Frédéric Brioude

Non-syndromic congenital hypogonadotropic hypogonadism: clinical presentation and genotype–phenotype relationships

Congenital hypogonadotropic hypogonadism (CHH) results from abnormal gonadotropin secretion, and it is characterized by impaired pubertal development. CHH is caused by defective GNRH release, or by a gonadotrope cell dysfunction in the pituitary. Identification of genetic abnormalities related to CHH has provided major insights into the pathways critical for the development, maturation, and function of the reproductive axis. Mutations in five genes have been found specifically in Kallmanns syndrome, a disorder in which CHH is related to abnormal GNRH neuron ontogenesis and is associated with anosmia or hyposmia. In combined pituitary hormone deficiency or in complex syndromic CHH in which gonadotropin deficiency is either incidental or only one aspect of a more complex endocrine disorder or a non-endocrine disorder, other mutations affecting GNRH and/or gonadotropin secretion have been reported. Often, the CHH phenotype is tightly linked to an isolated deficiency of gonadotropin secretion. These patients, who have no associated signs or hormone deficiencies independent of the deficiency in gonadotropin and sex steroids, have isolated CHH. In some familial cases, they are due to genetic alterations affecting GNRH secretion (mutations in GNRH1, GPR54/KISS1R and TAC3 and TACR3) or the GNRH sensitivity of the gonadotropic cells (GNRHR). A minority of patients with Kallmanns syndrome or a syndromic form of CHH may also appear to have isolated CHH, but close clinical, familial, and genetic studies can reorient the diagnosis, which is important for genetic counseling in the context of assisted reproductive medicine. This review focuses on published cases of isolated CHH, its clinical and endocrine features, genetic causes, and genotype-phenotype relationships.

Beckwith-Wiedemann syndrome: growth pattern and tumor risk according to molecular mechanism, and guidelines for tumor surveillance

Background: Beckwith-Wiedemann syndrome (BWS) is an overgrowth syndrome associated with an increased risk of pediatric tumors. The underlying molecular abnormalities may be genetic (CDKN1C mutations or 11p15 paternal uniparental isodisomy, pUPD) or epigenetic (imprinting center region 1, ICR1, gain of methylation, ICR1 GOM, or ICR2 loss of methylation, ICR2 LOM). Aim: We aimed to describe a cohort of 407 BWS patients with molecular defects of the 11p15 domain followed prospectively after molecular diagnosis. Results: Birth weight and length were significantly higher in patients with ICR1 GOM than in the other groups. ICR2 LOM and CDKN1C mutations were associated with a higher prevalence of exomphalos. Mean adult height (regardless of molecular subtype, n = 35) was 1.8 ± 1.2 SDS, with 18 patients having a final height above +2 SDS. The prevalence of tumors was 8.6% in the whole population; 28.6 and 17.3% of the patients with ICR1 GOM (all Wilms tumors) and 11p15 pUPD, respectively, developed a tumor during infancy. Conversely, the prevalence of tumors in patients with ICR2 LOM and CDKN1C mutations were 3.1 and 8.8%, respectively, with no Wilms tumors. Conclusion: Based on these results for a large cohort, we formulated guidelines for the follow-up of these patients according to the molecular subtype of BWS.

CDKN1C mutation affecting the PCNA-binding domain as a cause of familial Russell Silver syndrome

Background Russell Silver syndrome (RSS) leads to prenatal and postnatal growth retardation. About 55% of RSS patients present a loss-of-methylation of the paternal ICR1 domain on chromosome 11p15. CDKN1C is a cell proliferation inhibitor encoded by an imprinted gene in the 11p15 ICR2 domain. CDKN1C mutations lead to Beckwith Wiedemann syndrome (BWS, overgrowth syndrome) and in IMAGe syndrome which associates growth retardation and adrenal insufficiency. We searched for CDKN1C mutations in a cohort of clinically diagnosed RSS patients with no molecular anomaly. Method The coding sequence and intron–exon boundaries of CDKN1C were analysed in 97 RSS patients. The impact of CDKN1C variants on the cell cycle in vitro were determined by flow cytometry. Stability of CDKN1C was studied by western immunoblotting after inhibition of translation with cycloheximide. Results We identified the novel c.836G>[G;T] (p.Arg279Leu) mutation in a familial case of intrauterine growth retardation (IUGR) with RSS phenotype and no evidence of IMAGe. All the RSS patients inherited this mutation from their mothers (consistent with monoallelic expression from the maternal allele of the gene). A mutation of this amino acid (p.Arg279Pro) has been reported in cases of IMAGe. Functional analysis showed that Arg279Leu (RSS) did not affect the cell cycle, whereas the Arg279Pro mutation (IMAGe) led to a gain of function. Arg279Leu (RSS) led to an increased stability which could explain an increased activity of CDKN1C. Conclusions CDKN1C mutations cause dominant maternally transmitted RSS, completing the molecular mirror with BWS. CDKN1C should be investigated in cases with family history of RSS.

Extensive investigation of the IGF2/H19 Imprinting Control Region reveals novel OCT4/SOX2 binding site defects associated with specific methylation patterns in Beckwith-Wiedemann Syndrome

Isolated gain of methylation (GOM) at the IGF2/H19 imprinting control region 1 (ICR1) accounts for about 10% of patients with BWS. A subset of these patients have genetic defects within ICR1, but the frequency of these defects has not yet been established in a large cohort of BWS patients with isolated ICR1 GOM. Here, we carried out a genetic analysis in a large cohort of 57 BWS patients with isolated ICR1 GOM and analyzed the methylation status of the entire domain. We found a new point mutation in two unrelated families and a 21 bp deletion in another unrelated child, both of which were maternally inherited and affected the OCT4/SOX2 binding site in the A2 repeat of ICR1. Based on data from this and previous studies, we estimate that cis genetic defects account for about 20% of BWS patients with isolated ICR1 GOM. Methylation analysis at eight loci of the IGF2/H19 domain revealed that sites surrounding OCT4/SOX2 binding site mutations were fully methylated and methylation indexes declined as a function of distance from these sites. This was not the case in BWS patients without genetic defects identified. Thus, GOM does not spread uniformly across the IGF2/H19 domain, suggesting that OCT4/SOX2 protects against methylation at local sites. These findings add new insights to the mechanism of the regulation of the ICR1 domain. Our data show that mutations and deletions within ICR1 are relatively common. Systematic identification is therefore necessary to establish appropriate genetic counseling for BWS patients with isolated ICR1 GOM.

CDKN1C mutations: two sides of the same coin

Cyclin-dependent kinase (CDK)-inhibitor 1C (CDKN1C) negatively regulates cellular proliferation and it has been shown that loss-of-function mutations in the imprinted CDKN1C gene (11p15.5) are associated with the overgrowth disorder Beckwith-Wiedemann syndrome (BWS). With recent reports of gain-of-function mutations of the PCNA domain of CDKN1C in growth-retarded patients with IMAGe syndrome or Silver-Russell syndrome (SRS), its key role for growth has been confirmed. Thereby, the last gap in the spectrum of molecular alterations in 11p15.5 in growth-retardation and overgrowth syndromes could be closed. Recent functional studies explain the strict association of CDKN1C mutations with clinically opposite phenotypes and thereby contribute to our understanding of the function and regulation of the gene in particular and epigenetic regulation in general.

EMQN best practice guidelines for the molecular genetic testing and reporting of chromosome 11p15 imprinting disorders: Silver–Russell and Beckwith–Wiedemann syndrome

Molecular genetic testing for the 11p15-associated imprinting disorders Silver–Russell and Beckwith–Wiedemann syndrome (SRS, BWS) is challenging because of the molecular heterogeneity and complexity of the affected imprinted regions. With the growing knowledge on the molecular basis of these disorders and the demand for molecular testing, it turned out that there is an urgent need for a standardized molecular diagnostic testing and reporting strategy. Based on the results from the first external pilot quality assessment schemes organized by the European Molecular Quality Network (EMQN) in 2014 and in context with activities of the European Network of Imprinting Disorders (EUCID.net) towards a consensus in diagnostics and management of SRS and BWS, best practice guidelines have now been developed. Members of institutions working in the field of SRS and BWS diagnostics were invited to comment, and in the light of their feedback amendments were made. The final document was ratified in the course of an EMQN best practice guideline meeting and is in accordance with the general SRS and BWS consensus guidelines, which are in preparation. These guidelines are based on the knowledge acquired from peer-reviewed and published data, as well as observations of the authors in their practice. However, these guidelines can only provide a snapshot of current knowledge at the time of manuscript submission and readers are advised to keep up with the literature.

Two Families with Normosmic Congenital Hypogonadotropic Hypogonadism and Biallelic Mutations in KISS1R (KISS1 Receptor): Clinical Evaluation and Molecular Characterization of a Novel Mutation

Context KISS1R mutations have been reported in few patients with normosmic congenital hypogonadotropic hypogonadism (nCHH) (OMIM #146110). Objective To describe in detail nCHH patients with biallelic KISS1R mutations belonging to 2 unrelated families, and to functionally characterize a novel KISS1R mutation. Results An original mutant, p.Tyr313His, was found in the homozygous state in 3 affected kindred (2 females and 1 male) from a consanguineous Portuguese family. This mutation, located in the seventh transmembrane domain, affects a highly conserved amino acid, perturbs the conformation of the transmembrane segment, and impairs MAP kinase signaling and intracellular calcium release. In the second family, a French Caucasian male patient with nCHH was found to carry two recurrent mutations in the compound heterozygous state (p.Leu102Pro/Stop399Arg). In this man, pulsatile GnRH (Gonadotropin Releasing Hormone) administration restored pulsatile LH (Luteinizing Hormone) secretion and testicular hormone secretion. Later, long-term combined gonadotropin therapy induced spermatogenesis, enabling 3 successive pregnancies that resulted in 2 miscarriages and the birth of a healthy boy. Conclusion We show that a novel loss-of-function mutation (p.Tyr313His) in the KISS1R gene can cause familial nCHH, revealing the crucial role of this amino acid in KISS1R function. The observed restoration of gonadotropin secretion by exogenous GnRH administration further supports, in humans, the hypothalamic origin of the gonadotropin deficiency in this genetic form of nCHH.

Mutations of the Imprinted CDKN1C Gene as a Cause of the Overgrowth Beckwith–Wiedemann Syndrome: Clinical Spectrum and Functional Characterization

Beckwith–Wiedemann syndrome (BWS) is an imprinting disorder associating macroglossia, abdominal wall defects, visceromegaly, and a high risk of childhood tumor. Molecular anomalies are mostly epigenetic; however, mutations of CDKN1C are implicated in 8% of cases, including both sporadic and familial forms. We aimed to describe the phenotype of BWS patients with CDKN1C mutations and develop a functional test for CDKN1C mutations. For each propositus, we sequenced the three exons and intron–exon boundaries of CDKN1C in patients presenting a BWS phenotype, including abdominal wall defects, without 11p15 methylation defects. We developed a functional test based on flow cytometry. We identified 37 mutations in 38 pedigrees (50 patients and seven fetuses). Analysis of parental samples when available showed that all mutations tested but one was inherited from the mother. The four missense mutations led to a less severe phenotype (lower frequency of exomphalos) than the other 33 mutations. The following four tumors occurred: one neuroblastoma, one ganglioneuroblastoma, one melanoma, and one acute lymphoid leukemia. Cases of BWS caused by CDKN1C mutations are not rare. CDKN1C sequencing should be performed for BWS patients presenting with abdominal wall defects or cleft palate without 11p15 methylation defects or body asymmetry, or in familial cases of BWS.

Complex tissue-specific epigenotypes in Russell-Silver Syndrome associated with 11p15 ICR1 hypomethylation.

Russell–Silver Syndrome (RSS) is a prenatal and postnatal growth retardation syndrome caused mainly by 11p15 ICR1 hypomethylation. Clinical presentation is heterogeneous in RSS patients with 11p15 ICR1 hypomethylation. We previously identified a subset of RSS patients with 11p15 ICR1 and multilocus hypomethylation. Here, we examine the relationships between IGF2 expression, 11p15 ICR1 methylation, and multilocus imprinting defects in various cell types from 39 RSS patients with 11p15 ICR1 hypomethylation in leukocyte DNA. 11p15 ICR1 hypomethylation was more pronounced in leukocytes than in buccal mucosa cells. Skin fibroblast IGF2 expression was correlated with the degree of ICR1 hypomethylation. Different tissue‐specific multilocus methylation defects coexisted in 38% of cases, with some loci hypomethylated and others hypermethylated within the same cell type in some cases. Our new results suggest that tissue‐specific epigenotypes may lead to clinical heterogeneity in RSS.

Prenatal molecular testing for Beckwith-Wiedemann and Silver-Russell syndromes: a challenge for molecular analysis and genetic counseling.

Beckwith–Wiedemann and Silver–Russell syndromes (BWS/SRS) are two imprinting disorders (IDs) associated with disturbances of the 11p15.5 chromosomal region. In BWS, epimutations and genomic alterations within 11p15.5 are observed in >70% of patients, whereas in SRS they are observed in about 60% of the cases. In addition, 10% of the SRS patients carry a maternal uniparental disomy of chromosome 7 11p15.5. There is an increasing demand for prenatal testing of these disorders owing to family history, indicative prenatal ultrasound findings or aberrations involving chromosomes 7 and 11. The complex molecular findings underlying these disorders are a challenge not only for laboratories offering these tests but also for geneticists counseling affected families. The scope of counseling must consider the range of detectable disturbances and their origin, the lack of precise quantitative knowledge concerning the inheritance and recurrence risks for the epigenetic abnormalities, which are hallmarks of these developmental disorders. In this paper, experts in the field of BWS and SRS, including members of the European network of congenital IDs (EUCID.net; www.imprinting-disorders.eu), put together their experience and work in the field of 11p15.5-associated IDs with a focus on prenatal testing. Altogether, prenatal tests of 160 fetuses (122 referred for BWS, 38 for SRS testing) from 5 centers were analyzed and reviewed. We summarize the current knowledge on BWS and SRS with respect to diagnostic testing, the consequences for prenatal genetic testing and counseling and our cumulative experience in dealing with these disorders.