Large Family With Maturity-Onset Diabetes of the Young and a Novel V121I Mutation in HNF4A

Maturity-onset diabetes of the young (MODY) is a subtype of early-onset diabetes mellitus which is characterized by autosomal dominant inheritance. Several genes are known to induce MODY : HNF4A/MODY1, GCK/MODY2, TCF1/MODY3, IPF1/MODY4, TCF2/MODY5 and NEUROD1/MODY6. We studied a Swiss family with 13 diabetic patients over 3 generations. The average age at diagnosis was 35 +/- 15 years (7 subjects before 30). In addition, 2 individuals had an abnormal oral glucose tolerance. The mutation present in this family was located in the DNA binding domain of HNF4A, a strongly conserved region across almost all species, and segregated in all the MODY patients. Identification of this missense mutation allowed for presymptomatic diagnosis in the younger generations and will improve medical follow-up of the predisposed individuals.     

Don't change that (calcium) channel: mutations in the same calcium channel gene can cause multiple distinct phenotypes

Scapuloperoneal spinal muscular atrophy and CMT2C are allelic disorders caused by alterations in TRPV4 Deng et al. (2010) Nature Genetics 42(2):165–169 Mutations in TRPV4 cause Charcot–Marie–Tooth disease type 2C Landouré et al. (2010) Nature Genetics 42(2):170–174 Alterations in the ankyrin domain of TRPV4 cause congenital distal SMA, scapuloperoneal SMA and HMSN2C Auer‐Grumbach et al. (2010) Nature Genetics 42(2):160–164     

Subcortical band heterotopia in rare affected males can be caused by missense mutations in DCX (XLIS) or LIS1.

Subcortical band heterotopia (SBH) are bilateral and symmetric ribbons of gray matter found in the central white matter between the cortex and the ventricular surface, which comprises the less severe end of the lissencephaly (agyria-pachygyria-band) spectrum of malformations. Mutations in DCX (also known as XLIS ) have previously been described in females with SBH. We have now identified mutations in either the DCX or LIS1 gene in three of 11 boys studied, demonstrating for the first time that mutations of either DCX or LIS1 can cause SBH or mixed pachygyria-SBH (PCH-SBH) in males. All three changes detected are missense mutations, predicted to be of germline origin. They include a missense mutation in exon 4 of DCX in a boy with PCH-SBH (R78H), a different missense mutation in exon 4 of DCX in a boy with mild SBH and in his mildly affected mother (R89G) and a missense mutation in exon 6 of LIS1 in a boy with SBH (S169P). The missense mutations probably account for the less severe brain malformations, although other patients with missense mutations in the same exons have had diffuse lissencephaly. Therefore, it appears likely that the effect of the specific amino acid change on the protein determines the severity of the phenotype, with some mutations enabling residual protein function and allowing normal migration in a larger proportion of neurons. However, we expect that somatic mosaic mutations of both LIS1 and DCX will also prove to be an important mechanism in causing SBH in males.     

NTNG1 mutations are a rare cause of Rett syndrome

A translocation that disrupted the netrin G1 gene (NTNG1) was recently reported in a patient with the early seizure variant of Rett syndrome (RTT). The netrin G1 protein (NTNG1) has an important role in the developing central nervous system, particularly in axonal guidance, signalling and NMDA receptor function and was a good candidate gene for RTT. We recruited 115 patients with RTT (females: 25 classic and 84 atypical; 6 males) but no mutation in the MECP2 gene. For those 52 patients with epileptic seizure onset in the first 6 months of life, CDKL5 mutations were also excluded. We aimed to determine whether mutations in NTNG1 accounted for a significant subset of patients with RTT, particularly those with the early onset seizure variant and other atypical presentations. We sequenced the nine coding exons of NTNG1 and identified four sequence variants, none of which were likely to be pathogenic. Mutations in the NTNG1 gene appear to be a rare cause of RTT but NTNG1 function demands further investigation in relation to the central nervous system pathophysiology of the disorder.     

Novel mutations in the human sucrase-isomaltase gene (SI) that cause congenital carbohydrate malabsorption

Disaccharide intolerance I or congenital sucrase-isomaltase deficiency (CSID) is a disorder leading to maldigestion of disaccharides, which is autosomal recessively inherited. Here we analyzed the sucrase-isomaltase (SI) gene from 11 patients of Hungarian origin with congenital sucrase-isomaltase deficiency. Variants in the SI gene had previously been described in CSID patients, which cause amino acid exchanges that affect the transport, the processing, or the function of the SI protein. None of our patients had known mutations for CSID. Our analyses revealed 43 SI variants in total, 15 within exons and one at a splice site. Eight of the exonic mutations lead to amino acid exchanges, causing hypomorph or null alleles. One new variation affects a splice site, which is also predicted to result in a null allele. All potential pathological alterations were present on one allele only. In six out of the 11 patients the phenotype of CSID could be explained by compound heterozygosity.     

Infectious diseases: Further evidence that infection is an infrequent cause of first trimester spontaneous abortion

A previous cohort study found no clinical evidence that infectionoccurred more often in subjects experiencing pregnancy losscompared with those experiencing success ful pregnancy [Simpsonet al (1996) Hum. Reprod., 11, 668—672]. Given these surprisingfindings, we conducted a similar analysis on another cohortalso followed prospectively. Using couples practising naturalfamily planning for conception or contraception, Informationon clinical evidence of infection was gathered beginning withweek 5 of gestation. Information on fever and signs of overtinfection was specilically sought by interview and physicalexamination. Frequencies of urinary, vaginal and other Infectionsin subjects experiencing pregnancy loss were 11.1, 9.5 and 8.7%respectively, not significantly different from rates in subjectshaving liveborns (10.1, 10.2 and 10.3% respectively). Thus,no association between clinical infection and early pregnancyloss (16 weeks) was observed. Cohort studies utilizing biologicallybased assays are awaited because extant data do not provideevidence that clinically evident infections play major rolesin first trimester pregnancy losses.     

Linearizing the thermistory: a reminder that the thermistor can be tamed

The thermistor, a preferred temperature transducer, has a non-linear resistance vs. temperature characteristic. However, the non-linear characteristic of the Wheatstone bridge circuit in which thermistors are usually used can compensate for this, so that, over a selected range, quite accurate linear voltage outputs may be obtained. A selected set of bridge resistor and excitation voltage values are presented together with accuracy data. Comments concerning the application of these circuits include safety considerations.     

Confirmation of EP300 gene mutations as a rare cause of Rubinstein-Taybi syndrome

The Rubinstein-Taybi syndrome (RSTS, MIM 180849), a dominant Mendelian disorder with typical face, short stature, skeletal abnormalities, and mental retardation, is usually caused by heterozygous mutations of the CREBBP gene, but recently, EP300 gene mutations were reported in three individuals. Using quantitative PCR (for the CREBBP and EP300 genes) and genomic sequencing (for the EP300 gene), we studied here 13 patients who had shown no mutation after genomic sequencing of the CREBBP gene in a previous investigation. Two new disease-causing mutations were identified, including a partial deletion of CREBBP and a 1-bp deletion in EP300, c.7100delC (p.P2366fsX2401). The 1-bp deletion represents the fourth EP300 mutation reported to date and was identified in a patient with non-classical RSTS. Based on the very similar structure of the CREBBP and EP300 genes and the higher rate of single-nucleotide polymorphisms in EP300 (2.23 per individual) as compared to CREBBP (0.71 per individual) (P>0.001, Wilcoxon test), it may be assumed that EP300 gene mutations should be as frequent as CREBBP gene mutations. Based on the location of the EP300 gene mutations identified so far (outside the histone acetyl transferase domain) and the observed (although not very striking) phenotypical differences with the EP300 mutations, we propose that most EP300 mutations could be associated with other phenotypes, not classical RSTS.     

KMeyeDB: a graphical database of mutations in genes that cause eye diseases

KMeyeDB ( http://mutview.dmb.med.keio.ac.jp/ ) is a database of human gene mutations that cause eye diseases. We have substantially enriched the amount of data in the database, which now contains information about the mutations of 167 human genes causing eye‐related diseases including retinitis pigmentosa, cone‐rod dystrophy, night blindness, Oguchi disease, Stargardt disease, macular degeneration, Leber congenital amaurosis, corneal dystrophy, cataract, glaucoma, retinoblastoma, Bardet–Biedl syndrome, and Usher syndrome. KMeyeDB is operated using the database software MutationView, which deals with various characters of mutations, gene structure, protein functional domains, and polymerase chain reaction (PCR) primers, as well as clinical data for each case. Users can access the database using an ordinary Internet browser with smooth user‐interface, without user registration. The results are displayed on the graphical windows together with statistical calculations. All mutations and associated data have been collected from published articles. Careful data analysis with KMeyeDB revealed many interesting features regarding the mutations in 167 genes that cause 326 different types of eye diseases. Some genes are involved in multiple types of eye diseases, whereas several eye diseases are caused by different mutations in one gene. Hum Mutat 31:1–8, 2010. © 2010 Wiley‐Liss, Inc.     

Further evidence that genotypically closely related strains of Legionella pneumophila can express different serogroup specific antigens.

The relationship between serogroup and genotype of Legionella pneumophila strains was investigated by restriction fragment length polymorphism (RFLP) typing with a previously standardised method. Of the 51 RFLP types identified, 19 comprised strains of more than one serogroup. Several RFLP types included strains of five or more serogroups. To determine if sharing the same RFLP type indicates that strains are genotypically indistinguishable or merely that they are superficially similar, 31 strains were selected for further analysis with an extended range of restriction endonucleases and nucleic acid probes. In some cases, strains of a particular RFLP type were indistinguishable, while in others the restriction fragment patterns showed minor differences. It is possible that in the latter case the strains are diverging representatives of a parent clone. We conclude that analysis of restriction fragment patterns, either probed or unprobed, provides a more accurate measure of the ancestral relationship between strains than can be obtained with serological methods.     

Further evidence that de novo missense and truncating variants in ZBTB18 cause intellectual disability with variable features

Identification of rare genetic variants in patients with intellectual disability (ID) has been greatly accelerated by advances in next generation sequencing technologies. However, due to small numbers of patients, the complete phenotypic spectrum associated with pathogenic variants in single genes is still emerging. Among these genes is ZBTB18 (ZNF238), which is deleted in patients with 1q43q44 microdeletions who typically present with ID, microcephaly, corpus callosum (CC) abnormalities, and seizures. Here we provide additional evidence for haploinsufficiency or dysfunction of the ZBTB18 gene as the cause of ID in five unrelated patients with variable syndromic features who underwent whole exome sequencing revealing separate de novo pathogenic or likely pathogenic variants in ZBTB18 (two missense alterations and three truncating alterations). The neuroimaging findings in our cohort (CC hypoplasia seen in 4/4 of our patients who underwent MRI) lend further support for ZBTB18 as a critical gene for CC abnormalities. A similar phenotype of microcephaly, CC agenesis, and cerebellar vermis hypoplasia has been reported in mice with central nervous system‐specific knockout of Zbtb18. Our five patients, in addition to the previously described cases of de novo ZBTB18 variants, add to knowledge about the phenotypic spectrum associated with ZBTB18 haploinsufficiency/dysfunction.     

Identification of 21 novel glucokinase (GCK) mutations in UK and European Caucasians with maturity-onset diabetes of the young (MODY)

Maturity-onset diabetes of the young (MODY) resulting from mutations in the glucokinase (GCK) gene accounts for approximately 20% of MODY in the UK. We have performed fluorescent single stranded conformation polymorphism (F-SSCP) analysis or direct sequencing of the GCK gene in 212 patients referred as part of a research cohort or for diagnostic molecular genetic testing. Mutation screening has identified 43 different mutations in 61 individuals, of which 21 are novel. This report details the mutations identified and their associated clinical features.