Test Code: 5235

Legius Syndrome: SPRED1 Gene Sequencing
Test Code: 5235
Turnaround time: 7 weeks

CONDITION DESCRIPTION

Legius syndrome, originally termed neurofibromatosis type 1 (NF1)-like syndrome, is caused by mutations in the SPRED1 gene (15q13.2). Individuals with Legius syndrome frequently fulfill NIH diagnostic criteria for NF1 based on pigmentary manifestations of café-au-lait spots and inguinal freckling, but do not have mutations in the NF1 gene. Other characteristics may include macrocephaly, learning disabilities, and Noonan-like dysmorphology. To date, no affected individuals have been found to have neurofibromas, central nervous system tumors, NF1-type osseous lesions, or Lisch nodules.

A study by Messiaen et al. found that among 1086 patients fulfilling NIH criteria for a clinical diagnosis of NF1, an NF1 mutation was found in 823 (76%), a SPRED1 mutation in 21 (1.9%), and no NF1/SPRED1 mutation in 243 (22%). Of 94 probands with familial café-au-lait spots with or without freckling and no other NF1 features, 69 (73%) has an NF1 mutation and 18 (19%) had a SPRED1 mutation; 7 (7%) did not have mutations in either gene. In another cohort in this study, 20 of 42 individuals (48%) with a SPRED1 mutation fulfilled NIH NF1 diagnostic criteria. The dermatologic phenotype in young children with a SPRED1 mutation could not be differentiated from NF1. The authors recommend that in cases of diagnostic uncertainty, the NF1 gene be analyzed first and, if negative, SPRED1 testing be considered in patients with café-au-lait spots with or without freckling and no other NF1 diagnostic features.

A study by Muram-Zborovski et al. found percentages similar to those seen in the Messiaen study. In 151 individuals who met NIH NF1 diagnostic criteria, 2 (1.3%) were found to have SPRED1 mutations. The percentage increased to 20% when selecting for individuals who lacked Lisch nodules, optic gliomas, neurofibromas, long bone dysplasia and sphenoid wing dysplasia, or a family history.

SPRED1 analysis is recommended in individuals with dermatologic manifestations of NF1 after NF1 analysis is negative. This testing is for mutations in the SPRED1 gene only, and does NOT include analysis of the NF1 gene.

References:
• Brems, H. et al. Germline loss-of-function mutations in SPRED1 cause a neurofibromatosis 1-like phenotype. Nat Genet. 2007, 39(9):1120-1126.
• Messiaen, L. et al. Clinical and mutational spectrum of neurofibromatosis type 1-like syndrome. JAMA 2009, 302(19):2111-2118. Muram- Zborovski, T. et al. SPRED1 mutations in a neurofibromatosis clinic. J Child Neurol. 2010, February 22, http://jcn.sagepub.com/cgi/rapidpdf/0883073809359540v1.
• OMIM #611431 Legius Syndrome

GENES

SPRED1

INDICATIONS
This test is indicated for:

  • Individuals with dermatologic manifestations of NF1 after NF1 gene analysis is negative

METHODOLOGY

PCR amplification of 7 exons contained in the SPRED1 gene is performed on the patient’s genomic DNA. Direct sequencing of amplification products is performed in both forward and reverse directions, using automated fluorescence dideoxy sequencing methods. The patient’s gene sequences are then compared to a normal reference sequence. Sequence variations are classified as mutations, benign variants unrelated to disease, or variations of unknown clinical significance. Variants of unknown clinical significance may require further studies of the patient and/or family members. This assay does not interrogate the promoter region, deep intronic regions, or other regulatory elements, and does not detect large deletions.

DETECTION

Clinical Sensitivity: Molecular genetic testing identifies mutations in SPRED2 in approximately 2% of individuals that meet NIH NF1 diagnostic criteria. That percentage rises to approximately 20% in individuals with only café-au-lait spots with or without freckling and no other NF1 features. Mutations in the promoter region, some mutations in the introns and other regulatory element mutations cannot be detected by this analysis. Large deletions will not be detected by this analysis. Results of molecular analysis should be interpreted in the context of the patient’s biochemical phenotype.

Analytical Sensitivity: ~99%

SPECIMEN REQUIREMENTS

Submit only 1 of the following specimen types
* Preferred specimen type: Whole Blood

Type: Whole Blood
Specimen Requirements:
In EDTA (purple top) or ACD (yellow top) tube: Infants (2 years): 3-5 ml
Older Children & Adults: 5-10 ml

Specimen Collection and Shipping: Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.

Type: Saliva
Specimen Requirements:
OrageneTM Saliva Collection kit (available through CEN4GEN) used according to manufacturer instructions.

Specimen Collection and Shipping: Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.

SPECIAL INSTRUCTIONS
Submit copies of diagnostic biochemical test results with the sample, if appropriate.

RELATED TESTS

• Custom diagnostic mutation analysis (test code: 6875) is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.