Condition Description

Bloom syndrome should be considered in the following individuals:

  • An individual with unexplained, severe intrauterine growth retardation that persists into infancy and childhood
  • An unusually small, well-proportioned individual with a sun-sensitive erythematous skin lesion in a \"butterfly distribution\" on the face
  • An unusually small individual who develops cancer

Bloom syndrome is an autosomal recessive disorder characterized by severe prenatal and postnatal growth retardation and a sun-sensitive erythematous skin lesion that occurs most commonly on the face. Recurrent infections (otitis media and pneumonia), chronic pulmonary disease, and diabetes mellitus are common. Many affected individuals have learning disabilities. Males are infertile; females enter menopause prematurely. The most common cause of death is cancer (epithelial, hematopoietic, lymphoid, connective tissue, germ cell, nervous system, and kidney), which occurs at younger-than-usual ages.

The diagnosis of Bloom syndrome can be confirmed or ruled out by chromosome analysis of any cell type that can be cultured. The most commonly used cells are blood lymphocytes, but cultures of skin fibroblasts and amniocytes also can be studied. The cytogenetic features of Bloom syndrome cells in mitosis are increased numbers of chromatid gaps, breaks, and rearrangements and increased numbers of quadriradial configurations. A greatly increased frequency (e.g., greater than 50 per metaphase) of sister chromatid exchanges is demonstrable in Bloom syndrome cells exposed to bromodeoxyuridine (BrdU). BLM (15q26.1) is the only gene known to be mutated in Bloom syndrome.

Fewer than 300 cases of Bloom syndrome have been reported. Although very rare in all populations, Bloom syndrome is less rare in Ashkenazi Jews. Approximately 25% of persons in the Bloom Syndrome Registry have Ashkenazi Jewish ancestry. The carrier frequency in the Ashkenazi Jewish population is estimated to be approximately 1%.

For patients with suspected Bloom syndrome, sequence analysis is recommended as the first step in mutation identification. For patients in whom mutations are not identified by full gene sequencing, deletion/duplication analysis is appropriate.

References:

  • GeneTests: http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=gene&part=bloom

Genes (1)

Indications

This test is indicated for:

  • Confirmation of a clinical diagnosis of Bloom syndrome

Methodology

Next Generation Sequencing: In-solution hybridization of all coding exons is performed on the patient's genomic DNA. Although some deep intronic regions may also be analyzed, this assay is not meant to interrogate most promoter regions, deep intronic regions, or other regulatory elements, and does not detect single or multi-exon deletions or duplications. Direct sequencing of the captured regions is performed using next generation sequencing. The patient's gene sequences are then compared to a standard reference sequence. Potentially causative variants and areas of low coverage are Sanger-sequenced. Sequence variations are classified as pathogenic, likely pathogenic, benign, likely benign, or variants of unknown significance. Variants of unknown significance may require further studies of the patient and/or family members.

Detection

Clinical Sensitivity: Unknown. 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

When sample fails to meet the acceptable criteria, please call 470.378.2200 and ask to speak with a laboratory genetic counselor (eglgc@egl-eurofins.com).
Submit only 1 of the following specimen types
Saliva
SLV

Requirements
Oragene™ Saliva Collection Kit
Orangene™ Saliva Collection Kit used according to manufacturer instructions. Please contact EGL for a Saliva Collection Kit for patients that cannot provide a blood sample.
Collection and Shipping
Please do not refrigerate or freeze saliva sample. Please store and ship at room temperature.
DNA, Isolated
DNA

Requirements
Microtainer
8µg
Isolation using the Perkin Elmer™Chemagen™ Chemagen™ Automated Extraction method or Qiagen™ Puregene kit for DNA extraction is recommended.
Collection and Shipping
Refrigerate until time of shipment in 100 ng/µL in TE buffer. Ship sample at room temperature with overnight delivery.
Whole Blood (EDTA)
WBP

Requirements
EDTA (Purple Top)
Infants and Young Children (<2 years of age): 2-3 ml
Children > 2 years of age to 10 years old: 3-5 ml
Older Children & Adults: 5-10 ml
Autopsy: 2-3 ml unclotted cord or cardiac blood
Collection and Shipping
Ship sample at room temperature for receipt at EGL within 24 hours of collection. Do not refrigerate or freeze.

Special Instructions

Submit copies of diagnostic biochemical test results with the sample, if appropriate. Contact the laboratory if further information is needed.

Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed outside of EGL Genetics, please submit a copy of the sequencing report with the test requisition.

  • Deletion/duplication analysis of the BLM gene by CGH array is available for those individuals in whom sequence analysis is negative.
  • Custom diagnostic mutation analysis (KM) is available to family members if mutations are identified by targeted mutation testing or sequencing analysis.
  • Prenatal testing is available to adults who are confirmed carriers of mutations. Please contact the laboratory genetic counselor to discuss appropriate testing prior to collecting a prenatal specimen.

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