Macrocephaly / Overgrowth Syndrome Panel

ICD codes
Commonly used ICD-10 code(s) when ordering the Macrocephaly / Overgrowth Syndrome Panel

ICD-10	Disease
Q75.3	Macrocephaly
Q87.3	Congenital malformation syndromes involving early overgrowth

Sample requirements:

• EDTA blood, min. 1 ml
• Purified DNA, min. 3μg
• Saliva (Oragene DNA OG-500 kit)

Label the sample tube with your patient’s name, date of birth and the date of sample collection. Note that we do not accept DNA samples isolated from formalin-fixed paraffin-embedded (FFPE) tissue.

Macrocephaly is a condition in which the head is abnormally large (circumference > +2.5 SD of normal for weight and gender). Many people with an unusually large head and large skull are healthy, however macrocephaly is also a feature of several syndromes. Macrocephaly may be due to megalencephaly (true enlargement of the brain) or due to other conditions such as hydrocephalus or cranial thickening and is a common reason for referral to the genetics clinic. Macrocephaly is associated with many genetic disorders and this panel can be used for their differential diagnostics. Syndromic and nonsyndromic forms of pathologic macrocephaly may be caused by congenital anatomic abnormalities or genetic conditions, but the disease may also be nongenetic and caused by environmental events. The genetic macrocephaly conditions cover a broad spectrum of gene disorders and their related proteins have diverse biological functions. As of yet it is not clear what precise biological pathways lead to generalized brain overgrowth, but several genes have been identified. Genetic types of macrocephaly include: 1) familial macrocephaly (benign asymptomatic), 2) autism disorder (multifactorial, non-syndromic type), 3) syndrome associations (multiple types) 3A) with cutaneous findings (PTEN hamartoma syndromes, neurofibromatosis, type 1 hemimegalencephaly), 3B) with overgrowth (Sotos, Weaver, Macrocephaly-Cutis Marmorata Telangiectasia Congenita, Simpson-Golabi-Behmel, Beckwith-Wiedemann Syndrome), 3C) neuro-cardio-facial-cutaneous syndromes (Noonan, Costello, Cardiofaciocutaneous, LEOPARD) with intellectual disability (Fragile X syndromes), 4) metabolic types with leukodystrophy (Alexander, Canavan, megalencephalic leukodystrophy, organic acidurias, glutaric aciduria, type 1, D-2-hydroxyglutaric aciduria) and 5) hydrocephalus (aqueductal stenosis types and multifactorial, non-obstructive types).

Genes in the Macrocephaly / Overgrowth Syndrome Panel and their clinical significance

Non-coding variants covered by the panel

The strengths of this test include:

• CAP and ISO-15189 accreditations covering all operations at GHC Genetics including all Whole Exome Sequencing, NGS panels and confirmatory testing
• CLIA-certified personnel performing clinical testing in a CLIA-certified laboratory
• Powerful sequencing technologies, advanced target enrichment methods and precision bioinformatics pipelines ensure superior analytical performance
• Careful construction of clinically effective and scientifically justified gene panels
• Our Nucleus online portal providing transparent and easy access to quality and performance data at the patient level
• Our publically available analytic validation demonstrating complete details of test performance
• ~1,500 non-coding disease causing variants in GHC WES assay (please see below ‘Non-coding disease causing variants covered by this panel’)
• Our rigorous variant classification based on modified ACMG variant classification scheme
• Our systematic clinical interpretation workflow using proprietary software enabling accurate and traceable processing of NGS data
• Our comprehensive clinical statements

Test limitations The following exons are not included in the panel as they are not sufficiently covered with high quality sequence reads: *PPA2* (11, 12). Genes with partial, or whole gene, segmental duplications in the human genome are marked with an asterisk if they overlap with the UCSC pseudogene regions. The technology may have limited sensitivity to detect variants in genes marked with these symbols (please see the Panel content table above).

This test does not detect the following:

• Complex inversions
• Gene conversions
• Balanced translocations
• Mitochondrial DNA variants
• Repeat expansion disorders unless specifically mentioned
• Non-coding variants deeper than ±20 base pairs from exon-intron boundary unless otherwise indicated (please see above Panel Content / non-coding variants covered by the panel).

This test may not reliably detect the following:

• Low level mosaicism
• Stretches of mononucleotide repeats
• Indels larger than 50bp
• Single exon deletions or duplications
• Variants within pseudogene regions/duplicated segments

The sensitivity of this test may be reduced if DNA is extracted by a laboratory other than GHC Genetics.

For additional information, please refer to the Test performance section and see our Analytic Validation.

The GHC Genetics panel covers classical genes associated with Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia (CPVT), cardiac arrest underlying cardiac condition, cardiac arrest cause unspecified, syncope and collapse, abnormal ECG, Long QT syndrome, arrhythmogenic right ventricular cardiomyopathy (ARVC) and Short QT syndrome. The genes on the panel have been carefully selected based on scientific literature, mutation databases and our experience.

Our panels are sliced from our high-quality whole exome sequencing data. Please see our sequencing and detection performance table for different types of alterations at the whole exome level (Table).

Assays have been validated for different starting materials including EDTA-blood, isolated DNA (no FFPE), saliva and dry blood spots (filter card) and all provide high-quality results. The diagnostic yield varies substantially depending on the assay used, referring healthcare professional, hospital and country. GHC Genetics’ Plus Analysis (Seq+Del/Dup) maximizes the chance to find a molecular genetic diagnosis for your patient although Sequence Analysis or Del/Dup Analysis may be a cost-effective first line test if your patient’s phenotype is suggestive of a specific mutation type.

Performance of GHC Genetics Whole Exome Sequencing (WES) assay.
All individual panels are sliced from WES data.

Our mission is to improve the quality of the sequencing process and each modification is followed by our standardized validation process. Detection of Del/Dup of several genes is by MLPA analysis (MS Holland). All genes are performed by CNV analysis through the genome depending on exon size, sequencing coverage and sequence content. We have validated the assays for different starting materials including isolated DNA from EDTA blood that provide high-quality results.

The sequencing data generated in our laboratory is analysed by our bioinformatic pipeline, integrating state-of-the art algorithms and industry-standard software solutions. We use also JSI medical systems software for sequencing data analysis. JSI medical systems is a certified system offering sophisticated bioinformatic software solutions covering a wide field of sequencing techniques.

Incorporation of rigorous quality control steps throughout the workflow of the pipeline ensures the consistency, validity and accuracy of results.

Every pathogenic or probably pathogenic variant is confirmed by the Sanger sequencing method. Sanger sequencing is also used occasionally with other variants reported in the statement. In the case of variant of uncertain significance (VUS) we do not recommend risk stratification based on the genetic finding. The analysis of detected variants was performed on the basis of the reference database of polymorphisms and international mutation databases: UMD, LOVD and ClinVar.

The consequence of variants in coding and splice regions are estimated using Alamut software. The Alamut database contains more than 28000 coding genes, non-protein coding genes and pseudogenes. This database (shared with the high throughput annotation engine for NGS data, Alamut Batch) is frequently updated. Information comes from different public databases such as NCBI, EBI, and UCSC, as well as other sources including gnomAD, ESP, Cosmic, ClinVar, or HGMD and CentoMD (for those a separate subscription from Qiagen/Biobase and Centogene respectively is required). Alamut Visual finds information about nucleotide conservation data through many vertebrates’ species, with the phastCons and phyloP scores, amino acid conservation data through orthologue alignments and information on protein domains.

Moreover, we integrate several missense variant pathogenicity prediction tools and algorithms such as SIFT, PolyPhen, AlignGVGD or MutationTaster. It also offers a window dedicated to the in silico study of variants’ effect on RNA splicing, allowing the assessment of their potential impact on splice junctions and visualization of cryptic or de novo splice sites. Impact on splicing regulation is also assessed.

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Clinical interpretation

At GHC Genetics our geneticists and clinicians, who together evaluate the results from the sequence analysis pipeline in the context of phenotype information provided in the requisition form, prepare the clinical report. We recommend an interpretation of the findings of this molecular genetic analysis, including subsequent oncological consultation for the patient in the context of genetic counselling for the patient.

We strive to continuously monitor current genetic literature identifying new relevant information and findings and adapting them to our diagnostics. This enables relevant novel discoveries to be rapidly translated and adopted into our ongoing diagnostics development without delay. The undertaking of such comprehensive due diligence ensures that our diagnostic panels and clinical statements are the most up-to-date on the market.

Variant classification is the corner stone of clinical interpretation and resulting patient management decisions. Minor modifications were made to increase reproducibility of the variant classification and improve the clinical validity of the report. Our experience with tens of thousands of clinical cases analysed at our laboratories enables us to further develop the industry standard.

The final step in the analysis of sequence variants is confirmation of variants classified as pathogenic or likely pathogenic using bi-directional Sanger sequencing. Variant(s) fulfilling all of the following criteria are not Sanger confirmed: 1) the variant quality score is above the internal threshold for a true positive call, 2) an unambiguous IGV in-line with the variant call and 3) previous Sanger confirmation of the same variant three times at GHC Genetics. Reported variants of uncertain significance (VUS) are confirmed with bi-directional Sanger sequencing only if the quality score is below our internally defined quality score for true positive call. Reported copy number variations with a size >10 exons are confirmed by orthogonal methods such as qPCR if the specific CNV has been seen less than three times at GHC Genetics.

Our clinical statement includes tables for sequencing and copy number variants that include basic variant information (genomic coordinates, HGVS nomenclature, zygosity, allele frequencies, in silico predictions, OMIM phenotypes and classification of the variant). In addition, the statement includes detailed descriptions of the variant, gene and phenotype(s) including the role of the specific gene in human disease, the mutation profile, information about the gene’s variation in population cohorts and detailed information about related phenotypes. We also provide links to the references used, and mutation databases to help our customers further evaluate the reported findings if desired. The conclusion summarizes all of the existing information and provides our rationale for the classification of the variant.

Identification of pathogenic or likely pathogenic variants in dominant disorders or their combinations in different alleles in recessive disorders are considered molecular confirmation of the clinical diagnosis. In these cases, family member testing can be used for risk stratification within the family. In the case of variants of uncertain significance (VUS), we do not recommend family member risk stratification based on the VUS result. Furthermore, in the case of VUS, we do not recommend the use of genetic information in patient management or genetic counselling.

Our Clinical interpretation team analyses millions of variants from thousands of individuals with rare diseases. Thus, our database, and our understanding of variants and related phenotypes, is growing by leaps and bounds. Our laboratories are therefore well positioned to re-classify previously reported variants as new information becomes available. If a variant previously reported by GHC Genetics is re-classified, our laboratories will issue a follow-up statement to the original ordering health care provider at no additional cost.