR4. Their phenotype differs from that of the first 2 described patients: they both have a severe microcephaly but only one of the 2 sisters had a head circumference at birth below -2 SD, their intellectual deficiency is less severe, and they have a growth hormone deficiency and a partial hypogonadotropic hypogonadotropism. One of the 2 variants is a frameshift mutation, and the other one is a missense occurring in the same nucleotide affected by the first reported pathogenic variant, which could therefore be a mutational hot spot. The description of these 2 sisters allow us to confirm that biallelic variants in the WDR4 gene can lead to a specific phenotype, characterized by severe growth retardation and microcephaly.

Xq28 duplication including MECP2 in six unreported affected females: what can we learn for diagnosis and genetic counselling?

Duplication of the Xq28 region, involving MECP2 (dupMECP2), has been primarily described in males with severe developmental delay, spasticity, epilepsy, stereotyped movements and recurrent infections. Carrier mothers are usually asymptomatic with an extremely skewed X chromosome inactivation (XCI) pattern. We report a series of six novel symptomatic females carrying a de novo interstitial dupMECP2, and review the 14 symptomatic females reported to date, with the aim to further delineate their phenotype and give clues for genetic counselling. One patient was adopted and among the other 19 patients, seven (37%) had inherited their duplication from their mother, including three mildly (XCI: 70/30, 63/37, 100/0 in blood and random in saliva), one moderately (XCI: random) and three severely (XCI: uninformative and 88/12) affected patients. After combining our data with data from the literature, we could not show a correlation between XCI in the blood or duplication size and the severity of the phenotype, or explain the presence of a phenotype in these females. These findings confirm that an abnormal phenotype, even severe, can be a rare event in females born to asymptomatic carrier mothers, making genetic counselling difficult in couples at risk in terms of prognosis, in particular in prenatal cases.

Refining the phenotypical and mutational spectrum of Taybi-Linder syndrome.

Taybi-Linder syndrome (TALS, OMIM 210710) is a rare autosomal recessive disorder belonging to the group of microcephalic osteodysplastic primordial dwarfisms (MOPD). This syndrome is characterized by short stature, skeletal anomalies, severe microcephaly with brain malformations and facial dysmorphism, and is caused by mutations in RNU4ATAC. RNU4ATAC is transcribed into a non-coding small nuclear RNA which is a critical component of the minor spliceosome. We report here four foetuses and four unrelated patients with RNU4ATAC mutations. We provide antenatal descriptions of this rare syndrome including unusual features found in two twin foetuses with compound heterozygosity for two rare mutations who presented with mild intrauterine growth retardation and atypical dysmorphic facial features. We also carried out a literature review of the patients described up to now with RNU4ATAC mutations, affected either with TALS or Roifman syndrome, a recently described allelic disorder.

Update on Kleefstra Syndrome.

Kleefstra syndrome is characterized by the core phenotype of developmental delay/intellectual disability, (childhood) hypotonia and distinct facial features. The syndrome can be either caused by a microdeletion in chromosomal region 9q34.3 or by a mutation in the euchromatin histone methyltransferase 1 (EHMT1) gene. Since the early 1990s, 85 patients have been described, of which the majority had a 9q34.3 microdeletion (>85%). So far, no clear genotype-phenotype correlation could be observed by studying the clinical and molecular features of both 9q34.3 microdeletion patients and patients with an intragenic EHMT1 mutation. Thus, to further expand the genotypic and phenotypic knowledge about the syndrome, we here report 29 newly diagnosed patients, including 16 patients with a 9q34.3 microdeletion and 13 patients with an EHMT1 mutation, and review previous literature. The present findings are comparable to previous reports. In addition to our former findings and recommendations, we suggest cardiac screening during follow-up, because of the possible occurrence of cardiac arrhythmias. In addition, clinicians and caretakers should be aware of the regressive behavioral phenotype that might develop at adolescent/adult age and seems to have no clear neurological substrate, but is rather a so far unexplained neuropsychiatric feature.

Homozygous SMN1 exons 1-6 deletion: pitfalls in genetic counseling and general recommendations for spinal muscular atrophy molecular diagnosis.

We report on a rare homozygous intragenic deletion encompassing exons 1-6 of the SMN1 gene in a patient with spinal muscular atrophy (SMA) born into a consanguineous family. This exceptional configuration induced misinterpretation of the molecular defect involved in this patient, who was first reported as having a classic SMN1 exon 7 deletion. This case points out the possible pitfalls in molecular diagnosis of SMA in affected patients and their relatives: exploration of the SMN1 exon 7 (c.840C/T alleles) may be disturbed by several non-pathological or pathological variants around the SMN1 exon 7. In order to accurately describe the molecular defect in an SMA-affected patient, we propose to apply the Human Genome Variation Society nomenclature. This widely accepted nomenclature would improve the reporting of the molecular defect observed in SMA patients and thus would avoid the commonly used but imprecise terminology "absence of SMN1 exon 7."

Genotype-phenotype relationship in 2 SMA III patients with novel mutations in the Tudor domain.

OBJECTIVE: We report the cases of 2 patients with late-onset spinal muscular atrophy (SMA) type III, who were hemizygous for SMN1 deletion and carriers of novel SMN1 intragenic missense mutations, and we investigate the genotype-phenotype relationship. METHODS: Patients were tested for SMN1 deletions with standard methodology. Sequencing of all exons, exon-intron junctions, and flanking sequences of SMN1 by nested PCR was used to detect intragenic point mutations. SMN1 and SMN2 quantification was undertaken to investigate the genotype-phenotype relationship. RESULTS: Two novel point mutations were identified in exon 3 of SMN1 (p.Tyr130Cys and p.Tyr130His) in the highly conserved Tudor domain of the Smn protein. CONCLUSIONS: The genetic basis of SMA in the rare cases of compound heterozygous carriers of SMN1 deletions is complex. Small intragenic SMN1 mutations often lead to severe SMA phenotypes, especially if the point mutations lie in exon 3 that codes for the highly conserved Tudor domain of the Smn protein. Although both our patients were carriers of intragenic SMN1 mutations in the coding region of the Tudor domain, they presented with a mild SMA phenotype despite a low SMN2 copy number. We discuss the possible determinant role of these novel missense mutations in the phenotypic outcome and compensatory mechanisms that may account for the genotype-phenotype discrepancy.

Chromosome 22q13.3 deletion syndrome with a de novo interstitial 22q13.3 cryptic deletion disrupting SHANK3.

BACKGROUND: The 22q13.3 deletion syndrome (or Phelan-McDermid syndrome, MIM 606232) is characterized by developmental delay, absent or severely delayed speech, neonatal hypotonia, autistic behavior, normal to accelerated growth, and minor dysmorphic facial features. Among the three genes in the minimal critical region (from the centromere to the telomere: SHANK3, ACR and RABL2B), the defect in the SHANK3 gene is considered to be the cause of the neurobehavioral symptoms. OBJECTIVE: We describe the molecular characterization of a de novo interstitial del(22)(q13.3q13.3) disrupting the SHANK3 gene in a child with a phenotype compatible with the 22q13.3 deletion syndrome. METHODS: Clinical work-up included clinical histories, physical, neurological, and ophthalmological examinations, and imaging of the brain. Commercially available MLPA for subtelomeric analysis, FISH specific probes and quantitative real-time PCR were used to characterize the rearrangement. RESULTS: Subtelomere analysis by MLPA showed a discrepancy between P036B and P070 kits (MCR Holland): the P070 MLPA 22q probe (targeting the ARSA gene) showed a deletion but the P036B one (targeting the RABL2B gene) showed a normal result. FISH analysis using LSI TUPLE1/LSI ARSA (Vysis) probes confirmed deletion of ARSA, whereas FISH with N25/N85A3 (Cytocell) probes, targeting the SHANK3 locus was normal. Supplemented FISH analysis using BAC clones allowed us to specify the centromeric breakpoint region of the interstitial deletion between clones RP11-354I12 and RP11-232E17, at less than 2 Mb from the telomere. Quantitative real-time PCR of exon 5, 22 and 24 and intron 9 of SHANK3 showed that the telomeric breakpoint occurred between intron 9 and exon 22. CONCLUSIONS: These data highlight the difficulty of performing an appropriate test aimed at looking for cryptic 22q13.3 deletion. Furthermore, the molecular characterization of this interstitial 22q13.3 deletion contributes to the clinical and genetic delineation of the 22q13.3 deletion syndrome.

Homocysteine-induced decrease in endothelin-1 production is initiated at the extracellular level and involves oxidative products.

The increased cardiovascular risk associated with hyperhomocysteinemia has been partly related to homocysteine (Hcy)-induced endothelial cell dysfunction. However, the intra or extracellular starting point of the interaction between Hcy and endothelial cells, leading to cellular dysfunction, has not yet been identified. We investigated the effects of both intracellular and extracellular Hcy accumulation on endothelin-1 (ET-1) synthesis by cultured human endothelial cells. Incubation of cultures with methionine (1.0 mmol x L(-1)) for 2 h induced a slight increase in cellular Hcy content but no change in ET-1 production. Incubation of cells with Hcy (0.2 mmol x L(-1)) led to a significant fall in ET-1 generation, accompanied by a significant increase in cellular Hcy content. Addition of the amino-acid transport system L substrate 2-amino-2-norbornane carboxylic acid had no effect on the Hcy-induced decrease in ET-1 production but significantly inhibited the Hcy-induced increase in the cellular Hcy content. Incubation of cells with a lower Hcy concentration (0.05 mmol x L(-1)) also reduced ET-1 production without increasing the cellular Hcy content. Co-incubation with extracellular free-radical inhibitors (superoxide dismutase, catalase and mannitol) markedly reduced the effect of Hcy on ET-1 production. Thus, it is extracellular Hcy accumulation that triggers the decrease in ET-1 production by endothelial cells through oxidative products.

Quantification of TEL-AML1 transcript for minimal residual disease assessment in childhood acute lymphoblastic leukaemia.

Strategies currently used for residual disease detection in acute lymphoblastic leukaemia (ALL) rely on polymerase chain reaction (PCR) detection of immunoglobulin and T-cell receptor rearrangements. The TEL-AML1 fusion transcript, which is associated with t(12;21) (p13;q22), is found in 25% of childhood B-cell precursor ALL, and represents an interesting alternative target. We compared two methods for quantitating TEL-AML1 fusion transcripts: competitive PCR and real-time PCR. These techniques showed similar sensitivity (5 x 10(-5)) and reproducibility. Giving highly correlated results, both techniques can be conveniently used for TEL-AML1 transcript quantification. The constancy of TEL-AML1 expression was evaluated by measuring TEL-AML1 transcripts at different steps of the cell cycle, and in 21 cases of ALL at diagnosis. No major variation in TEL-AML1 expression was observed during the cell cycle or in 20/21 of the ALL patients. Residual disease was then determined after completion of induction therapy in 20 patients with a TEL-AML1-positive ALL. Seven patients out of 20 (35%) were still positive, including two patients with high level of residual blasts (close to or beyond 10(-2)). When comparison was possible, results obtained using TEL-AML1 quantification were in accordance with those obtained using T-cell receptor rearrangements analysis.

Clinical, histologic, and ultrastructural features of the corneal dystrophy caused by the R124L mutation of the BIGH3 gene.

OBJECTIVE: This study was designed to describe the clinical, histologic, and ultrastructural features of the corneal dystrophy associated with the R124L mutation of the BIGH3 gene. DESIGN: Retrospective clinical and histologic review of a new genetic mutation. PARTICIPANTS: Thirty-four patients from five unrelated French families with corneal dystrophy caused by the R124L mutation of the BIGH3 gene were studied at the clinical, histologic, and ultrastructural levels. Records of patients carrying this mutation were compared with those from three unrelated patients with corneal dystrophy of Bowman's layer (CDB) type 2 (R555Q mutation) and from three unrelated patients with classic corneal granular dystrophy (R555W mutation). INTERVENTION: The mutational genetic status of the BIGH3 gene was determined for each patient, and the histologic and ultrastructural data available after corneal graft were analyzed. MAIN OUTCOMES MEASURES: Genomic DNA was extracted from peripheral blood leukocytes. Exons 4 and 12 of the BIGH3 gene were amplified by the polymerase chain reaction (PCR), and the PCR products were directly sequenced. RESULTS: All 34 patients with the R124L mutation displayed the clinical, histologic, and electron microscopic features of the dystrophy previously described as a superficial variant of corneal granular dystrophy. Combining molecular genetics with clinical and histologic findings established a clear distinction between the R555Q and R555W dystrophies. CONCLUSIONS: The R124L mutation of the BIGH3 gene is associated with specific clinical and morphologic criteria. This indicates that molecular studies are needed for an adequate classification of corneal dystrophies. All criteria are presently available to segregate the dystrophy caused by the R124L mutation (known as CDB1) from the dystrophy caused by the R555Q mutation (known as CDB2).

A novel variant of granular corneal dystrophy caused by association of 2 mutations in the TGFBI gene-R124L and DeltaT125-DeltaE126.

OBJECTIVE: To characterize the molecular defect in the TGFBI gene in a French family affected with an atypical granular corneal dystrophy. PATIENTS: This family comprises 9 affected individuals across 3 generations without consanguineous marriage. METHODS: Light and electron microscopy were used to examine corneal buttons from patients. Exons of the TGFBI gene were amplified by polymerase chain reaction and sequenced directly using an automated method. Restriction digestion analysis and heteroduplex screening were performed to confirm that the mutations identified were not polymorphisms. RESULTS: Round or snow-flakes-like deposits that stained red with Masson trichrome and appeared as dense, rod-shaped structures were observed in the most anterior layers of the central stroma. All patients were heterozygous for the R124L mutation and a novel mutation predicting the deletion of 2 amino acid residues-threonine (T) and glutamic acid (E)-at codons 125 and 126. CONCLUSIONS: This French family is affected with a novel variant of granular dystrophy that is caused by a molecular defect in the TGFBI gene, reported here for the first time. CLINICAL RELEVANCE: These 2 mutations cause a novel variant of granular dystrophy that is intermediate in severity between the classical and superficial variant forms. Arch Ophthalmol. 2000;118:814-818

A new mutation (A546T) of the betaig-h3 gene responsible for a French lattice corneal dystrophy type IIIA.

PURPOSE: To characterize the betaig-h3 gene defect in a French family affected with lattice corneal dystrophy type IIIA (LCDIIIA). METHODS: Histologic examination was performed from corneal buttons of two patients. Genomic DNA was extracted from leukocytes, and exons of the betaig-h3 gene were amplified by polymerase chain reaction to be directly sequenced. RESULTS: Numerous deposits were evident in the stroma and beneath the Bowman membrane, which had all the features of amyloid deposits. Analysis of exon 12 revealed a heterozygous G to A transition on codon 546. CONCLUSION: In contrast to Japanese patients, these French patients affected with LCDIIIA carry a distinct mutation of the betaig-h3 gene (A546T instead of P501T). Therefore, it is unclear whether different mutations could result in the same dystrophy or whether we are dealing with clinical heterogeneity of LCDIIIA.

Refinement of the 6q chromosomal region implicated in transient neonatal diabetes.

Transient neonatal diabetes mellitus (TNDM) is estimated to occur in approximately 1 in 500,000 births and represents 50-60% of cases of neonatal diabetes. The pattern of inheritance of TNDM and its association with chromosome 6 uniparental disomy is consistent with the presence on chromosome 6 of an imprinted gene involved in pancreatic beta-cell development. Systematic screening for chromosome 6 abnormalities in nine families with 13 individuals affected by TNDM revealed paternal isodisomy of chromosome 6 in one child and paternally derived trisomy of the chromosomal region 6q in six children from three unrelated families. To delineate more accurately the region suspected of harboring the gene of interest, precise mapping of the duplicated area was performed in children exhibiting partial 6q trisomy by using microsatellite markers. The smallest region of duplication observed in our patients was flanked by markers D6S308 and D6S1010, which are separated by <1 cM. These findings confirm that TNDM may result from the overexpression of a gene located on chromosome 6q that is exclusively expressed from the paternal allele at least during some periods of life and further refine the localization of this gene.