Molecular testing in holoprosencephaly Kruszka, Paul; Martinez, Ariel F.; Muenke, Maximilian
American journal of medical genetics. Part C, Seminars in medical genetics,
June 2018, Letnik:
178, Številka:
2
Journal Article
Odprti dostop
Holoprosencephaly (HPE) is a structural brain anomaly characterized by failure of the forebrain to separate during early embryogenesis. Both genetic and environmental etiologies of HPE have been ...discovered over the last three decades. Traditionally, the genetic workup for HPE has been a karyotype, chromosomal microarray, and/or Sanger sequencing of select genes. The recent increased availability of next‐generation sequencing has changed the molecular diagnostic landscape for HPE, associating new genes with this disorder such as FGFR1. We conducted a systematic review of the medical literature for the molecular testing of HPE for studies published in the last 20 years. We also queried known commercial diagnostic laboratories and used information on their websites to construct a list of available commercial testing. Our group released its first recommendations in 2010 and this update incorporates the technology shifts and gene discoveries over the last decade. These recommendations provide a guide for genetic diagnosis of HPE, which is paramount for patients and their families for prognosis, treatment, and genetic counseling.
Catel-Manzke syndrome is characterized by the combination of Pierre Robin sequence and radial deviation, shortening as well as clinodactyly of the index fingers, due to an accessory ossification ...center. Mutations in TGDS have been identified as one cause of Catel-Manzke syndrome, but cannot be found as causative in every patient with the clinical diagnosis. We performed a chromosome microarray and/or exome sequencing in three patients with hand hyperphalangism, heart defect, short stature, and mild to severe developmental delay, all of whom were initially given a clinical diagnosis of Catel-Manzke syndrome. In one patient, we detected a large deletion of exons 1–8 and the missense variant c.1282C > T (p.Arg428Trp) in KYNU (NM_003937.2), whereas homozygous missense variants in KYNU were found in the other two patients (c.989G > A (p.Arg330Gln) and c.326G > C (p.Trp109Ser)). Plasma and urine metabolomic analysis of two patients indicated a block along the tryptophan catabolic pathway and urine organic acid analysis showed excretion of xanthurenic acid. Biallelic loss-of-function mutations in KYNU were recently described as a cause of NAD deficiency with vertebral, cardiac, renal and limb defects; however, no hand hyperphalangism was described in those patients, and Catel-Manzke syndrome was not discussed as a differential diagnosis. In conclusion, we present unrelated patients identified with biallelic variants in KYNU leading to kynureninase deficiency and xanthurenic aciduria as a very likely cause of their hyperphalangism, heart defect, short stature, and developmental delay. We suggest performance of urine organic acid analysis in patients with suspected Catel-Manzke syndrome, particularly in those with cardiac or vertebral defects or without mutations in TGDS.
•We describe a new genetic etiology of Catel-Manzke syndrome.•Multisystemic features other than hyperphalangism include spine, heart, renal, and inner ear malformations.•Detection of xanthurenic aciduria on biochemical testing can aid in the differential diagnosis of hyperphalangism.
Chromodomain helicase DNA-binding protein 4 (CHD4) is an ATP-dependent chromatin remodeler involved in epigenetic regulation of gene transcription, DNA repair, and cell cycle progression. Also known ...as Mi2β, CHD4 is an integral subunit of a well-characterized histone deacetylase complex. Here we report five individuals with de novo missense substitutions in CHD4 identified through whole-exome sequencing and web-based gene matching. These individuals have overlapping phenotypes including developmental delay, intellectual disability, hearing loss, macrocephaly, distinct facial dysmorphisms, palatal abnormalities, ventriculomegaly, and hypogonadism as well as additional findings such as bone fusions. The variants, c.3380G>A (p.Arg1127Gln), c.3443G>T (p.Trp1148Leu), c.3518G>T (p.Arg1173Leu), and c.3008G>A, (p.Gly1003Asp) (GenBank: NM_001273.3), affect evolutionarily highly conserved residues and are predicted to be deleterious. Previous studies in yeast showed the equivalent Arg1127 and Trp1148 residues to be crucial for SNF2 function. Furthermore, mutations in the same positions were reported in malignant tumors, and a de novo missense substitution in an equivalent arginine residue in the C-terminal helicase domain of SMARCA4 is associated with Coffin Siris syndrome. Cell-based studies of the p.Arg1127Gln and p.Arg1173Leu mutants demonstrate normal localization to the nucleus and HDAC1 interaction. Based on these findings, the mutations potentially alter the complex activity but not its formation. This report provides evidence for the role of CHD4 in human development and expands an increasingly recognized group of Mendelian disorders involving chromatin remodeling and modification.
De novo variants (DNVs) represent an important fraction of the pathogenic variant burden in holoprosencephaly (HPE). However, unexpected recurrences can occur, as evidenced by multiple affected ...children harboring the same apparently DNV. This study was performed to estimate the rate of parental mosaicism in a cohort of patients with HPE.
We developed a targeted capture next-generation sequencing (NGS) panel of 153 genes with potential implication in HPE. Sequencing data from a cohort of 136 HPE family trios were analyzed to identify probands with apparently DNVs. DNVs were examined in the proband and their parents to detect any deviations from the expected ~50/50 allele ratio of true heterozygosity. Selected variants were confirmed by Droplet Digital™ polymerase chain reaction (ddPCR).
We identified 28 high-confidence DNVs, 20 of which occurred in known HPE genes. Nineteen of the 20 variants (95%) were pathogenic or likely pathogenic. Sequence data analysis showed evidence of parental mosaicism in five cases, for an overall mosaicism rate of 26%. In addition, we found evidence for likely postzygotic events in four cases (50%).
High sensitivity methods, such as high-depth NGS and ddPCR, are essential to providing an accurate assessment of recurrence risk in HPE families with apparently DNVs.
Holoprosencephaly is the incomplete separation of the forebrain during embryogenesis. Both genetic and environmental etiologies have been determined for holoprosencephaly; however, a genetic etiology ...is not found in most cases. In this report, we present two unrelated individuals with semilobar holoprosencephaly who have the identical de novo missense variant in the gene CCR4-NOT transcription complex, subunit 1 (CNOT1). The variant (c.1603C>T p.Arg535Cys) is predicted to be deleterious and is not present in public databases. CNOT1 has not been previously associated with holoprosencephaly or other brain malformations. In situ hybridization analyses of mouse embryos show that Cnot1 is expressed in the prosencephalic neural folds at gestational day 8.25 during the critical period for subsequent forebrain division. Combining human and mouse data, we show that CNOT1 is associated with incomplete forebrain division.
Genetic factors predispose individuals to attention-deficit/hyperactivity disorder (ADHD). Previous studies have reported linkage and association to ADHD of gene variants within ADGRL3. In this ...study, we functionally analyzed noncoding variants in this gene as likely pathological contributors.
In silico, in vitro, and in vivo approaches were used to identify and characterize evolutionary conserved elements within the ADGRL3 linkage region (~207 Kb). Family-based genetic analyses of 838 individuals (372 affected and 466 unaffected patients) identified ADHD-associated single nucleotide polymorphisms harbored in some of these conserved elements. Luciferase assays and zebrafish green fluorescent protein transgenesis tested conserved elements for transcriptional enhancer activity. Electromobility shift assays were used to verify transcription factor–binding disruption by ADHD risk alleles.
An ultraconserved element was discovered (evolutionary conserved region 47) that functions as a transcriptional enhancer. A three-variant ADHD risk haplotype in evolutionary conserved region 47, formed by rs17226398, rs56038622, and rs2271338, reduced enhancer activity by 40% in neuroblastoma and astrocytoma cells (pBonferroni < .0001). This enhancer also drove green fluorescent protein expression in the zebrafish brain in a tissue-specific manner, sharing aspects of endogenous ADGRL3 expression. The rs2271338 risk allele disrupts binding of YY1 transcription factor, an important factor in the development and function of the central nervous system. Expression quantitative trait loci analysis of postmortem human brain tissues revealed an association between rs2271338 and reduced ADGRL3 expression in the thalamus.
These results uncover the first functional evidence of common noncoding variants with potential implications for the pathology of ADHD.
Lysine methyltransferase 2D (KMT2D; OMIM 602113) encodes a histone methyltransferase involved in transcriptional regulation of the beta‐globin and estrogen receptor as part of a large protein complex ...known as activating signal cointegrator‐2‐containing complex (ASCOM). Heterozygous germline mutations in the KMT2D gene are known to cause Kabuki syndrome (OMIM 147920), a developmental multisystem disorder. Neither holoprosencephaly nor other defects in human forebrain development have been previously associated with Kabuki syndrome. Here we report two patients diagnosed with alobar holoprosencephaly in their antenatal period with de novo monoallelic KMT2D variants identified by trio‐based exome sequencing. The first patient was found to have a stop‐gain variant c.12565G>T (p.Gly4189*), while the second patient had a missense variant c.5A>G (p.Asp2Gly). Phenotyping of each patient did not reveal any age‐related feature of Kabuki syndrome. These two cases represent the first report on association between KMT2D and holoprosencephaly.
Nonchromosomal, nonsyndromic holoprosencephaly (NCNS‐HPE) has traditionally been considered as a condition of brain and craniofacial maldevelopment. In this review, we present the results of a ...comprehensive literature search supporting a wide spectrum of extracephalic manifestations identified in patients with NCNS‐HPE. These manifestations have been described in case reports and in large cohorts of patients with “single‐gene” mutations, suggesting that the NCNS‐HPE phenotype can be more complex than traditionally thought. Likely, a complex network of interacting genetic variants and environmental factors is responsible for these systemic abnormalities that deviate from the usual brain and craniofacial findings in NCNS‐HPE. In addition to the systemic consequences of pituitary dysfunction (as a direct result of brain midline defects), here we describe a number of extracephalic findings of NCNS‐HPE affecting various organ systems. It is our goal to provide a guide of extracephalic features for clinicians given the important clinical implications of these manifestations for the management and care of patients with HPE and their mutation‐positive relatives. The health risks associated with some manifestations (e.g., fatty liver disease) may have historically been neglected in affected families.
Sifrim-Hitz-Weiss syndrome (SIHIWES) is a recently described multisystemic neurodevelopmental disorder caused by de novo variants inCHD4. In this study, we investigated the clinical spectrum of the ...disorder, genotype-phenotype correlations, and the effect of different missense variants on CHD4 function.
We collected clinical and molecular data from 32 individuals with mostly de novo variants in CHD4, identified through next-generation sequencing. We performed adenosine triphosphate (ATP) hydrolysis and nucleosome remodeling assays on variants from five different CHD4 domains.
The majority of participants had global developmental delay, mild to moderate intellectual disability, brain anomalies, congenital heart defects, and dysmorphic features. Macrocephaly was a frequent but not universal finding. Additional common abnormalities included hypogonadism in males, skeletal and limb anomalies, hearing impairment, and ophthalmic abnormalities. The majority of variants were nontruncating and affected the SNF2-like region of the protein. We did not identify genotype-phenotype correlations based on the type or location of variants. Alterations in ATP hydrolysis and chromatin remodeling activities were observed in variants from different domains.
The CHD4-related syndrome is a multisystemic neurodevelopmental disorder. Missense substitutions in different protein domains alter CHD4 function in a variant-specific manner, but result in a similar phenotype in humans.
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