Genotype–phenotype study of familial haemophagocytic lymphohistiocytosis type 3Sieni, Elena; Cetica, Valentina; Santoro, Alessandra; Beutel, Karin; Mastrodicasa, Elena; Meeths, Marie; Ciambotti, Benedetta; Brugnolo, Francesca; zur Stadt, Udo; Pende, Daniela; Moretta, Lorenzo; Griffiths, Gillian M; Henter, Jan-Inge; Janka, Gritta; Aricò, Maurizio
doi: 10.1136/jmg.2010.085456pmid: 21248318
BackgroundMutations of UNC13D are causative for familial haemophagocytic lymphohistiocytosis type 3 (FHL3; OMIM 608898).ObjectiveTo carry out a genotype–phenotype study of patients with FHL3.MethodsA consortium of three countries pooled data on presenting features and mutations from individual patients with biallelic UNC13D mutations in a common database.Results84 patients with FHL3 (median age 4.1 months) were reported from Florence, Italy (n=54), Hamburg, Germany (n=18), Stockholm, Sweden (n=12). Their ethnic origin was Caucasian (n=57), Turkish (n=10), Asian (n=7), Hispanic (n=4), African (n=3) (not reported (n=3)). Thrombocytopenia was present in 94%, splenomegaly in 96%, fever in 89%. The central nervous system (CNS) was involved in 49/81 (60%) patients versus 36% in patients with FHL2 (p=0.001). A combination of fever, splenomegaly, thrombocytopenia and hyperferritinaemia was present in 71%. CD107a expression, NK activity and Munc 13-4 protein expression were absent or reduced in all but one of the evaluated patients. 54 different mutations were observed, including 15 new ones: 19 missense, 14 deletions or insertions, 12 nonsense, nine splice errors. None was specific for ethnic groups. Patients with two disruptive mutations were younger than patients with two missense mutations (p<0.001), but older than comparable patients with FHL2 (p=0.001).ConclusionUNC13D mutations are scattered over the gene. Ethnic-specific mutations were not identified. CNS involvement is more common than in FHL2; in patients with FHL3 and disruptive mutations, age at diagnosis is significantly higher than in FHL2. The combination of fever, splenomegaly, thrombocytopenia and hyperferritinaemia appears to be the most easily and frequently recognised clinical pattern and their association with defective granule release assay may herald FHL3.
Identification of clinically relevant mosaicism in type I hereditary haemorrhagic telangiectasiaLee, Nadia Prigoda; Matevski, Donco; Dumitru, Daniela; Piovesan, Beata; Rushlow, Diane; Gallie, Brenda L
doi: 10.1136/jmg.2010.088112pmid: 21415079
BackgroundHereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant genetic disorder affecting the vascular system, characterised by epistaxis, arteriovenous malformations and mucocutaneous and gastrointestinal telangiectases. Mutations in two genes, ENG and ACVRL1, account for the majority of cases. Almost all cases of HHT show a family history of HHT-associated symptoms; few cases are de novo. Mutational mosaicism is the presence of two populations of cells, with both mutant and normal genotypes in one individual and generally occurs through de novo mutation events in embryogenesis. Some isolated cases of HHT with no detectable ENG or ACVRL1 mutation may be caused by a mosaic ENG or ACVRL1 mutation that is present at levels below the limit of detection of current molecular screening methods.ObjectiveTo identify clinically relevant mosaicism in type I HHT.MethodsSequencing, quantitative multiplex-PCR and marker analysis were used to identify three HHT families with founders who showed mosaicism for endoglin mutations. Where available, mosaicism was verified by testing different sampling sites, including blood, hair and buccal swabs.ResultsAll three mosaic samples exhibited the mutation in an estimated ≤25% of the DNA. Two of the mosaic patients had clinically confirmed HHT by the Curaçao criteria and the other showed symptoms of HHT. In each case the heterozygous mutation had already been identified in another family member before detection in the mosaic founder.ConclusionsThe results show the importance of investigating patients without prior family history for the presence of mutational mosaicism, as detecting this would enable appropriate genetic screening and targeted medical care for at-risk children of mosaic patients.
A 4.6 kb genomic duplication on 20p12.2–12.3 is associated with brachydactyly type A2 in a Chinese familySu, Peiqiang; Ding, Hongke; Huang, Dongsheng; Zhou, Yan; Huang, Weijun; Zhong, Liangying; Vyse, Tim J; Wang, Yiming
doi: 10.1136/jmg.2010.084814pmid: 21357617
BackgroundBrachydactyly type A2 (BDA2) is an autosomal dominant disorder. It was recently reported that a 5.9 kb duplication and a 5.5 kb duplication in the region 20p12.2–12.3 are associated with BDA2 in two European families.ObjectiveTo characterise a 6-generation Chinese family with 16 members affected by BDA2 and map the gene to 20p12.2–12.3.Methods and resultsA 4.6 kb duplication downstream of the bone morphogenetic protein 2 (BMP2) was identified in the family. The duplication co-segregated with the phenotype and was absent in unaffected family members and control subjects. Coding and splice-site mutations of all annotated genes in the critical region were also excluded. The duplication partially overlaps with the reported duplications but has a different breakpoint. The most conserved 2.1 kb fragment in the duplication was cloned into the pGL3-promoter vector downstream of the firefly luciferase reporter gene in the 5′ to 3′ orientation and transfected into osteosarcoma U-2OS and Hela cells. A reduced luciferase activity was observed.ConclusionThe smallest duplication is described, which partially overlaps the reported duplications but has a different breakpoint, and its association with BDA2 in a Chinese family is confirmed. The results also provide evidence for cis-regulatory sequences in the duplication 3′ of BMP2.
Mosaic trisomy 13: understanding origin using SNP arrayJinawath, Natini; Zambrano, Regina; Wohler, Elizabeth; Palmquist, Maria K; Hoover-Fong, Julie; Hamosh, Ada; Batista, Denise A S
doi: 10.1136/jmg.2010.083931pmid: 21097773
BackgroundTrisomy 13 occurs in 1/10 000–20 000 live births, and mosaicism accounts for 5% of these cases. Phenotype and outcome of mosaic trisomy 13 are variable and poorly understood. Microsatellite analyses of trisomy 13 have indicated the high incidence of maternal meiotic origin and reduced recombination, but no study has focused on mosaic trisomy 13 in live born patients.Methods and resultsSingle-nucleotide polymorphism (SNP) array, fluorescence in situ hybridisation and bioinformatics analyses were performed in three cases of mosaic trisomy 13. Two cases of complete mosaic trisomy 13 originated from meiosis I non-disjunction followed by trisomic rescue; one had crossovers resulting in segmental uniparental disomy in the disomic line, and one had no crossover. Mosaicism for partial trisomy 13 in the third complex case either arose from meiosis II non-disjunction without crossover or in early mitosis followed by anaphase lags. The extra chromosome 13 was maternal in origin in all three cases. Mosaicism percentage calculated from B allele frequencies ranged from 30 to 50.ConclusionsGenotypes and copy number information provided by SNP array allow determination of parental origin and uniparental disomy status and direct quantification of mosaicism. Such information may lead to a better understanding of mechanisms underlying mosaic aneuploidies and the observed phenotypic variability and better prediction of recurrent risk.
Decreased dyskerin levels as a mechanism of telomere shortening in X-linked dyskeratosis congenitaParry, Erin M; Alder, Jonathan K; Lee, Stella S; Phillips, John A; Loyd, James E; Duggal, Priya; Armanios, Mary
doi: 10.1136/jmg.2010.085100pmid: 21415081
Dyskeratosis congenita (DC) is a premature ageing syndrome characterised by short telomeres. An X-linked form of DC is caused by mutations in DKC1 which encodes dyskerin, a telomerase component that is essential for telomerase RNA stability. However, mutations in DKC1 are identifiable in only half of X-linked DC families. A four generation family with pulmonary fibrosis and features of DC was identified. Affected males showed the classic mucocutaneous features of DC and died prematurely from pulmonary fibrosis. Although there were no coding sequence or splicing variants, genome wide linkage analysis of 16 individuals across four generations identified significant linkage at the DKC1 locus, and was accompanied by reduced dyskerin protein levels in affected males. Decreased dyskerin levels were associated with compromised telomerase RNA levels and very short telomeres. These data identify decreased dyskerin levels as a novel mechanism of DC, and indicate that intact dyskerin levels, in the absence of coding mutations, are critical for telomerase RNA stability and for in vivo telomere maintenance.
CHD7 mutations and CHARGE syndrome: the clinical implications of an expanding phenotypeBergman, J E H; Janssen, N; Hoefsloot, L H; Jongmans, M C J; Hofstra, R M W; van Ravenswaaij-Arts, C M A
doi: 10.1136/jmg.2010.087106pmid: 21378379
BackgroundCHARGE syndrome is a highly variable, multiple congenital anomaly syndrome, of which the complete phenotypic spectrum was only revealed after identification of the causative gene in 2004. CHARGE is an acronym for ocular coloboma, congenital heart defects, choanal atresia, retardation of growth and development, genital hypoplasia, and ear anomalies associated with deafness. This typical combination of clinical features is caused by autosomal dominant mutations in the CHD7 gene.ObjectiveTo explore the emerging phenotypic spectrum of CHD7 mutations, with a special focus on the mild end of the spectrum.MethodsWe evaluated the clinical characteristics in our own cohort of 280 CHD7 positive patients and in previously reported patients with CHD7 mutations and compared these with previously reported patients with CHARGE syndrome but an unknown CHD7 status. We then further explored the mild end of the phenotypic spectrum of CHD7 mutations.ResultsWe discuss that CHARGE syndrome is primarily a clinical diagnosis. In addition, we propose guidelines for CHD7 analysis and indicate when evaluation of the semicircular canals is helpful in the diagnostic process. Finally, we give updated recommendations for clinical surveillance of patients with a CHD7 mutation, based on our exploration of the phenotypic spectrum and on our experience in a multidisciplinary outpatient clinic for CHARGE syndrome.ConclusionCHARGE syndrome is an extremely variable clinical syndrome. CHD7 analysis can be helpful in the diagnostic process, but the phenotype cannot be predicted from the genotype.