Establishing a reference group for distal 18q-: clinical description and molecular basis

Case report: genetic analysis of a child with 18q deletion syndrome and developmental dysplasia of the hip

OBJECTIVE

To analyze the genotypes and phenotypes of a child with developmental dysplasia of the hip (DDH), developmental delays, recurrent fever, hypothyroidism and cleft palate.

METHODS

G-banding karyotyping analysis and next-generation sequencing (NGS) were performed for the patient. The genotypes of the parents of the patient were verified by copy number variation analysis and Sanger sequencing to determine the source of variations.

RESULTS

The karyotype of the patient was 46, XX. A 10.44 Mb deletion (chr18:67562936-78005270del) at 18q22.2q23 was found by NGS. We identified 2 HSPG2 mutations (chr1: 22206699, c.2244C > A, exon 17, p.H748Q; chr1: 22157321-22157321, c.11671 + 154insA, intron). One mutation was inherited from the father, and the other was inherited from the mother.

CONCLUSION

This is the first 18q deletion syndrome case accompanied by DDH. Most phenotypes of this patient, such as developmental delays and cleft palate, may be related to the 18q22.2q23 deletion, but no variants in genes related to DDH were found in this deletion region. DDH may be related to mutations of HSPG2.

Increased Diagnostic Yield of Array Comparative Genomic Hybridization for Autism Spectrum Disorder in One Institution in Taiwan

Background and Objectives: Chromosomal microarray offers superior sensitivity for identification of submicroscopic copy number variants (CNVs) and is recommended for the initial genetic testing of patients with autism spectrum disorder (ASD). This study aims to determine the diagnostic yield of array comparative genomic hybridization (array-CGH) in ASD patients from a cohort of Chinese patients in Taiwan. Materials and Methods: Enrolled in this study were 80 ASD children (49 males and 31 females; 2–16 years old) followed up at Taipei MacKay Memorial Hospital between January 2010 and December 2020. The genomic DNA extracted from blood samples was analyzed by array-CGH via the Affymetrix GeneChip Genome-Wide Human single nucleotide polymorphism (SNP) and NimbleGen International Standards for Cytogenomic Arrays (ISCA) Plus Cytogenetic Arrays. The CNVs were classified into five groups: pathogenic (pathologic variant), likely pathogenic (potential pathologic variant), likely benign (potential normal genomic variant), benign (normal genomic variant), and uncertain clinical significance (variance of uncertain significance), according to the American College of Medical Genetics (ACMG) guidelines. Results: We identified 47 CNVs, 31 of which in 27 patients were clinically significant. The overall diagnostic yield was 33.8%. The most frequently clinically significant CNV was 15q11.2 deletion, which was present in 4 (5.0%) patients. Conclusions: In this study, a satisfactory diagnostic yield of array-CGH was demonstrated in a Taiwanese ASD patient cohort, supporting the clinical usefulness of array-CGH as the first-line testing of ASD in Taiwan.

Immune Dysregulation in Patients With Chromosome 18q Deletions-Searching for Putative Loci for Autoimmunity and Immunodeficiency

Introduction

Autoimmune disorders, IgA deficiency, and allergies seem to be common among individuals with 18q deletion syndrome [OMIM 601808]. We aimed to determine the prevalence, mechanism, and genetic background of autoimmunity, immune deficiency, and allergy in a cohort of patients with 18q deletions.

Material and Methods

Medical registries and social media were used to recruit the patients. Microarray oligonucleotide comparative genomic hybridization (aCGH) (Agilent, Santa Clara, CA, USA) was performed in all patients to identify size and location of chromosome 18 deletion. Clinical evaluation and medical record collection were performed in each of the study participants. The history of autoimmune disorders, severe and/or recurrent infections, and symptoms of allergy were noted. Total immunoglobulin IgG, IgA, IgM, IgE, and IgG1-4 serum levels were measured using nephelometry and ELISA methods. Lymphocyte T subset phenotyping was performed in 24 subjects from 18q del cohort. To predict the most promising candidate genes, we used the ENDEAVOUR-a free web resource for gene prioritization.

Results

18q deletion was confirmed by means of array CGH analysis in 27 individuals, 15 (55.6%) females and 12 males, referred to the project by specialists in medical genetics, diabetology, or pediatric endocrinology between May 2015 and December 2019. The mean age at examination was 11.8 years (min-max: 4.0-33.5). Autoimmune disorders were present in 14/27 (51.8%) of the cohort. In eight of patients, symptoms of immune deficiency coexisted with autoimmunity. Allergy was reported in nine of 27 (33.4%) patients. Over 89% of patients presented with at list one type of immunoglobulin (IgA, IgM, IgG, IgE, and IgG1-4) deficiency and eight of 25 (32%) had abnormalities in at least two major immunoglobulin (IgG, IgA, IgM) measurements (CVID-like phenotype). Patients with 18q del exhibited a significantly decreased CD4, Treg FOXP3+, TregFOXP3+Helios+, and TemCD4 cell numbers in comparison with the control groups of 24 T1DM patients and 28 healthy controls.

Conclusions

Patients with 18q deletions frequently suffer from autoimmune disorders, recurrent infections, and allergy due to immune dysregulation presenting with variable antibody deficiencies and T-regulatory cell deficiency (CD4+CD25+CD127lowFOXP3+). The spectrum of speculations regarding which gene might be responsible for such phenotype ranges from single gene haploinsufficiency to deletion of a cluster of immunogenes located distally to 18q21.

Subcutaneous immunoglobulin replacement therapy in a patient with 18q deletion syndrome, primary immune deficiency, and type 1 diabetes

18q deletion syndrome (OMIM #601808) results from a deletion of a part of a long arm of 18 chromosome and is characterized by mental retardation and congenital malformations. We present an exceptional case of a 12-year-old girl with severe phenotype of 18q deletion syndrome, frequent infections, type 1 diabetes, autoimmune thyroiditis, and vitiligo. At first, the patient was diagnosed with selective immunoglobulin A (sIgAD) which explained her susceptibility to both infections and autoimmunity. With time, sIgAD progressed to common variable immune deficiency-like (CVID-like) disorder. She had a minimum of 12 infections per year, approximately twice as many courses of different antibiotics and up to three hospitalizations annually, making the treatment of diabetes difficult. Due to safety issues (increased risk of adverse reaction to blood products) and patient’s convenience, subcutaneous IgG (SCIG) replacement therapy was initiated. We noticed a substantial decrease in the number of infections and improvement of metabolic control of diabetes.

[Congenital hypopituitarism with monosomy of chromosome 18]

Congenital hypopituitarism is a rare disease. It can be caused by isolated inborn defects of the pituitary, gene mutations (PROP1, PIT1), and chromosomal abnormalities.Deletions of chromosome 18 (De Grouchy syndrome types 1 and 2) are a group of rare genetic diseases with a frequency of 1:50,000. Hypopituitarism in these syndromes is detected in from 13 to 56% of cases and depends on the size and location of the deleted segment.We have described a series of clinical cases of patients with congenital hypopituitarism due to deletions in chromosome 18. All children had a characteristic dysmorphic features and delayed mental and speech development. Within first months of life, patients developed muscular hypotension, dysphagia, and respiratory disorders. The patients had various congenital malformations in combination with hypopituitarism (isolated growth hormone deficiency and multiple pituitaryhormone deficiencies). In the neonatal period, there were the presence of hypoglycemia in combination with cholestasis.Hormone replacement therapy led to rapid relief of symptoms.Сhromosomal microarray analysis in 2 patients allowed us to identify exact location of deleted area and deleted genes and optimize further management for them.

Clinical and Cytogenomic Characterization of De Novo 11p14.3-p15.5 Duplication Associated with 18q23 Deletion in an Egyptian Female Infant

Paternal microduplication of 11p14.3-p15.5 causes the clinical manifestations of Beckwith-Wiedemann syndrome (BWS), while microdeletion of 18q23-ter is clinically characterized by short stature, congenital malformations, and developmental delay. We describe a 15-month-old girl presenting with protruding tongue, dysmorphic facial features, moderate developmental delay, umbilical hernia, hypotonia, mild-to-moderate pulmonary hypertension, small patent ductus arteriosus, and mild ventricular septal hypertrophy. Brain magnetic resonance imaging showed mild atrophic changes. Chromosomal analysis revealed 46, XX, add(18)(q23). Fluorescence in situ hybridization using subtelomere 18q and whole chromosome painting 18 showed subtelomere deletion in 18q, and the add segment was not derived from chromosome 18. Microarray-based comparative genomic hybridization detected a 22 Mb duplication of chromosome 11p15.5p14.3 and a 3.7 Mb deletion of chromosome 18q23. The phenotype of the chromosomal rearrangements is probably resulted from a combination of dosage-sensitive genes. Our patient had clinical manifestations of both 18q deletion and BWS.

Clinical Characteristics and Long-Term Recombinant Human Growth Hormone Treatment of 18q- Syndrome: A Case Report and Literature Review

BACKGROUND

18q- syndrome is a rare chromosomal disease caused by the deletion of the long arm of chromosome 18. Some cases with 18q- syndrome can be combined with growth hormone deficiency (GHD), but data on the efficacy of recombinant human growth hormone (rhGH) treatment in 18q- syndrome are limited.

METHODS

Here, we report one case of 18q- syndrome successfully treated with long-term rhGH supplement. Previously reported cases in the literature are also reviewed to investigate the karyotype-phenotype relationship and their therapeutic response to rhGH.

RESULTS

A 7.9-year-old girl was referred for evaluation for short stature. Physical exam revealed proportionally short stature with a height of 111.10 cm (-3.02 SD score (SDS)), low-set ears, a high-arched palate, a small jaw, webbed neck, widely spaced nipples, long and tapering fingers, and cubitus valgus. Thyroid function test indicated subclinical hypothyroidism. The peak value of growth hormone was 10.26 ng/ml in the levodopa provocation test. Insulin-like growth factor 1 (IGF-1) was 126 ng/ml (57-316 ng/ml). Other laboratory investigations, including complete blood cell count, liver and kidney function, gonadal function, serum adrenocorticotropin levels, and serum cortisol levels, were all within normal ranges. Karyotype analysis showed 46, XX, del (18) (q21). L-Thyroxine replacement and rhGH treatment were initiated and maintained in the following 7 years. At the age of 14.8, her height has reached 159.5 cm with a height SDS increase of 2.82 SDS (from -3.02 SDS to -0.20 SDS). No significant side effects were found during the treatment. The literature review indicated the average rhGH treatment duration of 16 patients was 5.9 ± 3.3 years, and the average height SDS significantly increased from -3.12 ± 0.94 SDS to -1.38 ± 1.29 SDS after the rhGH treatment (p < 0.0001).

CONCLUSION

The main clinical manifestations of 18q- syndrome include characteristic appearance, intellectual disability, and abnormal genital development. The literature review suggested a significant height benefit for short stature with 18q- syndrome from long-term rhGH treatment.

Biallelic ZNF407 mutations in a neurodevelopmental disorder with ID, short stature and variable microcephaly, hypotonia, ocular anomalies and facial dysmorphism

We describe five members of a consanguineous Pakistani family (Family I) plus two affected children from families of different ethnic origins presenting with neurodevelopmental disorders with overlapping features. All affected individuals from families have intellectual disability (ID), ranging from mild to profound, and reduced motor and cognitive skills plus variable features including short stature, microcephaly, developmental delay, hypotonia, dysarthria, deafness, visual problems, enuresis, encopresis, behavioural anomalies, delayed pubertal onset and facial dysmorphism. We first mapped the disease locus in the large family (Family I), and by exome sequencing identified homozygous ZNF407 c.2814_2816dup (p.Val939dup) in four affected members where DNA samples were available. By exome sequencing we detected homozygous c.2405G>T (p.Gly802Val) in the affected member of Family II and compound heterozygous variants c.2884C>G (p.Arg962Gly) and c.3642G>C (p.Lys1214Asn) in the affected member of Family III. Homozygous c.5054C>G (p.Ser1685Trp) has been reported in two brothers with an ID syndrome. Affected individuals we present did not exhibit synophrys, midface hypoplasia, kyphosis, 5th finger camptodactyly, short 4th metatarsals or limited knee mobility observed in the reported family.

Central and peripheral dysmyelination in a 3-year-old girl with ring chromosome 18

Myelin basic protein (MBP) contributes to peripheral and central nervous system myelin. Developmental myelinopathies exist on a clinical spectrum, but MBP is not included on leukodystrophy or CMT gene panels. This ring chromosome 18 case presents serial MRI and EMG/NCS, shedding light on the early clinical course of the disorder.

Chromosome 18 gene dosage map 2.0

In 2009, we described the first generation of the chromosome 18 gene dosage maps. This tool included the annotation of each gene as well as each phenotype associated region. The goal of these annotated genetic maps is to provide clinicians with a tool to appreciate the potential clinical impact of a chromosome 18 deletion or duplication. These maps are continually updated with the most recent and relevant data regarding chromosome 18. Over the course of the past decade, there have also been advances in our understanding of the molecular mechanisms underpinning genetic disease. Therefore, we have updated the maps to more accurately reflect this knowledge. Our Gene Dosage Map 2.0 has expanded from the gene and phenotype maps to also include a pair of maps specific to hemizygosity and suprazygosity. Moreover, we have revamped our classification from mechanistic definitions (e.g., haplosufficient, haploinsufficient) to clinically oriented classifications (e.g., risk factor, conditional, low penetrance, causal). This creates a map with gradient of classifications that more accurately represents the spectrum between the two poles of pathogenic and benign. While the data included in this manuscript are specific to chromosome 18, they may serve as a clinically relevant model that can be applied to the rest of the genome.

Atrial septal defect can be easily missed in chromosome 18q deletion syndrome

The frequency of 18q− is estimated to be approximately 1/40 000 live births and is more commonly associated with certain clinical features including short stature, intellectual disability and malformations of many major organ systems. Congenital cardiac abnormalities are present in 24–36% of cases and screening can prove difficult. A 28-year-old Caucasian female with a history of long arm chromosome 18q deletion was evaluated for persistent dyspnea and decreased activity level. Multiple hospitalizations failed to identify the etiology of her symptoms. Initial transthoracic echocardiogram failed to show any underlying cardiac etiology of her symptoms. Multiple recurrent hospitalizations with the same chief complaint. A transesophageal echo (TEE) showed large secundum atrial septal defect (ASD). Successful surgical closure of her large secundum ASD provided significant symptoms relief. The threshold of obtaining TEE should be low in patients with 18q− which permits early recognition and treatment of underlying structural heart disease.

Importance and usage of chromosomal microarray analysis in diagnosing intellectual disability, global developmental delay, and autism; and discovering new loci for these disorders

Background

Chromosomal microarray analysis is a first-stage test that is used for the diagnosis of intellectual disability and global developmental delay. Chromosomal microarray analysis can detect well-known microdeletion syndromes. It also contributes to the identification of genes that are responsible for the phenotypes in the new copy number variations.

Results

Chromosomal microarray analysis was conducted on 124 patients with intellectual disability and global developmental delay. Multiplex ligation-dependent probe amplification was used for the confirmation of chromosome 22q11.2 deletion/duplication. 26 pathogenic and likely pathogenic copy number variations were detected in 23 patients (18.55%) in a group of 124 Turkish patients with intellectual disability and global developmental delay. Chromosomal microarray analysis revealed pathogenic de novo Copy number variations, such as a novel 2.9-Mb de novo deletion at 18q22 region with intellectual disability and autism spectrum disorder, and a 22q11.2 region homozygote duplication with new clinical features.

Conclusion

Our data expand the spectrum of 22q11.2 region mutations, reveal new loci responsible from autism spectrum disorder and provide new insights into the genotype–phenotype correlations of intellectual disability and global developmental delay.

Expansion of the clinical phenotype of the distal 10q26.3 deletion syndrome to include ataxia and hyperemia of the hands and feet

Distal deletion of the long arm of chromosome 10 is associated with a dysmorphic craniofacial appearance, microcephaly, behavioral issues, developmental delay, intellectual disability, and ocular, urogenital, and limb abnormalities. Herein, we present clinical, molecular, and cytogenetic investigations of four patients, including two siblings, with nearly identical terminal deletions of 10q26.3, all of whom have an atypical presentation of this syndrome. Their prominent features include ataxia, mild-to-moderate intellectual disability, and hyperemia of the hands and feet, and they do not display many of the other features commonly associated with deletions of this region. These results point to a novel gene locus associated with ataxia and highlight the variability of the clinical presentation of patients with deletions of this region.

Interstitial de novo 18q22.3q23 deletion: clinical, neuroradiological and molecular characterization of a new case and review of the literature

Background

Deletions of the long arm of chromosome 18 cause a common autosomal syndrome clinically characterized by a protean clinical phenotype.

Case presentation

We report on a 16-month-old male infant affected by fever attacks apparently unrelated with any infectious or inflammatory symptoms, growth retardation, bilateral vertical talus, congenital aural atresia, dysmorphisms, mild psychomotor delay, and peculiar neuroradiological features. Array-CGH analysis revealed one of the smallest 18q22.3q23 interstitial deletions involving five genes: TSHZ1, ZNF516, ZNF236, MBP, and GALR1.

Conclusions

Herein we focus on previously unreported heralding symptoms and neuroradiological abnormalities which enlarge the spectrum of 18q deletion syndrome demonstrating that a small deletion can determine a complex phenotype.

Making chromosome abnormalities treatable conditions

Individuals affected by the classic chromosome deletion syndromes which were first identified at the beginning of the genetic age, are now positioned to benefit from genomic advances. This issue highlights five of these conditions (4p-, 5p-, 11q-, 18p-, and 18q-). It focuses on the increased in understanding of the molecular underpinnings and envisions how these can be transformed into effective treatments. While it is scientifically exciting to see the phenotypic manifestations of hemizygosity being increasingly understood at the molecular and cellular level, it is even more amazing to consider that we are now on the road to making chromosome abnormalities treatable conditions.

Diagnostic yield of array CGH in patients with autism spectrum disorder in Hong Kong

Background

Chromosomal microarray offers superior sensitivity for identification of submicroscopic copy number variants (CNV) and it is advocated to be the first tier genetic testing for patients with autism spectrum disorder (ASD). In this regard, diagnostic yield of array comparative genomic hybridization (CGH) for ASD patients is determined in a cohort of Chinese patients in Hong Kong.

Methods

A combined adult and paediatric cohort of 68 Chinese ASD patients (41 patients in adult group and 27 patients in paediatric group). The genomic DNA extracted from blood samples were analysed by array CGH using NimbleGen CGX-135K oligonucleotide array.

Results

We identified 15 CNV and eight of them were clinically significant. The overall diagnostic yield was 11.8 %. Five clinically significant CNV were detected in the adult group and three were in the paediatric group, providing diagnostic yields of 12.2 and 11.1 % respectively. The most frequently detected CNV was 16p13.11 duplications which were present in 4 patients (5.9 % of the cohort).

Conclusions

In this study, a satisfactory diagnostic yield of array CGH was demonstrated in a Chinese ASD patient cohort which supported the clinical usefulness of array CGH as the first line testing of ASD in Hong Kong.

Electronic supplementary material

The online version of this article (doi:10.1186/s40169-016-0098-1) contains supplementary material, which is available to authorized users.

MECHANISMS IN ENDOCRINOLOGY: Novel genetic causes of short stature

The fast technological development, particularly single nucleotide polymorphism array, array-comparative genomic hybridization, and whole exome sequencing, has led to the discovery of many novel genetic causes of growth failure. In this review we discuss a selection of these, according to a diagnostic classification centred on the epiphyseal growth plate. We successively discuss disorders in hormone signalling, paracrine factors, matrix molecules, intracellular pathways, and fundamental cellular processes, followed by chromosomal aberrations including copy number variants (CNVs) and imprinting disorders associated with short stature. Many novel causes of GH deficiency (GHD) as part of combined pituitary hormone deficiency have been uncovered. The most frequent genetic causes of isolated GHD are GH1 and GHRHR defects, but several novel causes have recently been found, such as GHSR, RNPC3, and IFT172 mutations. Besides well-defined causes of GH insensitivity (GHR, STAT5B, IGFALS, IGF1 defects), disorders of NFκB signalling, STAT3 and IGF2 have recently been discovered. Heterozygous IGF1R defects are a relatively frequent cause of prenatal and postnatal growth retardation. TRHA mutations cause a syndromic form of short stature with elevated T3/T4 ratio. Disorders of signalling of various paracrine factors (FGFs, BMPs, WNTs, PTHrP/IHH, and CNP/NPR2) or genetic defects affecting cartilage extracellular matrix usually cause disproportionate short stature. Heterozygous NPR2 or SHOX defects may be found in ∼3% of short children, and also rasopathies (e.g., Noonan syndrome) can be found in children without clear syndromic appearance. Numerous other syndromes associated with short stature are caused by genetic defects in fundamental cellular processes, chromosomal abnormalities, CNVs, and imprinting disorders.

Complex Rearrangement Involving Three Chromosomes, Four Breakpoints and a 2.7-Mb Deletion in the 18q Segment Observed in a Girl with Mild Learning Difficulties

Complex chromosomal rearrangements (CCRs) are balanced or unbalanced structural rearrangements involving 3 or more cytogenetic break events on 2 or more different chromosomes. Here, we report a 7-year-old girl referred to our unit because of mild dysmorphic facial features, mild learning difficulties together with very mild mental retardation. Standard cytogenetic banding analysis revealed a de novo CCR involving chromosomes 1, 2 and 18. Further molecular investigation with aCGH revealed a cryptic interstitial deletion of 2.7 Mb in 18q22.1, which does not elicit a significant clinical phenotype. FISH was performed to confirm both molecular and cytogenetic results.

Consequences of chromsome18q deletions

Providing clinically relevant prognoses and treatment information for people with a chromsome18q deletion is particularly challenging because every unrelated person has a unique region of hemizygosity. The hemizygous region can involve almost any region of 18q including between 1 and 101 genes (30 Mb of DNA). Most individuals have terminal deletions, but in our cohort of over 350 individuals 23% have interstitial deletions. Because of this heterogeneity, we take a gene by gene approach to understanding the clinical consequences. There are 196 genes on 18q. We classified 133 of them as dosage insensitive, 15 (8%) as dosage sensitive leading to haploinsufficiency while another 10 (5%) have effects that are conditionally haploinsufficient and are dependent on another factor, genetic or environmental in order to cause an abnormal phenotype. Thirty-seven genes (19%) have insufficient information to classify their dosage effect. Phenotypes attributed to single genes include: congenital heart disease, minor bone morphology changes, central nervous system dysmyelination, expressive speech delay, vesicouretreral reflux, polyposis, Pitt-Hopkins syndrome, intellectual disability, executive function impairment, male infertility, aural atresia, and high frequency sensorineural hearing loss. Additionally, identified critical regions for other phenotypes include: adolescent idiopathic scoliosis and pectus excavatum, Virchow-Robin perivascular spaces, small corpus callosum, strabismus, atopic disorders, mood disorder, IgA deficiency, nystagmus, congenital heart disease, kidney malformation, vertical talus, CNS dysmyelination growth hormone deficiency and cleft palate. Together these findings make it increasingly feasible to compile an individualized syndrome description based on each person's individuated genotype. Future work will focus on understanding molecular mechanisms leading to treatment.

Terminal 18q deletions are stabilized by neotelomeres

BACKGROUND

All human chromosomes are capped by tandem repeat (TTAGGG)n sequences that protect them against end-to-end fusion and are essential to chromosomal replication and integrity. Therefore, after a chromosomal breakage, the deleted chromosomes must be stabilized by retaining the telomere or acquiring a new cap, by telomere healing or telomere capture. There are few reports with molecular approaches on the mechanisms involved in stabilization of 18q terminal deletions.

RESULTS

In this study we analyzed nine patients with 18q terminal deletion identified by G-banding and genomic array. FISH using PNA probe revealed telomeric signals in all deleted chromosomes tested. We fine-mapped breakpoints with customized arrays and sequenced six terminal deletion junctions. In all six deleted chromosomes sequenced, telomeric sequences were found directly attached to the breakpoints. Little or no microhomology was found at the breakpoints and none of the breaks sequenced were located in low copy repeat (LCR) regions, though repetitive elements were found around the breakpoints in five patients. One patient presented a more complex rearrangement with two deleted segments and an addition of 17 base pairs (bp).

CONCLUSIONS

We found that all six deleted chromosomes sequenced were probably stabilized by the healing mechanism leading to a neotelomere formation.

Ring 18 molecular assessment and clinical consequences

Ring chromosome 18 is a rare condition which has predominantly been described by case reports and small case series. We assessed a cohort of 30 individuals with ring 18 using both microarray comparative genomic hybridization (aCGH) and fluorescence in situ hybridization (FISH). We determined that each participant had a unique combination of hemizygosity for the p and q arms. Four ring chromosomes had no detectable deletion of one of the chromosome arms using aCGH. However, two of these ring chromosomes had telomeric sequences detected using FISH. These data confirm the importance of molecular and cytogenetic analysis to determine both chromosome content and morphology. We failed to find dramatic changes in mosaicism percentage between cytogenetic measurements made at the time of diagnosis and those made years later at the time of this study, demonstrating that dynamic ring mosaicism is unlikely to be a major cause of phenotypic variability in the ring 18 population. Lastly, we present data on the clinical features present in our cohort, though the extreme genotypic variability makes it impossible to draw direct genotype-phenotype correlations. Future work will focus on determining the role of specific hemizygous genes in order to create individualized projections of the effect of each person's specific ring 18 compliment.

Mutations in zinc finger 407 [ZNF407] cause a unique autosomal recessive cognitive impairment syndrome

Background

A consanguineous Arab family is affected by an apparently novel autosomal recessive disorder characterized by cognitive impairment, failure-to-thrive, hypotonia and dysmorphic features including bilateral ptosis and epicanthic folds, synophrys, midface hypoplasia, downturned mouth corners, thin upper vermillion border and prominent ears, bilateral 5th finger camptodactyly, bilateral short 4th metatarsal bones, and limited knee mobility bilaterally.

Methods

The family was studied by homozygosity mapping, candidate gene mutation screening and whole Exome Next Generation Sequencing of a single affected member to identify the offending gene and mutation. The mutated gene product was studied by structural bioinformatics methods.

Results

A damaging c.C5054G mutation affecting an evolutionary highly conserved amino acid p.S1685W was identified in the ZNF407 gene at 18q23. The Serine to Tryptophane mutation affects two of the three ZNF407 isoforms and is located in the last third of the protein, in a linker peptide adjoining two zinc-finger domains. Structural analyses of this mutation shows disruption of an H-bond that locks the relative spatial position of the two fingers, leading to a higher flexibility of the linker and thus to a decreased probability of binding to the target DNA sequence essentially eliminating the functionality of downstream domains and interfering with the expression of various genes under ZNF407 control during fetal brain development.

Conclusions

ZNF407 is a transcription factor with an essential role in brain development. When specific and limited in number homozygosity intervals exist that harbor the offending gene in consanguineous families, Whole Exome Sequencing of a single affected individual is an efficient approach to gene mapping and mutation identification.