11p13 microduplication: a differential diagnosis of Silver-Russell syndrome?

BACKGROUND: Silver-Russel syndrome (SRS) is a congenital disorder which is mainly characterized by intrauterine and postnatal growth retardation, relative macrocephaly, and characteristic (facial) dysmorphisms. The majority of patients shows a hypomethylation of the imprinting center region 1 (IC1) in 11p15 and maternal uniparental disomy of chromosome 7 (upd(7)mat), but in addition a broad spectrum of copy number variations (CNVs) and monogenetic variants (SNVs) has been reported in this cohort. These heterogeneous findings reflect the clinical overlap of SRS with other congenital disorders, but some of the CNVs are recurrent and have therefore been suggested as SRS-associated loci. However, this molecular heterogeneity makes the decision on the diagnostic workup of patients with SRS features challenging. CASE PRESENTATION: A girl with clinical features of SRS but negatively tested for the IC1 hypomethylation and upd(7)mat was analyzed by whole genome sequencing in order to address both CNVs and SNVs in the same run. We identified a 11p13 microduplication affecting a region overlapping with a variant reported in a previously published patient with clinical features of Silver-Russel syndrome. CONCLUSIONS: The identification of a 11p13 microduplication in a patient with SRS features confirms the considerable contribution of CNVs to SRS-related phenotypes, and it strengthens the evidence for a 11p13 microduplication syndrome as a differential diagnosis SRS. Furthermore, we could confirm that WGS is a valuable diagnostic tool in patients with SRS and related disorders, as it allows CNVs and SNV detection in the same run, thereby avoiding a time-consuming diagnostic testing process.

Bi-allelic variants in CELSR3 are implicated in central nervous system and urinary tract anomalies.

CELSR3 codes for a planar cell polarity protein. We describe twelve affected individuals from eleven independent families with bi-allelic variants in CELSR3. Affected individuals presented with an overlapping phenotypic spectrum comprising central nervous system (CNS) anomalies (7/12), combined CNS anomalies and congenital anomalies of the kidneys and urinary tract (CAKUT) (3/12) and CAKUT only (2/12). Computational simulation of the 3D protein structure suggests the position of the identified variants to be implicated in penetrance and phenotype expression. CELSR3 immunolocalization in human embryonic urinary tract and transient suppression and rescue experiments of Celsr3 in fluorescent zebrafish reporter lines further support an embryonic role of CELSR3 in CNS and urinary tract formation.

Human Reproduction and Disturbed Genomic Imprinting.

Genomic imprinting is a specific mode of gene regulation which particularly accounts for the factors involved in development. Its disturbance affects the fetus, the course of pregnancy and even the health of the mother. In children, aberrant imprinting signatures are associated with imprinting disorders (ImpDis). These alterations also affect the function of the placenta, which has consequences for the course of the pregnancy. The molecular causes of ImpDis comprise changes at the DNA level and methylation disturbances (imprinting defects/ImpDefs), and there is an increasing number of reports of both pathogenic fetal and maternal DNA variants causing ImpDefs. These ImpDefs can be inherited, but prediction of the pregnancy complications caused is difficult, as they can cause miscarriages, aneuploidies, health issues for the mother and ImpDis in the child. Due to the complexity of imprinting regulation, each pregnancy or patient with suspected altered genomic imprinting requires a specific workup to identify the precise molecular cause and also careful clinical documentation. This review will cover the current knowledge on the molecular causes of aberrant imprinting signatures and illustrate the need to identify this basis as the prerequisite for personalized genetic and reproductive counselling of families.

Genetic landscape of congenital insensitivity to pain and hereditary sensory and autonomic neuropathies.

Congenital insensitivity to pain (CIP) and hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders exclusively or predominantly affecting the sensory and autonomic neurons. Due to the rarity of the diseases and findings based mainly on single case reports or small case series, knowledge about these disorders is limited. Here, we describe the molecular workup of a large international cohort of CIP/HSAN patients including patients from normally under-represented countries. We identify 80 previously unreported pathogenic or likely pathogenic variants in a total of 73 families in the >20 known CIP/HSAN-associated genes. The data expand the spectrum of disease-relevant alterations in CIP/HSAN, including novel variants in previously rarely recognized entities such as ATL3-, FLVCR1- and NGF-associated neuropathies and previously under-recognized mutation types such as larger deletions. In silico predictions, heterologous expression studies, segregation analyses and metabolic tests helped to overcome limitations of current variant classification schemes that often fail to categorize a variant as disease-related or benign. The study sheds light on the genetic causes and disease-relevant changes within individual genes in CIP/HSAN. This is becoming increasingly important with emerging clinical trials investigating subtype or gene-specific treatment strategies.

First-time application of droplet digital PCR for methylation testing of the 11p15.5 imprinting regions.

BACKGROUND: Beckwith-Wiedemann syndrome and Silver-Russel syndrome are two imprinting disorders caused by opposite molecular alterations in 11p15.5. With the current diagnostic tests, their molecular diagnosis is challenging due to molecular heterogeneity and mosaic occurrence of the most frequent alterations. As the determination of precise (epi)genotype of patients is relevant as the basis for a personalized treatment, different approaches are needed to increase the sensitivity of diagnostic testing of imprinting disorders. METHODS: We established methylation-specific droplet digital PCR approaches (MS-ddPCR) for the two imprinting centers in 11p15.5, and analyzed patients with paternal uniparental disomy of chromosome 11p15.5 (upd(11)pat) and other imprinting defects in the region. The results were compared to those from MS-MLPA (multiplex ligation-dependent probe amplification) and MS-pyrosequencing. RESULTS: MS-ddPCR confirmed the molecular alterations in all patients and the results matched well with MS-MLPA. The results of MS-pyrosequencing varied between different runs, whereas MS-ddPCR results were reproducible. CONCLUSION: We show for the first time that MS-ddPCR is a reliable and easy applicable method for determination of MS-associated changes in imprinting disorders. It is therefore an additional tool for multimethod diagnostics of imprinting disorders suitable to improve the diagnostic yield.

Prenatal testing for imprinting disorders: A laboratory perspective.

Imprinting Disorders (ImpDis) are a group of congenital syndromes associated with up to four different types of molecular disturbances affecting the monoallelic and parent-of-origin specific expression of genomically imprinted genes. Though each ImpDis is characterized by aberrations at a distinct genetic site and a specific set of postnatal clinical signs, there is a broad overlap between several of them. In particular, the prenatal features of ImpDis are non-specific. Therefore, the decision on the appropriate molecular testing strategy is difficult. A further molecular characteristic of ImpDis is (epi)genetic mosaicism, which makes prenatal testing for ImpDis challenging. Accordingly, sampling and diagnostic workup has to consider the methodological limitations. Furthermore, the prediction of the clinical outcome of a pregnancy can be difficult. False-negative results can occur, and therefore fetal imaging should be the diagnostic tool on which decisions on the management of the pregnancy should be based. In summary, the decision for molecular prenatal testing for ImpDis should be based on close exchanges between clinicians, geneticists, and the families before the initiation of the test. These discussions should weigh the chances and challenges of the prenatal test, with focus on the need of the family.

Imprinting disorders.

Imprinting disorders (ImpDis) are congenital conditions that are characterized by disturbances of genomic imprinting. The most common individual ImpDis are Prader-Willi syndrome, Angelman syndrome and Beckwith-Wiedemann syndrome. Individual ImpDis have similar clinical features, such as growth disturbances and developmental delay, but the disorders are heterogeneous and the key clinical manifestations are often non-specific, rendering diagnosis difficult. Four types of genomic and imprinting defect (ImpDef) affecting differentially methylated regions (DMRs) can cause ImpDis. These defects affect the monoallelic and parent-of-origin-specific expression of imprinted genes. The regulation within DMRs as well as their functional consequences are mainly unknown, but functional cross-talk between imprinted genes and functional pathways has been identified, giving insight into the pathophysiology of ImpDefs. Treatment of ImpDis is symptomatic. Targeted therapies are lacking owing to the rarity of these disorders; however, personalized treatments are in development. Understanding the underlying mechanisms of ImpDis, and improving diagnosis and treatment of these disorders, requires a multidisciplinary approach with input from patient representatives.

Prenatal testing for Imprinting Disorders: A clinical perspective.

Imprinting Disorders (ImpDis) are a group of congenital conditions caused by aberrant imprinting resulting in disturbed expression of parentally imprinted genes. ImpDis are rarely associated with major malformations, but pre- and/or postnatal growth and nutrition are often affected. In some ImpDis, behavioral, developmental, metabolic and neurological symptoms might present in the perinatal context or later in life, and in single ImpDis, there is a higher risk of tumors in childhood. Prognosis depends in part on the molecular cause of each ImpDis, but due to high clinical variability and (epi)genetic mosaicism, predicting the clinical outcome of a pregnancy solely based on the underlying molecular disturbance is difficult. Therefore, interdisciplinary care and treatment approaches play an important role in the management and decision making of affected pregnancies, especially taking into account fetal imaging in addition to genetic findings. Prenatal findings influence perinatal management, and thereby improve the prognosis of ImpDis associated with severe but sometimes transient clinical complications in the neonatal period. Therefore, prenatal diagnosis can be crucial for appropriate management not only to the pregnancy itself but might also have a life-long effect.

Molecular characterisation of 36 multilocus imprinting disturbance (MLID) patients: a comprehensive approach.

BACKGROUND: Imprinting disorders (ImpDis) comprise diseases which are caused by aberrant regulation of monoallelically and parent-of-origin-dependent expressed genes. A characteristic molecular change in ImpDis patients is aberrant methylation signatures at disease-specific loci, without an obvious DNA change at the specific differentially methylated region (DMR). However, there is a growing number of reports on multilocus imprinting disturbances (MLIDs), i.e. aberrant methylation at different DMRs in the same patient. These MLIDs account for a significant number of patients with specific ImpDis, and several reports indicate a central role of pathogenic maternal effect variants in their aetiology by affecting the maturation of the oocyte and the early embryo. Though several studies on the prevalence and the molecular causes of MLID have been conducted, homogeneous datasets comprising both genomic and methylation data are still lacking. RESULTS: Based on a cohort of 36 MLID patients, we here present both methylation data obtained from next-generation sequencing (NGS, ImprintSeq) approaches and whole-exome sequencing (WES). The compilation of methylation data did not reveal a disease-specific MLID episignature, and a predisposition for the phenotypic modification was not obvious as well. In fact, this lack of epigenotype-phenotype correlation might be related to the mosaic distribution of imprinting defects and their functional relevance in specific tissues. CONCLUSIONS: Due to the higher sensitivity of NGS-based approaches, we suggest that ImprintSeq might be offered at reference centres in case of ImpDis patients with unusual phenotypes but MLID negative by conventional tests. By WES, additional MLID causes than the already known maternal effect variants could not be identified, neither in the patients nor in the maternal exomes. In cases with negative WES results, it is currently unclear to what extent either environmental factors or undetected genetic variants contribute to MLID.

Functional connectivity signatures of NMDAR dysfunction in schizophrenia-integrating findings from imaging genetics and pharmaco-fMRI.

Both, pharmacological and genome-wide association studies suggest N-methyl-D-aspartate receptor (NMDAR) dysfunction and excitatory/inhibitory (E/I)-imbalance as a major pathophysiological mechanism of schizophrenia. The identification of shared fMRI brain signatures of genetically and pharmacologically induced NMDAR dysfunction may help to define biomarkers for patient stratification. NMDAR-related genetic and pharmacological effects on functional connectivity were investigated by integrating three different datasets: (A) resting state fMRI data from 146 patients with schizophrenia genotyped for the disease-associated genetic variant rs7191183 of GRIN2A (encoding the NMDAR 2 A subunit) as well as 142 healthy controls. (B) Pharmacological effects of the NMDAR antagonist ketamine and the GABA-A receptor agonist midazolam were obtained from a double-blind, crossover pharmaco-fMRI study in 28 healthy participants. (C) Regional gene expression profiles were estimated using a postmortem whole-brain microarray dataset from six healthy donors. A strong resemblance was observed between the effect of the genetic variant in schizophrenia and the ketamine versus midazolam contrast of connectivity suggestive for an associated E/I-imbalance. This similarity became more pronounced for regions with high density of NMDARs, glutamatergic neurons, and parvalbumin-positive interneurons. From a functional perspective, increased connectivity emerged between striato-pallido-thalamic regions and cortical regions of the auditory-sensory-motor network, while decreased connectivity was observed between auditory (superior temporal gyrus) and visual processing regions (lateral occipital cortex, fusiform gyrus, cuneus). Importantly, these imaging phenotypes were associated with the genetic variant, the differential effect of ketamine versus midazolam and schizophrenia (as compared to healthy controls). Moreover, the genetic variant was associated with language-related negative symptomatology which correlated with disturbed connectivity between the left posterior superior temporal gyrus and the superior lateral occipital cortex. Shared genetic and pharmacological functional connectivity profiles were suggestive of E/I-imbalance and associated with schizophrenia. The identified brain signatures may help to stratify patients with a common molecular disease pathway providing a basis for personalized psychiatry.

Further understanding of paternal uniparental disomy in Beckwith-Wiedemann syndrome.

INTRODUCTION: Paternal uniparental disomy of chromosome 11 (upd(11)pat) accounts for up to 20% of molecularly confirmed Beckwith-Wiedemann spectrum (BWSp) cases. It belongs to the BWSp subgroup with the second highest tumor risk, and therefore needs particular awareness in research, diagnostics and clinical management. AREAS COVERED: We overview the contribution of paternal (mosaic) uniparental disomy of chromosome 11 (UPD, upd(11)pat) and mosaic paternal uniparental diploidy in patients with Beckwith-Wiedemann features. The review comprises the current knowledge on their formation and their molecular and clinical consequences. Accordingly, the consequences for diagnostic testing and clinical monitoring are compiled. EXPERT OPINION: The necessity to diagnostically identify and thus discriminate genome-wide paternal uniparental disomy, and upd(11)pat becomes obvious, due to the differences in the clinical course, disease prognosis, and treatment. In particular, monitoring of tumor development by liquid biopsy might be a promising option in the future. From the research point of view, it should be addressed why 11p is prone to mitotic recombination and thus also provide to the role of upd(11) as second hit in tumorigenesis.

First step towards a consensus strategy for multi-locus diagnostic testing of imprinting disorders.

BACKGROUND: Imprinting disorders, which affect growth, development, metabolism and neoplasia risk, are caused by genetic or epigenetic changes to genes that are expressed from only one parental allele. Disease may result from changes in coding sequences, copy number changes, uniparental disomy or imprinting defects. Some imprinting disorders are clinically heterogeneous, some are associated with more than one imprinted locus, and some patients have alterations affecting multiple loci. Most imprinting disorders are diagnosed by stepwise analysis of gene dosage and methylation of single loci, but some laboratories assay a panel of loci associated with different imprinting disorders. We looked into the experience of several laboratories using single-locus and/or multi-locus diagnostic testing to explore how different testing strategies affect diagnostic outcomes and whether multi-locus testing has the potential to increase the diagnostic efficiency or reveal unforeseen diagnoses. RESULTS: We collected data from 11 laboratories in seven countries, involving 16,364 individuals and eight imprinting disorders. Among the 4721 individuals tested for the growth restriction disorder Silver-Russell syndrome, 731 had changes on chromosomes 7 and 11 classically associated with the disorder, but 115 had unexpected diagnoses that involved atypical molecular changes, imprinted loci on chromosomes other than 7 or 11 or multi-locus imprinting disorder. In a similar way, the molecular changes detected in Beckwith-Wiedemann syndrome and other imprinting disorders depended on the testing strategies employed by the different laboratories. CONCLUSIONS: Based on our findings, we discuss how multi-locus testing might optimise diagnosis for patients with classical and less familiar clinical imprinting disorders. Additionally, our compiled data reflect the daily life experiences of diagnostic laboratories, with a lower diagnostic yield than in clinically well-characterised cohorts, and illustrate the need for systematising clinical and molecular data.

Comprehensive genetic testing approaches as the basis for personalized management of growth disturbances: current status and perspectives.

The implementation of high-throughput and deep sequencing methods in routine genetic diagnostics has significantly improved the diagnostic yield in patient cohorts with growth disturbances and becomes increasingly important as the prerequisite of personalized medicine. They provide considerable chances to identify even rare and unexpected situations; nevertheless, we must be aware of their limitations. A simple genetic test in the beginning of a testing cascade might also help to identify the genetic cause of specific growth disorders. However, the clinical picture of genetically caused growth disturbance phenotypes can vary widely, and there is a broad clinical overlap between different growth disturbance disorders. As a consequence, the clinical diagnosis and therewith connected the decision on the appropriate genetic test is often a challenge. In fact, the clinician asking for genetic testing has to weigh different aspects in this decision process, including appropriateness (single gene test, stepwise procedure, comprehensive testing), turnaround time as the basis for rapid intervention, and economic considerations. Therefore, a frequent question in that context is 'what to test when'. In this review, we aim to review genetic testing strategies and their strengths and limitations and to raise awareness for the future implementation of interdisciplinary genome medicine in diagnoses, treatment, and counselling of growth disturbances.

ADGRL1 haploinsufficiency causes a variable spectrum of neurodevelopmental disorders in humans and alters synaptic activity and behavior in a mouse model.

ADGRL1 (latrophilin 1), a well-characterized adhesion G protein-coupled receptor, has been implicated in synaptic development, maturation, and activity. However, the role of ADGRL1 in human disease has been elusive. Here, we describe ten individuals with variable neurodevelopmental features including developmental delay, intellectual disability, attention deficit hyperactivity and autism spectrum disorders, and epilepsy, all heterozygous for variants in ADGRL1. In vitro, human ADGRL1 variants expressed in neuroblastoma cells showed faulty ligand-induced regulation of intracellular Ca2+ influx, consistent with haploinsufficiency. In vivo, Adgrl1 was knocked out in mice and studied on two genetic backgrounds. On a non-permissive background, mice carrying a heterozygous Adgrl1 null allele exhibited neurological and developmental abnormalities, while homozygous mice were non-viable. On a permissive background, knockout animals were also born at sub-Mendelian ratios, but many Adgrl1 null mice survived gestation and reached adulthood. Adgrl1-/- mice demonstrated stereotypic behaviors, sexual dysfunction, bimodal extremes of locomotion, augmented startle reflex, and attenuated pre-pulse inhibition, which responded to risperidone. Ex vivo synaptic preparations displayed increased spontaneous exocytosis of dopamine, acetylcholine, and glutamate, but Adgrl1-/- neurons formed synapses in vitro poorly. Overall, our findings demonstrate that ADGRL1 haploinsufficiency leads to consistent developmental, neurological, and behavioral abnormalities in mice and humans.

Molecular Basis of Beckwith-Wiedemann Syndrome Spectrum with Associated Tumors and Consequences for Clinical Practice.

Beckwith-Wiedemann syndrome (BWS, OMIM 130650) is a congenital imprinting condition with a heterogenous clinical presentation of overgrowth and an increased childhood cancer risk (mainly nephroblastoma, hepatoblastoma or neuroblastoma). Due to the varying clinical presentation encompassing classical, clinical BWS without a molecular diagnosis and BWS-related phenotypes with an 11p15.5 molecular anomaly, the syndromic entity was extended to the Beckwith-Wiedemann spectrum (BWSp). The tumor risk of up to 30% depends on the molecular subtype of BWSp with causative genetic or epigenetic alterations in the chromosomal region 11p15.5. The molecular diagnosis of BWSp can be challenging for several reasons, including the range of causative molecular mechanisms which are frequently mosaic. The molecular basis of tumor formation appears to relate to stalled cellular differentiation in certain organs that predisposes persisting embryonic cells to accumulate additional molecular defects, which then results in a range of embryonal tumors. The molecular subtype of BWSp not only influences the overall risk of neoplasia, but also the likelihood of specific embryonal tumors.

Microdeletions in 1q21 and 8q12.1 depict two additional molecular subgroups of Silver-Russell syndrome like phenotypes.

BACKGROUND: Silver-Russell syndrome (SRS) is a genetic disorder characterized by intrauterine and postnatal growth restriction, relative macrocephaly at birth, body asymmetry and typical facial features. Clinical and molecular heterogeneity is described in SRS. Common causes are loss of methylation of the imprinting center 1 in 11p15 and maternal uniparental disomy of chromosome 7. Other genetic alterations include disturbances of imprinted regions in 14q32, 7q32 and 11p15 as well as submicroscopic deletions and duplications. Single nucleotide variants in genes like IGF2, HMGA2, PLAG1, CDKN1C have also been identified in patients with SRS phenotypes. However, routine molecular diagnostics usually focus on 11p15 and chromosome 7, while less frequent causes are not systematically addressed. RESULTS: Here we report two patients with SRS features in which molecular karyotyping revealed microdeletions in 1q21 and 8q12.1 respectively. In a 3.5-year-old girl with postnatal growth restriction, feeding difficulties, relative macrocephaly and distinct SRS features a 2 Mb deletion in 1q21.1q21.2 was identified. Our second case is a 1.5-year-old boy with intrauterine and postnatal growth restriction, feeding difficulties and distinct facial features with a 77 kb deletion in 8q12.1 affecting PLAG1 as the only protein-encoding gene with known function. CONCLUSIONS: The 1q21 region has not yet been assigned as an SRS region, although six patients with the same deletion and SRS features including relative macrocephaly have been described before. This new case adds to the evidence that distal 1q21 should be annotated as an SRS candidate region. The PLAGL1 alteration is the smallest deletion in 8q12.1 ever reported in a patient with SRS phenotype and it finally confirms that PLAG1 is the SRS causing gene in 8q12.1. To increase the diagnostic yield in patients with suspected SRS, we recommend both molecular karyotyping and next generation sequencing-based approaches.

Childhood adversity and approach/avoidance-related behaviour in boys.

Childhood adversity has been suggested to affect the vulnerability for developmental psychopathology, including both externalizing and internalizing symptoms. This study examines spontaneous attention biases for negative and positive emotional facial expressions as potential intermediate phenotypes. In detail, typically developing boys (6-13 years) underwent an eye-tracking paradigm displaying happy, angry, sad and fearful faces. An approach bias towards positive emotional facial expressions with increasing childhood adversity levels was found. In addition, an attention bias away from negative facial expressions was observed with increasing childhood adversity levels, especially for sad facial expressions. The results might be interpreted in terms of emotional regulation strategies in boys at risk for reactive aggression and depressive behaviour.

Novel homozygous nonsense mutation in the P5'N-1 coding gene as an alternative cause for hereditary anemia with basophilic stippling.

Hereditary pyrimidine 5-nucleotidase (P5'N-1) deficiency is a very rare disorder. Here, we describe a new mutation in a Turkish family. Although functional tests have not been performed, our findings confirm that the homozygous mutational state leads to clinical manifest P5'N-1 deficiency, while heterozygosity does not lead to hemolysis or anemia.

Trans-acting genetic variants causing multilocus imprinting disturbance (MLID): common mechanisms and consequences.

BACKGROUND: Imprinting disorders are a group of congenital diseases which are characterized by molecular alterations affecting differentially methylated regions (DMRs). To date, at least twelve imprinting disorders have been defined with overlapping but variable clinical features including growth and metabolic disturbances, cognitive dysfunction, abdominal wall defects and asymmetry. In general, a single specific DMR is affected in an individual with a given imprinting disorder, but there are a growing number of reports on individuals with so-called multilocus imprinting disturbances (MLID), where aberrant imprinting marks (most commonly loss of methylation) occur at multiple DMRs. However, as the literature is fragmented, we reviewed the molecular and clinical data of 55 previously reported or newly identified MLID families with putative pathogenic variants in maternal effect genes (NLRP2, NLRP5, NLRP7, KHDC3L, OOEP, PADI6) and in other candidate genes (ZFP57, ARID4A, ZAR1, UHRF1, ZNF445). RESULTS: In 55 families, a total of 68 different candidate pathogenic variants were identified (7 in NLRP2, 16 in NLRP5, 7 in NLRP7, 17 in PADI6, 15 in ZFP57, and a single variant in each of the genes ARID4A, ZAR1, OOEP, UHRF1, KHDC3L and ZNF445). Clinical diagnoses of affected offspring included Beckwith-Wiedemann syndrome spectrum, Silver-Russell syndrome spectrum, transient neonatal diabetes mellitus, or they were suspected for an imprinting disorder (undiagnosed). Some families had recurrent pregnancy loss. CONCLUSIONS: Genomic maternal effect and foetal variants causing MLID allow insights into the mechanisms behind the imprinting cycle of life, and the spatial and temporal function of the different factors involved in oocyte maturation and early development. Further basic research together with identification of new MLID families will enable a better understanding of the link between the different reproductive issues such as recurrent miscarriages and preeclampsia in maternal effect variant carriers/families and aneuploidy and the MLID observed in the offsprings. The current knowledge can already be employed in reproductive and genetic counselling in specific situations.