Interstitial 6q microdeletion syndrome and epilepsy: A new patient and review of the literature

Rare genetic forms of obesity in childhood and adolescence, a comprehensive review of their molecular mechanisms and diagnostic approach

Obesity represents a major health problem in the pediatric population with an increasing prevalence worldwide, associated with cardiovascular and metabolic disorders, and due to both genetic and environmental factors. Rare forms of obesity are mostly monogenic, and less frequently due to polygenic influence. Polygenic form of obesity is usually the common obesity with single gene variations exerting smaller impact on weight and is commonly non-syndromic.Non-syndromic monogenic obesity is associated with variants in single genes typically related to the hypothalamic leptin-melanocortin signalling pathway, which plays a key role in hunger and satiety regulation, thus body weight control. Patients with these genetic defects usually present with hyperphagia and early-onset severe obesity. Significant progress in genetic diagnostic testing has recently made for early identification of patients with genetic obesity, which guarantees prompt intervention in terms of therapeutic management of the disease. What is Known: • Obesity represents a major health problem among children and adolescents, with an increasing prevalence worldwide, associated with cardiovascular disease and metabolic abnormalities, and it can be due to both genetic and environmental factors. • Non-syndromic monogenic obesity is linked to modifications in single genes usually involved in the hypothalamic leptin-melanocortin signalling pathway, which plays a key role in hunger and satiety regulation. What is New: • The increasing understanding of rare forms of monogenic obesity has provided significant insights into the genetic causes of pediatric obesity, and our current knowledge of the various genes associated with childhood obesity is rapidly expanding. • A useful diagnostic algorithm for early identification of genetic obesity has been proposed, which can ensure a prompt intervention in terms of therapeutic management of the disease and an early prevention of the development of associated metabolic conditions.

Interstitial 6q deletion in a patient presenting with drug-resistant epilepsy and Prader-Willi like phenotype: An electroclinical description with literature review

PURPOSE

Interstitial 6q deletions are associated with rare genetic syndromes characterized by different signs, including developmental delay, dysmorphisms, and Prader-Willi (PWS)-like features. Drug-resistant epilepsy, a relatively rare finding in this condition, is often a challenge in terms of therapeutic approach. Our aim is to present a new case of interstitial 6q deletion and to conduct a systematic review of the literature with an emphasis on the neurophysiological and clinical traits of afflicted individuals.

METHODS

We report a patient with an interstitial 6q deletion. Standard electroencephalograms (EEG), video-EEG with polygraphy and MRI features are discussed. We also conducted a literature review of previously described cases.

RESULTS

We describe a relatively small interstitial 6q deletion (2 Mb circa), detected by CGH-Array, not encompassing the previously described 6q22 critical region for epilepsy occurrence. The patient, a 12-year-old girl, presented with multiple absence-like episodes and startle-induced epileptic spasms since the age of 11, with partial polytherapy control. Treatment with lamotrigine induced the resolution of startle-induced phenomena. From the literature review, we identified 28 patients with overlapping deletions, often larger than our patient's mutation. Seventeen patients presented with PWS-like features. Epilepsy was reported in 4 patients, and 8 patients presented abnormal EEG findings. In our patient, the deletion included genes MCHR2, SIM1, ASCC3, and GRIK2, but, interestingly, it did not encompass the 6q22 critical region for epilepsy occurrence. The involvement of GRIK2 in the deletion may play a role.

CONCLUSION

Literature data are limited, and specific EEG or epileptological phenotypes cannot yet be identified. Epilepsy, although uncommon in the syndrome, deserves a specific diagnostic workup. We speculate on the existence of an additional locus in the 6q16.1-q21 region, different from the already hypothesized q22, promoting the development of epilepsy in affected patients.

Interstitial deletions in the proximal regions of 6q: 12 original cases and a literature review

Interstitial microdeletions in the proximal region of the long arm of chromosome 6 are rare. Herein we have reported 12 patients with developmental delays associated with interstitial microdeletions in 6q ranging from q12 to q22. The microdeletions were detected by chromosomal microarray testing. To confirm the clinical significance of these deletions, genotype-phenotype correlation analysis was performed using genetic and predicted loss-of-function data. SIM1 was recognized as the gene responsible for developmental delay, particularly in Prader-Willi syndrome-like phenotypes. Other genes possibly related to developmental delay were ZNF292, PHIP, KCNQ5, and NUS1. To further establish the correlation between the genotype and phenotype, more patient information is required.

The Spectrum of the Prader-Willi-like Pheno- and Genotype: A Review of the Literature

Prader-Willi syndrome (PWS) is a rare genetic syndrome, caused by the loss of expression of the paternal chromosome 15q11-q13 region. Over the past years, many cases of patients with characteristics similar to PWS, but without a typical genetic aberration of the 15q11-q13 region, have been described. These patients are often labelled as Prader-Willi-like (PWL). PWL is an as-yet poorly defined syndrome, potentially affecting a significant number of children and adults. In the current clinical practice, patients labelled as PWL are mostly left without treatment options. Considering the similarities with PWS, children with PWL might benefit from the same care and treatment as children with PWS. This review gives more insight into the pheno- and genotype of PWL and includes 86 papers, containing 368 cases of patients with a PWL phenotype. We describe mutations and aberrations for consideration when suspicion of PWS remains after negative testing. The most common genetic diagnoses were Temple syndrome (formerly known as maternal uniparental disomy 14), Schaaf-Yang syndrome (truncating mutation in the MAGEL2 gene), 1p36 deletion, 2p deletion, 6q deletion, 6q duplication, 15q deletion, 15q duplication, 19p deletion, fragile X syndrome, and Xq duplication. We found that the most prevalent symptoms in the entire group were developmental delay/intellectual disability (76%), speech problems (64%), overweight/obesity (57%), hypotonia (56%), and psychobehavioral problems (53%). In addition, we propose a diagnostic approach to patients with a PWL phenotype for (pediatric) endocrinologists. PWL comprises a complex and diverse group of patients, which calls for multidisciplinary care with an individualized approach.

Síndrome de deleção 6q

Objetivos: Síndrome da deleção 6q é considerada uma anomalia cromossômica rara. Assim, nosso objetivo foi relatar um caso de um menino com essa síndrome, em Manaus/Amazonas.Descrição do caso: Menino com quatro anos de idade que apresenta atraso do crescimento e do desenvolvimento neuropsicomotor, dificuldades de ganho de peso e anormalidades na retina. A análise citogenética do paciente revelou cariótipo com 46, XY, del(6)(q25-qter).Conclusões: Este relato demonstrou a importância das análises citogenéticas para o diagnóstico preciso das anomalias congênitas, pois auxiliam no encaminhamento de tratamentos adequados aos pacientes e na ampliação de conhecimento científico relacionado a essa deleção.

A Chinese multicenter retrospective study of isolated increased nuchal translucency associated chromosome anomaly and prenatal diagnostic suggestions

Extensive researches involving fetuses with multiple ultrasound anomalies have been conducted over the years, but only few were focused on the isolated increased nuchal translucency (NT). On top of that, these limited number of researches were all designed as single-arm studies and the control group was missing. In this study, we conducted a multicenter, retrospective study using amniotic fluid samples collected from 1197 pregnant women having fetuses with isolated increased NT (INT group) or normal NT values (NNT group). Copy number variation sequencing (CNV-seq) was performed to determine their chromosome status and pathogenic variations were validated using SNP array. Overall, 59 chromosome aneuploidies, 34 pathogenic CNVs and 23 copy number variants of unknown significance (VOUS CNVs) were discovered. the INT group had a significantly higher proportion of aneuploidy (19.44%) and pathogenic CNV (8.33%) than the control group (3.49% and 2.30% respectively), and 88.89% of the pathogenic CNVs were related to heart defects. Additionally, more male fetuses were presented in the INT group (68.51%), but they did not have a higher risk (Relative Risk = 1.03) of carrying pathogenic chromosome variations than female fetuses. Our results demonstrated that fetuses with isolated increased NT had a distinct pattern of chromosome abnormality and majority of detected pathogenic CNVs could be linked to the congenital heart disease. Furthermore, because a considerable proportion of pathogenic CNVs were detected, we strongly recommend to perform a joint test of karyotyping and CNV analysis in prenatal diagnosis for fetuses with isolated increased NT in order to decrease the incident of missed diagnosis.

Clinical, molecular genetics and therapeutic aspects of syndromic obesity

Obesity has become a major health problem worldwide. To date, more than 25 different syndromic forms of obesity are known in which one (monogenic) or multiple (polygenic) genes are involved. This review gives an overview of these forms and focuses more in detail on 6 syndromes: Prader Willi Syndrome and Prader Willi like phenotype, Bardet Biedl Syndrome, Alström Syndrome, Wilms tumor, Aniridia, Genitourinary malformations and mental Retardation syndrome and 16p11.2 (micro)deletions. Years of research provided plenty of information on the molecular genetics of these disorders and the obesity phenotype leading to a more individualized treatment of the symptoms, however, many questions still remain unanswered. As these obesity syndromes have different signs and symptoms in common, it makes it difficult to accurately diagnose patients which may result in inappropriate treatment of the disease. Therefore, the big challenge for clinicians and scientists is to more clearly differentiate all syndromic forms of obesity to provide conclusive genetic explanations and eventually deliver accurate genetic counseling and treatment. In addition, further delineation of the (functions of the) underlying genes with the use of array- or next-generation sequencing-based technology will be helpful to unravel the mechanisms of energy metabolism in the general population.

DNA sequencing and copy number variation analysis of MCHR2 in a cohort of Prader Willi like (PWL) patients

BACKGROUND

Prader Willi Syndrome (PWS) is a syndromic form of obesity caused by a chromosomal aberration on chromosome 15q11.2-q13. Patients with a comparable phenotype to PWS not carrying the 15q11.2-q13 defect are classified as Prader Willi like (PWL). In literature, PWL patients do frequently harbor deletions at 6q16, which led to the identification of the single-minded 1 (SIM1) gene as a possible cause for the presence of obesity in these patients. However, our previous work in a PWL cohort showed a rather limited involvement of SIM1 in the obesity phenotype. In this paper, we investigated the causal role of the melanin-concentrating hormone receptor 2 (MCHR2) gene in PWL patients, as most of the reported 6q16 deletions also encompass this gene and it is suggested to be active in the control of feeding behavior and energy metabolism.

METHODS

Copy number variation analysis of the MCHR2 genomic region followed by mutation analysis of MCHR2 was performed in a PWL cohort.

RESULTS

Genome-wide microarray analysis of 109 patients with PWL did not show any gene harboring deletions on chromosome 6q16. Mutation analysis in 92 patients with PWL demonstrated three MCHR2 variants: p.T47A (c.139A>G), p.A76A (c.228T>C) and c.*16A>G. We identified a significantly higher prevalence of the c.228T>C C allele in our PWL cohort compared to previously published results and controls of the ExAC Database.

CONCLUSION

Overall, our results are in line with some previously performed studies suggesting that MCHR2 is not a major contributor to human obesity and the PWL phenotype.

Rare presentation of 6q16.3 microdeletion syndrome with severe upper limb reduction defects and duodenal atresia

We present a patient with a 17.31 MB interstitial deletion of 6q16.3‐6q22.31, who demonstrates a unique constellation of 6q‐ features. Among 6q‐ patients, he has limb reduction among the most severe reported, he is the second patient with duodenal atresia, and is the first documented case of diaphragmatic eventration.

Insights into 6q21-q22: Refinement of the critical region for acro-cardio-facial syndrome

Deletions on chromosome 6q are rarely reported in the literature, and genotype-phenotype correlations are poorly understood. We report a child with a deletion of the 6q21-q22 chromosomal region, providing some intriguing results about the correlation between this region and acro-cardio-facial syndrome, congenital heart disease, split hand and foot malformation, and epilepsy.

Copy number variation (CNV) analysis and mutation analysis of the 6q14.1-6q16.3 genes SIM1 and MRAP2 in Prader Willi like patients

BACKGROUND

Prader-Willi syndrome (PWS), caused by a paternal defect on 15q11.2-q13, is the most common form of syndromic obesity. However, patients clinically diagnosed with PWS do not always show this defect on chromosome 15q and are therefore molecularly categorized as Prader Willi like (PWL). Deletions at 6q14.1-q16.3 encompassing MRAP2 and SIM1 were reported in some individuals with a PWL phenotype. In addition, a few mutations in SIM1 and MRAP2 were also previously identified in cohorts of obese individuals. Therefore, we decided to perform copy number variation analysis of the 6q14.1-6q16.3 region followed by mutation analysis of SIM1 and MRAP2 in a PWL cohort.

METHODS

A genome-wide microarray analysis was performed in a group of 109 PWL patients. Next, we screened 94 PWL patients for mutations in SIM1 and MRAP2 using high-resolution melting curve analysis and Sanger sequencing. Additionally, 363 obese children and adolescents were screened for mutations in MRAP2.

RESULTS

No gene harboring deletions were identified at the 6q14.1-q16.3 region in the 109 PWL patients. SIM1 mutation analysis resulted in the identification of one very rare nonsynonymous variant p.P352S (rs3734354). Another rare nonsynonymous variant, p.A40S, was detected in the MRAP2 gene. No variants were identified in the 363 obese individuals.

CONCLUSIONS

In contrast to literature reports, no gene harboring deletions were identified in the SIM1 and MRAP2 regions in our PWL cohort. Secondly, taking into account their very low minor allele frequencies in public sequencing databases and the results of in silico prediction programs, further functional analysis of p.P352S found in SIM1 and p.A40S found in MRAP2 is useful. This would provide further support for a possible role of SIM1 and MRAP2 in the pathogenesis of the PWL phenotype albeit in a limited number of patients.

A de novo 0.63 Mb 6q25.1 deletion associated with growth failure, congenital heart defect, underdeveloped cerebellar vermis, abnormal cutaneous elasticity and joint laxity

Deletions of the long arm of chromosome 6 are rare and are characterized by great clinical variability according to the deletion breakpoint. We report a on 6-year-old girl with a de novo 0.63 Mb deletion on chromosome 6q25.1 who demonstrated multiple congenital anomalies including a ventricular septal defect and an underdeveloped cerebellar vermis. She presented with severe pre- and post-natal growth failure, hyperextensible small joints (Beighton scores = 8/9; with normal parental scores), and an abnormally elastic, redundant skin. Abnormally high upper/lower segment ratio (i.e., 1.34 = > 3SD), mild dysmorphic facial features and developmental delay were also present. The girl's phenotype was compared with: (i) two girls, each previously reported by Bisgaard et al. and Caselli et al. with similar albeit larger (2.6-7.21 Mb) deletions; (ii) seven additional individuals (6 M; 1 F) harboring deletions within the 6q25.1 region reported in the literature; and (iii) ten further patients (5 M; 4 F; 1 unrecorded sex) recorded in the DECIPHER 6.0 database. We reported on the present girl as her findings could contribute to advance the phenotype of 6q deletions. In addition, the present deletion is the smallest so far recorded in the 6q25 region encompassing eight known genes [vs. 41 of Bisgaard et al., and 23 of Caselli et al.,], including the TAB2 (likely responsible for the girl's congenital heart defect), LATS1 gene, and the UST gene (a regulator of the homeostasis of proteoglycans, which could have played a role in the abnormal dermal and cartilage elasticity).