De novo gain-of-function variants in KCNT2 as a novel cause of developmental and epileptic encephalopathy.

Variants in several potassium channel genes have been found in developmental and epileptic encephalopathies (DEE). We report on 2 females with de novo variants in KCNT2 with West syndrome followed by Lennox-Gastaut syndrome or with DEE with migrating focal seizures. After in vitro analysis suggested quinidine-responsive gain-of-function effects, we treated 1 of the girls with quinidine add-on therapy and achieved marked clinical improvements. This suggests that the new spectrum of KCNT2-related disorders do not only share similar phenotypic and in vitro functional and pharmacological features with previously known KCNT1-related disorders, but also represents a further example for possible precision medicine approaches. Ann Neurol 2018;83:1198-1204.

A novel immunodeficiency syndrome associated with partial trisomy 19p13.

BACKGROUND: Subtelomeric deletions and duplications may cause syndromic disorders that include features of immunodeficiency. To date, no phenotype of immunological pathology has been linked to partial trisomy 19. We report here on two unrelated male patients showing clinical and laboratory signs of immunodeficiency exhibiting a duplication involving Chromosome 19p13. METHODS: Both patients underwent a detailed clinical examination. Extended laboratory investigations for immune function, FISH and array comparative genome hybridization (CGH) analyses were performed. RESULTS: The reported patients were born prematurely with intrauterine growth retardation and share clinical features including neurological impairment, facial dysmorphy and urogenital malformations. Array CGH analyses of both patients showed a largely overlapping terminal duplication affecting Chromosome 19p13. In both affected individuals, the clinical course was marked by recurrent severe infections. Signs of humoral immunodeficiency were detected, including selective antibody deficiency against polysaccharide antigens in patient 1 and reduced IgG1, IgG3 subclass levels and IgM deficiency in patient 2. Class-switched B memory cells were almost absent in both patients. Normal numbers of T cells, B cells and natural killer cells were observed in both boys. Lymphocytic proliferation showed no consistent functional pathology, however, function of granulocytes and monocytes as assessed by oxidative burst test was moderately reduced. Moreover, natural killer cytotoxicity was reduced in both patients. Immunoglobulin substitution resulted in a decreased number and severity of infections and improved thriving in both patients. CONCLUSIONS: Partial trisomy 19p13 represents a syndromic disorder associating organ malformation and hitherto unrecognised immunodeficiency.

Congenital pulmonary lymphangiectasis.

Congenital pulmonary lymphangiectasis (CPL) is a rare vascular malformation causing dilated lymph vessels and disturbed drainage of lymph fluid. Based on the pathogenesis and clinical phenotype it can be classified as primary or secondary CPL. Associated genetic syndromes with or without lymphedema, familial occurrence and gene mutations have been described. In utero, it may present as non-immune hydrops with pleural effusions. At birth neonates may have respiratory failure due to chylothorax and pulmonary hypoplasia, causing very high short term mortality rates. Other cases may become symptomatic any time later in childhood or even during adult life. CPL is usually diagnosed based on the combination of clinical signs, imaging and histological findings. Open-lung biopsy is considered the gold standard for the diagnosis of CPL. Treatment is primarily supportive featuring aggressive mechanical ventilation and the management of problems associated with congenital chylothorax including chest-drainage, medium-chain triglycerides (MCT) diet, and octreotide.

A second hotspot for pathogenic exon-skipping variants in CDC45.

Biallelic pathogenic variants in CDC45 are associated with Meier-Gorlin syndrome with craniosynostosis (MGORS type 7), which also includes short stature and absent/hypoplastic patellae. Identified variants act through a hypomorphic loss of function mechanism, to reduce CDC45 activity and impact DNA replication initiation. In addition to missense and premature termination variants, several pathogenic synonymous variants have been identified, most of which cause increased exon skipping of exon 4, which encodes an essential part of the RecJ-orthologue's DHH domain. Here we have identified a second cohort of families segregating CDC45 variants, where patients have craniosynostosis and a reduction in height, alongside common facial dysmorphisms, including thin eyebrows, consistent with MGORS7. Skipping of exon 15 is a consequence of two different variants, including a shared synonymous variant that is enriched in individuals of East Asian ancestry, while other variants in trans are predicted to alter key intramolecular interactions in α/ß domain II, or cause retention of an intron within the 3'UTR. Our cohort and functional data confirm exon skipping is a relatively common pathogenic mechanism in CDC45, and highlights the need for alternative splicing events, such as exon skipping, to be especially considered for variants initially predicted to be less likely to cause the phenotype, particularly synonymous variants.

Left ventricular hypertrabeculation/noncompaction with epilepsy, other heart defects, minor facial anomalies and new copy number variants.

BACKGROUND: Left ventricular hypertrabeculation/noncompaction (LVHT) is a cardiac abnormality of unknown etiology which has been described in children as well as in adults with and without chromosomal aberrations. LVHT has been reported in association with various cardiac and extracardiac abnormalities like epilepsy and facial dysmorphism. CASE PRESENTATION: A unique combination of LVHT, atrial septal defect, pulmonary valve stenosis, aortic stenosis, epilepsy and minor facial anomalies is presented in a 5.5 years old girl. Microarray-based genomic hybridization (array-CGH) detected six previously not described copy number variants (CNVs) inherited from a clinically unaffected father and minimally affected mother, thus, most likely, not clinically significant but rare benign variants. CONCLUSIONS: Despite this complex phenotype de novo microdeletions or microduplications were not detected by array CGH. Further investigations, such as whole exome sequencing, could reveal point mutations and small indels as the possible cause.

Pheochromocytoma in a 2.75-year-old-girl with a germline von Hippel-Lindau mutation Q164R.

Pheochromocytomas are rare tumors of the adrenal gland occurring sporadically or as part of familial cancer syndromes. Here we report on the case of a pheochromocytoma due to the germline missense mutation c.491A>G (Q164R) in exon 3 of the von Hippel-Lindau gene in a girl as young as 2.75 years. Extended analyses of her relatives showed that the mutation occurred de novo in the patient's father who was subsequently diagnosed with bilateral pheochromocytomas and a retinal angioma. To the best of our knowledge, this is the youngest patient presenting with pheochromocytoma so far described in the literature. The same VHL mutation has been reported in a patient who developed a pheochromocytoma at the age of 10 years; therefore, for known VHL Q164R mutation carriers, we suggest screening for pheochromocytoma beginning at 2 years of age.

[Genetic counseling in multiple pregnancies]. / Humangenetische Beratung bei Mehrlingsschwangerschaften.

Genetic counseling in cases of multiple pregnancies shows marked differences compared to singleton pregnancies. The rising rate of multiple pregnancies and its association with advanced maternal age has expanded the need for prenatal diagnosis in twins and higher-order gestations. However, the request for invasive prenatal diagnostic procedures often differs in multiple and singleton pregnancies. This is in particular true when the multiple pregnancy occurred after assisted reproductive technology. In case of twin pregnancies, the distinction between a mono- and dizygotic pregnancy may facilitate the decision about obtaining a single or two samples. Discordant anomalies pose a special problem. Discordant anomalies are in rare instances even observed in monozygotic pregnancies. Here, we summarize the clinical, analysis-related and ethical problems regarding genetic counseling in multiple pregnancies.

Combined Respiratory Chain Deficiency and UQCC2 Mutations in Neonatal Encephalomyopathy: Defective Supercomplex Assembly in Complex III Deficiencies.

Vertebrate respiratory chain complex III consists of eleven subunits. Mutations in five subunits either mitochondrial (MT-CYB) or nuclear (CYC1, UQCRC2, UQCRB, and UQCRQ) encoded have been reported. Defects in five further factors for assembly (TTC19, UQCC2, and UQCC3) or iron-sulphur cluster loading (BCS1L and LYRM7) cause complex III deficiency. Here, we report a second patient with UQCC2 deficiency. This girl was born prematurely; pregnancy was complicated by intrauterine growth retardation and oligohydramnios. She presented with respiratory distress syndrome, developed epileptic seizures progressing to status epilepticus, and died at day 33. She had profound lactic acidosis and elevated urinary pyruvate. Exome sequencing revealed two homozygous missense variants in UQCC2, leading to a severe reduction of UQCC2 protein. Deficiency of complexes I and III was found enzymatically and on the protein level. A review of the literature on genetically distinct complex III defects revealed that, except TTC19 deficiency, the biochemical pattern was very often a combined respiratory chain deficiency. Besides complex III, typically, complex I was decreased, in some cases complex IV. In accordance with previous observations, the presence of assembled complex III is required for the stability or assembly of complexes I and IV, which might be related to respirasome/supercomplex formation.

Missense variant in CCDC22 causes X-linked recessive intellectual disability with features of Ritscher-Schinzel/3C syndrome.

Ritscher-Schinzel syndrome (RSS)/3C (cranio-cerebro-cardiac) syndrome (OMIM#220210) is a rare and clinically heterogeneous developmental disorder characterized by intellectual disability, cerebellar brain malformations, congenital heart defects, and craniofacial abnormalities. A recent study of a Canadian cohort identified homozygous sequence variants in the KIAA0196 gene, which encodes the WASH complex subunit strumpellin, as a cause for a form of RSS/3C syndrome. We have searched for genetic causes of a phenotype similar to RSS/3C syndrome in an Austrian family with two affected sons. To search for disease-causing variants, whole-exome sequencing (WES) was performed on samples from two affected male children and their parents. Before WES, CGH array comparative genomic hybridization was applied. Validation of WES and segregation studies was done using routine Sanger sequencing. Exome sequencing detected a missense variant (c.1670A>G; p.(Tyr557Cys)) in exon 15 of the CCDC22 gene, which maps to chromosome Xp11.23. Western blots of immortalized lymphoblastoid cell lines (LCLs) from the affected individual showed decreased expression of CCDC22 and an increased expression of WASH1 but a normal expression of strumpellin and FAM21 in the patients cells. We identified a variant in CCDC22 gene as the cause of an X-linked phenotype similar to RSS/3C syndrome in the family described here. A hypomorphic variant in CCDC22 was previously reported in association with a familial case of syndromic X-linked intellectual disability, which shows phenotypic overlap with RSS/3C syndrome. Thus, different inactivating variants affecting CCDC22 are associated with a phenotype similar to RSS/3C syndrome.

Manifestations of juvenile polyposis syndrome in SMAD4 mutation carriers of a kindred.

The autosomal dominantly inherited juvenile polyposis syndrome (JPS) leads to the development of multiple hamartomatous polyps in the gastrointestinal tract and is a precancerous condition. In a large family with a newly identified SMAD4 mutation (c.543delC), we describe the clinical manifestations of JPS. Nine affected SMAD4 mutation-positive family members were screened and treated for manifestations of JPS. Two family members were symptomatic at the time of diagnosis; seven were asymptomatic - independent of the severity of the manifestation. Each mutation carrier presented with colonic juvenile polyps, seven out of nine with additional gastric manifestations. One asymptomatic patient had early gastric cancer; another patient had a villous adenoma with high-grade intraepithelial neoplasia in the colon. Three patients had biliary lesions including a bile duct hamartoma in one and gallbladder polyps in two. Three patients had gastrointestinal vascular malformations. All mutation carriers were affected by JPS. Interestingly, the manifestations and their severity differed considerably between the patients, suggesting secondary factors influencing JPS manifestations such as Helicobacter pylori infection.

Alterations in the ankyrin domain of TRPV4 cause congenital distal SMA, scapuloperoneal SMA and HMSN2C.

Spinal muscular atrophies (SMA, also known as hereditary motor neuropathies) and hereditary motor and sensory neuropathies (HMSN) are clinically and genetically heterogeneous disorders of the peripheral nervous system. Here we report that mutations in the TRPV4 gene cause congenital distal SMA, scapuloperoneal SMA, HMSN 2C. We identified three missense substitutions (R269H, R315W and R316C) affecting the intracellular N-terminal ankyrin domain of the TRPV4 ion channel in five families. Expression of mutant TRPV4 constructs in cells from the HeLa line revealed diminished surface localization of mutant proteins. In addition, TRPV4-regulated Ca(2+) influx was substantially reduced even after stimulation with 4alphaPDD, a TRPV4 channel-specific agonist, and with hypo-osmotic solution. In summary, we describe a new hereditary channelopathy caused by mutations in TRPV4 and present evidence that the resulting substitutions in the N-terminal ankyrin domain affect channel maturation, leading to reduced surface expression of functional TRPV4 channels.

Multiplex-fluorescence in situ hybridization for chromosome karyotyping.

Multiplex-fluorescence in situ hybridization (M-FISH) was initially developed to stain human chromosomes--the 22 autosomes and X and Y sex chromosomes--with uniquely distinctive colors to facilitate karyotyping. The characteristic spectral signatures of all different combinations of fluorochromes are determined by multichannel image-analysis methods. Advantages of M-FISH include rapid analysis of metaphase spreads, even in complex cases with multiple chromosomal rearrangements, and identification of marker chromosomes. The M-FISH technology has been extended to other species, such as the mouse. Furthermore, in addition to painting probes, the method has been used with a variety of region-specific probes. M-FISH has even recently been used for 3D studies to analyze the distribution of human chromosomes in intact and preserved interphase nuclei. Hence, M-FISH has evolved into an essential tool for both clinical diagnostics and basic research. In this protocol, we describe how to use M-FISH to karyotype chromosomes, a procedure that takes approximately 14 d if new M-FISH probes have to be generated and 3 d if the M-FISH probes are ready to use.

Micro-array analyses decipher exceptional complex familial chromosomal rearrangement.

Recently there has been an increased interest in large-scale genomic variation and clinically in the consequences of haploinsufficiency of genomic segments or disruption of normal gene function by chromosome rearrangements. Here, we present an extraordinary case in which both mother and daughter presented with unexpected chromosomal rearrangement complexity, which we characterized with array-CGH, array painting and multicolor large insert clone hybridizations. We found the same 12 breakpoints involving four chromosomes in both mother and daughter. In addition, the daughter inherited a microdeletion from her father. We mapped all breakpoints to the resolution level of breakpoint spanning clones. Genes were found within 7 of the 12 breakpoint regions, some of which were disrupted by the chromosome rearrangement. One of the rearrangements disrupted a locus, which has been discussed as a quantitative trait locus for fetal hemoglobin expression in adults. Interestingly, both mother and daughter show persistent fetal hemoglobin levels. We detail the most complicated familial complex chromosomal rearrangement reported to date and thus an extreme example of inheritance of chromosomal rearrangements without error in meiotic segregation.

PHOX2B genotype allows for prediction of tumor risk in congenital central hypoventilation syndrome.

The Phox2b gene is necessary for autonomic nervous-system development. Phox2b-/- mice die in utero with absent autonomic nervous system circuits, since autonomic nervous system neurons either fail to form or degenerate. We first identified the Phox2b human ortholog, PHOX2B, as the gene underlying congenital central hypoventilation syndrome (CCHS, or Ondine curse), with an autosomal dominant mode of inheritance and de novo mutation at the first generation. We have subsequently shown that heterozygous mutations of PHOX2B may account for several combined or isolated disorders of autonomic nervous-system development--namely, tumors of the sympathetic nervous system (TSNS), such as neuroblastoma and late-onset central hypoventilation syndrome. Here, we report the clinical and molecular assessments of a cohort of 188 probands with CCHS, either isolated or associated with Hirschsprung disease and/or TSNS. The mutation-detection rate was 92.6% (174/188) in our series, and the most prevalent mutation was an in-frame duplication leading to an expansion of +5 to +13 alanines in the 20-alanine stretch at the carboxy terminal of the protein. Such findings suggest PHOX2B mutation screening as a simple and reliable tool for the diagnosis of CCHS, independent of the clinically variable phenotype. In addition, somatic mosaicism was detected in 4.5% of parents. Most interestingly, analysis of genotype-phenotype interactions strongly supports the contention that patients with CCHS who develop malignant TSNS will harbor either a missense or a frameshift heterozygous mutation of the PHOX2B gene. These data further highlight the link between congenital malformations and tumor predisposition when a master gene in development is mutated.