This report describes Bloom syndrome; this disease exhibits autosomal recessive inheritance. The human gene implicated in this disease is BLM, which encodes Bloom Syndrome, RecQ Helicase-Like (also called RECQL3). There is one high-scoring fly ortholog, Blm, for which classical amorphic and hypomorphic alleles, RNAi-targeting constructs, and alleles caused by insertional mutagenesis have been generated.
A UAS construct of the wild-type human Hsap\BLM gene has been introduced into flies; heterologous rescue (functional complementation) has been demonstrated for the IR sensitivity phenotype.
Females homozygous for a null allele of Dmel\Blm are sterile due to maternal-effect embryonic lethality; males exhibit reduced fertility. Homozygotes are hypersensitive to chemical mutagens and radiation; in sperm, chromosome nondisjunction and chromosome loss are increased more than tenfold. Genetic and physical interactions have been described for Dmel\Blm; see below and in the Blm gene report.
[updated Jun. 2020 by FlyBase; FBrf0222196]
[BLOOM SYNDROME; BLM](https://omim.org/entry/210900)
[RECQ PROTEIN-LIKE 3; RECQL3](https://omim.org/entry/604610)
Bloom's syndrome (BSyn) is characterized by severe pre- and postnatal growth deficiency, highly characteristic sparseness of subcutaneous fat tissue throughout infancy and early childhood, and short stature throughout postnatal life that in most affected individuals is accompanied by an erythematous and sun-sensitive skin lesion of the face. Gastroesophageal reflux (GER) is common and very possibly responsible for infections of the upper respiratory tract, the middle ear, and the lung that occur repeatedly in most persons with BSyn. Although most affected individuals have normal intellectual ability, many exhibit a poorly defined (and little studied) learning disability. Women may be fertile, but menopause occurs unusually early; men are infertile. Serious medical complications that are much more common than in the general population and that also appear at unusually early ages are chronic obstructive pulmonary disease, diabetes mellitus resembling the adult-onset type, and cancer of a wide variety of types and anatomic sites. BSyn is very rare in all national and ethnic groups but is relatively less rare in Ashkenazi Jews. [From GeneReviews, Blooms's syndrome, pubmed:20301572 2015.12.21]
Bloom syndrome is an autosomal recessive disorder characterized by proportionate pre- and postnatal growth deficiency; sun-sensitive, telangiectatic, hypo- and hyperpigmented skin; predisposition to malignancy; and chromosomal instability. [From MIM:210900, 2015.12.21]
Bloom syndrome (BLM) is caused by recessive mutation in the gene BLM (RECQL3). [From MIM:210900, 2015.12.21]
Bloom syndrome can be cytogenetically confirmed in either of two ways, preferably both: either by demonstrating a certain symmetric, four-armed chromatid interchange configuration known as a quadriradial (Qr) in cultured blood lymphocytes, or by a greatly increased frequency of sister-chromatid exchanges (SCEs) in cultured cells of any type. [From GeneReviews, Blooms's syndrome, pubmed:20301572 2015.12.21]
Lymphocytes from patients with Bloom syndrome showed an incidence of cell resistance to the purine analog 6-thioguanine about 8 times the normal. Cells with specific locus mutations have been reported to be present in abnormally great numbers in Bloom syndrome fibroblast cultures, e.g., 6-thioguanine-resistant and diphtheria toxin-resistant cells (Vijayalaxmi et al., 1983, pubmed:6879180). Blood from persons with Bloom syndrome showed 50- to 100-fold increases in the frequency of variants of 3 types, those with a hemizygous phenotype, those with a homozygous phenotype, and those with what appeared to be partial loss of the expression of 1 locus. The high frequency of homozygous variants, indicating altered allelic segregation, could be taken as evidence for increased somatic crossing-over in vivo (Langlois, et al., 1989, pubmed: 2911598). [From MIM:210900, 2015.12.21]
The Bloom syndrome gene product is related to the RecQ subset of DExH box-containing DNA helicases and has both DNA-stimulated ATPase and ATP-dependent DNA helicase activities. Mutations causing Bloom syndrome delete or alter helicase motifs and may disable the 3'-5' helicase activity. The normal protein may act to suppress inappropriate recombination (McDaniel and Schultz, 1994, pubmed:1518822). [provided by RefSeq, Jul 2008]
One to one: 1 human to 1 Drosophila.
Ortholog of human BLM (1 Drosophila to 1 human).
Dmel\Blm shares 30% identity and 47% similarity with human BLM.
