Challenges in genetic diagnosis, co-occurrence of 22q11.2 deletion syndrome and Noonan syndrome.

Noonan syndrome (NS) is caused by pathogenic variants in genes involved in the RAS/MAPK pathway. On the other hand, 22q11.2 Deletion Syndrome (22q11.2DS) is caused by heterozygous microdeletion on chromosome 22q11.2. The clinical characteristics of both syndromes are expected to be relatively distinct, and, in fact, there is only one report of these syndromes occurring together, but on daily clinical practice and especially in early childhood phenotypes may overlap. In this study, we describe a patient with NS and 22q11.2DS features harboring a heterozygous 2.54 Mb deletion of chromosome 22q11.2 and a variant in LZTR1, c.1531G > A p.(Val511Met). In 1993, Wilson et al reported a patient with both 22q11.2DS and NS, proposing that probably more than one gene is deleted in the proband and that one of the deleted genes is responsible for Noonan's phenotype. In our patient, one of the deleted genes within the 22q11.2 region was the LZTR1 gene which was associated with NS in 2015. This case also highlights the importance of the long-term patients' follow-up to detect evolutionary changes that may appear in the phenotype and alerts clinicians of the co-occurrence of two syndromes that may manifest over time.

Noonan syndrome with loose anagen hair with variants in the PPP1CB gene: First familial case reported.

Rasopathies are a group of phenotypically overlapping conditions that include Noonan, Noonan with multiple lentigines, Noonan with loose anagen hair, Costello, Cardio-facio-cutaneous, and Neurofibromatosis-Noonan syndromes. Noonan syndrome with loose anagen hair (NS-LAH) is clinically characterized by prominent forehead, macrocephaly, growth hormone deficiency, sparse, loose and slow-growing anagen hair, hyperpigmented skin with eczema or ichthyosis, mild psychomotor delays, hypernasal voices, and attention deficit hyperactivity disorder. Variants in SHOC2 are responsible for the majority of the cases. Gripp et al. identified four unrelated individuals with similar phenotype to NS-LAH with pathogenic variants in PPP1CB. In this study, we present one family and one patient with NS-LAH and variants in PPP1CB. The first patient belongs to a family with a likely pathogenic variant, c.545T>A (p.Met182Lys), the first family published so far with a variant in this gene. The second patient harbors a de novo pathogenic variant, c.146C>G (p.Pro49Arg). This study presents two additional patients with this rare syndrome in order to increase the clinical characterization of the syndrome and provide more evidence of the pathogenicity of the c.545T>A (p.Met182Lys) variant in PPP1CB, a gene recently associated with NS-LAH.

Providing more evidence on LZTR1 variants in Noonan syndrome patients.

Noonan syndrome (NS, OMIM 163950) is a common autosomal dominant RASopathy caused mainly by gain-of-function germline pathogenic variants in genes involved in the RAS/MAPK signaling pathway. LZTR1 gene has been associated with both dominant and recessive NS. Here, we present seven patients with NS and variants in the LZTR1 gene from seven unrelated families, 14 individuals in total. The detection rAte of LZTR1 variants in our NS cohort was 4% similar to RAF1 and KRAS genes, indicating that variants in this gene might be frequent among our population. Three different variants were detected, c.742G>A (p.Gly248Arg), c.360C>A (p.His120Gln), and c.2245T>C (p.Tyr749His). The pathogenic variant c.742G>A (p.Gly248Arg) was found in five/seven patients. In our cohort 50% of patients presented heart defects and neurodevelopment delay or learning disabilities, short stature was present in 21% of them and one patient had acute lymphoblastic leukemia. This study broadens the spectrum of variants in the LZTR1 gene and provides increased knowledge of the clinical phenotypes observed in Argentinean NS patients.

Influence of ß(2)-adrenergic receptor polymorphisms on asthma exacerbation in children with severe asthma regularly receiving salmeterol.

BACKGROUND: New evidence suggests that different ß(2)-adrenergic receptor (ß2AR) polymorphisms may influence asthma control in patients receiving long-acting ß(2)agonists (LABAs) as regular therapy. OBJECTIVES: To determine the influence of ß2AR polymorphisms on asthma exacerbations in children with severe asthma from Argentina receiving inhaled corticosteroid (ICS) and LABAs regularly. METHODS: Ninety-seven children with severe asthma were genotyped for polymorphisms of ß2AR at codons 16 and 27. The number of severe exacerbations, the time of first asthma exacerbation, and the number of hospitalizations during 12 months were assessed. Changes on pulmonary function from the beginning to the end of the study were also evaluated. RESULTS: The number of overall asthma exacerbations and the proportion of children with these events were similar among ß2AR genotypes at position 16 (Arg/Arg, Arg/Gly, and Gly/Gly) and at position 27 (Gln/Gln, Gln/Glu, and Glu/Glu). The time to first asthma exacerbation was similar among individuals carrying different ß2AR polymorphisms. No ß2AR genotype association was found in relation to the number of hospitalizations. Longitudinal analysis of forced expiratory volume in 1 second from baseline to the end of the study also showed no differences among ß2AR genotypes at position 16 or 27. No association was observed among the 3 most common haplotypes (Arg/Arg-Gln/Gln, Gly/Gly-Gln/Gln, and Gly/Gly-Glu/Glu) and the number of participants with asthmatic crisis or with the overall number of exacerbations. CONCLUSION: ß2AR polymorphisms were not associated with an increased risk of having asthma exacerbations or lung function decline in a population of Argentinian children with severe asthma receiving ICS and LABAs regularly.

Molecular analysis of GALT gene in Argentinian population: Correlation with enzyme activity and characterization of a novel Duarte-like allele.

BACKGROUND: Classical galactosemia is an autosomal recessive inherited metabolic disorder caused by mutations in the galactose-1-phosphate uridyltransferase (GALT) gene. GALT enzyme deficiency leads to the accumulation of galactose-1-phosphate in various organs, causing hepatic, renal and cerebral impairment. Over 300 mutations have been reported in the GALT gene. The aim of this study was to describe molecular characterization of GALT gene in Argentinian patients with decreased GALT activity, and to correlate molecular results with enzyme activity. METHODS: 37 patients with enzyme activity below 6.3 µmol/h/g Hb (35% of normal value) were included. GALT activity was measured on red blood cells. DNA was extracted from peripheral blood. p.Gln188Arg mutation was studied by PCR-RFLP and, on samples negative or heterozygous, GALT gene was sequenced. In vivo splicing analysis of the GALT gene was performed on RNA extracted from leukocytes of one patient. RESULTS: 14 different sequence variations were identified among 72 unrelated alleles. The two most common disease-causing mutations were p.Gln188Arg (24/72) and p.Lys285Asn (9/72). Three novel mutations were detected. One of them, c.688G>A, caused partial skipping of exon 9 of the GALT gene. Enzyme activity correlated with GALT genotype in 36 of the 37 patients. CONCLUSION: This is the first report of sequence variations in the GALT gene in the Argentinian population. This study highlights the contribution of the molecular analysis to the diagnosis of Galactosemia and reveals c.688G>A as a novel Duarte-like variant, with a high prevalence in our population.

Population pharmacokinetics of amikacin in patients with pediatric cystic fibrosis.

INTRODUCTION: Amikacin is commonly used in patients with pediatric cystic fibrosis (CF) for the treatment of pulmonary exacerbations. Amikacin efficacy is related to maximum plasma concentration/minimum inhibitory concentration (Cmax/MIC) ratio >8. Pharmacokinetic data in patients with pediatric CF are scarce. The aim of this study was to develop a population pharmacokinetic (PopPK) model describing amikacin disposition in patients with pediatric CF. METHODS: CF patients under 18 years of age with pulmonary exacerbation who received amikacin were enrolled. Patients received different amikacin regimens (30 mg-1 kg-1 day-1 every 8, 12, or 24 hours) depending on the patient's status and hospital protocols. Amikacin serum levels were obtained for therapeutic drug monitoring. PopPK model was developed using MONOLIX Suite-2018R1 (Lixoft). RESULTS: A total of 39 patients (114 amikacin concentrations) were included in this study. Population estimates for the elimination rate constant (k) and the volume of distribution (V) were 0.541 hours-1 and 0.451 L/kg, respectively. Between-subject and between-occasion variability were 53% and 16.5% for k and 31% and 22% for V, respectively. Bodyweight was a significant covariate associated with V. Based on simulations, almost 70% of the patients receiving 30 mg-1 kg-1 day-1 every 24 hours would achieve a Cmax/MIC ratio >8 which is an appropriate therapeutic goal while no patient in the other two groups (Q8 and Q12) would achieve that objective. CONCLUSIONS: The regimen of 30 mg-1 kg-1 day-1 every 24 hours more adequately fulfilled the therapeutic target for amikacin. Although all our patients had good clinical results and a good adverse-events profile, further studies are necessary to redefine the optimal treatment strategy.

Controles de calidad externos en el diagnóstico molecular de enfermedades genéticas. Impacto sobre la calidad de los estudios genéticos / External quality controls in the molecular diagnosis of genetic diseases. Impact on the quality of the genetic studies / Controles de qualidade externos no diagnóstico molecular de doenças genéticas. Impacto na qualidade dos estudos genéticos

Resumen La participación en programas de evaluación externa de la calidad (PEEC) dirigidos al diagnóstico de enfermedades genéticas permite obtener una medida objetiva del desempeño técnico y analítico de los laboratorios y es un requisito para la acreditación de los laboratorios clínicos bajo la norma ISO 15189. El objetivo de este estudio fue evaluar retrospectivamente el desempeño en los esquemas EMQN (European Molecular Genetics Quality Network) y CF Network (Cystic Fibrosis European Network) en el período 2014-2022. Se participó en un total de 88 esquemas. Se recolectó la información de nuestros puntajes y las medias de los laboratorios participantes en las categorías genotipificación, interpretación y exactitud de la información del paciente/informe. Se informó en forma completa el 90,9% (n=80) de los esquemas. El desempeño en genotipificación mostró puntajes superiores a la media en el 89,3% de los esquemas; 0,8% de los informes correspondieron a falsos negativos. En interpretación, el 66,7% de los esquemas evidenció un desempeño superior a la media y el 33,3% debajo de la media. La exactitud de la información del paciente/informe presentó puntajes superiores a la media en el 97,6% de los esquemas. Se observó una diferencia estadísticamente significativa en el porcentaje de esquemas con puntaje por encima de la media en el año 2022 (10/12 esquemas) respecto al año 2014 (1/6 esquemas) en la categoría interpretación (p=0,0128). En conclusión, la participación regular en PEEC tuvo impacto positivo en la calidad de los estudios y permite realizar mejoras continuas a partir de las recomendaciones sugeridas por estos programas.

Abstract Participation in external quality assessment programmes focused on rare genetic diseases makes it possible to assess the laboratory technical and analytical performance and it is a prerequisite for accreditation according to ISO 15189. The objective of this study was to perform a retrospective evaluation of our performance in the EMQN (European Molecular Genetics Quality Network) and the CF Network (Cystic Fibrosis European Network) programmes in the 2014-2022 period. The laboratory performance on genotyping, interpretation and clerical accuracy and patient identifiers in a total of 88 schemes were assessed. The information of our scores and the mean scores of all participating laboratories in the three categories were collected. A total of 90.9% of the schemes were fully completed. The performance in genotyping showed scores above the mean scores in 89.3% of the schemes; 0.8% of the reports correspond to false negative results. Regarding interpretation category, 66.7% of the schemes presented scores above the mean scores and 33.3% below the mean scores. The clerical accuracy and patient identifiers were above the mean scores in 97.6% of the schemes. A statistically significant difference in the percentage of schemes with a score above the mean for the interpretation category in the year 2022 (10/12 schemes) was observed compared to the year 2014 (1/6 schemes) (p=0.0128). In conclusion, regular participation in external quality assessment programmes had a positive impact on the quality of the studies and allows for continuous improvements based on the recommendations suggested by these programmes.

Resumo A participação em programas de avaliação externa da qualidade (PEECs) voltados para o diagnóstico de doenças genéticas permite obter uma mensuração objetiva do desempenho técnico e analítico dos laboratórios e é requisito para a acreditação dos laboratórios clínicos sob a norma ISO 15189. O objetivo desse estudo foi avaliar retrospectivamente o desempenho nos esquemas EMQN (European Molecular Genetics Quality Network) e CF Network (Cystic Fibrosis European Network) no período 2014-2022. Participou-se em um total de 88 esquemas. Foram coletadas informações de nossos escores e das médias dos laboratórios participantes nas categorias genotipagem, interpretação e precisão da informação do paciente/laudo. 90,9% (n=80) dos esquemas foram informados em sua totalidade. O desempenho na genotipagem apresentou escores acima da média em 89,3% dos esquemas; 0,8% dos laudos corresponderam a falsos negativos. Na interpretação, 66,7% dos esquemas apresentaram desempenho acima da média e 33,3% abaixo da média. A precisão das informações do paciente/laudo apresentou escores acima da média em 97,6% dos esquemas. Observou-se diferença estatisticamente significativa no percentual de esquemas com pontuação acima da média no ano de 2022 (10/12 esquemas) em relação ao ano de 2014 (1/6 esquemas) na categoria interpretação (p=0,0128). Em conclusão, a participação regular em PEECs teve um impacto positivo na qualidade dos estudos e permite fazer melhorias contínuas com base nas recomendações sugeridas por esses programas.

Carrier frequency of the 35delG and A1555G deafness mutations in the Argentinean population. Impact on the newborn hearing screening.

OBJECTIVE: Hearing loss is a complex multifactorial disorder caused by genetic and environmental factors. The 35delG mutation in the GJB2 gene is the most prevalent mutation in Caucasian patients with genetic sensorineural deafness. The A1555G mutation in the mitochondrial 12S rRNA is the main genetic alteration associated with aminoglycoside-induced deafness. The aim of this study was to evaluate the prevalence of both mutations in general population of Argentina. METHODS: A total of 712 samples of unrelated healthy blood donors and 330 newborn dried blood spots were studied by PCR-RFLP. RESULTS: The 35delG mutation was detected in 11/ 712 unrelated blood donors. The carrier frequency found in this sample (1/65) proved to be lower than that found in Southern European countries, mainly Spain and Italy, from where Argentina originally received its major immigration waves. When the populations of Southern Europe were considered altogether, this difference reached statistical significance. The A1555G mutation was not found in any of the 1042 samples tested. CONCLUSIONS: Taking into account the 35delG carrier frequency found in this study, it could be estimated that 130-160 children with congenital deafness due to mutations in the connexin genes would be born per year in Argentina. In contrast, the mitochondrial mutation A1555G appears to be infrequent in general Argentinean population.

Genotype-phenotype correlation of SMN locus genes in spinal muscular atrophy children from Argentina.

BACKGROUND/PURPOSE: Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder, considered one of the leading causes of infant mortality. It is caused by mutations in the SMN1 gene. A highly homologous copy of this gene named SMN2 and other neighbouring genes, SERF1A and NAIP, are considered phenotypic modifiers of the disease. In recent years, notable advances have been made in SMA research regarding evaluation, prognosis, and therapeutic options. Thus, genotype-phenotype studies in SMA are important to stratify patients for motor function tests and for envisaged clinical trials. The aim of this study was to provide clinical and molecular data of a series of Argentinean children with SMA to establish a comprehensive genotype-phenotype correlation. METHODS: 144 Argentinean children with SMA (56 children with type I, 58 with type II, and 30 with type III) were evaluated. The copy number of SMN2, SERF1A, and NAIP genes was established using MLPA (Multiplex Ligation-dependent Probe Amplification) and then correlated with the patients clinical subtypes. To improve clinical characterization we considered the initial symptoms that prompted the consultation, age of acquisition of motor abilities to independent walking and age at loss of gait. We also evaluated clinical and molecular features of sibling pairs in seven families. RESULTS: A strong correlation was observed between the SMN2 copy number and SMA phenotype while SERF1A and NAIP copy number showed a moderate correlation. We observed intra- and inter-family differences among the SMA types. CONCLUSION: This first genotype-phenotype correlation study in Argentinean SMA children provides data to improve patient stratification and define more adequate follow-up parameters.

Mannose-binding lectin gene as a modifier of the cystic fibrosis phenotype in Argentinean pediatric patients.

BACKGROUND: There is a considerable variation in the phenotype and course of the disease in cystic fibrosis (CF) even in patients with the same CFTR genotype, suggesting that other factors are important for prognosis. Mannose-binding lectin (MBL) has been proposed as one of these factors. We therefore investigated the influence of MBL2 gene variants on disease severity, age at acquisition of Pseudomonas aeruginosa, and survival in CF patients. METHODS: MBL2 variants were studied in 106 Argentinean pediatric CF patients carrying two severe CFTR mutations. Clinical phenotype was defined according to the Shwachman score and lung function tests. Age at infection with P. aeruginosa and age at death were also recorded. RESULTS: MBL insufficiency was associated with a 3.5-fold risk of having a severe phenotype (CI 95%: 1.2-10.3, p=0.03). It was also associated with an earlier onset of infection with P. aeruginosa (p=0.035). No statistically significant differences were found in FEV1 and survival. CONCLUSIONS: MBL insufficiency was associated with detrimental progression of the disease. These results together with previous findings suggest that the effect of MBL2 expression may be a major determinant of the severity of the clinical phenotype in patients with CF.

Prevalence of DFNB1 mutations in Argentinean children with non-syndromic deafness. Report of a novel mutation in GJB2.

OBJECTIVE: Mutations in DFNB1 locus, containing GJB2 (connexin 26) and GJB6 (connexin 30) genes, are the most common cause of autosomal recessive non-syndromic hearing loss. More than 100 mutations in GJB2 have been reported worldwide. Two deletions in GJB6, del(GJB6-D13S1830) and del(GJB6-D13S1854), have been found to be frequent in the Spanish population. The aim of this study was to determine the prevalence of GJB2 mutations and both GJB6 deletions in Argentinean children with non-syndromic deafness. METHODS: This study included 94 unrelated children with moderate to profound non-syndromic sensorineural hearing impairment. Molecular analysis was performed using a tiered approach. All DNA samples were screened for c.35delG mutation by PCR/RFLP. Samples from patients who were not homozygous for c.35delG were analysed for the presence of GJB6 deletions by PCR multiplex. The samples that remained unresolved after screening were further analysed by direct sequencing of GJB2 coding region. Finally, the splice site mutation IVS1+1G-->A was analysed by PCR/RFLP. RESULTS: Sequence variations in the GJB2 and GJB6 genes were found in 49 of the 94 unrelated patients. The most prevalent GJB2 mutation, c.35delG, was found in 40 of the 68 pathogenic alleles with the second most common allele being p.R143W (4/68). Fourteen sequence variations other than c.35delG were identified. Seven already described mutations were present in more than one allele; among them, IVS1+1G-->A, the rare splice site mutation flanking exon 1. In addition to known disease-related alterations, a novel GJB2 mutation, c.262G>C (p.A88P), was also identified. Six alleles were identified carrying GJB6 deletions; the most prevalent was del(GJB6-D13S1830). The frequency of the latter was found to be as high as that found in Spain from where Argentina has received one of its major immigration waves. CONCLUSIONS: The overall frequency of GJB2/GJB6 mutations in the present sample is in agreement with other Caucasian populations. As expected, c.35delG was the most prevalent mutation. The deletion del(GJB6-D13S1830) was the second most common mutation. These findings reinforce the importance of the study of GJB2/GJB6 genes in diagnosis to provide early treatment and genetic counselling.

Beta 2-adrenergic polymorphisms and total serum IgE levels in children with asthma from Argentina.

BACKGROUND: Beta 2-Adrenergic receptor polymorphisms occurring at amino acid positions 16 (arginine/glycine) and 27 (glutamine/glutamic acid) are known to be functionally relevant. Associations with several asthma-related phenotypes, such as total serum IgE, have been investigated with different results. OBJECTIVE: To determine the contribution of polymorphisms and haplotypes of beta 2-adrenergic receptor with serum IgE levels in children from Argentina with mild, moderate, and severe asthma. METHODS: Beta 2-Adrenergic receptor polymorphisms were analyzed in 124 white asthmatic children using polymerase chain reaction during a 3-year period (January 1, 2005, through December 31, 2007). Total serum IgE level was measured by standard methods in all study participants, and age-adjusted values were determined for each individual. RESULTS: Serum levels of IgE were 4.3-fold higher than age-adjusted normal values in the study population. No association was found in regard to asthma severity. A significant difference of IgE serum levels was observed among polymorphisms at position 16, with the highest IgE level in the arginine/arginine group (P = .04). At position 27, even though median levels of IgE in homozygous glutamine were 2.2 times higher than homozygous glutamic acid, this increase did not reach statistical significance. When the population was stratified according to the most common homozygous haplotypes (arginine-arginine 16/glutamine-glutamine 27, glycine-glycine 16/glutamine-glutamine 27, and glycine-glycine 16/glutamic acid-glutamic acid 27), no association was found in relation to the serum levels of IgE. CONCLUSIONS: Beta 2-Adrenergic receptor polymorphisms, especially homozygous arginine 16, were associated with higher serum IgE levels in children with asthma. These genetic variants appear to contribute to the IgE level in asthmatic children from Argentina.

Influence of beta2-adrenoceptor polymorphisms on the response to chronic use of albuterol in asthmatic children.

BACKGROUND: Several studies have suggested that after regular use of short acting beta2-agonists the bronchodilator effect of the drug may decline and this condition would be related to polymorphisms of the beta2-adrenergic receptor (beta2-AR). OBJECTIVE: To assess the frequency of beta2-AR polymorphisms in asthmatic children from Argentina, and to evaluate their influence on bronchodilator desensitization to albuterol over a 4-week treatment. METHODS: beta2-AR genotypes were determined in 117 children with asthma and 101 of them were under 4 weeks treatment with albuterol. Spirometric changes in FEV(1) were recorded at the beginning (day 1) and at the end of the study (day 30) and compared to genotypes at position 16 and 27 of the receptor. The frequency of the polymorphisms was calculated in all population. RESULTS: The presence of glutamine at position 27 (Gln27) was significantly more frequent in this Argentinean study population than in other Caucasian populations. The homozygosity for Gln27 polymorphism was associated to a desensitization of the receptor with a decline in the bronchodilator response to albuterol after chronic use. CONCLUSION: Gln27 polymorphism might be a marker for adverse clinical outcomes with chronic beta2-agonist exposure in children with asthma from Argentina.

High specificity of head circumference to recognize N540K mutation in hypochondroplasia.

Hypochondroplasia (HCH) is a skeletal dysplasia characterized by short stature with disproportionately short arms and legs. Anthopometrics and skeletal features are very similar to achondroplasia but milder. Seventy per cent of affected individuals are heterozygous for a mutation of the FGFR3 gene. Differences in some anthropometric measurements in affected patients with and without N540K mutation were analysed. Diagnosis of the disease was made on the presence of previously standardized criteria: short stature, short limbs and three or more X-ray features. Genomic DNA was extracted from peripheral blood leukocytes by standard procedures. PCR amplification of exons 10, 13 and 15 of FGFR3 was performed. Twenty-six patients were studied (median age was 7.31, range 0.27-20.0 years). Sitting height, body proportions and head circumference (HC) were statistically different in the mutated group. Receiver Operating Characteristic (ROC) analysis was carried out in order to estimate the discriminating power of different cut-off points of HC for recognizing patients with and without the mutation. A figure of 1.86 SD for HC was found to have a sensitivity of 73.3% and specificity of 100% for detecting HCH patients with the mutation. All of them had a HC greater than 1.86?SD. These results contribute to a better characterization of the clinical-molecular relationships in HCH.