The features of BSLD include small size and dermatologic findings, such as cafe-au-lait spots, and the presence of the once pathognomonic elevated SCEs is reported for persons with mutations in TOP3A and RMI1.Bloom syndrome shares some features with Fanconi anemia possibly because there is overlap in the function of the proteins mutated in this related disorder. Genetics
Bloom syndrome is an autosomal recessive disorder, caused by mutations in the maternally- and paternally-derived copies of the gene BLM. As in other autosomal recessive conditions, the parents of an individual with Bloom syndrome do not necessarily exhibit any features of the syndrome. The mutations in BLM associated with Bloom syndrome are nulls and missense mutations that are catalytically inactive. The cells from persons with Bloom syndrome exhibit a striking genomic instability that is characterized by hyper-recombination and hyper-mutation. Human BLM cells are sensitive to DNA damaging agents such as UV and methyl methanesulfonate, indicating deficient repair capability. At the level of the chromosomes, the rate of sister chromatid exchange in Blooms syndrome is approximately 10 fold higher than normal and quadriradial figures, which are the cytologic manifestations of crossing-over between homologous chromosome, are highly elevated. Other chromosome manifestations include chromatid breaks and gaps, telomere associations, and fragmented chromosomes. The hyper-recombination can also be detected by molecular assays  The BLM gene is a member of the protein family referred to as RecQ helicases.
Bloom syndrome (often abbreviated as BS in literature) is a rare autosomal recessive genetic disorder characterized by short stature, predisposition to the development of cancer, and genomic instability. BS is caused by mutations in the BLM gene which is a member of the RecQ DNA helicase family. Mutations in other members of this family, namely WRN and RECQL4, are associated with the clinical entities Werner syndrome and Rothmund–Thomson syndrome, respectively. More broadly, Bloom syndrome is a member of a class of clinical entities that are characterized by chromosomal instability, genomic instability, or both and by cancer predisposition. Cells from a person with Bloom syndrome exhibit a striking genomic instability that includes excessive crossovers between homologous chromosomes and sister chromatid exchanges (SCEs). The condition was discovered and first described by New York dermatologist Dr. David Bloom in 1954.Bloom syndrome has also appeared in the older literature as Bloom–Torre–Machacek syndrome. Presentation
The most prominent feature of Bloom syndrome is proportional small size. The small size is apparent in utero. At birth, neonates exhibit rostral to caudal lengths, head circumferences, and birth weights that are typically below the third percentile.The second most commonly noted feature is a rash on the face that develops early in life as a result of sun exposure. The facial rash appears most prominently on the cheeks, nose, and around the lips. It is described as erythematous, that is red and inflamed, and telangiectatic, that is characterized by dilated blood vessels at the skins surface.