Improving detection and genetic counseling in carriers of spinal muscular atrophy with two copies of the SMN1 gene.

Spinal muscular atrophy (SMA) is an autosomal recessive disease caused by mutations in the survival motor neuron1 gene (SMN1). Global carrier frequency is around 1 in 50 and carrier detection is crucial to define couples at risk to have SMA offspring. Most SMA carriers have one SMN1 copy and are currently detected using quantitative methods. A few, however, have two SMN1 genes in cis (2/0 carriers), complicating carrier diagnosis in SMA. We analyzed our experience in detecting 2/0 carriers from a cohort of 1562 individuals, including SMA parents, SMA relatives, and unrelated individuals of the general population. Interestingly, in three couples who had an SMA child, both the parents had two SMN1 copies. Families of this type have not been previously reported. Our results emphasize the importance of performing a detailed carrier study in SMA parents with two SMN1 copies. Expanding the analysis to other key family members might confirm potential 2/0 carriers. Finally, when a partner of a known carrier presents two SMN1 copies, the study of both parents will provide a more accurate diagnosis, thus optimizing genetic counseling.

The c.859G>C variant in the SMN2 gene is associated with types II and III SMA and originates from a common ancestor.

Homozygous mutations of the telomeric SMN1 gene lead to degeneration of motor neurons causing spinal muscular atrophy (SMA). A highly similar centromeric gene (SMN2) can only partially compensate for SMN1 deficiency. The c.859G>C variant in SMN2 has been recently reported as a positive disease modifier. We identified the variant in 10 unrelated chronic SMA patients with a wide spectrum of phenotypes ranging from type II patients who can only sit to adult walkers. Haplotype analysis strongly suggests that the variant originated from a common ancestor. Our results confirm that the c.859G>C variant is a milder SMN2 allele and predict a direct correlation between SMN activity and phenotypic severity.

Genotyping the HFE gene by melting point analysis with the LightCycler system: Pros and cons.

The assay that combines rapid-cycle PCR with allele-specific fluorescent probe melting profiles performed on the Roche Diagnostics LightCycler is commonly employed for genotyping the HFE gene. We report three illustrative cases of the pros and cons of this method. In two cases, atypical melting curves allows the identification of new DNA substitutions in the HFE gene, whereas, in the third case, a typical melting curve of c.845G>A mutation (C282Y) homozygosity overlooks a nucleotide change and promotes misdiagnosis of HH.

SMN2 copy number predicts acute or chronic spinal muscular atrophy but does not account for intrafamilial variability in siblings.

Spinal muscular atrophy (SMA) is an autosomal recessive disorder that affects motor neurons. It is caused by mutations in the survival motor neuron gene 1 (SMN1). The SMN2 gene, which is the highly homologous SMN1 copy that is present in all the patients, is unable to prevent the disease. An SMN2 dosage method was applied to 45 patients with the three SMA types (I-III) and to four pairs of siblings with chronic SMA (II-III) and different phenotypes. Our results confirm that the SMN2 copy number plays a key role in predicting acute or chronic SMA. However, siblings with different SMA phenotypes show an identical SMN2 copy number and identical markers, indicating that the genetic background around the SMA locus is insufficient to account for the intrafamilial variability. In our results, age of onset appears to be the most important predictor of disease severity in affected members of the same family. Given that SMN2 is regarded as a target for potential pharmacological therapies in SMA, the identification of genetic factors other than the SMN genes is necessary to better understand the pathogenesis of the disease in order to implement additional therapeutic approaches.

Autosomal dominant hereditary hemochromatosis associated with two novel Ferroportin 1 mutations in Spain.

Hereditary hemochromatosis is a common disorder of iron metabolism most frequently associated with mutations in the HFE gene. Hereditary hemochromatosis may be caused by other genetic mutations including those in the SLC40A1 gene. This report describes the clinical and laboratory findings of two Spanish families with autosomal dominant iron overload associated with previously unrecognized Ferroportin 1 mutations (p.R88T and p.I180T). The phenotype of iron overload in the patients carrying these mutations could correspond to the group of clinical mutations that lose their iron export function.

Survival and respiratory decline are not related to homozygous SMN2 deletions in ALS patients.

The presence of the SMN2 deletion in 124 patients with ALS was investigated. Eleven patients had the homozygous deletion of SMN2 (8.8%) in comparison with 20 of 200 (10%) of the healthy control population. No significant differences in sex, age at onset, initial symptoms, form of inheritance, decline in ventilatory function, or survival time were found between patients with and without the deletion. The hypothesis that SMN2 is a prognostic factor in sporadic or familial ALS was not confirmed in this study.

Prenatal diagnosis for risk of spinal muscular atrophy.

OBJECTIVES: Prenatal diagnosis of spinal muscular atrophy is usually performed in high risk couples by detection of a homozygous deletion in the survival motor neurone gene (SMN1). However, other relatives at risk of being carriers very often request genetic counselling and the possibility of prenatal diagnosis. The aim of this study was to validate a SMN1 gene quantitative test to help the couples formed by one spinal muscular atrophy carrier and a partner of the general population (1/200 potential risk) to achieve a less ambiguous risk result for the pregnancy. DESIGN: Spinal muscular atrophy carrier studies in at-risk individuals. SETTING: Department of Genetics and Gynaecology and Obstetrics in a large university hospital. POPULATION: Seventy-nine obligate carriers (more than one affected child with deletion in the offspring) and 58 non-carriers (relatives of spinal muscular atrophy families defined by marker studies) were tested to set up a quantitative analysis. The method was applied in different situations in 126 members from 34 families with spinal muscular atrophy patients. METHODS: DNA studies of the SMNI gene by marker analysis and quantitative assay. MAIN OUTCOME MEASURES: To determine double (non-carrier) or single dose (carrier) of exon 7 of the SMN1 gene in relatives of spinal muscular atrophy patients. Bayesian calculation of risk. RESULTS: The sensitivity and specificity of the method were 96% and 100%, respectively. Studies on different couples with an a priori risk of 1/200 allowed us to reduce the final risk to 1/5000 or to increase it to 1/4. CONCLUSIONS: The quantitative method can be used to achieve a less ambiguous risk in pregnancies with a 1/200 risk and in families where no sample is available to study the index case. Screening of gamete donors when the recipient is a known carrier should also be considered.

[Interest in the study of genetic variants of the promoter region of the UGT1A1 gene in neonatal jaundice]. / Interés del estudio de las variantes genéticas del promotor del gen UGT1A1 en la ictericia neonatal.

BACKGROUND: A relationship between polymorphism in the promoter region of the UGT1A1 gene (associated with Gilbert's syndrome) and the development of jaundice has recently been demonstrated. This polymorphism is due to (TA)7 instead of wild-type (TA)6. OBJECTIVE: To investigate the relationship between Gilbert's syndrome and neonatal jaundice by evaluating the distribution of (TA)7 in a population of newborns. METHODS: A total of 136 newborns were studied: 21 had neonatal jaundice, 69 were healthy and the remaining newborns had various diseases. DNA from each patient was used to amplify, by polymerase chain reaction, the promoter region of the UGT1A1 gene, which flanks the TATA box where the polymorphism is located. RESULTS: In the group without jaundice, 53 % of the newborns were normal (6/6 genotype), 40 % were 6/7 and 7 % were 7/7. In the group with jaundice, 33 % of the newborns were normal, 53 % were heterozygous (6/7) and 14 % were homozygous (7/7). Comparison of the groups revealed that the prevalence of UGTA1A polymorphism tended to be greater among jaundiced newborns (p 0.09). CONCLUSION: The results of this study suggest that there is a relationship between neonatal jaundice and Gilbert's syndrome among the Spanish population. These results, together with those of other authors, suggest that genetic screening for Gilbert's syndrome should be included in the investigation of neonatal jaundice in our population. Further studies with a greater number of subjects would determine the exact relationship between marked neonatal jaundice and IGTA1A polymorphism. Key words:

Interés del estudio de las variantes genéticas del promotor del gen en la ictericia neonatal / Interest in the study of genetic variants of the promoter region of the ugt1a1 gene in neonatal jaundice

Antecedentes: Recientemente se ha mostrado la asociación entre un polimorfismo en el promotor del gen UGT1A1 (asociado con el síndrome de Gilbert) y la presencia de ictericia. Este polimorfismo consiste en la existencia de siete repeticiones TA (TA)7, en lugar de seis (TA)6. Objetivo: Analizar la distribución del genotipo (TA)7 en una población de recién nacidos para determinar la posible relación entre el síndrome de Gilbert y la ictericia neonatal. Métodos: Se estudiaron 136 recién nacidos: 21 presentaron ictericia del resto de recién nacidos, 69 eran sanos y el resto mostró diferentes procesos, incluyendo 7 prematuros. El ADN de cada paciente fue utilizado para amplificar, mediante la reacción en cadena de la polimerasa, la región del promotor del gen de la UGT-1 que flanquea la caja TATA donde se encuentra el polimorfismo. Resultados: Grupo sin ictericia: 53% normales (genotipo 6/6); 40 % genotipo 6/7, y 7%, 7/7. Grupo con ictericia: 33% normales, 53% heterozigotos (6/7) y 14% homozigotos (7/7). Al comparar entre los grupos, los recién nacidos con ictericia tenían una tendencia a tener una mayor prevalencia del polimorfismo para el gen de la UGT-1 (p = 0,09). Conclusión: Este estudio sugiere una relación en la población española entre la ictericia neonatal y el síndrome de Gilbert. Estos datos y otros similares obtenidos por varios autores indican la idoneidad de incluir el escrutinio molecular para el síndrome de Gilbert en el protocolo diagnóstico de la ictericia neonatal. Evidentemente, estudios más amplios permitirán definir cuál es el grado exacto de relación entre la presencia de una ictericia neonatal marcada y la presencia de este polimorfismo (AU)

Characterisation of SMN hybrid genes in Spanish SMA patients: de novo, homozygous and compound heterozygous cases.

Autosomal recessive spinal muscular atrophy (SMA) is classified, by age of onset and maximal motor milestones achieved, into type I (severe form), type II (intermediate form) and type III (mild/moderate form). SMA is caused by mutations in the survival motor neuron telomeric gene (SMN1) and a centromeric functional copy of this gene (SMN2) exists, both genes being located at 5q13. Homozygous deletion of exons 7 and 8 of SMN1 has been detected in approx 85% of Spanish SMA patients regardless of their phenotype. Nineteen cases with the sole deletion of exon 7 but not exon 8 (2 cases of type I, 13 cases of type II, four cases of type III) were further analysed for the presence of SMN2-SMN1 hybrid genes. We detected four different hybrid structures. Most of the patients were carriers of a hybrid structure: centromeric intron 6- centromeric exon 7- telomeric exon 8 (CCT), with or without neuronal apoptosis-inhibitor protein (NAIP). In two patients, a different hybrid structure, viz. telomeric intron 6- centromeric exon 7- telomeric exon 8 (TCT), was detected with or without NAIP. A phenotype-genotype correlation comparing the different structures of the hybrid alleles was delineated. Type I cases in our series are attributable to intrachromosomal deletion with a smaller number of SMN2 copies. Most cases with hybrid genes are type II occurring by a combination of a classical deletion in one chromosome and a hybrid gene in the other. Type III cases are closely associated with homozygozity or compound heterozygozity for hybrid genes resulting from two conversion events and have more copies of hybrid genes and SMN2 than type I or II cases.

The S65C mutation in Spain. Implications for iron overload screening.

Hereditary hemochromatosis is related to mutations of the HFE gene. The role of the S65C mutation of this gene was evaluated in a Spanish population, consisting of 100 controls and 41 patients who had resulted positive to screening for iron overload. Only one patient was heterozygous for the S65C mutation, so the S65C mutation is infrequent in our area. Nevertheless, it is advisable to search for this mutation in cases with iron overload and heterozygosity for the C282Y or H63D mutations of the HFE gene.

Serum erythropoietin in the diagnosis of polycythemia vera. A follow-up study.

BACKGROUND AND OBJECTIVE: It has been suggested that the determination of serum erythropoietin (sEpo) may be useful in distinguishing between polycythemia vera (PV), relative polycythemia and secondary polycythemia (SP), but no conclusive evidence has yet been provided for this. In the present work, we evaluated the role of sEpo in the differential diagnosis of polycythemia vera and its usefulness in the follow-up of PV patients. METHODS: sEpo was assessed in 190 patients with polycythemia of different etiologies. A follow-up study was carried out in some of these patients (27 with secondary polycythemia and 17 with polycythemia vera). RESULTS: sEpo levels were higher in SP than in PV and relative polycythemia. There were, however, differences with regard to the various etiologies of SP. Polycythemia related to congenital heart disorders showed the highest levels of sEpo of the SP. When a study was conducted, sEpo alone as a diagnostic parameter displayed an efficiency of more than 90% and the most discriminating value was 5 U/L. Using lower levels (below 2 U/L) and higher levels (above 12 U/L), it was possible to distinguish between SP and PV, although an important overlap was detected between these limits (approximately 50% of cases). The follow-up study showed that in half the patients with SP the levels of sEpo were at times < 12 U/L and at other times greater than this value. At least three determinations were necessary to detect an elevated reading. In PV after venesection there was an increase in sEpo in some cases, although most of the time there was no change. INTERPRETATION AND CONCLUSIONS: Using sEpo, it was possible to differentiate between PV and SP, despite an important overlap. A follow-up study demonstrated that the increase in sEpo was intermittent in SP and that in many of these cases more than one determination could be helpful.

The deoxyuridine suppression test in HIV-1 positive patients: the role of azydothymidine (AZT).

The deoxyuridine suppression test (dUST) was used to evaluate human immunodeficiency virus type 1 positive (HIV-1) patients with low serum levels of vitamin B12 and/or low red cell folate and to assess any possible interferences of azydothymidine (AZT) in this test. The dUST was studied in 29 HIV-1 positive patients, 18 without low serum vitamin B12 or low red cell folate and 11 with low serum vitamin B12 (6 patients), low red cell folate (4 patients) and 1 case with both. The role of AZT was studied using different concentrations (0.2, 2.5 and 10 microM/ml) in 2 groups: 1 group of 5 patients with vitamin B12 and/or folate deficiency and another group consisting of 13 healthy subjects. Methotrexate (MTX)(50 micrograms/ml) was added to induce a folate megaloblastic pattern in the latter group. Results of the dUST in the HIV-1 group without low levels of serum vitamin B12 fell within the health-related reference interval values. A vitamin B12 deficiency was only detected in 1 case in the HIV-1 group with low serum vitamin B12, although a folate deficiency pattern was observed in the 4 patients with low red cell folate. In the healthy subjects AZT induced a dose-dependent decrease of the MTX-induced folate megaloblastic pattern. The pattern was also observed in the group of patients with vitamin B12 or folate deficiency, although AZT did not entirely interfere with the dUST. The effect of AZT on the dUST was attributed to a decrease in the incorporation of the isotope in the absence of deoxyuridine. The dUST is useful in differentiating vitamin B12 deficient patients from HIV-1 infected patients with low levels of serum vitamin B12.

Evaluation of erythropoietin in endurance runners.

To evaluate the role of erythropoietin (Epo) in the erythroid abnormalities often found in athletes, Epo was evaluated by radioimmunoassay in endurance runners (ER). In a first study, 46 experienced ER, 11 with iron deficiency (ID group), were studied during a training period. In ID and non-ID runners, serum Epo (SEpo) levels were similar to sedentary controls (ID = 19.1 +/- 4.9 U/L, non-ID = 19.7 +/- 5.5 U/L and controls 19.7 +/- 9.2 U/L). In a second study, serum and urine erythropoietin (UEpo) levels were evaluated in 17 ER during a 6-hour race. Samples were taken before the race (pre-race), immediately following (6-hour) and 4 days after (post-race). No differences were observed in SEpo levels (pre-race = 19.8 +/- 4.1 U/L, 6-hour = 21.2 +/- 4.9 U/L and post-race = 21 +/- 4 U/L), but UEpo increased following the race (pre-race = 15.4 +/- 9.6 U/L, 6-hour = 26.1 +/- 6.2 U/L and post-race = 14.1 +/- 6.5 U/L) (p < 0.0001) and this UEpo increase was related to urine creatinine changes (rs = 0.79, p < 0.00001). In conclusion, SEpo in ER does not differ from sedentary values and does not vary with competition; however, UEpo increases during a long-distance race. These data may be important for a correct evaluation of Epo abusers and sports anemia.