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Bloom syndrome (BS) is an autosomal recessive disorder with characteristic clinical features of primary microcephaly, growth deficiency, cancer predisposition, and immunodeficiency. Here, we report the clinical and molecular findings of eight patients from six families diagnosed with BS. We identified causative pathogenic variants in all families including three different variants in BLM and one variant in RMI1. The homozygous c.581_582delTT;p.Phe194* and c.3164G>C;p.Cys1055Ser variants in BLM have already been reported in BS patients, while the c.572_573delGA;p.Arg191Lysfs*4 variant is novel. Additionally, we present the detailed clinical characteristics of two cases with BS in which we previously identified the biallelic loss-of-function variant c.1255_1259delAAGAA;p.Lys419Leufs*5 in RMI1. All BS patients had primary microcephaly, intrauterine growth delay, and short stature, presenting the phenotypic hallmarks of BS. However, skin lesions and upper airway infections were observed only in some of the patients. Overall, patients with pathogenic BLM variants had a more severe BS phenotype compared to patients carrying the pathogenic variants in RMI1, especially in terms of immunodeficiency, which should be considered as one of the most important phenotypic characteristics of BS., (© 2022 The Authors. Clinical Genetics published by John Wiley & Sons Ltd.)

Pathogenic biallelic variants in the BLM/RECQL3 gene cause a rare autosomal recessive disorder called Bloom syndrome (BS). This syndrome is characterized by severe growth delay, immunodeficiency, dermatological manifestations and a predisposition to a wide variety of cancers, often multiple and very early in life. Literature shows that the main mode of BLM inactivation is protein translation termination. We expanded the molecular spectrum of BS by reporting the first deep intronic variant causing intron exonisation. We describe a patient with a clinical phenotype of BS and a strong increase in sister chromatid exchanges (SCE), who was found to be compound heterozygous for a novel nonsense variant c.3379C>T, p.(Gln1127Ter) in exon 18 and a deep intronic variant c.3020-258A>G in intron 15 of the BLM gene. The deep intronic variant creates a high-quality de novo donor splice site, which leads to retention of two intron segments. Both pseudo-exons introduce a premature stop codon into the reading frame and abolish BLM protein expression, confirmed by Western Blot analysis. These findings illustrate the role of non-coding variation in Mendelian disorders and herewith highlight an unmet need in routine testing of Mendelian disorders, being the added value of RNA-based approaches to provide a complete molecular diagnosis., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Cells with abnormally high rates of sister-chromatid exchange (SCE) are uniquely characteristic of Bloom's syndrome (BS). However, in one in five persons a minor population of cells with a low-SCE phenotype circulates in the blood. The origin and significance of the low-SCE cells in BS have never been understood, although they are assumed to arise by somatic mutation. In the present investigation, the enigmatic high-SCE/low-SCE mosaicism was investigated by comparing the incidence in several subpopulations of persons in the Bloom's Syndrome Registry who exhibit the two types of cells, and a striking negative correlation emerged: in persons with BS whose parents share a common ancestor, the case in approximately half of registered persons, low-SCE cells are found only rarely; conversely, the mosaicism occurs almost exclusively in persons with BS whose parents are not known to share a common ancestor. Because those who share a common ancestor are predominantly homozygous-by-descent at the mutated BS locus, the negative correlation is interpreted to mean that the emergence of low-SCE cells in BS in some way depends on the pre-existence of compound heterozygosity. A corollary to this is that BS is genetically heterogeneous.

Two children presenting with sporadic unilateral retinoblastoma and exhibiting a high degree of chromosome breakage were noted to have unusual facies, microcephaly and abnormal skin pigmentation. In the first child the pattern of both spontaneous and mitomycin-C-induced chromosome breakage was characteristic of Fanconi's anaemia although the degree of breakage was extreme. She also exhibited a striking increase in X-ray-induced chromosomal damage in G0 lymphocytes as measured by dicentric formation and increase in chromatid-type aberrations. She had a number of typical clinical features, including cafe-au-lait patches and abnormalities involving the kidney; however, she demonstrated neither the hypoplasia of radius and thumb nor the typical aplastic phase of this disorder. At age 22 months the child became anaemic with trilineage myelodysplasia, which was rapidly followed by the development of acute myeloblastic leukaemia. The early onset (at age 4 months) of retinoblastoma may have been associated with the underlying genomic instability. The second child exhibited a pattern of chromosome breakage characteristic of Bloom's syndrome, in addition to a moderate increase in damage induced by mytomycin-C. She had the typical stunted growth and malar hypoplasia of Bloom's syndrome although she did not demonstrate the frequently described erythematous 'butterfly rash' Although patients with Fanconi's anaemia and Bloom's syndrome are recognised to be at an increased risk of cancer, retinoblastoma has not previously been described in patients with either condition. We suggest that underlying recessive chromosome breakage syndromes may be underdiagnosed in paediatric cancer patients, with important implications for prognosis and genetic counselling.

Bloom's syndrome (BS) is a rare autosomal recessive genetic disorder in which diabetes mellitus unusually frequently develops as a complication. We report on a 21-year-old Japanese male patient with BS who exhibited impaired glucose tolerance (IGT) in the initial oral glucose tolerance test (OGTT) and had developed patterns of diabetes mellitus by the second OGTT at the 2-years-and-2-months follow-up. German and Passarge reported that the onset of diabetes in patients with BS was in late adolescence or early adulthood. Our results support the findings of German and Passarge. Therefore, when a person with BS reaches late adolescence or early adulthood, an OGTT is necessary to ascertain whether the patient has IGT or diabetes mellitus as a complication, regardless of whether or not diabetic signs such as glucosuria are present.

During the 30 years since its description as a clinical entity, Bloom's syndrome has been diagnosed in more than 100 persons. It is believed that most of these have been accessioned to the Bloom's Syndrome Registry, which now includes 103 persons. Of those 103, 80 are alive, with a mean age of 18.2 years. Twenty-eight malignant neoplasms have been detected, at a mean age of 20.7 years. Periodically, progress reports are being made in this journal of the long-term surveillance of affected families.

Fourteen persons have been diagnosed Bloom's syndrome in Japan, with cytological verification in 11. Widely separated birthplaces throughout Honshu, Shikoku, and Kyushu and a parental consanguinity incidence greater than in the general population suggest that the Bloom's syndrome mutation, although very rare, is distributed widely throughout the Japanese population. The locus mutated is the same as in Jews and persons of Western European extraction. The phenotype differs somewhat from most cases recognized elsewhere, in that dolichocephaly is a less constant feature, the facial skin lesion is less prominent, and life-threatening infections are less common. The characteristic predisposition to neoplasia exists, however, as probably does that to diabetes mellitus.

Bloom's syndrome has been known as a clinical entity for 34 years. Careful records of cases diagnosed throughout the world have been maintained since its recognition as an entity, and most instances of cytologically verified Bloom's syndrome have been accessioned to what has been referred to as the Bloom's Syndrome Registry since the mid-1960s. Presented here is the fourth in a series of progress reports from the Registry of information accumulated during this long-term surveillance of affected families, along with mention of selected recent advances that have been made in the understanding of the syndrome. 130 persons had been accessioned to the Registry by the end of 1987; 96 of these were alive, their mean age being 18.9 years. Although a number of clinical complications occur in Bloom's syndrome, the most important is malignant neoplasia. In the 130 persons in the Registry, 57 malignant neoplasms had been detected, the mean age at diagnosis being 24.8 years. Neoplasia in Bloom's syndrome is noteworthy not only because of its frequency and exceptionally early age of emergence but for its variety of histological types and sites of origin.