First Report of a Low-Frequency Mosaic Mutation in the Hydroxymethylbilane Synthase Gene Causing Acute Intermittent Porphyria

Acute porphyrias are a group of monogenetic inborn errors of heme biosynthesis, characterized by acute and potentially life-threatening neurovisceral attacks upon exposure to certain triggering factors. Biochemical analyses can determine the type of acute porphyria, and subsequent genetic analysis allows for the identification of pathogenic variants in the specific gene, which provides information for family counselling. In 2017, a male Swiss patient was diagnosed with an acute porphyria while suffering from an acute attack. The pattern of porphyrin metabolite excretion in urine, faeces, and plasma was typical for an acute intermittent porphyria (AIP), which is caused by inherited autosomal dominant mutations in the gene for hydroxymethylbilane synthase (HMBS), the third enzyme in the heme biosynthetic pathway. However, the measurement of HMBS enzymatic activity in the erythrocytes was within the normal range and Sanger sequencing of the HMBS gene failed to detect any pathogenic variants. To explore the molecular basis of the apparent AIP in this patient, we performed third-generation long-read single-molecule sequencing (nanopore sequencing) on a PCR product spanning the entire HMBS gene, including the intronic sequences. We identified a known pathogenic variant, c.77G>A, p.(Arg26His), in exon 3 at an allelic frequency of ~22% in the patient's blood. The absence of the pathogenic variant in the DNA of the parents and the results of additional confirmatory studies supported the presence of a de novo mosaic mutation. To our knowledge, such a mutation has not been previously described in any acute porphyria. Therefore, de novo mosaic mutations should be considered as potential causes of acute porphyrias when no pathogenic genetic variant can be identified through routine molecular diagnostics.

The genetic landscape and clinical implication of pediatric Moyamoya angiopathy in an international cohort

Pediatric Moyamoya Angiopathy (MMA) is a progressive intracranial occlusive arteriopathy that represents a leading cause of transient ischemic attacks and strokes in childhood. Despite this, up to now no large, exclusively pediatric MMA cohort has been subjected to systematic genetic investigation. In this study, we performed molecular karyotyping, exome sequencing and automated structural assessment of missense variants on a series of 88 pediatric MMA patients and correlated genetic, angiographic and clinical (stroke burden) findings. The two largest subgroups in our cohort consisted of RNF213 and neurofibromatosis type 1 (NF1) patients. While deleterious RNF213 variants were associated with a severe MMA clinical course with early symptom onset, frequent posterior cerebral artery involvement and higher stroke rates in multiple territories, NF1 patients had a similar infarct burden compared to non-NF1 individuals and were often diagnosed incidentally during routine MRIs. Additionally, we found that MMA-associated RNF213 variants have lower predicted functional impact compared to those associated with aortic disease. We also raise the question of MMA as a feature of recurrent as well as rare chromosomal imbalances and further support the possible association of MMA with STAT3 deficiency. In conclusion, we provide a comprehensive characterization at the genetic and clinical level of a large exclusively pediatric MMA population. Due to the clinical differences found across genetic subgroups, we propose genetic testing for risk stratification as part of the routine assessment of pediatric MMA patients.

Pathogenic SCN2A variants cause early-stage dysfunction in patient-derived neurons

Pathogenic heterozygous variants in SCN2A, which encodes the neuronal sodium channel NaV1.2, cause different types of epilepsy or intellectual disability (ID)/autism without seizures. Previous studies using mouse models or heterologous systems suggest that NaV1.2 channel gain-of-function typically causes epilepsy, whereas loss-of-function leads to ID/autism. How altered channel biophysics translate into patient neurons remains unknown. Here, we investigated iPSC-derived early-stage cortical neurons from ID patients harboring diverse pathogenic SCN2A variants [p.(Leu611Valfs*35); p.(Arg937Cys); p.(Trp1716*)] and compared them with neurons from an epileptic encephalopathy (EE) patient [p.(Glu1803Gly)] and controls. ID neurons consistently expressed lower NaV1.2 protein levels. In neurons with the frameshift variant, NaV1.2 mRNA and protein levels were reduced by ~ 50%, suggesting nonsense-mediated decay and haploinsufficiency. In other ID neurons, only protein levels were reduced implying NaV1.2 instability. Electrophysiological analysis revealed decreased sodium current density and impaired action potential (AP) firing in ID neurons, consistent with reduced NaV1.2 levels. In contrast, epilepsy neurons displayed no change in NaV1.2 levels or sodium current density, but impaired sodium channel inactivation. Single-cell transcriptomics identified dysregulation of distinct molecular pathways including inhibition of oxidative phosphorylation in neurons with SCN2A haploinsufficiency and activation of calcium signaling and neurotransmission in epilepsy neurons. Together, our patient iPSC-derived neurons reveal characteristic sodium channel dysfunction consistent with biophysical changes previously observed in heterologous systems. Additionally, our model links the channel dysfunction in ID to reduced NaV1.2 levels and uncovers impaired AP firing in early-stage neurons. The altered molecular pathways may reflect a homeostatic response to NaV1.2 dysfunction and can guide further investigations.

A Xp22.11-p21.3 microdeletion in a three-generation family supports male lethality of POLA1 nullisomy resulting in reduced fertility of female carriers

POLA1 encodes a subunit of the DNA polymerase alpha, a key enzyme for the initiation of DNA synthesis. In males, hemizygous hypomorphic variants in POLA1 have been identified as the cause of X-linked pigmentary reticulate disorder (XLPDR) and a novel X-linked neurodevelopmental disorder termed Van Esch-O'Driscoll syndrome (VEODS), while female carriers have been reported to be healthy. Nullisomy for POLA1 was speculated to be lethal due to its crucial function, while the effect of loss of one allele in females remained unknown. Here, we report on a three-generation family harboring a deletion of POLA1 in females showing subfertility as the only phenotype. Our findings show that heterozygous deletions or truncating variants in females with skewed X inactivation do not cause VEODS and support the hypothesis of very early embryonic lethality in males with POLA1 nullisomy.

Epidemiology and impact of frailty in patients with atrial fibrillation in Europe

BACKGROUND

Frailty is a medical syndrome characterised by reduced physiological reserve and increased vulnerability to stressors. Data regarding the relationship between frailty and atrial fibrillation (AF) are still inconsistent.

OBJECTIVES

We aim to perform a comprehensive evaluation of frailty in a large European cohort of AF patients.

METHODS

A 40-item frailty index (FI) was built according to the accumulation of deficits model in the AF patients enrolled in the ESC-EHRA EORP-AF General Long-Term Registry. Association of baseline characteristics, clinical management, quality of life, healthcare resources use and risk of outcomes with frailty was examined.

RESULTS

Among 10,177 patients [mean age (standard deviation) 69.0 (11.4) years, 4,103 (40.3%) females], 6,066 (59.6%) were pre-frail and 2,172 (21.3%) were frail, whereas only 1,939 (19.1%) were considered robust. Baseline thromboembolic and bleeding risks were independently associated with increasing FI. Frail patients with AF were less likely to be treated with oral anticoagulants (OACs) (odds ratio 0.70, 95% confidence interval 0.55-0.89), especially with non-vitamin K antagonist OACs and managed with a rhythm control strategy, compared with robust patients. Increasing frailty was associated with a higher risk for all outcomes examined, with a non-linear exponential relationship. The use of OAC was associated with a lower risk of outcomes, except in patients with very/extremely high frailty.

CONCLUSIONS

In this large cohort of AF patients, there was a high burden of frailty, influencing clinical management and risk of adverse outcomes. The clinical benefit of OAC is maintained in patients with high frailty, but not in very high/extremely frail ones.

Assessing clinical utility of preconception expanded carrier screening regarding residual risk for neurodevelopmental disorders

The magnitude of clinical utility of preconception expanded carrier screening (ECS) concerning its potential to reduce the risk of affected offspring is unknown. Since neurodevelopmental disorders (NDDs) in their offspring is a major concern of parents-to-be, we addressed the question of residual risk by assessing the risk-reduction potential for NDDs in a retrospective study investigating ECS with different criteria for gene selection and definition of pathogenicity. We used exome sequencing data from 700 parents of children with NDDs and blindly screened for carrier-alleles in up to 3046 recessive/X-linked genes. Depending on variant pathogenicity thresholds and gene content, NDD-risk-reduction potential was up to 43.5% in consanguineous, and 5.1% in nonconsanguineous couples. The risk-reduction-potential was compromised by underestimation of pathogenicity of missense variants (false-negative-rate 4.6%), inherited copy-number variants and compound heterozygosity of one inherited and one de novo variant (0.9% each). Adherence to the ACMG recommendations of restricting ECS to high-frequency genes in nonconsanguineous couples would more than halve the detectable inherited NDD-risk. Thus, for optimized clinical utility of ECS, screening in recessive/X-linked genes regardless of their frequency (ACMG Tier-4) and sensible pathogenicity thresholds should be considered for all couples seeking ECS.

Confirmation of Ogden syndrome as an X-linked recessive fatal disorder due to a recurrent NAA10 variant and review of the literature

Ogden syndrome is a rare lethal X‐linked recessive disorder caused by a recurrent missense variant (Ser37Pro) in the NAA10 gene, encoding the catalytic subunit of the N‐terminal acetyltransferase A complex (NatA). So far eight boys of two different families have been described in the literature, all presenting the distinctive and recognizable phenotype, which includes mostly postnatal growth retardation, global severe developmental delay, characteristic craniofacial features, and structural cardiac anomalies and/or arrhythmias. Here, we report the ninth case of Ogden syndrome with an independent recurrence of the Ser37Pro variant. We were able to follow the clinical course of the affected boy and delineate the evolving phenotype from his birth until his unfortunate death at 7 months. We could confirm the associated phenotype as well as the natural history of this severe disease. By describing new presenting features, we are further expanding the clinical spectrum associated with Ogden syndrome and review other phenotypes associated with NAA10 variants.

Further corroboration of distinct functional features in SCN2A variants causing intellectual disability or epileptic phenotypes

BACKGROUND

Deleterious variants in the voltage-gated sodium channel type 2 (Na_v1.2) lead to a broad spectrum of phenotypes ranging from benign familial neonatal-infantile epilepsy (BFNIE), severe developmental and epileptic encephalopathy (DEE) and intellectual disability (ID) to autism spectrum disorders (ASD). Yet, the underlying mechanisms are still incompletely understood.

METHODS

To further elucidate the genotype-phenotype correlation of SCN2A variants we investigated the functional effects of six variants representing the phenotypic spectrum by whole-cell patch-clamp studies in transfected HEK293T cells and in-silico structural modeling.

RESULTS

The two variants p.L1342P and p.E1803G detected in patients with early onset epileptic encephalopathy (EE) showed profound and complex changes in channel gating, whereas the BFNIE variant p.L1563V exhibited only a small gain of channel function. The three variants identified in ID patients without seizures, p.R937C, p.L611Vfs*35 and p.W1716*, did not produce measurable currents. Homology modeling of the missense variants predicted structural impairments consistent with the electrophysiological findings.

CONCLUSIONS

Our findings support the hypothesis that complete loss-of-function variants lead to ID without seizures, small gain-of-function variants cause BFNIE and EE variants exhibit variable but profound Na_v1.2 gating changes. Moreover, structural modeling was able to predict the severity of the variant impact, supporting a potential role of structural modeling as a prognostic tool. Our study on the functional consequences of SCN2A variants causing the distinct phenotypes of EE, BFNIE and ID contributes to the elucidation of mechanisms underlying the broad phenotypic variability reported for SCN2A variants.

CUGC for Simpson-Golabi-Behmel syndrome (SGBS)

NAME OF THE DISEASE (SYNONYMS)

Simpson-Golabi-Behmel syndrome (SGBS). OMIM# OF THE DISEASE: 312870.

NAME OF THE ANALYSED GENES OR DNA/CHROMOSOME SEGMENTS

GPC3. OMIM# OF THE GENE(S): 300037. Review of the analytical and clinical validity as well as of the clinical utility of DNA-based testing for mutations in the GPC3 gene(s) in ⊠ diagnostic, ☐ predictive and ⊠ prenatal settings and for ⊠ risk assessment in relatives.

The role of recessive inheritance in early-onset epileptic encephalopathies: a combined whole-exome sequencing and copy number study

Early-onset epileptic encephalopathy (EE) and combined developmental and epileptic encephalopathies (DEE) are clinically and genetically heterogeneous severely devastating conditions. Recent studies emphasized de novo variants as major underlying cause suggesting a generally low-recurrence risk. In order to better understand the full genetic landscape of EE and DEE, we performed high-resolution chromosomal microarray analysis in combination with whole-exome sequencing in 63 deeply phenotyped independent patients. After bioinformatic filtering for rare variants, diagnostic yield was improved for recessive disorders by manual data curation as well as molecular modeling of missense variants and untargeted plasma-metabolomics in selected patients. In total, we yielded a diagnosis in ∼42% of cases with causative copy number variants in 6 patients (∼10%) and causative sequence variants in 16 established disease genes in 20 patients (∼32%), including compound heterozygosity for causative sequence and copy number variants in one patient. In total, 38% of diagnosed cases were caused by recessive genes, of which two cases escaped automatic calling due to one allele occurring de novo. Notably, we found the recessive gene SPATA5 causative in as much as 3% of our cohort, indicating that it may have been underdiagnosed in previous studies. We further support candidacy for neurodevelopmental disorders of four previously described genes (PIK3AP1, GTF3C3, UFC1, and WRAP53), three of which also followed a recessive inheritance pattern. Our results therefore confirm the importance of de novo causative gene variants in EE/DEE, but additionally illustrate the major role of mostly compound heterozygous or hemizygous recessive inheritance and consequently high-recurrence risk.

Overlapping SETBP1 gain-of-function mutations in Schinzel-Giedion syndrome and hematologic malignancies

Schinzel-Giedion syndrome (SGS) is a rare developmental disorder characterized by multiple malformations, severe neurological alterations and increased risk of malignancy. SGS is caused by de novo germline mutations clustering to a 12bp hotspot in exon 4 of SETBP1. Mutations in this hotspot disrupt a degron, a signal for the regulation of protein degradation, and lead to the accumulation of SETBP1 protein. Overlapping SETBP1 hotspot mutations have been observed recurrently as somatic events in leukemia. We collected clinical information of 47 SGS patients (including 26 novel cases) with germline SETBP1 mutations and of four individuals with a milder phenotype caused by de novo germline mutations adjacent to the SETBP1 hotspot. Different mutations within and around the SETBP1 hotspot have varying effects on SETBP1 stability and protein levels in vitro and in in silico modeling. Substitutions in SETBP1 residue I871 result in a weak increase in protein levels and mutations affecting this residue are significantly more frequent in SGS than in leukemia. On the other hand, substitutions in residue D868 lead to the largest increase in protein levels. Individuals with germline mutations affecting D868 have enhanced cell proliferation in vitro and higher incidence of cancer compared to patients with other germline SETBP1 mutations. Our findings substantiate that, despite their overlap, somatic SETBP1 mutations driving malignancy are more disruptive to the degron than germline SETBP1 mutations causing SGS. Additionally, this suggests that the functional threshold for the development of cancer driven by the disruption of the SETBP1 degron is higher than for the alteration in prenatal development in SGS. Drawing on previous studies of somatic SETBP1 mutations in leukemia, our results reveal a genotype-phenotype correlation in germline SETBP1 mutations spanning a molecular, cellular and clinical phenotype.

N(8)-acetylspermidine as a potential plasma biomarker for Snyder-Robinson syndrome identified by clinical metabolomics

Clinical metabolomics has emerged as a powerful tool to study human metabolism in health and disease. Comparative statistical analysis of untargeted metabolic profiles can reveal perturbations of metabolite levels in diseases and thus has the potential to identify novel biomarkers. Here we have applied a simultaneous genetic-metabolomic approach in twin boys with epileptic encephalopathy of unclear etiology. Clinical exome sequencing identified a novel missense mutation in the spermine synthase gene (SMS) that causes Snyder-Robinson syndrome (SRS). Untargeted plasma metabolome analysis revealed significantly elevated levels of N(8)-acetylspermidine, a precursor derivative of spermine biosynthesis, as a potential novel plasma biomarker for SRS. This result was verified in a third patient with genetically confirmed SRS. This study illustrates the potential of metabolomics as a translational technique to support exome data on a functional and clinical level.

A recurrent germline mutation in the PIGA gene causes Simpson-Golabi-Behmel syndrome type 2

Hypomorphic germline mutations in the PIGA (phosphatidylinositol glycan class A) gene recently were recognized as the cause of a clinically heterogeneous spectrum of X-linked disorders including (i) early onset epileptic encephalopathy with severe muscular hypotonia, dysmorphism, multiple congenital anomalies, and early death ("MCAHS2"), (ii) neurodegenerative encephalopathy with systemic iron overload (ferro-cerebro-cutaneous syndrome, "FCCS"), and (iii) intellectual disability and seizures without dysmorphism. Previous studies showed that the recurrent PIGA germline mutation c.1234C>T (p.Arg412*) leads to a clinical phenotype at the most severe end of the spectrum associated with early infantile lethality. We identified three additional individuals from two unrelated families with the same PIGA mutation. Major clinical findings include early onset intractable epileptic encephalopathy with a burst-suppression pattern on EEG, generalized muscular hypotonia, structural brain abnormalities, macrocephaly and increased birth weight, joint contractures, coarse facial features, widely spaced eyes, a short nose with anteverted nares, gingival overgrowth, a wide mouth, short limbs with short distal phalanges, and a small penis. Based on the phenotypic overlap with Simpson-Golabi-Behmel syndrome type 2 (SGBS2), we hypothesized that both disorders might have the same underlying cause. We were able to confirm the same c.1234C>T (p.Arg412*) mutation in the DNA sample from an affected fetus of the original family affected with SGBS2. We conclude that the recurrent PIGA germline mutation c.1234C>T leads to a recognizable clinical phenotype with a poor prognosis and is the cause of SGBS2.

Variants in CUL4B are associated with cerebral malformations

Variants in cullin 4B (CUL4B) are a known cause of syndromic X-linked intellectual disability. Here, we describe an additional 25 patients from 11 families with variants in CUL4B. We identified nine different novel variants in these families and confirmed the pathogenicity of all nontruncating variants. Neuroimaging data, available for 15 patients, showed the presence of cerebral malformations in ten patients. The cerebral anomalies comprised malformations of cortical development (MCD), ventriculomegaly, and diminished white matter volume. The phenotypic heterogeneity of the cerebral malformations might result from the involvement of CUL-4B in various cellular pathways essential for normal brain development. Accordingly, we show that CUL-4B interacts with WDR62, a protein in which variants were previously identified in patients with microcephaly and a wide range of MCD. This interaction might contribute to the development of cerebral malformations in patients with variants in CUL4B.

Recurrent Nonconvulsive Status Epilepticus in a Patient with Coffin-Lowry Syndrome

Coffin-Lowry syndrome (CLS) is a rare neurodevelopmental condition caused by heterogeneous mutations in the RPS6KA3 gene on the X chromosome, leading to severe intellectual disability and dysmorphism in men, while women are carriers and only weakly affected. CLS is well known for stimulus-induced drop episodes; however, epilepsy is not commonly reported in this condition. We report on a CLS patient presenting with recurrent episodes of nonconvulsive status epilepticus (NCSE) with generalized epileptic activity, for which investigations did not find any other cause than the patient's genetic condition. This case underlines that the possibility of nonconvulsive epileptic seizures and status epilepticus should, therefore, be considered in those patients. The treatable diagnosis of NCSE may easily be overlooked, as symptoms can be unspecific.

Microcephalic osteodysplastic primordial dwarfism type II (MOPD II) with multiple vascular complications misdiagnosed as Dubowitz syndrome

To date, the genetic basis of Dubowitz syndrome (short stature, microcephaly, facial abnormalities, eczema) is unknown and vascular complications are not known to be associated with this syndrome. In microcephalic osteodysplastic primordial dwarfism type II (MOPD II; disproportionate short statue, microcephaly, facial abnormalities), however, cerebral aneurysms and other vascular abnormalities are frequent complications. MOPD II is a genetic disorder caused by mutations in the pericentrin (PCNT) gene (21q22). We report on a patient who came to our attention as a 22-year-old with subarachnoid bleeding due to a ruptured cranial aneurysm. Until then, the patient was thought and published to have Dubowitz syndrome; previously, he was treated with coronary bypass surgery for extensive coronary angiopathy. Consecutive genetic testing revealed MOPD II. After clinical stabilization, the patient was discharged to a specialized rehabilitation center where he died due to re-rupture of a cranial aneurysm.

CONCLUSION

In patients with short stature-especially when clinical features are accompanied by vascular complications-MOPD II should be considered as a differential diagnosis leading to consecutive genetic testing. After detection of mutations in the PCNT gene, a full vascular status including cerebral imaging and cardiac evaluation needs to be determined in order to analyze vascular abnormalities and initiate prophylactic treatment.

The clinical significance of small copy number variants in neurodevelopmental disorders

BACKGROUND

Despite abundant evidence for pathogenicity of large copy number variants (CNVs) in neurodevelopmental disorders (NDDs), the individual significance of genome-wide rare CNVs <500 kb has not been well elucidated in a clinical context.

METHODS

By high-resolution chromosomal microarray analysis, we investigated the clinical significance of all rare non-polymorphic exonic CNVs sizing 1-500 kb in a cohort of 714 patients with undiagnosed NDDs.

RESULTS

We detected 96 rare CNVs <500 kb affecting coding regions, of which 58 (60.4%) were confirmed. 6 of 14 confirmed de novo, one of two homozygous and four heterozygous inherited CNVs affected the known microdeletion regions 17q21.31, 16p11.2 and 2p21 or OMIM morbid genes (CASK, CREBBP, PAFAH1B1, SATB2; AUTS2, NRXN3, GRM8). Two further de novo CNVs affecting single genes (MED13L, CTNND2) were instrumental in delineating novel recurrent conditions. For the first time, we here report exonic deletions of CTNND2 causing low normal IQ with learning difficulties with or without autism spectrum disorder. Additionally, we discovered a homozygous out-of-frame deletion of ACOT7 associated with features comparable to the published mouse model. In total, 24.1% of the confirmed small CNVs were categorised as pathogenic or likely pathogenic (median size 130 kb), 17.2% as likely benign, 3.4% represented incidental findings and 55.2% remained unclear.

CONCLUSIONS

These results verify the diagnostic relevance of genome-wide rare CNVs <500 kb, which were found pathogenic in ∼2% (14/714) of cases (1.1% de novo, 0.3% homozygous, 0.6% inherited) and highlight their inherent potential for discovery of new conditions.

Infantile epileptic encephalopathy, transient choreoathetotic movements, and hypersomnia due to a De Novo missense mutation in the SCN2A gene

Mutations of the SCN2A gene have originally been described in association with benign familial neonatal-infantile seizures (BFNIS). Recently, single patients with more severe phenotypes and persisting epileptic encephalopathies have been recognized. We report the case of a girl with severe infantile onset epileptic encephalopathy and a de novo missense mutation in the SCN2A gene (c.4025T > C/ = ; p.L1342P/ = ), who presented with a transient choreatic movement disorder, hypersomnia, and progressive brain atrophy. Whole exome sequencing did not reveal any other disease causing mutation. Our patient contributes to the expanding phenotypic spectrum of SCN2A-related disorders and underlines the importance of genetic workup in epileptic encephalopathies.

High-resolution chromosomal microarrays in prenatal diagnosis significantly increase diagnostic power

OBJECTIVE

The objective of this study was to determine for the first time the reliability and the diagnostic power of high-resolution microarray testing in routine prenatal diagnostics.

METHODS

We applied high-resolution chromosomal microarray testing in 464 cytogenetically normal prenatal samples with any indication for invasive testing.

RESULTS

High-resolution testing revealed a diagnostic yield of 6.9% and 1.6% in cases of fetal ultrasound anomalies and cases of advanced maternal age (AMA), respectively, which is similar to previous studies using low-resolution microarrays. In three (0.6%) additional cases with an indication of AMA, an aberration in susceptibility risk loci was detected. Moreover, one case (0.2%) showed an X-linked aberration in a female fetus, a finding relevant for future family planning. We found the rate of cases, in which the parents had to be tested for interpretation of unreported copy number variants (3.7%), and the rate of remaining variants of unknown significance (0.4%) acceptably low. Of note, these findings did not cause termination of pregnancy after expert genetic counseling. The 0.4% rate of confined placental mosaicism was similar to that observed by conventional karyotyping and notably involved a case of placental microdeletion.

CONCLUSION

High-resolution prenatal microarray testing is a reliable technique that increases diagnostic yield by at least 17.3% when compared with conventional karyotyping, without an increase in the frequency of variants of uncertain significance.

Long-term follow-up of four patients with Langer-Giedion syndrome: clinical course and complications

Long-term observations of individuals with the so-called Langer-Giedion (LGS) or tricho-rhino-phalangeal type II (TRPS2) are scarce. We report here a on follow-up of four LGS individuals, including one first described by Andres Giedion in 1969, and review the sparse publications on adults with this syndrome which comprises ectodermal dysplasia, multiple cone-shaped epiphyses prior to puberty, multiple cartilaginous exostoses, and mostly mild intellectual impairment. LGS is caused by deletion of the chromosomal segment 8q24.11-q24.13 containing among others the genes EXT1 and TRPS1. Most patients with TRPS2 are only borderline or mildly cognitively delayed, and few are of normal intelligence. Their practical skills are better than their intellectual capability, and, for this reason and because of their low self-esteem, they are often underestimated. Some patients develop seizures at variable age. Osteomas on processes of cervical vertebrae may cause pressure on cervical nerves or dissection of cerebral arteries. Joint stiffness is observed during childhood and changes later to joint laxity causing instability and proneness to trauma. Perthes disease is not rare. Almost all males become bald at or soon after puberty, and some develop (pseudo) gynecomastia. Growth hormone deficiency was found in a few patients, TSH deficiency so far only in one. Puberty and fertility are diminished, and no instance of transmission of the deletion from a non-mosaic parent to a child has been observed so far. Several affected females had vaginal atresia with consequent hydrometrocolpos.

Epidemiology of cyprinid herpesvirus-3 infection in latently infected carp from aquaculture

Cyprinid herpesvirus-3 (CyHV-3, koi herpesvirus, KHV) is the causative agent of an economically important disease in carp. The mode of transmission of this virus, especially how the infectious agent is introduced into ponds de novo, is not known in detail. The aim of this study was to investigate the shedding of CyHV-3 from fish with latent infections, under aquaculture conditions. Ponds in Saxony, Germany, with latently infected carp were examined at different times during the production cycle to investigate the influence of fish farming procedures on virus activation and shedding. Carp and water samples were investigated by quantitative real-time PCR. Some of the latently infected carp shed CyHV-3. Virus shedding was induced mainly when the ponds were drained and the carp either harvested or moved to different ponds, and was independent of the water temperature. This indicated that during these times there was a risk that effluent water from the ponds could disseminate the infectious agent. During summer, on-growing carp are infected with low numbers of CyHV-3. These findings are important for disease management strategies in carp aquaculture and for the design of testing protocols for the detection of latent infection in carp populations.

Further delineation of genotype-phenotype correlation in homozygous 2p21 deletion syndromes: first description of patients without cystinuria

Homozygous contiguous gene deletion syndromes are rare. On 2p21, however, several overlapping homozygous gene deletion syndromes have been described, all presenting with cystinuria but otherwise distinct phenotypes. Hypotonia-cystinuria syndrome (HCS, OMIM606407) is characterized by infantile hypotonia, poor feeding, and growth hormone deficiency. Affected individuals carry homozygous deletions including the cystinuria gene SLC3A1 and the adjacent PREPL gene. Larger homozygous deletions in this region encompassing the PPM1B, SLC3A1, PREPL, and C2orf34 (CAMKMT) genes result in a more severe phenotype, the 2p21 deletion syndrome. A phenotype intermediate to HCS and the 2p21 deletion syndrome is termed atypical HCS and is caused by deletion of SLC3A1, PREPL, and C2orf34 (CAMKMT). Using high resolution SNP array molecular karyotyping we identified two siblings with a homozygous deletion of 83 kb partially encompassing the genes PREPL and C2orf34 (CAMKMT), but not the SLC3A1 gene. The affected siblings display a recognizable phenotype which is similar to atypical HCS with regard to growth failure and neuro-muscular features, but is characterized by lack of cystinuria. The patients also exhibit features which have not been reported to date such as cleft palate and genital abnormalities. In conclusion, we report the first patients with a homozygous 2p21 deletion syndrome without cystinuria and further delineate the complex genotype-phenotype correlations of homozygous microdeletion syndromes of this region.

Do wild fish species contribute to the transmission of koi herpesvirus to carp in hatchery ponds?

The koi herpesvirus (KHV) has spread worldwide since its discovery in 1998 and causes disease and mortality in koi and common carp populations with a high impact on the carp production industry. Many investigations have been conducted to examine ways of distribution and to identify possible transmission vectors. The answers, however, raise many new questions. In the present study, different wild fish species taken from carp ponds with a history of KHV infection were examined for their susceptibility to the virus. In the tissue of these fish, the virus load was determined and it was tested whether a release of the virus could be induced by stress and the virus then could be transferred to naive carp. Wild fish were gathered from carp ponds during acute outbreaks of virus-induced mortality in summer and from ponds stocked with carp carrying a latent KHV infection. From these ponds, wild fish were collected during the harvesting process in autumn or spring when the ponds were drained. We found that regardless of season, temperature variation, age and infection status of the carp stock, wild fish from carp ponds and its outlets could be tested positive for the KHV genome using real-time PCR with a low prevalence and virus load. Furthermore, virus transfer to naive carp was observed after a period of cohabitation. Cyprinid and non-cyprinid wild fish can therefore be considered as an epidemiological risk for pond carp farms.

Dosage changes of MED13L further delineate its role in congenital heart defects and intellectual disability

A chromosomal balanced translocation disrupting the MED13L (Mediator complex subunit13-like) gene, encoding a subunit of the Mediator complex, was previously associated with transposition of the great arteries (TGA) and intellectual disability (ID), and led to the identification of missense mutations in three patients with isolated TGA. Recently, a homozygous missense mutation in MED13L was found in two siblings with non-syndromic ID from a consanguineous family. Here, we describe for the first time, three patients with copy number changes affecting MED13L and delineate a recognizable MED13L haploinsufficiency syndrome. Using high resolution molecular karyotyping, we identified two intragenic de novo frameshift deletions, likely resulting in haploinsufficiency, in two patients with a similar phenotype of hypotonia, moderate ID, conotruncal heart defect and facial anomalies. In both, Sanger sequencing of MED13L did not reveal any pathogenic mutation and exome sequencing in one patient showed no evidence for a non-allelic second hit. A further patient with hypotonia, learning difficulties and perimembranous VSD showed a 1 Mb de novo triplication in 12q24.2, including MED13L and MAP1LC3B2. Our findings show that MED13L haploinsufficiency in contrast to the previously observed missense mutations cause a distinct syndromic phenotype. Additionally, a MED13L copy number gain results in a milder phenotype. The clinical features suggesting a neurocristopathy may be explained by animal model studies indicating involvement of the Mediator complex subunit 13 in neural crest induction.

Defect in proline synthesis: pyrroline-5-carboxylate reductase 1 deficiency leads to a complex clinical phenotype with collagen and elastin abnormalities

Pyrroline-5-carboxylate reductase 1 (PYCR1) catalyzes the last step in proline synthesis. Deficiency of PYCR1, caused by a defect in PYCR1, was recently described in patients with cutis laxa, intrauterine growth retardation, developmental dysplasia of the hips and mental retardation. In this paper, we describe additional six patients (ages ranging from 4 months to 55 years) from four Iranian families with clinical manifestations of a wrinkly skin disorder. All patients have distinct facial features comprising triangular face, loss of adipose tissue and thin pointed nose. Additional features are short stature, wrinkling over dorsum of hand and feet, visible veins over the chest and hyperextensible joints. Three of the patients from a large consanguineous family do not have mental retardation, while the remaining three patients from three unrelated families have mental and developmental delay. Mutation analysis revealed the presence of disease-causing variants in PYCR1, including a novel deletion of the entire PYCR1 gene in one family, and in each of the other patients the homozygous missense mutations c.616G > A (p.Gly206Arg), c.89T > A (p.Ile30Lys) and c.572G > A (p.Gly191Glu) respectively, the latter two of which are novel. Light- and electron microscopy investigations of skin biopsies showed smaller and fragmented elastic fibres, abnormal morphology of the mitochondria and their cristae, and slightly abnormal collagen fibril diameters with irregular outline and variable size. In conclusion, this study adds information on the natural course of PYCR1 deficiency and sheds light on the pathophysiology of this disorder. However, the exact pathogenesis of this new disorder and the role of proline in the development of the clinical phenotype remain to be fully explained.

Identification of a novel loss-of-function calcium channel gene mutation in short QT syndrome (SQTS6)

AIMS

Short QT syndrome (SQTS) is a genetically determined ion-channel disorder, which may cause malignant tachyarrhythmias and sudden cardiac death. Thus far, mutations in five different genes encoding potassium and calcium channel subunits have been reported. We present, for the first time, a novel loss-of-function mutation coding for an L-type calcium channel subunit.

METHODS AND RESULTS

The electrocardiogram of the affected member of a single family revealed a QT interval of 317 ms (QTc 329 ms) with tall, narrow, and symmetrical T-waves. Invasive electrophysiological testing showed short ventricular refractory periods and increased vulnerability to induce ventricular fibrillation. DNA screening of the patient identified no mutation in previously known SQTS genes; however, a new variant at a heterozygous state was identified in the CACNA2D1 gene (nucleotide c.2264G > C; amino acid p.Ser755Thr), coding for the Ca(v)α(2)δ-1 subunit of the L-type calcium channel. The pathogenic role of the p.Ser755Thr variant of the CACNA2D1 gene was analysed by using co-expression of the two other L-type calcium channel subunits, Ca(v)1.2α1 and Ca(v)β(2b), in HEK-293 cells. Barium currents (I(Ba)) were recorded in these cells under voltage-clamp conditions using the whole-cell configuration. Co-expression of the p.Ser755Thr Ca(v)α(2)δ-1 subunit strongly reduced the I(Ba) by more than 70% when compared with the co-expression of the wild-type (WT) variant. Protein expression of the three subunits was verified by performing western blots of total lysates and cell membrane fractions of HEK-293 cells. The p.Ser755Thr variant of the Ca(v)α(2)δ-1 subunit was expressed at a similar level compared with the WT subunit in both fractions. Since the mutant Ca(v)α(2)δ-1 subunit did not modify the expression of the pore-forming subunit of the L-type calcium channel, Ca(v)1.2α1, it suggests that single channel biophysical properties of the L-type channel are altered by this variant.

CONCLUSION

In the present study, we report the first pathogenic mutation in the CACNA2D1 gene in humans, which causes a new variant of SQTS. It remains to be determined whether mutations in this gene lead to other manifestations of the J-wave syndrome.

A homoallelic FECH mutation in a patient with both erythropoietic protoporphyria and palmar keratoderma

BACKGROUND

Erythropoietic protoporphyria (EPP) is a hereditary disorder caused by the deficiency of ferrochelatase (FECH) in the haem biosynthetic pathway. In the majority of families, EPP is transmitted as a pseudodominant trait. Autosomal recessive form of EPP is found in only about 3% of the families.

OBJECTIVES

In this study, we describe a 6-year-old boy who suffered from both EPP and palmar keratoderma.

METHODS AND RESULTS

A novel homoallelic missense mutation (p.Ser318Tyr) was identified in the FECH gene. In addition, a region of homozygosity of approximately 6.8 Mb was observed in chromosome 18 of the patient by both microsatellite and SNP array. The parents of the patient, both of Palestinian (Jordanian) origin, were heterozygous for the S318Y mutation, although no history of consanguinity was known. Microsatellite genotyping identified a partial haplotype from each parent that corresponds to the region of homozygosity in the patient. Assuming S318Y is a founder mutation, the number of generations separating the two parents from their common ancestor from whom they inherited S318Y was estimated as 21.7 (95% CI 3.42–69.7).

CONCLUSION

EPP was therefore inherited as an autosomal recessive trait in the family. This study confirms the association between palmar keratoderma and autosomal recessive EPP.

Pericentric inversion of chromosome 18 in parents leading to a phenotypically normal child with segmental uniparental disomy 18

In this study, we report a familial inversion of chromosome 18, inv(18)(p11.31q21.33), in both members of a consanguineous couple. Their first child had inherited one balanced pericentric inversion along with a recombinant chromosome 18 resulting in dup(18q)/del(18p), and had mild dysmorphic features in the absence of mental and developmental retardation. The second child had received two recombinant chromosomes 18, from the mother a derivative chromosome 18 with dup(18p)/del(18q) and from the father a derivative chromosome 18 with dup(18q)/del(18p). The aberration was prenatally detected; however, as the two opposite aneuploidies were thought to compensate each other, the family decided to carry on with the pregnancy, knowing that uniparental disomy for the segments outside the inversion could have an adverse influence on the development of the child. Uniparental disomy was confirmed by SNP arrays. The child, who has been followed up until the age of 20 months, is healthy and normal. It seems to be the first reported case with two opposite recombinant chromosomes that compensate each other and lead to segmental uniparental disomy for two segments on the chromosome, one maternal and the other paternal.

Methylation profiling in individuals with uniparental disomy identifies novel differentially methylated regions on chromosome 15

The maternal and paternal genomes possess distinct epigenetic marks that distinguish them at imprinted loci. In order to identify imprinted loci, we used a novel method, taking advantage of the fact that uniparental disomy (UPD) provides a system that allows the two parental chromosomes to be studied independently. We profiled the paternal and maternal methylation on chromosome 15 using immunoprecipitation of methylated DNA and hybridization to tiling oligonucleotide arrays. Comparison of six individuals with maternal versus paternal UPD15 revealed 12 differentially methylated regions (DMRs). Putative DMRs were validated by bisulfite sequencing, confirming the presence of parent-of-origin-specific methylation marks. We detected DMRs associated with known imprinted genes within the Prader-Willi/Angelman syndrome region, such as SNRPN and MAGEL2, validating this as a method of detecting imprinted loci. Of the 12 DMRs identified, eight were novel, some of which are associated with genes not previously thought to be imprinted. These include a site within intron 2 of IGF1R at 15q26.3, a gene that plays a fundamental role in growth, and an intergenic site upstream of GABRG3 that lies within a previously defined candidate region conferring an increased maternal risk of psychosis. These data provide a map of parent-of-origin-specific epigenetic modifications on chromosome 15, identifying DNA elements that may play a functional role in the imprinting process. Application of this methodology to other chromosomes for which UPD has been reported will allow the systematic identification of imprinted sites throughout the genome.

Longitudinal observation of a patient with Rieger syndrome and interstitial deletion 4 (q25-q31.1)

Rieger syndrome (RS; OMIM 180500) is a rare autosomal dominant disorder of morphogenesis, with ocular and systemic abnormalities and variability in phenotypic expression. Some patients with RS presented with a deletion of the band 4q25 to which the homeobox gene PIT X2 (former RIEG) was mapped. To study the natural history and perform a genotype-phenotype correlation, we followed a girl with RS from the age of 1 year to puberty. The study included physical examination, clinical and psychological evaluation, and cytogenetic analysis with GTG-banded karyotype and array CGH. Additionally, molecular analysis using microsatellite markers for chromosome 4 (D4S427, D4S194 and D4S1615) was performed. Conventional chromosome analysis showed a 4q deletion, and aCGH confirmed the determination of the breakpoints at 4q25 and 4q31. With the exception of the typical features of RS is the patient, the clinical manifestations were relatively mild, despite the relatively large size of the deleted chromosome segment. The patient was periodically re-evaluated for several years. The teeth are still abnormal, and she is still under orthodontic treatment. The facial features were attenuated with age. Currently, she is under constant monitoring of eye pressure. She benefited from early intervention program, and her tonus is normal. She attends a normal school with minor learning difficulties. In conclusion, this study offers a comprehensive phenotypic delineation of RS through almost two decades and may contribute to a more accurate genetic counseling in cases of this syndrome.

Quantitative 1-Step DNA Methylation Analysis with Native Genomic DNA as Template

Background: DNA methylation analysis currently requires complex multistep procedures based on bisulfite conversion of unmethylated cytosines or on methylation-sensitive endonucleases. To facilitate DNA methylation analysis, we have developed a quantitative 1-step assay for DNA methylation analysis.

Methods: The assay is based on combining methylation-sensitive FastDigest® endonuclease digestion and quantitative real-time PCR (qPCR) in a single reaction. The first step consists of DNA digestion, followed by endonuclease inactivation and qPCR. The degree of DNA methylation is evaluated by comparing the quantification cycles of a reaction containing a methylation-sensitive endonuclease with the reaction of a sham mixture containing no endonuclease. Control reactions interrogating an unmethylated locus allow the detection and correction of artifacts caused by endonuclease inhibitors, while simultaneously permitting copy number assessment of the locus of interest.

Results: With our novel approach, we correctly diagnosed the imprinting disorders Prader–Willi syndrome and Angelman syndrome in 35 individuals by measuring methylation levels and copy numbers for the SNRPN (small nuclear ribonucleoprotein polypeptide N) promoter. We also demonstrated that the proposed correction model significantly (P &lt; 0.05) increases the assay’s accuracy with low-quality DNA, allowing analysis of DNA samples with decreased digestibility, as is often the case in retrospective studies.

Conclusions: Our novel DNA methylation assay reduces both the hands-on time and errors caused by handling and pipetting and allows methylation analyses to be completed within 90 min after DNA extraction. Combined with its precision and reliability, these features make the assay well suited for diagnostic procedures as well as high-throughput analyses.

No evidence for mutations of CTCFL/BORIS in Silver-Russell syndrome patients with IGF2/H19 imprinting control region 1 hypomethylation

BACKGROUND

Silver-Russell syndrome (SRS) is a genetically and clinically heterogeneous disease. Although no protein coding gene defects have been reported in SRS patients, approximately 50% of SRS patients carry epimutations (hypomethylation) at the IGF2/H19 imprinting control region 1 (ICR1). Proper methylation at ICR1 is crucial for the imprinted expression of IGF2, a fetal growth factor. CTCFL, a testis-specific protein, has recently been proposed to play a role in the establishment of DNA methylation at the murine equivalent of ICR1. A screen was undertaken to assess whether CTCFL is mutated in SRS patients with hypomethylation, to explore a link between the observed epimutations and a genetic cause of the disease.

METHODOLOGY/PRINCIPAL FINDINGS

DNA was obtained from 36 SRS patients with hypomethylation at ICR1. All CTCFL coding exons were sequenced and analyzed for duplications/deletions using both multiplex ligation-dependent probe amplification, with a custom CTCFL probe set, and genomic qPCR. Novel SNP alleles were analyzed for potential differential splicing in vitro utilizing a splicing assay. Neither mutations of CTCFL nor duplications/deletions were observed. Five novel SNPs were identified and have been submitted to dbSNP. In silico splice prediction suggested one novel SNP, IVS2-66A>C, activated a cryptic splice site, resulting in aberrant splicing and premature termination. In vitro splicing assays did not confirm predicted aberrant splicing.

CONCLUSIONS/SIGNIFICANCE

As no mutations were detected at CTCFL in the patients examined, we conclude that genetic alterations of CTCFL are not responsible for the SRS hypomethylation. We suggest that analysis of other genes involved in the establishment of DNA methylation at imprinted genes, such as DNMT3A and DNMT3L, may provide insight into the genetic cause of hypomethylation in SRS patients.

[Avian influenza: wildbird monitoring in Switzerland between 2003-2006]

During various surveillance programs more than 3500 cloacal swabs and organ samples from songbirds, waterbirds and poultry have been tested for avian influenza using real time RT-PCR. Switzerland carried out the first wildbird monitoring between autumn 2003 and spring 2005. 1053 samples, mostly from songbirds, were tested. LPAI-strains were found in two cases. A second intensified surveillance program started in October 2005 along with the first ban on free range poultry farming. Until the end of April 2006 2455 cloacal swabs from dead wildbirds have been analysed. By the end of february H5N1 was for the first time detected in Switzerland and by the end of march 32 waterbirds have been found positive for H5N1. 146 poultry flocks with a special permission for free range management proved to be AI negative.

Identification of non-recurrent submicroscopic genome imbalances: the advantage of genome-wide microarrays over targeted approaches

Genome-wide analysis of DNA copy-number changes using microarray-based technologies has enabled the detection of de novo cryptic chromosome imbalances in approximately 10% of individuals with mental retardation. So far, the majority of these submicroscopic microdeletions/duplications appear to be unique, hampering clinical interpretation and genetic counselling. We hypothesised that the genomic regions involved in these de novo submicroscopic aberrations would be candidates for recurrent copy-number changes in individuals with mental retardation. To test this hypothesis, we used multiplex ligation-dependent probe amplification (MLPA) to screen for copy number changes at eight genomic candidate regions in a European cohort of 710 individuals with idiopathic mental retardation. By doing so, we failed to detect additional submicroscopic rearrangements, indicating that the anomalies tested are non-recurrent in this cohort of patients. The break points flanking the candidate regions did not contain low copy repeats and/or sequence similarities, thus providing an explanation for its non-recurrent nature. On the basis of these data, we propose that the use of genome-wide microarrays is indicated when testing for copy-number changes in individuals with idiopathic mental retardation.

Duplications in addition to terminal deletions are present in a proportion of ring chromosomes: clues to the mechanisms of formation

BACKGROUND AND METHODS

Ring chromosomes are often associated with abnormal phenotypes because of loss of genomic material at one or both ends. In some cases no deletion has been detected and the abnormal phenotype has been attributed to mitotic ring instability. We investigated 33 different ring chromosomes in patients with phenotypic abnormalities by array based comparative genomic hybridisation (CGH) and fluorescence in situ hybridisation (FISH).

RESULTS

In seven cases we found not only the expected terminal deletion but also a contiguous duplication. FISH analysis in some of these cases demonstrated that the duplication was inverted. Thus these ring chromosomes derived through a classical inv dup del rearrangement consisting of a deletion and an inverted duplication.

DISCUSSION

Inv dup del rearrangements have been reported for several chromosomes, but hardly ever in ring chromosomes. Our findings highlight a new mechanism for the formation of some ring chromosomes and show that inv dup del rearrangements may be stabilised not only through telomere healing and telomere capture but also through circularisation. This type of mechanism must be kept in mind when evaluating possible genotype-phenotype correlations in ring chromosomes since in these cases: (1) the deletion may be larger or smaller than first estimated based on the size of the ring, with a different impact on the phenotype; and (2) the associated duplication will in general cause further phenotypic anomalies and might confuse the genotype-phenotype correlation. Moreover, these findings explain some phenotypic peculiarities which previously were attributed to a wide phenotypic variation or hidden mosaicism related to the instability of the ring.

Initial maternal meiotic I error leading to the formation of a maternal i(2q) and a paternal i(2p) in a healthy male

We report on the investigation of the parental origin and mode of formation of the two isochromosomes, i(2p) and i(2q), detected in a healthy adult male. Conventional cytogenetic analysis revealed the proband's lack of structurally normal chromosomes 2, these being replaced by an i(2p) and an i(2q). Investigation of the parental origin of the isochromosomes revealed a paternal origin of the i(2p) chromosome and a maternal origin of the i(2q) chromosome. Thus, the formation of both isochromosomes, or at least of the paternal i(2p), appears to have occurred postzygotically. Interestingly, whilst a paternal isodisomy was observed for the entire 2p, maternal heterodisomy was detected for two segments of 2q, separated by a segment showing isodisomy. The results are indicative of an initial error (non-disjunction or i(2q) formation) concerning the maternal chromosomes 2 during meiosis I, which likely favored the subsequent mitotic recombination event resulting in the presence of two isochromosomes. To the best of our knowledge this is the first case of an initial meiotic error, followed by postzygotic trisomy rescue through the formation of isochromosomes, resulting in a normal phenotype. A prenatal detection, by cytogenetic and molecular analysis, of such chromosome abnormality would have led to the incorrect conclusion of a most likely poor prognosis for the fetus.

Jacobsen syndrome and Beckwith-Wiedemann syndrome caused by a parental pericentric inversion inv(11)(p15q24)

Here we report on a male infant presenting the typical pattern of Jacobsen syndrome including trigonocephaly, thrombocytopenia, congenital heart defect, urethral stenosis, and partial agenesis of the corpus callosum. Conventional karyotyping, FISH, SKY and CGH analyses showed that the region distal to the MLL locus on 11q23 was lost and replaced by the distal region of 11p, leading to a partial trisomy of 11p and a partial monosomy of 11q. According to ISCN (1995) the karyotype can be described as 46,XY,add(11)(q2?3). ish 11ptel(D11S2071x3),11qtel(VIJyRM2072x1). Array-CGH analysis allowed us to narrow down the breakpoints to 11p15.1 and 11q24.1. Methylation analyses of genes located on 11p showed an increased level of the non-methylated paternal allele of the KCNQ1OT1 gene, confirming the concomitant presence of Beckwith-Wiedemann syndrome (BWS). The phenotype resulting from the 11q deletion seems to dominate the phenotype due to the distal 11p trisomy. Investigation of the parents revealed that this chromosomal rearrangement was caused by a paternal pericentric inversion inv(11)(p15q24). Since chromosomal aberrations like the one described here can easily be overlooked during routine chromosome analysis, combined FISH analysis using subtelomeric and possibly additional probes should be applied if there is any doubt about the integrity of telomeric regions.

A novel PITX2 mutation and a polymorphism in a 5-generation family with Axenfeld-Rieger anomaly and coexisting Fuchs' endothelial dystrophy

PURPOSE

To investigate the clinical and genetic appearance of Axenfeld-Rieger anomaly or syndrome (ARAS) and Fuchs' endothelial dystrophy (FED) in a 5-generation pedigree coexpressing both pathologic features in a large number of family members.

DESIGN

Observational case-control and DNA linkage and screening study.

PARTICIPANTS

Of 114 family members, 50 underwent clinical investigation and DNA analysis between July 2001 and March 2004.

METHODS

Linkage at the PITX2 locus was demonstrated using a number of microsatellites mapping to the critical region 4q25 to 4q26. The PITX2 gene was subsequently screened for mutations in all investigated family members.

MAIN OUTCOME MEASURE

Linkage of the ARAS and FED phenotype and mutation detection in the PITX2 gene.

RESULTS

Twenty-seven patients were identified as being affected by ARAS. Fuchs' endothelial dystrophy was found in 19 patients. Fifteen patients presented both kinds of anomaly. Deoxyribonucleic acid sequencing revealed 2 heteroallelic DNA variants that segregated together (on the same allele) and were present in all severely affected ARAS individuals. The first variant, g.20913G>T, assumed to be the causative mutation for ARAS, causes amino acid substitution at codon 137 (G137V). A statistically significant 2-point logarithm of the odds score of 4.06 was obtained with marker D4S406. The second variant is likely a polymorphism in the intron between exons 2 and 3 (IVS2+8delCinsGTT) and was detected in heterozygous form in 20% of control individuals.

CONCLUSION

This gene analysis revealed a novel PITX2 mutation and a polymorphism in a family with ARAS. Whether FED, also manifested in the severely affected individuals, is due to a different but cosegregating gene is to be determined.

A new chromosome 17q21.31 microdeletion syndrome associated with a common inversion polymorphism

Submicroscopic genomic copy number changes have been identified only recently as an important cause of mental retardation. We describe the detection of three interstitial, overlapping 17q21.31 microdeletions in a cohort of 1,200 mentally retarded individuals associated with a clearly recognizable clinical phenotype of mental retardation, hypotonia and a characteristic face. The deletions encompass the MAPT and CRHR1 genes and are associated with a common inversion polymorphism.

Clinical profiles of four patients with Rett syndrome carrying a novel exon 1 mutation or genomic rearrangement in the MECP2 gene

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the X-linked MECP2 gene encoding methyl CpG binding protein 2 (MeCP2). Recently, a new isoform of MeCP2 including exon 1 was identified. This new isoform is more abundantly expressed in brain than the isoform including exons 2-4. Very little is known about the phenotypes associated with mutations in exon 1 of MECP2 since only a limited number of RTT patients carrying such mutations have been identified so far. In this study, we screened a cohort of 20 girls with RTT for exon 1 mutations by sequencing and multiplex ligation-dependent probe amplification (MLPA). We identified one girl with a novel exon 1 mutation (c.30delCinsGA) by sequencing and three with genomic rearrangements by MLPA. Comparison of the phenotypes showed that the girls carrying a mutation or rearrangement encompassing exon 1 were more severely affected than the girls with rearrangements not affecting exon 1.

Pre- and postnatal findings in trisomy 17 mosaicism

Trisomy 17 mosaicism is one of the rarest autosomal trisomies in humans. Thus far, only 23 cases have been described, most of them detected prenatally. In only five instances has mosaicism been demonstrated in lymphocytes and/or fibroblasts postnatally, and only in these have multiple congenital anomalies (MCA), facial dysmorphisms, and mental retardation been reported. Patients with trisomy 17 mosaicism at amniocentesis and a normal karyotype in blood and fibroblasts (n = 17) were always healthy. Here, we report on pre- and postnatal clinical, cytogenetic, molecular-cytogenetic, and molecular findings in four patients with trisomy 17 mosaicism. The first case was detected in cultured but not in short-term chorionic villi and amniocytes. Due to MCA on prenatal ultrasound examination the pregnancy was terminated. The second patient is a 13-month-old healthy boy, in whom low level trisomy 17 mosaicism was detected in cultured chorionic villi only. The third patient is a 2-year-old girl with growth retardation, developmental delay, MCA, and trisomy 17 mosaicism in amniocytes, fibroblasts, and placenta, but not in blood and buccal smear. The fourth patient is a 9-year-old boy with growth and mental retardation, sensoneurinal hearing loss, and MCA. Cytogenetic analyses showed trisomy 17 mosaicism in amniocytes, skin fibroblasts, and urinary sediment cells, whereas in blood and buccal smear a 46,XY karyotype was found. Molecular investigations in all four cases indicated biparental inheritance of chromosome 17. Formation of trisomy was most likely due to a maternal meiosis I error in Patient 1 and a postzygotic non-disjunction of the paternal chromosome 17 in Patient 4. Cerebellar malformations, reported in two cases from the literature and in two reported here may be a specific feature of trisomy 17 mosaicism. Since the aberration has rarely been reported in lymphocytes, chordocentesis is not indicated in prenatal diagnosis. Prenatal genetic counseling for trisomy 17 mosaicism in chorionic villi or amniocytes should consider that the clinical significance remains uncertain.