Background:
Craniosynostosis is the premature fusion (closure) of one or more sutures of the skull. It is a developmental anomaly with age of onset in utero and infancy. The early sutural closure often leads to abnormal head shape and facial dysmorphia. Craniosynostosis can occur in isolation (nonsyndromic) or as part of a larger syndrome with additional facial, skeletal, and organ anomalies (syndromic). There are approximately 200 syndromes associated with craniosynostosis. Clinical phenotype indicating a syndromic cause of craniosynostosis include limb defects, ear and eye abnormalities, maxillary and mandibular hypoplasia, and or cardiovascular malformations. It is a genetically heterogeneous disorder with mutations identified in multiple genes. Inheritance is autosomal dominant and recessive depending on syndrome. Chromosomal alterations are a causative mechanism of the syndromic forms of craniosynostosis in more than 10% of the cases.
Reasons for Referral:
- Patient displays craniofacial phenotype consistent with craniosynostosis
- Radiography and CT reveal premature fusion of one or more cranial sutures. Patient may one or more of the following: Chiari malformations, facial dysmorphia and or asymmetry, ptosis, blepharophimosis, hypertelorism, proptosis, down slanting palpebral fissures, choanal atresia or stenosis, flat nasal bridge, midfacial hypoplasia, maxillary hypoplasia, micrognathia, mandibular prognathism, oral abnormalities, radiohumeral synostosis, radioulnar synostosis, syndactyly of the fingers and toes, brachydactyly, broad halluces with medial deviation
- Carrier testing
- Positive family history
Methodology:
Next generation sequencing (NGS) will analyze the exons or coding regions of the genes using Illumina NextSeq 500/550 technology and preparing samples using hybridization probes to enrich exonic regions. This assay does not assess regions of insufficient coverage, introns and promoter regions; pseudogenes; where the reference genome is inaccurate or contains gaps and insertions; and regions of high GC or polynucleotide repeats, but may contain variants that impact gene function.
Exon-level deletion/duplication analysis is performed by running the NGS data through the Genome Analysis Toolkit (GATK) Germline Copy Number Variation best practices pipeline from GATK, version 4.1.4.1. A Bayesian model was validated clinically in our lab. The model can detect copy changes at a resolution of three (3) or more probe targets (exons) for deletions and duplications in genes that do not have pseudogenes, and is not designed to detect low-level mosaicism or balanced alterations.
The 35 Craniosynostosis-associated genes are listed below:
ALPL, ALX4, ASXL1, CDC45, CYP26B1, EFNB1, ERF, FBN1, FGFR1, FGFR2, FGFR3, FREM1, GLI3, IFT122, IFT43, IL11RA, MASP1, MEGF8, MSX2, P4HB,PHEX, POR, RAB23, RECQL4, SEC24D, SKI, SLC25A24, TCF12, TGFBR1, TGFBR2, TMCO1, TWIST1, WDR19, WDR35, ZIC1
Specimen Requirements:
Blood: EDTA or ACD (Solution A or B):
- Adult: 5 mL
- Child: 5 mL
- Infant: 2-3 mL
Saliva: 2 ORAgene™ Saliva Collection Kit(s) (OGR-500). Please contact KDL Client Services for a Saliva Collection Kit for patients that cannot provide a blood sample.
Assisted Saliva: 4 ORAgene™ Saliva Collection Kit(s) (OGR-575) used per manufacturer instructions. Please contact KDL Client Services for a Saliva Collection Kit for patients that cannot provide a blood sample.
DNA: 10 µg at a minimum of 60-100ng/µL (DNA must be extracted in a CLIA-certified laboratory or a laboratory meeting equivalent requirements as determined by the CAP and/or CMS)
For routine testing of blood and saliva (or DNA extracted from them), KDL does NOT accept samples from patients within two (2) weeks of a packed cell/platelet transfusion or within four (4) weeks of a whole blood transfusion. For extraordinary circumstances, where testing must be performed outside of the above windows, please contact our lab.
A REQUISITION FORM MUST ACCOMPANY ALL SAMPLES. Please include detailed clinical information, including ethnicity, clinical history, and family history.
Test Performed (Days):
Weekly
Turn Around Time:
8 weeks
Shipment Sensitivity Requirements:
- Package and ship specimen to remain cold, but not frozen.
- Ship via overnight express, using the FedEx priority overnight label provided.
- Contact Client Services for shipping kits and instructions at (855) 535-1522.
References:
- Wilke AO, Bochukova EG, Hansen RM, et al. Clinical dividends from the molecular genetic diagnosis of craniosynostosis. Am J Med Genet A. 2007; 143A(16):1941-98
- Panigrahi I. Craniosynostosis genetics: The mystery unfolds. Indian J Hum Genet. 2011; 17(2):48-53
- Agochukwu NB, Solomon BD, Muenke M. Impact of genetics on the diagnosis and clinical management of syndromic craniosynostosis. Childs Nerv Syst. 2012;28(9):1447-63
Additional Info: