Bloom syndrome (BS)

In Bloom syndrome (McKusick 210900) (1), prenatal
and postnatal growth deficiency is pronounced
(birth weight 2000 g, birth length
!40 cm, adult height around 150 cm). The
phenotype (2) includes a narrow face. Usually,
but not always, a sunlight-induced erythema
develops on the cheeks, eyelids, mouth, ears,
and back of the hands (a and b). The photograph
on the right (c) shows a boy with Bloom syndrome
and acute leukemia. Metaphase cells
show about a tenfold increase in the rate of sister
chromatid exchanges (SCE), !60 instead of
about 6 per metaphase in normal cells (3). (Sister
chromatid exchanges are explained in the
glossary, p. 423). Metaphases of patients contain
increased breaks in one or both chromatids
and exchanges between homologous chromosomes
in about 1–2% of cells. In Bloom syndrome
patients, different types of malignancies
occur in a distribution comparable to that of the
general population, but at a much earlier age
(mean age 24.7, range 2–48 years). Some
patients have multiple primary tumors, which
underlines the striking susceptibility to cancer
in Bloom syndrome. Chemotherapy is very
poorly tolerated.