cGAS-mediated induction of type I interferon due to inborn errors of histone pre-mRNA processing

Inappropriate stimulation or defective negative regulation of the type I interferon response can lead to autoinflammation. In genetically uncharacterized cases of the type I interferonopathy Aicardi-Goutières syndrome, we identified biallelic mutations in LSM11 and RNU7-1, which encode components of the replication-dependent histone pre-mRNA-processing complex. Mutations were associated with the misprocessing of canonical histone transcripts and a disturbance of linker histone stoichiometry. Additionally, we observed an altered distribution of nuclear cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS) and enhanced interferon signaling mediated by the cGAS-stimulator of interferon genes (STING) pathway in patient-derived fibroblasts. Finally, we established that chromatin without linker histone stimulates cyclic guanosine monophosphate-adenosine monophosphate (cGAMP) production in vitro more efficiently. We conclude that nuclear histones, as key constituents of chromatin, are essential in suppressing the immunogenicity of self-DNA.

Bi-allelic Loss-of-Function CACNA1B Mutations in Progressive Epilepsy-Dyskinesia

The occurrence of non-epileptic hyperkinetic movements in the context of developmental epileptic encephalopathies is an increasingly recognized phenomenon. Identification of causative mutations provides an important insight into common pathogenic mechanisms that cause both seizures and abnormal motor control. We report bi-allelic loss-of-function CACNA1B variants in six children from three unrelated families whose affected members present with a complex and progressive neurological syndrome. All affected individuals presented with epileptic encephalopathy, severe neurodevelopmental delay (often with regression), and a hyperkinetic movement disorder. Additional neurological features included postnatal microcephaly and hypotonia. Five children died in childhood or adolescence (mean age of death: 9 years), mainly as a result of secondary respiratory complications. CACNA1B encodes the pore-forming subunit of the pre-synaptic neuronal voltage-gated calcium channel Ca_v2.2/N-type, crucial for SNARE-mediated neurotransmission, particularly in the early postnatal period. Bi-allelic loss-of-function variants in CACNA1B are predicted to cause disruption of Ca²⁺ influx, leading to impaired synaptic neurotransmission. The resultant effect on neuronal function is likely to be important in the development of involuntary movements and epilepsy. Overall, our findings provide further evidence for the key role of Ca_v2.2 in normal human neurodevelopment.

Bi-allelic Loss-of-Function Mutations in the NPR-C Receptor Result in Enhanced Growth and Connective Tissue Abnormalities

The natriuretic peptide signaling pathway has been implicated in many cellular processes, including endochondral ossification and bone growth. More precisely, different mutations in the NPR-B receptor and the CNP ligand have been identified in individuals with either short or tall stature. In this study we show that the NPR-C receptor (encoded by NPR3) is also important for the regulation of linear bone growth. We report four individuals, originating from three different families, with a phenotype characterized by tall stature, long digits, and extra epiphyses in the hands and feet. In addition, aortic dilatation was observed in two of these families. In each affected individual, we identified a bi-allelic loss-of-function mutation in NPR3. The missense mutations (c.442T>C [p.Ser148Pro] and c.1088A>T [p.Asp363Val]) resulted in intracellular retention of the NPR-C receptor and absent localization on the plasma membrane, whereas the nonsense mutation (c.1524delC [p.Tyr508^∗]) resulted in nonsense-mediated mRNA decay. Biochemical analysis of plasma from two affected and unrelated individuals revealed a reduced NTproNP/NP ratio for all ligands and also high cGMP levels. These data strongly suggest a reduced clearance of natriuretic peptides by the defective NPR-C receptor and consequently increased activity of the NPR-A/B receptors. In conclusion, this study demonstrates that loss-of-function mutations in NPR3 result in increased NPR-A/B signaling activity and cause a phenotype marked by enhanced bone growth and cardiovascular abnormalities.

Sudden Cardiac Death Due to Deficiency of the Mitochondrial Inorganic Pyrophosphatase PPA2

We have used whole-exome sequencing in ten individuals from four unrelated pedigrees to identify biallelic missense mutations in the nuclear-encoded mitochondrial inorganic pyrophosphatase (PPA2) that are associated with mitochondrial disease. These individuals show a range of severity, indicating that PPA2 mutations may cause a spectrum of mitochondrial disease phenotypes. Severe symptoms include seizures, lactic acidosis, cardiac arrhythmia, and death within days of birth. In the index family, presentation was milder and manifested as cardiac fibrosis and an exquisite sensitivity to alcohol, leading to sudden arrhythmic cardiac death in the second decade of life. Comparison of normal and mutant PPA2-containing mitochondria from fibroblasts showed that the activity of inorganic pyrophosphatase was significantly reduced in affected individuals. Recombinant PPA2 enzymes modeling hypomorphic missense mutations had decreased activity that correlated with disease severity. These findings confirm the pathogenicity of PPA2 mutations and suggest that PPA2 is a cardiomyopathy-associated protein, which has a greater physiological importance in mitochondrial function than previously recognized.

Fractional Quantum Hall States in a Ge Quantum Well

Measurements of the Hall and dissipative conductivity of a strained Ge quantum well on a SiGe/(001)Si substrate in the quantum Hall regime are reported. We analyze the results in terms of thermally activated quantum tunneling of carriers from one internal edge state to another across saddle points in the long-range impurity potential. This shows that the gaps for different filling fractions closely follow the dependence predicted by theory. We also find that the estimates of the separation of the edge states at the saddle are in line with the expectations of an electrostatic model in the lowest spin-polarized Landau level (LL), but not in the spin-reversed LL where the density of quasiparticle states is not high enough to accommodate the carriers required.

Comprehensive RNA Analysis of the NF1 Gene in Classically Affected NF1 Affected Individuals Meeting NIH Criteria has High Sensitivity and Mutation Negative Testing is Reassuring in Isolated Cases With Pigmentary Features Only

Background

The detection rate for identifying the underlying mutation in neurocutaneous syndromes is affected by the sensitivity of the mutation test and the heterogeneity of the disease based on the diagnostic criteria. Neurofibromatosis type (NF1) has been defined for 29 years by the National Institutes for Health (NIH) criteria which include ≥ 6 Café au Lait macules (CAL) as a defining criterion. The discovery of SPRED1 as a cause of Legius syndrome which is manifested by CAL, freckling and learning difficulties has introduced substantial heterogeneity to the NIH criteria.

Methods

We have defined the sensitivity of comprehensive RNA analysis on blood of presumed NF1 patients meeting NIH criteria with at least one nonpigmentary criterion and determined the proportion of children with ≥ 6 CAL and no family history that has an NF1 or SPRED1 genetic variant. RNA analysis was carried out from 04/2009–12/2015 on 361 NF1 patients.

Findings

A presumed causative NF1 mutation was found in 166/171 (97.08%–95% CI 94.56–99.6%) of familial cases and 182/190 (95.8%–95% CI 92.93–98.65%) sporadic de novo cases. Two of thirteen (15%) mutation negative individuals had dysembryoplastic neuroepithelial tumour (DNET) compared to 2/348 (0.6%) with an NF1 variant (p = 0.007). No SPRED1 variants were found in the thirteen individuals with no NF1 variant. Of seventy-one individuals with ≥ 6 CAL and no non-pigmentary criterion aged 0–20 years, 47 (66.2%) had an NF1 variant six (8.5%) a SPRED1 variant and 18 (25.3%) no disease causing variant. Using the 95.8% detection rate the likelihood of a child with ≥ 6 CAL having constitutional NF1 drops from 2/3 to 1/9 after negative RNA analysis.

Interpretation

RNA analysis in individuals with presumed NF1 has high sensitivity and includes a small subset with DNET without an NF1 variant. Furthermore negative analysis for NF1/SPRED1 provides strong reassurance to children with ≥ 6 CAL that they are unlikely to have NF1.

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RNA testing for NF1 mutations has very high sensitivity (c.96%) and is significantly more sensitive than DNA testing.

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Mosaicism is not a major feature in those with classical NF1.

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Around two thirds of children with just 6 or more café au lait spots have NF1, 8% Legius syndrome.

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Patients with normal RNA testing who meet NF1 criteria but also have a DNET may have a fault in a yet to be identified gene.

Identifying the underlying genetic mutation is of benefit to patients and their families as it clarifies the diagnosis, can give information on the likely disease course and allow predictive testing in pregnancy and early childhood. The present study has shown that testing of blood RNA has very high sensitivity (96%) and allows substantial reassurance to parents whose children have multiple Café au lait birthmarks that they are unlikely to have the poorer outcomes of NF1 if they test negative. Furthermore the study suggests that a different mechanism may underlie the association of NF1 features and a rare benign brain tumour called DNET.

Enhanced diagnostic yield in Meckel-Gruber and Joubert syndrome through exome sequencing supplemented with split-read mapping

Background

The widespread adoption of high-throughput sequencing technologies by genetic diagnostic laboratories has enabled significant expansion of their testing portfolios. Rare autosomal recessive conditions have been a particular focus of many new services. Here we report a cohort of 26 patients referred for genetic analysis of Joubert (JBTS) and Meckel-Gruber (MKS) syndromes, two clinically and genetically heterogeneous neurodevelopmental conditions that define a phenotypic spectrum, with MKS at the severe end.

Methods

Exome sequencing was performed for all cases, using Agilent SureSelect v5 reagents and Illumina paired-end sequencing. For two cases medium-coverage (9×) whole genome sequencing was subsequently undertaken.

Results

Using a standard analysis pipeline for the detection of single nucleotide and small insertion or deletion variants, molecular diagnoses were confirmed in 12 cases (4 %). Seeking to determine whether our cohort harboured pathogenic copy number variants (CNV), in JBTS- or MKS-associated genes, targeted comparative read-depth analysis was performed using FishingCNV. These analyses identified a putative intragenic AHI1 deletion that included three exons spanning at least 3.4 kb and an intergenic MPP4 to TMEM237 deletion that included exons spanning at least 21.5 kb. Whole genome sequencing enabled confirmation of the deletion-containing alleles and precise characterisation of the mutation breakpoints at nucleotide resolution. These data were validated following development of PCR-based assays that could be subsequently used for “cascade” screening and/or prenatal diagnosis.

Conclusions

Our investigations expand the AHI1 and TMEM237 mutation spectrum and highlight the importance of performing CNV screening of disease-associated genes. We demonstrate a robust increasingly cost-effective CNV detection workflow that is applicable to all MKS/JBTS referrals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0265-z) contains supplementary material, which is available to authorized users.

Mutations in CKAP2L, the human homolog of the mouse Radmis gene, cause Filippi syndrome

Filippi syndrome is a rare, presumably autosomal-recessive disorder characterized by microcephaly, pre- and postnatal growth failure, syndactyly, and distinctive facial features, including a broad nasal bridge and underdeveloped alae nasi. Some affected individuals have intellectual disability, seizures, undescended testicles in males, and teeth and hair abnormalities. We performed homozygosity mapping and whole-exome sequencing in a Sardinian family with two affected children and identified a homozygous frameshift mutation, c.571dupA (p.Ile191Asnfs(∗)6), in CKAP2L, encoding the protein cytoskeleton-associated protein 2-like (CKAP2L). The function of this protein was unknown until it was rediscovered in mice as Radmis (radial fiber and mitotic spindle) and shown to play a pivotal role in cell division of neural progenitors. Sanger sequencing of CKAP2L in a further eight unrelated individuals with clinical features consistent with Filippi syndrome revealed biallelic mutations in four subjects. In contrast to wild-type lymphoblastoid cell lines (LCLs), dividing LCLs established from the individuals homozygous for the c.571dupA mutation did not show CKAP2L at the spindle poles. Furthermore, in cells from the affected individuals, we observed an increase in the number of disorganized spindle microtubules owing to multipolar configurations and defects in chromosome segregation. The observed cellular phenotypes are in keeping with data from in vitro and in vivo knockdown studies performed in human cells and mice, respectively. Our findings show that loss-of-function mutations in CKAP2L are a major cause of Filippi syndrome.

An unusual phenotype of X-linked developmental delay and extreme behavioral difficulties associated with a mutation in the EBP gene

We report on a family in which four males over three generations are affected with X-linked recessive developmental delay, learning difficulties, severe behavioral difficulties and mild dysmorphic features. Plasma sterol analysis in three of the four affected males demonstrated increased concentrations of 8-dehydrocholesterol (8-DHC) and cholest-8(9)-enol. All four affected males had a novel hemizygous missense mutation, p.W47R (c.139T>C), in EBP. Functional studies showed raised levels of cholest-8(9)-enol in patient's cultured fibroblast cells, which were suppressed when the cells were incubated with simvastatin. EBP encodes 3β-hydroxysteroid-delta8, delta7-isomerase, a key enzyme involved in the cholesterol biosynthesis pathway. Mutations in EBP have previously been associated with Conradi-Hunermann-Happle syndrome (CHH), an X-linked dominant disorder characterized by skeletal dysplasia, skin, and ocular abnormalities, which is usually lethal in males. Four previous reports describe X-linked recessive multiple anomaly syndromes associated with non-mosaic EBP mutations in males, two at the same amino acid position, p.W47C. This phenotype has previously been described as "MEND" syndrome (male EBP disorder with neurological defects). The family reported herein represent either a novel phenotype, or an expansion of the MEND phenotype, characterized by extreme behavioral difficulties and a scarcity of structural anomalies. Simvastatin therapy is being evaluated in two males from this family.

SAMS, a syndrome of short stature, auditory-canal atresia, mandibular hypoplasia, and skeletal abnormalities is a unique neurocristopathy caused by mutations in Goosecoid

Short stature, auditory canal atresia, mandibular hypoplasia, and skeletal abnormalities (SAMS) has been reported previously to be a rare, autosomal-recessive developmental disorder with other, unique rhizomelic skeletal anomalies. These include bilateral humeral hypoplasia, humeroscapular synostosis, pelvic abnormalities, and proximal defects of the femora. To identify the genetic basis of SAMS, we used molecular karyotyping and whole-exome sequencing (WES) to study small, unrelated families. Filtering of variants from the WES data included segregation analysis followed by comparison of in-house exomes. We identified a homozygous 306 kb microdeletion and homozygous predicted null mutations of GSC, encoding Goosecoid homeobox protein, a paired-like homeodomain transcription factor. This confirms that SAMS is a human malformation syndrome resulting from GSC mutations. Previously, Goosecoid has been shown to be a determinant at the Xenopus gastrula organizer region and a segment-polarity determinant in Drosophila. In the present report, we present data on Goosecoid protein localization in staged mouse embryos. These data and the SAMS clinical phenotype both suggest that Goosecoid is a downstream effector of the regulatory networks that define neural-crest cell-fate specification and subsequent mesoderm cell lineages in mammals, particularly during shoulder and hip formation. Our findings confirm that Goosecoid has an essential role in human craniofacial and joint development and suggest that Goosecoid is an essential regulator of mesodermal patterning in mammals and that it has specific functions in neural crest cell derivatives.

SURF1 deficiency: a multi-centre natural history study

Background

SURF1 deficiency, a monogenic mitochondrial disorder, is the most frequent cause of cytochrome c oxidase (COX) deficient Leigh syndrome (LS). We report the first natural history study of SURF1 deficiency.

Methods

We conducted a multi-centre case notes review of 44 SURF1-deficient patients from ten different UK centres and two Australian centres. Survival data for LRPPRC-deficient LS and nuclear-encoded complex I-deficient LS patients were obtained from previous publications. The survival of SURF1-deficient patients was compared with these two groups using Kaplan-Meier survival analysis and logrank test.

Results

The majority of patients (32/44, 73%) presented in infancy (median 9.5 months). Frequent symptoms were poor weight gain (95%, median age 10 months), hypotonia (93%, median age 14 months), poor feeding/vomiting (89%, median age 10 months), developmental delay (88%, median age 14 months), developmental regression (71%, median age 19 months), movement disorder (52%, median age 24 months), oculomotor involvement (52%, median age 29 months) and central respiratory failure (78%, median age 31 months). Hypertrichosis (41%), optic atrophy (23%), encephalopathy (20%), seizures (14%) and cardiomyopathy (2%) were observed less frequently.

Lactate was elevated in CSF (mean 4.3 mmol/L) in all patients (30/30) and in blood (mean 4.4 mmol/L) in 31/38 (81%). Fibroblast COX activity was universally decreased (25/25). Normal COX histochemistry was noted in 30% of biopsies, whereas muscle COX activity was reduced in 96% (25/26). Neuroimaging demonstrated lesions characteristic of LS in 28/33 (85%) and atypical findings in 3/33 (9%). Peripheral neuropathy was present in 13/16 (81%) (demyelinating 7/16, axonal 2/16). Kaplan-Meier analysis demonstrated that SURF1-deficient patients experience longer survival (median 5.4 years, p < 0.001) compared to LRPPRC deficiency (median 1.8 years) and nuclear-encoded complex I-deficient LS (median 1.6 years). Survival >10 years was observed in 7 patients, 6 of these patients did not experience neurological regression. The most frequent mutation was c.312_320del10insAT. Five novel mutations (c.468_469delTC, c.799_800delCT, c.575G>A (p.Arg192Gln), c.751+5G>A and c.752-2A>G) were identified.

Conclusions

SURF1-deficient patients have a homogeneous clinical and biochemical phenotype. Early recognition is essential to expedite diagnosis and enable prenatal diagnosis.

Rapid visualisation of microarray copy number data for the detection of structural variations linked to a disease phenotype

Whilst the majority of inherited diseases have been found to be caused by single base substitutions, small insertions or deletions (<1Kb), a significant proportion of genetic variability is due to copy number variation (CNV). The possible role of CNV in monogenic and complex diseases has recently attracted considerable interest. However, until the development of whole genome, oligonucleotide micro-arrays, designed specifically to detect the presence of copy number variation, it was not easy to screen an individual for the presence of unknown deletions or duplications with sizes below the level of sensitivity of optical microscopy (3-5 Mb). Now that currently available oligonucleotide micro-arrays have in excess of a million probes, the problem of copy number analysis has moved from one of data production to that of data analysis. We have developed CNViewer, to identify copy number variation that co-segregates with a disease phenotype in small nuclear families, from genome-wide oligonucleotide micro-array data. This freely available program should constitute a useful addition to the diagnostic armamentarium of clinical geneticists.

Clinical characterization of a newly described neonatal diabetes syndrome caused by RFX6 mutations

Mutations in the RFX6 gene were recently described to underlie a distinct autosomal recessive syndrome of neonatal diabetes comprising intestinal atresia and hepatobiliary abnormalities. Until now, only six patients harboring RFX6 mutations have been reported. We report on a new case due to a novel homozygous splice site mutation and update on the clinical outcome of a previously reported patient. In addition we review the clinical and molecular features of all RFX6 mutated cases to better characterize the syndrome. Our results suggest that despite the early postnatal fulminant course, patients who survive may expect a relatively favorable prognosis.

Altered electroretinograms in patients with KCNJ10 mutations and EAST syndrome

The K+ channel expressed by the KCNJ10 gene (Kir4.1) has previously demonstrated importance in retinal function in animal experiments. Recently, mutations in KCNJ10 were recognised as pathogenic in man, causing a constellation of symptoms, including epilepsy, ataxia, sensorineural deafness and a renal tubulopathy designated as EAST syndrome. We have studied the impact of KCNJ10 mutations on the human electroretinogram (ERG) in four unrelated patients with EAST syndrome. Corneal ganzfeld ERGs were elicited in response to flash stimuli of strengths of 0.001–10 phot cd s/m2 presented scotopically, and 0.3–10 phot cd s/m2 presented photopically. ERG waveforms from light-adapted retinae of all patients showed reduced amplitudes of the photopic negative response (PhNR) (P < 0.001). The photopic ERGs showed a delay in b-wave time to peak, but the photopic hill, i.e. the relative variation of time to peak and amplitude with luminance flash strength, was preserved. Scotopic ERGs to flash strengths 0.01 to 0.1 phot cd s/m2 showed a delay of up to 20 ms before the onset of the b-wave in two patients compared to controls. Stimulus–response functions were fitted by Michaelis–Menten equations and showed significantly lower retinal sensitivity in two patients than in controls (P < 0.001). Our study for the first time in the human ERG shows changes in association with KCNJ10 mutations affecting a Muller cell K+ channel. These data illustrate the role of KCNJ10 function in the physiology of proximal and possibly also the distal human retina.

Mutational, functional, and expression studies of the TCF4 gene in Pitt-Hopkins syndrome

Pitt-Hopkins syndrome is a severe congenital encephalopathy recently ascribed to de novo heterozygous TCF4 gene mutations. We report a series of 13 novel PHS cases with a TCF4 mutation and show that EEG, brain magnetic resonance imagain (MRI), and immunological investigations provide valuable additional clues to the diagnosis. We confirm a mutational hot spot in the basic domain of the E-protein. Functional studies illustrate that heterodimerisation of mutant TCF4 proteins with a tissue-specific transcription factor is less effective than that homodimerisation in a luciferase reporter assay. We also show that the TCF4 expression pattern in human embryonic development is widespread but not ubiquitous. In summary, we further delineate an underdiagnosed mental retardation syndrome, highlighting TCF4 function during development and facilitating diagnosis within the first year of life.

Epilepsy, ataxia, sensorineural deafness, tubulopathy, and KCNJ10 mutations

BACKGROUND

Five children from two consanguineous families presented with epilepsy beginning in infancy and severe ataxia, moderate sensorineural deafness, and a renal salt-losing tubulopathy with normotensive hypokalemic metabolic alkalosis. We investigated the genetic basis of this autosomal recessive disease, which we call the EAST syndrome (the presence of epilepsy, ataxia, sensorineural deafness, and tubulopathy).

METHODS

Whole-genome linkage analysis was performed in the four affected children in one of the families. Newly identified mutations in a potassium-channel gene were evaluated with the use of a heterologous expression system. Protein expression and function were further investigated in genetically modified mice.

RESULTS

Linkage analysis identified a single significant locus on chromosome 1q23.2 with a lod score of 4.98. This region contained the KCNJ10 gene, which encodes a potassium channel expressed in the brain, inner ear, and kidney. Sequencing of this candidate gene revealed homozygous missense mutations in affected persons in both families. These mutations, when expressed heterologously in xenopus oocytes, caused significant and specific decreases in potassium currents. Mice with Kcnj10 deletions became dehydrated, with definitive evidence of renal salt wasting.

CONCLUSIONS

Mutations in KCNJ10 cause a specific disorder, consisting of epilepsy, ataxia, sensorineural deafness, and tubulopathy. Our findings indicate that KCNJ10 plays a major role in renal salt handling and, hence, possibly also in blood-pressure maintenance and its regulation.

A further example of a distinctive autosomal recessive syndrome comprising neonatal diabetes mellitus, intestinal atresias and gall bladder agenesis

We report a patient born to consanguineous parents as a further example of a recently described phenotype comprising neonatal diabetes, intestinal atresias and gall bladder agenesis. Other reports have described cases with overlapping patterns including malrotation, biliary atresia and pancreatic hypoplasia (e.g. as described by Martínez-Frías). We propose that these cases may represent variations of the same syndrome. It is likely that this disorder is inherited as an autosomal recessive trait. Our case is the first to have neonatal diabetes without a demonstrable structural pancreatic abnormality, showing that a deficit in pancreatic function is involved. We sequenced genes with a recognized role in monogenic forms of diabetes, including KCNJ11, ABCC8, GCK, IPF1, HNF1beta, NeuroD1 and TCF7L2, as well as a novel candidate gene, HNF6, known to be involved in hepatobiliary and pancreatic development, but did not identify mutations.

Mutations in different components of FGF signaling in LADD syndrome

Lacrimo-auriculo-dento-digital (LADD) syndrome is characterized by lacrimal duct aplasia, malformed ears and deafness, small teeth and digital anomalies. We identified heterozygous mutations in the tyrosine kinase domains of the genes encoding fibroblast growth factor receptors 2 and 3 (FGFR2, FGFR3) in LADD families, and in one further LADD family, we detected a mutation in the gene encoding fibroblast growth factor 10 (FGF10), a known FGFR ligand. These findings increase the spectrum of anomalies associated with abnormal FGF signaling.

Brachydactyly with extrahepatic biliary atresia, patent ductus arteriosus and seizures--a new syndrome?

Brachydactyly is a relatively common congenital anomaly and can be associated with many other malformations. However, brachydactyly in association with biliary atresia is rare. We present a male child with strikingly symmetrical brachydactyly and nail hypoplasia, extrahepatic biliary atresia, patent ductus arteriosus, seizures, developmental delay and cataracts. This combination of features has not previously been described and we suggest that this case represents a new syndrome.

Characterization of GATA3 Mutations in the Hypoparathyroidism, Deafness, and Renal Dysplasia (HDR) Syndrome

The hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome is an autosomal dominant disorder caused by mutations of the dual zinc finger transcription factor, GATA3. The C-terminal zinc finger (ZnF2) binds DNA, whereas the N-terminal finger (ZnF1) stabilizes this DNA binding and interacts with other zinc finger proteins, such as the Friends of GATA (FOG). We have investigated seven HDR probands and their families for GATA3 abnormalities and have identified two nonsense mutations (Glu-228 --> Stop and Arg-367 --> Stop); two intragenic deletions that result in frameshifts from codons 201 and 355 with premature terminations at codons 205 and 370, respectively; one acceptor splice site mutation that leads to a frameshift from codon 351 and a premature termination at codon 367; and two missense mutations (Cys-318 --> Arg and Asn-320 --> Lys). The functional effects of these mutations, together with a previously reported GATA3 ZnF1 mutation and seven other engineered ZnF1 mutations, were assessed by electrophoretic mobility shift, dissociation, yeast two-hybrid and glutathione S-transferase pull-down assays. Mutations involving GATA3 ZnF2 or adjacent basic amino acids resulted in a loss of DNA binding, but those of ZnF1 either lead to a loss of interaction with specific FOG2 ZnFs or altered DNA-binding affinity. These findings are consistent with the proposed three-dimensional model of ZnF1, which has separate DNA and protein binding surfaces. Thus, our results, which expand the spectrum of HDR-associated GATA3 mutations and report the first acceptor splice site mutation, help to elucidate the molecular mechanisms that alter the function of this zinc finger transcription factor and its role in causing this developmental anomaly.

Macrocephaly and sclerosis of the tubular bones in an isolated patient: a mild case of craniodiaphyseal dysplasia?

We report a 56-year-old woman, mainly suffering from painful legs and the inability to run. Radiologically, marked sclerosis and hyperostosis of the skull bones is present resulting in macrocephaly. Most tubular bones of the limbs, as well as the clavicles, are affected by sclerosis. By mutation analysis of the TGFB1, SOST and LRP5 genes, we were able to exclude the diagnoses of Camurati-Engelmann disease, Van Buchem disease, sclerosteosis, high-bone-mass trait and endosteal hyperostosis (Worth type). We believe this patient represents one of the very few examples of adult craniodiaphyseal dysplasia with a mild form of the disease and moderate facial changes.

A familial cryptic subtelomeric deletion 12p with variable phenotypic effect

A 15-year-old-boy and his mother, both carrying a cryptic deletion within 12p13.33, are described. The proband has a mild phenotype with moderate mental retardation and severe behavioural problems. The mother had some learning difficulties at school. Conventional GTL-banded high-resolution chromosome analysis showed normal karyotypes. Subsequent analysis by fluorescence in situ hybridization using a set of probes specific for the subtelomeric regions of all chromosomes, plus a series of probes at 12p13.33 extending from the 12p telomere, showed that both mother and son carry a 1.65 Mb terminal deletion in this region. There are 10 predicted genes within the deleted region. The unanticipated familial nature of the deletion emphasizes the value of family studies in all cases with subtelomeric abnormalities. It also demonstrates the difficulty in making a clinical diagnosis of individuals with this deletion. To the best of the present authors' knowledge, the proband and his mother are the first patients described with a submicroscopic deletion at 12p13.33.

Study of 250 children with idiopathic mental retardation reveals nine cryptic and diverse subtelomeric chromosome anomalies

Cryptic subtelomeric chromosome anomalies have been recognized as a significant cause of dysmorphology and mental retardation. To determine whether the clinical cytogenetics laboratory should screen routinely for these aberrations, we have tested 250 patients with idiopathic mental retardation/developmental delay, either isolated (53) or associated with dysmorphic features and/or malformations in the absence of a recognizable syndrome (197). All had normal karyotypes at the 550-850 band level. Subtelomeric anomalies were found in 1/53 of the first group (1.9%) and 8/197 of the second group (4.1%). In one patient, two separate anomalies were present: a deletion (not inherited) and a duplication (inherited). It is possible that one of these 10 observed aberrations might represent a rare and previously unreported polymorphism and one a rare cross-hybridization. Our study supports the proposition that cryptic subtelomeric rearrangements are a significant cause of idiopathic mental retardation/developmental delay, but both the diversity of the phenotypes of the positive cases and the wide diversity of their associated chromosome abnormalities emphasize the central problem for the clinical cytogenetics laboratory-that of choosing the most productive patient base for this useful diagnostic test.

Staphylococcal septicaemia complicating intracavernosal autoinjection therapy for impotence in a man with diabetes

Intracavernosal injection of vasoactive drugs is a safe, effective, and commonly used treatment for impotence in diabetic men. In prospective studies infection has rarely occurred. We report a case of life-threatening Staphylococcal septicaemia complicating this treatment in a 61-year-old man with Type 2 diabetes, probably due to a combination of an unsterile technique and drug-induced priapism. Infection is a potential risk in diabetic men using intracavernosal injection therapy and those offered it should be informed of the importance of a scrupulous sterile technique and the need to seek urgent medical help for decompression if an erection persists for more than 4-6 h.