Heterozygous germ-line mutations in the NBN gene predispose to medulloblastoma in pediatric patients.

The NBN (NBS1) gene belongs to a group of double-strand break repair genes. Mutations in any of these genes cause genome instability syndromes and contribute to carcinogenesis. NBN gene mutations cause increased tumor risk in Nijmegen breakage syndrome (NBS) homozygotes as well as in NBN heterozygotes. NBS patients develop different types of malignancies; among solid tumors, medulloblastoma (MB), an embryonal tumor of the cerebellum, has been reported most frequently. The majority of medulloblastomas occur sporadically, some of them manifest within familial cancer syndromes. Several signaling pathways are known to be engaged in hereditary and sporadic MB. The aim of our study was to identify mutations in selected exons of the NBN gene and to determine the frequency of the most common NBN gene mutations in pediatric patients with different types of medulloblastoma. We screened a total of 104 patients with MB and identified 7 heterozygous carriers (6.7%) of two different germ-line mutations of NBN gene; all of them had classic MB. Our results indicate that heterozygous carriers of the germ-line NBN gene mutations (c.511A>G and c.657_661del5) may exhibit increased susceptibility to developing MB. The risk of medulloblastoma is estimated to be 3.0 (for c.511A>G) and 4.86 (for c.657_661del5) times higher than in the general Polish population (p<0.05). These results suggest that heterozygous NBN germ-line mutations may contribute to the etiology of medulloblastoma.

The frequency of NBN molecular variants in pediatric astrocytic tumors.

Gliomas, particularly those of astrocytic origin, are the most frequent primary central nervous system tumors that develop in children. The majority of them are benign and slow growing, with relatively good prognosis. Several genomic and gene alterations are known to be involved in astrocytoma development, but the precise mechanisms remain poorly understood. The NBN gene, which participates in DNA double-strand break repair and maintenance of genome stability, has been postulated to be a susceptibility factor for a number of cancers. Here we report the results of NBN gene analyses performed in 127 children with various astrocytic tumors. PCR-SSCP analysis followed by DNA sequencing was used for molecular variant screening. Three carriers (2.37%) of different germline mutations on one NBN allele were found. The common Slavic deletion c.657_661del5 (p.K219fsX19) was detected in a patient with pilocytic astrocytoma; a known mutation, c.643C>T (p.R215W), and a new substitution, c.565C>G (p.Q189E), were identified in two patients with primary glioblastoma. The risk of developing astrocytic malignancies is estimated to be 1.33 times higher for c.657_661del5 and 3.2 times higher for c.643C>T than in the general Polish population (P > 0.05). Because of the low frequency of the mutations identified in the studied group, we were unable to determine the exact role of NBN in the development of astrocytoma in children. The presence of two potentially pathogenic NBN molecular variants among 16 glioblastoma cases (12.5%) could be a remarkable finding in our study. We thus cannot exclude a possible role of NBN in the tumorigenesis of a certain type of astrocytic tumors.

A comprehensive HADHA c.1528G>C frequency study reveals high prevalence of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency in Poland.

Isolated long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) is associated with c.1528G>C substitution in the HADHA gene, since most patients have the prevalent mutation on at least one allele. As it is known that the disease is relatively frequent in Europe, especially around the Baltic Sea, and that the majority of Polish LCHADD patients originate from the coastal Pomeranian province, partly inhabited by an ancient ethnic group, the Kashubians, we aimed to determine the carrier frequency of the prevalent HADHA mutation in various districts of Poland with special focus on the Kashubian district. A total of 6,854 neonatal dried blood samples from the entire country, including 2,976 Pomeranian neonates of Kashubian origin, were c.1528G>C genotyped. Fifty-nine heterozygous carriers for the prevalent c.1528G>C substitution (41 Pomeranian children) were detected in the studied group. Our data reveal a geographically skewed distribution of the c.1528C allele in the Polish population; in the northern Pomeranian province the carrier frequency is 1:73, which is the highest frequency ever reported, whereas in the remaining regions it is 1:217. Hence, the incidence of LCHADD in Poland is predicted to be 1:118,336 versus 1:16,900 in the Pomeranian district. Despite the relative rarity of the disease, screening for LCHADD in neonates born in the northern part of Poland, especially those of Kashubian origin, is justified. Our data allow us to suggest a probable Kashubian origin of the prevalent c.1528G>C mutation.

Twelve novel JAG1 gene mutations in Polish Alagille syndrome patients.

Alagille syndrome (AGS) is an autosomal dominant disorder with developmental abnormalities of the liver, heart, eyes, vertebrae, and face. Mutations in the JAG1 (Jagged 1) gene, coding a ligand in the evolutionarily conserved Notch signaling pathway, are responsible for AGS. Here we present sixteen different JAG1 gene mutations, among them twelve novel, not described previously. Seven frameshift: c. 172_178del7 (p.Ala58fs), c.509delT (p.Leu170fs), c.1197delG (p.Val399fs), c.1485_1486delCT (p.Pro495fs), c.1809_1810insTGGG (p.Lys604fs), c.2122_2125delCAGT (p.Gln708fs), c.2753delT (p.Ile918fs); five nonsense: c.383G>A (p.Trp128X), c.496C>T (p.Glu166X), c.841C>T (p.Gln281X), c.1207C>T (p.Gln403X), c.1603C>T (p.Gln535X); two splice site: c.388-1G>C, c.3048+1_3048+2insG and two missense mutations: c.359T>A (p.Ile120Asn), c.560G>A (p.Cys187Tyr) were found. Forty percent of the changes were identified in exons 2 and 4, the remaining mutations are distributed along the entire coding sequence of the gene. Seventy-five percent of the mutations lead to creation of premature termination codons. Family studies revealed that the specific mutations were inherited in 3 out of 11 investigated cases. No correlation between genotype and phenotype was observed.

Four novel RSK2 mutations in females with Coffin-Lowry syndrome.

Coffin-Lowry syndrome (CLS) is an X-linked semi-dominant disorder caused by mutations in the RSK2 gene and characterized by moderate to severe mental retardation, characteristic facial features, skeletal deformities, and tapering fingers in males. Females are usually much more mildly and variably affected thus more difficult to diagnose. In this study, molecular genetic analysis was carried out in four female patients presenting features of Coffin-Lowry syndrome. The probands were sporadic cases with no affected males in their families. The molecular analysis of the RSK2 gene revealed four novel mutations, including two frameshift and one missense mutation identified by sequencing, and one large deletion detected by multiplex ligation-dependent probe amplification (MLPA) analysis. Females exhibited a random X-chromosome inactivation pattern. To our knowledge, this is the first report of applying MLPA in the diagnostics of CLS and the first description of a large deletion in a CLS female. These results support including screening for large rearragements in the genetic analysis of female CLS patients.

A homozygous mutation in the SCO2 gene causes a spinal muscular atrophy like presentation with stridor and respiratory insufficiency.

UNLABELLED: Infants with deficiency of cytochrome c oxidase (COX) due to SCO2 mutations observed so far usually demonstrated early cardiomyopathy, encephalopathy and lactic acidosis. Milder spinal muscular atrophy-like (SMA-like) phenotype was also rarely reported. The aim is to present 18 Polish patients with SCO2 mutations. Molecular study revealed p.E140K mutation in all cases (on 32 alleles); p.Q53X mutation and novel p.M177T change were identified in single patients. In three families no second mutation was found. Thirteen p.E140K homozygotes presented in infancy with floppiness and remarkable stridor. Survival motor neuron (SMN) gene deletion was excluded. Mild to moderate lactic academia was found. Neurological involvement manifested as spasticity and psychomotor retardation. In some patients strabismus, ptosis and episodes of seizures were seen. During second half of the year chronic respiratory failure with artificial respiration dependency appeared in all homozygotes. Heart involvement was never present at the beginning. Rapidly progressive hypertrophic cardiomyopathy developed in several patients at the terminal stage. The stridor was constant and striking feature. Skeletal muscle biopsy was performed in 16 patients including 11 homozygotes. Four pathological patterns were discerned - from neurogenic muscle changes, including spinal muscular atrophy (SMA) to unspecific findings. Histochemical cytochrome c oxidase (COX) deficit was not a constant feature. Significant decrease in respiratory chain complex IV activity was detected in muscle homogenate by spectrophotometric method only in 7 out of 12 examined cases. CONCLUSIONS: 1/Mutations of SCO2 gene should be considered as a possible cause of neurogenic skeletal muscle features (including SMA-like) in infants with encephalomyopathy even in the absence of heart involvement and COX deficit; 2/Inspiratory stridor may be symptomatic of SCO2 gene mutation(s).

High prevalence of SURF1 c.845_846delCT mutation in Polish Leigh patients.

Leigh syndrome is a neuropathological disorder with typical morphological changes in brain, appearing regardless of diverse molecular background. One of the most common enzymatic defects in Leigh patients is cytochrome c oxidase deficiency associated with recessive mutations in the SURF1 gene. To assess the SURF1 mutation profile among Polish patients we studied 41 affected children from 34 unrelated families by PCR-SSCP and sequencing. Four novel mutations, c.39delG, c.752-1G>C, c.800_801insT, c.821A>G, and five described pathogenic changes, c.311_312insAT312_321del10, c.688C>T, c.704T>C, c.756_757delCA, c.845_846delCT, were identified in 85.3% of analysed probands. One mutation, c.845_846delCT, was identified in 77.6% of SURF1 alleles. Up to now, it has been reported only in 9% of alleles in other parts of the world. The deletion was used as LS(SURF1-) marker in population studies. Eight heterozygous carriers of the mutation were found in a cohort of 2890 samples. The estimated c.845_846delCT allele frequency is 1:357 (0.28+/-0.2%), and the lowest predicted LS(SURF1-) frequency in Poland 1:126,736.births. Relatively high frequency of LS(SURF1-) in Poland with remarkable c.845_846delCT mutation dominance allows one to start the differential diagnosis of LS in each patient of Polish (and probably Slavonic) origin from the direct search for c.845_846delCT SURF1 mutation.

Carrier frequency of mutation 657del5 in the NBS1 gene in a population of Polish pediatric patients with sporadic lymphoid malignancies.

Nijmegen breakage syndrome (NBS) is a human autosomal recessive disease characterized by genomic instability and enhanced cancer predisposition, in particular to lymphoma and leukemia. Recently, significantly higher frequencies of heterozygous carriers of the Slavic founder NBS1 mutation, 657del5, were found in Russian children with sporadic lymphoid malignancies, and in Polish adults with non-Hodgkin lymphoma (NHL). In addition, the substitution 643C>T (R215W) has also been found in excess among children with acute lymphoblastic leukemia (ALL). In an attempt to asses the contribution of both mutations to the development of sporadic lymphoid malignancies, we analyzed DNA samples from a large group of Polish pediatric patients. The NBS1 mutation 657del5 on one allele was found in 3 of 270 patients with ALL and 2 of 212 children and adolescents with NHL; no carrier was found among 63 patients with Hodgkin lymphoma (HL). No carriers of the variant R215W were detected in any studied group. The relative frequency of the 657del5 mutation was calculated from a total of 6,984 controls matched by place of patient residence, of whom 42 were found to be carriers (frequency = 0.006). In the analyzed population with malignancies, an increased odds ratio for the occurrence of mutation 657del5 was found in comparison with the control Polish population (OR range 1.48-1.85, 95% confidence interval 1.18-2.65). This finding indicates that the frequency of the mutation carriers was indeed increased in patients with ALL and NHL (p < 0.05). Nonetheless, NBS1 gene heterozygosity is not a major risk factor for lymphoid malignancies in childhood and adolescence.

Anthropometric characteristics of X-linked hypophosphatemia.

An anthropometric study was undertaken to assess head proportions of patients with X-linked hypophosphatemia (XLH). Fourteen morphometric parameters of the head were measured and 10 cephalic indices calculated in 82 affected persons (57 females and 25 males) from 55 unrelated families with XLH, and compared with the results obtained in the group of their healthy relatives (37 females and 33 males), as well as with general population control values. Normalized values (SD, z-score) were analyzed statistically. The group of healthy relatives, both males and females, differed significantly from Polish population control values in most of the normalized variables measured, making population control values useless as a control group for the analyzed XLH group. Intrafamilial values of cephalic parameters in healthy relatives of the XLH patients were finally applied for statistical analysis. Generally patients with XLH showed highly statistically significant increase in head length (males 0.95 +/- 1.07 vs. -0.37 +/- 1.02, females 0.57 +/- 1.59 vs. -0.06 +/- 1.15), significant decrease in occipital breadth (males -0.56 +/- 1.27 vs. 0.70 +/- 1.28, females -0.59 +/- 1.7 vs. 0.13 +/- 1.1) and several milder anomalies of craniofacial proportions. Mean cephalic index was significantly lower in XLH patients when compared with the healthy relatives (males -0.909 vs. 0.278 P < 0.0001, females -0.705 vs. 0.381 P = 0.007). The cephalic changes were found both in XLH children and XLH adults and were more pronounced in affected males than in females. There were no differences between offspring born by hypophosphatemic and normophosphatemic mothers.

Clinical heterogeneity and molecular findings in five Polish patients with glycerol kinase deficiency: investigation of two splice site mutations with computerized splice junction analysis and Xp21 gene-specific mRNA analysis.

Five cases of glycerol kinase deficiency are presented with clinical, biochemical, and genetic results. Two had the glycerol kinase deficiency as part of an Xp21 contiguous gene deletion syndrome-complex form-and three had an isolated form of the enzyme deficiency. In these we found two splice site mutations (IVS1+4A>G, IVS9-1G>T) and one insertion (1393_1394insG). In patients with the complex form, a deletion of the DAX1, GK genes and the distal part of the DMD gene was found. A computerized study was performed to predict the effects of the splice site mutations. It showed that the IVS9-1G>T mutation substantially altered and removed the wild-type site and enhanced a cryptic site seven nucleotides downstream, and that the IVS1+4A>G diminished the strength of the wild-type donor site from strong to leaky. To verify these predictions, we developed an RT-PCR system with gene-specific primers that exclusively amplifies the Xp21 glycerol kinase gene transcript. Identification of individuals at risk is motivated by a need to avoid delay in a correct diagnosis. For reliable identification of heterozygotes for isolated glycerol kinase deficiency, knowledge of the specific mutation in the proband is required. This is easily obtained with the RT-PCR analyses developed in this study.