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Bloom syndrome (BSyn) is a rare chromosomal breakage syndrome characterized by a marked genetic instability associated with pre- and postnatal growth retardation, facial sun-sensitive telangiectatic erythema, increased susceptibility to infections, and predisposition to cancer.
Overall prevalence is unknown, but in the Ashkenazi Jewish population it is estimated at approximately 1/ 48,000 births.
Individuals with BSyn show proportionate growth retardation of prenatal onset and have a short stature (average adult height of 150 cm). Respiratory and gastrointestinal tract infections of variable severity (e.g. otitis, pneumonia) occur frequently throughout childhood and are associated with variable immunodeficiency. Gastroesophageal reflux with tracheal aspiration, common during infancy, may contribute to respiratory infections. Telangiectatic erythema appears during the first 1-2 years of life on the face (in particular the cheek) and dorsum of the hands. One major feature of Bsyn is a greatly increased predisposition to cancers in a distribution corresponding to the general population but occurring at a much younger age. The most common malignancies are leukemias and lymphoma during childhood and adolescence, and various types of adenocarcinomas during adulthood (e.g. colon, esophagus, breast). Rare tumors such as Wilms tumor and osteosarcoma (see these terms) may occur during childhood. Several individuals have had more than one primary tumor. Other usual features are poor feeding during infancy, and an exceptionally sparse subcutaneous adipose tissue giving a wasted appearance. Dolichocephaly, narrow face, prominent nose and ears, and malar and mandibular hypoplasia can be observed. Additional features include blistering and bleeding from the lips, patchy areas of hyper- and hypopigmentation, male infertility, and premature menopause. Decreased attention span and reduced memory function result in lack of interest in learning, but intellectual disability is not present. Ocular anomalies (e.g. conjunctivitis, bilateral optic nerve hypoplasia) have been reported.
Bsyn is due to mutations of the BLM gene (15q26.1) which encodes the DNA helicase RecQl3, an enzyme involved in maintenance of genomic integrity. Such mutations lead to a spontaneous high level of sister chromatid exchanges due to a slowdown in replication speed and defective fork reactivation.
The clinical diagnosis is confirmed cytogenetically by demonstrating a 10-fold increase in the rate of sister chromatid exchanges in BSyn cells compared to normal cells, and a quadriradial chromatid interchange configuration in cultured blood lymphocytes. The diagnosis can also be confirmed by molecular genetic testing.
Differential diagnosis includes Silver-Russell syndrome, Rothmund-Thomson syndrome, ataxia-telangiectasia, Cockayne syndrome, and Nijmegen breakage syndrome (see these terms).
Prenatal diagnosis of at-risk pregnancies is possible by cytogenetic or molecular genetic testing of fetal cells obtained by amniocentesis or chorionic villus sampling.
Transmission is autosomal recessive. Recurrence risk is of 25%.
Management and treatment
Management is symptomatic. Antibiotics are used to treat infections. If the serum levels of immunoglobulins (Ig) are low, patients will benefit from Ig substitution therapy. Sun exposure must be avoided. An early follow-up is essential for cancer surveillance. Due to hypersensitivity of patients to DNA breaking agents, radiotherapy and chemotherapy is performed with reduced dosage and/or duration of therapy.
The high occurrence of cancer and complications that can result from infections, early-onset chronic obstructive pulmonary disease and diabetes mellitus reduce life expectancy, which does not exceed late adulthood (approximately 50 years old).