Bloom syndrome

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 genes encoding 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 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). New York dermatologist Dr. David Bloom discovered and first described the condition in 1954.

Bloom syndrome has also appeared in the older literature as Bloom–Torre–Machacek syndrome.

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 due to sun exposure. The facial rash appears most prominently on the cheeks, nose, and around the lips. It is described as erythematous, which is red and inflamed, and telangiectatic, which is characterized by dilated blood vessels at the skin's surface. The rash commonly also affects the backs of the hands and neck, and it can develop on any other sun-exposed areas of the skin. The rash is variably expressed, being present in a majority but not all persons with Bloom syndrome, and it is on average less severe in females than in males. Moreover, the sun sensitivity can resolve in adulthood. There are other dermatologic changes, including hypo-pigmented and hyper-pigmented areas, cafe-au-lait spots, and telangiectasias, which can appear on the face and on the ocular surface.^{[citation needed]}

There is a characteristic facial appearance that includes a long, narrow face; prominent nose, cheeks, and ears; and micrognathism or undersized jaw. The voice is high-pitched and squeaky.^{[citation needed]}

There are a variety of other features that are commonly associated with Bloom syndrome. There is a moderate immune deficiency, characterized by deficiency in certain immunoglobulin classes and a generalized proliferative defect of B and T cells. The immune deficiency is thought to be the cause of recurrent pneumonia and middle ear infections in persons with the syndrome. Infants can exhibit frequent gastrointestinal upsets, with reflux, vomiting, and diarrhea, and there is a remarkable lack in interest in food. There are endocrine disturbances, particularly abnormalities of carbohydrate metabolism, insulin resistance and susceptibility to type 2 diabetes, dyslipidemia, and compensated hypothyroidism. Persons with Bloom syndrome exhibit a paucity of subcutaneous fat. There is reduced fertility, characterized by a failure in males to produce sperm (azoospermia) and premature cessation of menses (premature menopause) in females. Despite these reductions, several women with Bloom syndrome have had children, and there is a single report of a male with Bloom syndrome bearing children.

Although some persons with Bloom syndrome can struggle in school with subjects that require abstract thought, there is no evidence that intellectual disability is more common in Bloom syndrome than in other people.^{[citation needed]}