Bloom syndrome

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

Bloom syndrome is an inherited disorder characterized by short stature, a skin rash that develops after exposure to the sun, and a greatly increased risk of cancer.

People with Bloom syndrome are usually smaller than 97 percent of the population in both height and weight from birth, and they rarely exceed 5 feet tall in adulthood.

Affected individuals have skin that is sensitive to sun exposure, and they usually develop a butterfly-shaped patch of reddened skin across the nose and cheeks. A skin rash can also appear on other areas that are typically exposed to the sun, such as the back of the hands and the forearms. Small clusters of enlarged blood vessels (telangiectases) often appear in the rash; telangiectases can also occur in the eyes. Other skin features include patches of skin that are lighter or darker than the surrounding areas (hypopigmentation or hyperpigmentation respectively). These patches appear on areas of the skin that are not exposed to the sun, and their development is not related to the rashes.

People with Bloom syndrome have an increased risk of cancer. They can develop any type of cancer, but the cancers arise earlier in life than they do in the general population, and affected individuals often develop more than one type of cancer.

Individuals with Bloom syndrome have a high-pitched voice and distinctive facial features including a long, narrow face; a small lower jaw; and prominent nose and ears. Other features can include learning disabilities, an increased risk of diabetes, chronic obstructive pulmonary disease (COPD), and mild immune system abnormalities leading to recurrent infections of the upper respiratory tract, ears, and lungs during infancy. Men with Bloom syndrome usually do not produce sperm and as a result are unable to father children (infertile). Women with the disorder generally have reduced fertility and experience menopause at an earlier age than usual.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

Mutations in the BLM gene cause Bloom syndrome. The BLM gene provides instructions for making a member of a protein family called RecQ helicases. Helicases are enzymes that attach (bind) to DNA and unwind the two spiral strands (double helix) of the DNA molecule. This unwinding is necessary for several processes in the cell nucleus, including copying (replicating) DNA in preparation for cell division and repairing damaged DNA. Because RecQ helicases help maintain the structure and integrity of DNA, they are known as the "caretakers of the genome."

When a cell prepares to divide to form two cells, the DNA that makes up the chromosomes is copied so that each new cell will have two copies of each chromosome, one from each parent. The copied DNA from each chromosome is arranged into two identical structures, called sister chromatids, which are attached to one another during the early stages of cell division. Sister chromatids occasionally exchange small sections of DNA during this time, a process known as sister chromatid exchange. Researchers suggest that these exchanges may be a response to DNA damage during the copying process. The BLM protein helps to prevent excess sister chromatid exchanges and is also involved in other processes that help maintain the stability of the DNA during the copying process.

BLM gene mutations result in the absence of functional BLM protein. As a result, the frequency of sister chromatid exchange is about 10 times higher than average. Exchange of DNA between chromosomes derived from the individual's mother and father are also increased in people with BLM gene mutations. In addition, chromosome breakage occurs more frequently in affected individuals. All of these changes are associated with gaps and breaks in the genetic material that impair normal cell activities and cause the health problems associated with this condition. Without the BLM protein, the cell is less able to repair DNA damage caused by ultraviolet light, which results in increased sun sensitivity. Genetic changes that allow cells to divide in an uncontrolled way lead to the cancers that occur in people with Bloom syndrome.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

Bloom syndrome is a rare disorder. Only a few hundred affected individuals have been described in the medical literature, about one-third of whom are of Central and Eastern European (Ashkenazi) Jewish background.

Reported clinical features and what the terms mean

The following findings are associated with this condition in Orphanet. They are not a checklist for diagnosing yourself, and they do not all occur in every affected person. Some are examination, imaging or laboratory findings that cannot be recognised at home.

The frequency labels describe how often a finding was reported among people with the condition in the source. They do not give the chance that a person with that symptom has the condition. Definitions below reproduce HPO terminology; they explain the term, not the likely severity in an individual.

Abnormality of the immune system · Very frequent (99-80%)

An abnormality of the immune system.

Adipose tissue loss · Very frequent (99-80%)

A reduction in the amount of adipose tissue (fat) compared with the amount previously present in an individual.

Decreased circulating antibody level · Very frequent (99-80%)

An abnormally decreased level of immunoglobulin in blood.

Growth delay · Very frequent (99-80%)

A deficiency or slowing down of growth pre- and postnatally.

Intrauterine growth retardation · Very frequent (99-80%)

An abnormal restriction of fetal growth with fetal weight below the tenth percentile for gestational age.

Severe postnatal growth retardation · Very frequent (99-80%)

Severely slow or limited growth after birth, being four standard deviations or more below age- and sex-related norms.

Small for gestational age · Very frequent (99-80%)

Smaller than normal size according to sex and gestational age related norms, defined as a weight below the 10th percentile for the gestational age.

Abnormal proportion of CD8 T cells · Frequent (79-30%)

Abnormal increase or decrease of the absolute number of cytotoxic CD3+CD8+ T cells (measured the absolute count per volume or as percentage of total CD3+ T cells in the blood), compared to a reference range for a given sex and age-group. These are usually measured within the TCR alpha/beta positive population.

Other findings in the same source

From: Orphanet

Additional reported features include Cafe-au-lait spot (Frequent (79-30%)); Cutaneous photosensitivity (Frequent (79-30%)); Decreased circulating IgA level (Frequent (79-30%)); Decreased circulating IgG level (Frequent (79-30%)); Decreased circulating total IgM (Frequent (79-30%)); Decreased head circumference (Frequent (79-30%)); Decreased proportion of CD4-positive T cells (Frequent (79-30%)); Gastroesophageal reflux (Frequent (79-30%)); Hypopigmentation of the skin (Frequent (79-30%)); Insulin resistance (Frequent (79-30%)). This is a selected summary, not a complete description of the condition.

Which doctor should you see?

The suggested department for discussing Bloom syndrome is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Bloom syndrome. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.