From contemplation to classification of chromosomal mosaicism in human preimplantation embryos.

Chromosomal mosaicism is a hallmark of early human embryo development. The last decade yielded an enormous amount of information about diversity and prevalence of mosaicism in preimplantation embryos due to progress in preimplantation genetic testing of aneuploidies (PGT-A) based exclusively on molecular karyotyping of trophectoderm biopsy. However, the inner cell mass karyotype is still missing for mosaic embryos affecting the success rate of assisted reproductive medicine. Here, a classification model of chromosomal mosaicism is proposed based on the analysis of the primary zygote karyotype, the timing and types of primary and secondary chromosome segregation errors, and the distribution of mosaic cell clones between different embryonic and extraembryonic compartments of the blastocyst. Five basic principles for mosaicism analysis are introduced, namely, the estimation of the primary zygote karyotype, the investigation of additional sample point, the requirement of the second time point analysis, the delineating of reciprocity of chromosome segregation, and comprehensive chromosome screening at the single-cell level. The suggested model allows the prediction of the inner cell mass karyotype of the blastocyst and its developmental potential based on information from trophectoderm biopsy and non-invasive PGT-A using blastocoele fluid sample or spent culture medium as additional sample and time points for analysis and considering the reciprocity as a basic process in chromosome segregation errors between daughter cells in postzygotic cell divisions.

Correlation of first-trimester thymus size with chromosomal anomalies.

OBJECTIVES: The aim of this study was to investigate the correlation between fetal thymus size measured during first-trimester screening and chromosomal anomalies. METHODS: This study is a retrospective evaluation, in which the anterior-posterior diameter of the thymus in a midsagittal plane was measured in first-trimester ultrasound between 11+0 and 13+6 weeks of gestation in 168 fetuses with chromosomal anomalies (study group) and 593 healthy fetuses (control group). The included cases were subdivided into six groups: (1) trisomy 21, (2) trisomy 18, (3) trisomy 13, (4) Turner syndrome, (5) triploidy and (6) normal controls. Thymus size measurements were adjusted to the week of gestation, which was determined by ultrasound using crown-rump-length (CRL), by calculating a ratio between CRL and thymus size (CRL-thymus-ratio). Each study group was compared with the control group separately. RESULTS: Thymus size in fetuses affected by trisomy 18 or trisomy 13 was noticeably smaller compared to the control group (1.4 mm [1.3, 1.5] and 1.3 mm [1.2, 1.4] vs. 1.8 mm [1.6, 2.1]; all p<0.001; respectively). The thymus size of fetuses with trisomy 21 and Turner syndrome did not differ from healthy fetuses. Between the CRL-thymus-ratios of the separate study groups no statistically noticeable differences could be found. CONCLUSIONS: Fetal thymus size appeared to be smaller in pregnancies affected by trisomy 18 and trisomy 13. The predictive value of fetal thymus size in first-trimester screening should be evaluated prospectively.

Multi-institutional experience of genetic diagnosis in Ecuador: National registry of chromosome alterations and polymorphisms.

BACKGROUND: Detection of chromosomal abnormalities is crucial in various medical areas; to diagnose birth defects, genetic disorders, and infertility, among other complex phenotypes, in individuals across a wide range of ages. Hence, the present study wants to contribute to the knowledge of type and frequency of chromosomal alterations and polymorphisms in Ecuador. METHODS: Cytogenetic registers from different Ecuadorian provinces have been merged and analyzed to construct an open-access national registry of chromosome alterations and polymorphisms. RESULTS: Of 28,806 karyotypes analyzed, 6,008 (20.9%) exhibited alterations. Down syndrome was the most frequent autosome alteration (88.28%), followed by Turner syndrome (60.50%), a gonosome aneuploidy. A recurrent high percentage of Down syndrome mosaicism (7.45%) reported here, as well as by previous Ecuadorian preliminary registries, could be associated with geographic location and admixed ancestral composition. Translocations (2.46%) and polymorphisms (7.84%) were not as numerous as autosomopathies (64.33%) and gonosomopathies (25.37%). Complementary to conventional cytogenetics tests, molecular tools have allowed identification of submicroscopic alterations regions or candidate genes which can be possibly implicated in patients' symptoms and phenotypes. CONCLUSION: The Ecuadorian National Registry of Chromosome Alterations and Polymorphisms provides a baseline to better understand chromosomal abnormalities in Ecuador and therefore their clinical management and awareness. This data will guide public policy makers to promote and financially support cytogenetic and genetic testing.

Comparison of quantitative fluorescent polymerase chain reaction and karyotype analysis for prenatal screening of chromosomal aneuploidies in 270 amniotic fluid samples.

Background Quantitative fluorescent polymerase chain reaction (QF-PCR) technique is a rapid prenatal aneuploidy detection method. This method can diagnose abnormality in chromosome 13, 18, 21, X and Y. Karyotyping is a technique in which, by the process of pairing and painting, all the chromosomes of an organism are displayed under a microscope. In the present study, a statistical comparison was made between karyotyping and QF-PCR for prenatal diagnosis. Methods A total of 270 samples were tested for QF-PCR and the results were compared with karyotyping. We also investigated heterozygosity of short tandem repeat (STR) markers by QF-PCR. Deoxyribonucleic acid (DNA) samples (n = 270) were extracted from amniotic fluid (AF) cells. After PCR amplifications, analysis was performed using GeneMarker. A Devyser QF-PCR kit containing 26 primers was used to estimate the observed heterozygosity of STR markers located on chromosome 13, 18, 21, X and Y. Results The results of karyotyping and QF-PCR were as follows: trisomy 13 (one case), trisomy 18 (five cases), trisomy 21 (five cases) and triploidy (one case). Chromosomal rearrangements and mosaicisms were not detected by QF-PCR but were detected by karyotyping. Maternal cell contamination (MCC) made the karyotyping fail but not the QF-PCR. Conclusion The QF-PCR method is especially important because it is fast, accurate, low cost and has a short turnaround time. This method will avoid ambiguity of karyotype results and parental anxiety. It will also shorten clinical management for high-risk families.

[Autosomal recessive limb-girdle muscular dystrophy]. / Distrofias musculares de cinturas autosomicas recesivas.

Muscular dystrophies are a heterogeneous group of hereditary diseases characterized by loss of muscle and weakness of non neurogenic origin. They are caused by mutations in one or more genes involved in the formation of muscle cells. The discovery of several proteins in the muscle began with the discovery of dystrophin, 130 years after the clinical description of muscular dystrophy. Currently, due to a better understanding of the biology of normal and diseased muscle, has achieved a classification at the molecular level of different types of muscular dystrophies, according to the protein that is affected. This has been particularly important for limb girdle muscular dystrophies, which present clinical features that can lead to confusion with Duchenne muscular dystrophy. Moreover, in recent years has encouraged the development of therapies in the near future could provide a solution for restoring the function of the muscle fiber.

[New chromosomal syndromes]. / Syndromes chromosomiques émergents.

Mental retardation occurs in 2-3% of the general population either in isolation or in combination with facial dysmorphism and/or malformations. Chromosomal abnormalities are a most common etiology. Karyotype displays chromosome aberrations in about 10% of patients but it has a limited resolution (5 Mb). Recently, the development of new molecular cytogenetic tools, especially array CGH, allowed to detect smaller abnormalities and increased the diagnosis capability of 15-20%. Among these newly detected rearrangements, some of them are recurrent and define new recognized syndromes. We will first briefly explain the non-allelic homologous recombination (NAHR) mechanism that underlines the origin of recurrent microdeletions and microduplications. Then we will describe eight new syndromes, four microdeletions (del 17q21.31, del 3q29, del 15q24, del 2q32.3q33) and four microduplications (dup 22q11.2, dup 7q11.23, dup 17p11.2, duplication of MECP2). A better knowledge of these new recurrent chromosomal syndromes will allow to improve care for patients, to develop targeted chromosomal diagnosis and to identify genes involved in neurocognitive functions.

The molar tooth sign: a new Joubert syndrome and related cerebellar disorders classification system tested in Egyptian families.

Joubert syndrome and related cerebellar disorders (JSRD) are a group of recessive congenital ataxia conditions usually showing neonatal hypotonia, dysregulated breathing rhythms, oculomotor apraxia, and mental retardation. The pathognomonic finding in JSRD is the unique molar tooth sign (MTS) on brain imaging. There is a tremendously broad spectrum of signs and symptoms mainly including kidney, retina, and liver disease, along with polydactyly and facial dysmorphisms. Here we propose a new diagnostic classification within JSRD that includes four major subtypes. To test this classification, we performed a systematic recruitment and genetic evaluation from a single referral center in Egypt. Thirteen families were identified, four showed evidence of linkage to one of the four known genetic loci, three showed novel AHI1 mutations, and nine were excluded from known loci. Each family could be classified into one of the four subtypes. This classification may thus be useful in the evaluation of patients with JSRD.

Development and evaluation of a comprehensive screening for orofacial dysfunction.

The aim was to develop a comprehensive screening instrument for evaluation of orofacial dysfunction that was easy to perform for different health professionals without special equipment. The Nordic Orofacial Test--Screening (NOT-S), consisting of a structured interview and clinical examination,was developed with a picture manual illustrating the different tasks in the examination. It was first tested in a Swedish version, and later translated to other Nordic languages, and to English. The interview reflected six domains, (I) Sensory function, (II) Breathing, (III) Habits, (IV) Chewing and swallowing, (V) Drooling, and (VI) Dryness of the mouth, and the examination included six domains representing (1) The face at rest, and tasks regarding (2) Nose breathing, (3) Facial expression, (4) Masticatory muscle and jaw function, (5) Oral motor function, and (6) Speech. One or more "yes" for impairment in a domain resulted in one point (maximum NOT-S score 12 points). The mean NOT-S score (+/- SD) in 120 patients (3-86 yr), referred to five centers for specialized dental care or speech and language pathology in Sweden, Norway and Denmark, was 4.1 +/- 2.6, and 0.4 +/- 0.6 in 60 control subjects (3-78 yr). The screening was easy to administer and the time spent 5-13 min. The scores from the clinic-referred sample differed significantly from the controls, and the sensitivity of the screening was 0.96 and specificity 0.63. Repeated evaluations of videotapes of 200 patients by 3 examiners, speech-language pathologists and dentists, with at least two-week intervals, showed inter- and intraexaminer agreement on the points given in the domains at respectively 83% and 92-95% which increased after recalibration to 85% and 95-99%. Kappa values for interexaminer agreement on the NOT-S scores were 0.42-0.44 (i.e. fair), and the method error was 5.3%. To conclude, NOT-S gave a reliable and valid screening for orofacial dysfunction.

Congenital heart defects--chromosomal anomalies, syndromes and extracardiac malformations.

AIM: To register chromosomal anomalies, syndromes and extracardiac malformations in patients with Congenital heart defects (CHDs). METHOD: Population-based prospective observational study. RESULTS: Of 57 027 live births during 1982-2005, CHDs were detected in 662 (11.6 per 1000), of whom 146 (22%) had associated anomalies. Of these 52 (36%) had chromosomal anomalies (exclusive microdeletions), 26 (18%) genetic syndromes/microdeletions, 1 (0.7%) a teratogenous syndrome and 67 (46%) extracardiac malformations. In perimembraneous ventricular septal defects (VSDs), associated anomalies occurred in 22 of 70 (31%) compared to 27 of 298 (9%) in VSDs located in the muscular part of the septum (p < 0.0001). The prevalence of CHDs with associated disorders increased significantly from the cohort born during 1982-1993 to those born during 1994-2005 (2.0 vs. 3.1 per 1000, respectively; p < 0.0001), mainly caused by an increase of chromosomal trisomies (0.5 vs. 1.1 per 1000; p = 0.026). The percentage of women giving live birth at 35 years of age or more was 7.6% for the period 1982-1993 compared to 13.4% for 1994-2005 (p = 0.001). CONCLUSIONS: Chromosomal anomalies, syndromes and extracardiac malformations occurred in nearly one-fourth of CHD cases. Muscular VSDs had a low prevalence of such conditions. The prevalence of CHDs with chromosomal trisomies increased, and was probably related to an increasing age of women giving birth.

Molecular genetics of autosomal-dominant axonal Charcot-Marie-Tooth disease.

The autosomal-dominant axonal peripheral neuropathies comprise a genetically heterogeneous group of disorders that are clinically subsumed under Charcot-Marie-Tooth disease type 2 (CMT2). A significant increase in the number of genes underlying major forms of CMT2 has improved the classification of specific CMT phenotypes. The molecular dissection of cellular functions of the related gene products has only begun and detailed pathophysiological models are still missing, but already the biological scope of genes linked to CMT2 is more diversified than CMT1. The known CMT2 genes present key players in these pathways and will likely prove as powerful tools in identifying eventual future targets for therapeutic intervention.

Unraveling the genetics of distal hereditary motor neuronopathies.

The hereditary motor neuronopathies (HMN [MIM 158590]) are a heterogeneous group of disorders characterized by an exclusive involvement of the motor part of the peripheral nervous system. They are usually subdivided in proximal HMN, i.e., the classical spinal muscular atrophy syndromes and distal hereditary motor neuronopathies (distal HMN) that clinically resemble Charcot-Marie-Tooth syndromes. In this review, we concentrate on distal HMN. The distal HMN are clinically and genetically heterogeneous and were initially subdivided in seven subtypes according to mode of inheritance, age at onset, and clinical evolution. Recent studies have shown that these subtypes are still heterogeneous at the molecular genetic level and novel clinical and genetic entities have been delineated. Since the introduction of positional cloning, 13 chromosomal loci and seven disease-associated genes have been identified for autosomal-dominant, autosomal-recessive, and X-linked recessive distal HMN. Most of the genes involved encode protein with housekeeping functions, such as RNA processing, translation synthesis, stress response, apoptosis, and others code for proteins involved in retrograde survival. Motor neurons of the anterior horn of the spinal cord seems to be vulnerable to defects in these housekeeping proteins, likely because their large axons have higher metabolic requirements for maintenance, transport over long distances and precise connectivity. Understanding the molecular pathomechanisms for mutations in these genes that are ubiquitous expressed will help unravel the neuronal mechanisms that underlie motor neuropathies leading to denervation of distal limb muscles, and might generate new insights for future therapeutic strategies.

Primer on medical genomics. Part VIII: Essentials of medical genetics for the practicing physician.

After the mapping and sequencing of the human genome, medical professionals from essentially all specialties turned their attention to investigating the role genes play in health and disease. Until recently, medical genetics was considered a specialty of minor practical relevance. This view has changed with the development of new diagnostic and therapeutic possibilities. It is now realized that genetic disease represents an important part of medical practice. Achievements in cancer genetics, in the field of prenatal diagnostics (including carrier testing for common recessive disorders), and in newborn screening for treatable metabolic disorders reinforce the rapidly expanding role of genetics in medicine. Diagnosing a genetic disorder not only allows for disease-specific management options but also has implications for the affected individual's entire family. A working understanding of the underlying concepts of genetic disease with regard to chromosome, single gene, mitochondrial, and multifactorial disorders is necessary for today's practicing physician. Routine clinical practice in virtually all medical specialties will soon require integration of these fundamental concepts for use in accurate diagnosis and ensuring appropriate referrals for patients with genetic disease and their families.