Bloom Syndrome

In: GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993.
[updated ].


Clinical characteristics: Bloom syndrome (BSyn) is characterized by severe pre- and postnatal growth deficiency, immune abnormalities, sensitivity to sunlight, insulin resistance, and a high risk for many cancers that occur at an early age. Despite their very small head circumference, most affected individuals have normal intellectual ability. Women may be fertile but often have early menopause, and men tend to be infertile, with only one confirmed case of paternity. Serious medical complications that are more common than in the general population and that also appear at unusually early ages include chronic obstructive pulmonary disease, diabetes mellitus as a result of insulin resistance, and cancer of a wide variety of types and anatomic sites.

Diagnosis/testing: The diagnosis of BSyn is established in a proband with characteristic clinical features and/or biallelic pathogenic variants in BLM identified on molecular genetic testing. Identification of increased frequency of sister-chromatid exchanges on specialized cytogenetic studies and exclusion of RMI1, RMI2, and TOP3A-related disorders may be helpful in establishing the diagnosis in those with characteristic clinical features who do not have biallelic pathogenic variants in BLM.

Management: Treatment of manifestations: Skin protection, including coverage of exposed skin and use of broad-spectrum sunscreen with SPF of at least 30 to reduce the sun-sensitive rash. Increased-calorie-density formulas and foods may promote weight gain. Although growth hormone treatment may improve linear growth, many clinicians caution against its use because of reports of early onset of cancer in some treated children. Developmental services and therapies as needed. Hyperglycemia from insulin resistance is treated as in type 2 diabetes. In persons with BSyn who have cancer, reduced chemotherapy dosage and duration to reduce risks of severe complications; caution should be exercised with use of ionizing radiation or alkylating agents, particularly busulfan, cyclophosphamide, or melphalan. Individuals with recurrent infections and defects in humoral immunity may be treated with gamma globulin infusions to decrease frequency and severity of infections.

Surveillance: Abdominal ultrasound examination every three months until age eight years for Wilms tumor. Screening and family education regarding signs/symptoms of leukemia and lymphoma at every health visit. Whole-body MRI every one to two years beginning at age 12-13 years for risk of lymphoma. Annual colonoscopy beginning at age 10-12 years. Fecal immunochemical testing every six months beginning at age 10-12 years. Annual breast MRI in women beginning at age 18 years. Annual fasting blood glucose and hemoglobin A1C beginning at age ten years. Annual serum TSH with reflex to T4 beginning at age ten years. Annual lipid profile beginning at age ten years.

Agents/circumstances to avoid: Sun exposure may provoke an erythematous rash, especially on the face. Exposure to ionizing radiation should be minimized.

Genetic counseling: BSyn is inherited in an autosomal recessive manner. Identification of both pathogenic BLM variants in the proband is required for carrier (heterozygote) testing in at-risk families. BLM is included in expanded carrier screening panels, and most pathogenic variants can be identified through sequencing. Prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are possible if the BLM pathogenic variants have been identified in the at-risk couple.

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