Genetic Overlap between Holoprosencephaly and Kallmann Syndrome

Coordination of canonical and noncanonical Hedgehog signalling pathways mediated by WDR11 during primordial germ cell development

WDR11, a gene associated with Kallmann syndrome, is important in reproductive system development but molecular understanding of its action remains incomplete. We previously reported that Wdr11-deficient embryos exhibit defective ciliogenesis and developmental defects associated with Hedgehog (HH) signalling. Here we demonstrate that WDR11 is required for primordial germ cell (PGC) development, regulating canonical and noncanonical HH signalling in parallel. Loss of WDR11 disrupts PGC motility and proliferation driven by the cilia-independent, PTCH2/GAS1-dependent noncanonical HH pathway. WDR11 modulates the growth of somatic cells surrounding PGCs by regulating the cilia-dependent, PTCH1/BOC-dependent canonical HH pathway. We reveal that PTCH1/BOC or PTCH2/GAS1 receptor context dictates SMO localisation inside or outside of cilia, respectively, and loss of WDR11 affects the signalling responses of SMO in both situations. We show that GAS1 is induced by PTCH2-specific HH signalling, which is lost in the absence of WDR11. We also provide evidence supporting a role for WDR11 in ciliogenesis through regulation of anterograde intraflagellar transport potentially via its interaction with IFT20. Since WDR11 is a target of noncanonical SMO signalling, WDR11 represents a novel mechanism by which noncanonical and canonical HH signals communicate and cooperate.

Case report: A case of Culler-Jones syndrome caused by a novel mutation of GLI2 gene and literature review

Culler-Jones syndrome is a rare clinical phenomenon with diverse manifestations and is prone to misdiagnosis. We report one patient who presented with a 10-year history of anosmia and a 1-year history of epididymal pain. Kallmann syndrome was suspected initially. The results of his laboratory tests, imaging, and genetic testing, however, combined to provide a conclusive diagnosis of Culler-Jones syndrome. With the aid of high-throughput sequencing technology, the GLI2 gene c.527A>G (p.Tyr176Cys) heterozygous mutation in the child was identified. No published works have yet described this mutation site. We described Culler-Jones syndrome in a child at length. We recommend that Culler-Jones syndrome be taken into account when considering the spectrum of disorders associated with abnormal growth and development in children. Once diagnosed, individualized hormone replacement treatment is required for each patient.

Whole Exome Sequencing Points towards a Multi-Gene Synergistic Action in the Pathogenesis of Congenital Combined Pituitary Hormone Deficiency

Combined pituitary hormone deficiency (CPHD) is characterized by deficiency of growth hormone and at least one other pituitary hormone. Pathogenic variants in more than 30 genes expressed during the development of the head, hypothalamus, and/or pituitary have been identified so far to cause genetic forms of CPHD. However, the etiology of around 85% of the cases remains unknown. The aim of this study was to unveil the genetic etiology of CPHD due to congenital hypopituitarism employing whole exome sequencing (WES) in two newborn patients, initially tested and found to be negative for PROP1, LHX3, LHX4 and HESX1 pathogenic variants by Sanger sequencing and for copy number variations by MLPA. In this study, the application of WES in these CPHD newborns revealed the presence of three different heterozygous gene variants in each patient. Specifically in patient 1, the variants BMP4; p.Ala42Pro, GNRH1; p.Arg73Ter and SRA1; p.Gln32Glu, and in patient 2, the SOX9; p.Val95Ile, HS6ST1; p.Arg306Gln, and IL17RD; p.Pro566Ser were identified as candidate gene variants. These findings further support the hypothesis that CPHD constitutes an oligogenic rather than a monogenic disease and that there is a genetic overlap between CPHD and congenital hypogonadotropic hypogonadism.

Truncating and zinc-finger variants in GLI2 are associated with hypopituitarism

Variants in transcription factor GLI2 have been associated with hypopituitarism and structural brain abnormalities, occasionally including holoprosencephaly (HPE). Substantial phenotypic variability and nonpenetrance have been described, posing difficulties in the counseling of affected families. We present three individuals with novel likely pathogenic GLI2 variants, two with truncating and one with a de novo missense variant p.(Ser548Leu), and review the literature for comprehensive phenotypic descriptions of individuals with confirmed pathogenic (a) intragenic GLI2 variants and (b) chromosome 2q14.2 deletions encompassing only GLI2. We show that most of the 31 missense variants previously reported as pathogenic are likely benign or, at most, low-risk variants. Four Zn-finger variants: p.(Arg479Gly), p.(Arg516Pro), p.(Gly518Lys), and p.(Tyr575His) were classified as likely pathogenic, and three other variants as possibly pathogenic: p.(Pro253Ser), p.(Ala593Val), and p.(Pro1243Leu). We analyze the phenotypic descriptions of 60 individuals with pathogenic GLI2 variants and evidence a morbidity spectrum that includes hypopituitarism (58%), HPE (6%) or other brain structure abnormalities (15%), orofacial clefting (17%) and dysmorphic facial features (35%). We establish that truncating and Zn-finger variants in GLI2 are associated with a high risk of hypopituitarism, and that a solitary median maxillary central incisor is part of the GLI2-related phenotypic variability. The most prevalent phenotypic feature is post-axial polydactyly (65%) which is also the mildest phenotypic expression of the condition, reported in many parents of individuals with systemic findings. Our approach clarifies clinical risks and the important messages to discuss in counseling for a pathogenic GLI2 variant.

Epidemiology of Male Hypogonadism

The epidemiology of male hypogonadism has been understudied. Of the known causes of endogenous androgen deficiency, only Klinefelter syndrome is common with a likely population prevalence of greater than 5:10,000 men (possibly as high as 10-25:10,000). Mild traumatic injury might also be a common cause of androgen deficiency (prevalence 5-10:10,000 men), but large, long-term studies must be completed to confirm this prevalence estimation that might be too high. The classic causes of male androgen deficiency-hyperprolactinemia, pituitary macroadenoma, endogenous Cushing syndrome, and iron overload syndrome-are rare (prevalence < 10,000 men).

Genetics of congenital olfactory dysfunction: a systematic review of the literature

Olfaction, as one of our 5 senses, plays an important role in our daily lives. It is connected to proper nutrition, social interaction, and protection mechanisms. Disorders affecting this sense consequently also affect the patients' general quality of life. Because the underlying genetics of congenital olfactory disorders (COD) have not been thoroughly investigated yet, this systematic review aimed at providing information on genes that have previously been reported to be mutated in patients suffering from COD. This was achieved by systematically reviewing existing literature on 3 databases, namely PubMed, Ovid Medline, and ISI Web of Science. Genes and the type of disorder, that is, isolated and/or syndromic COD were included in this study, as were the patients' associated abnormal features, which were categorized according to the affected organ(-system). Our research yielded 82 candidate genes/chromosome loci for isolated and/or syndromic COD. Our results revealed that the majority of these are implicated in syndromic COD, a few accounted for syndromic and isolated COD, and the least underly isolated COD. Most commonly, structures of the central nervous system displayed abnormalities. This study is meant to assist clinicians in determining the type of COD and detecting potentially abnormal features in patients with confirmed genetic variations. Future research will hopefully expand this list and thereby further improve our understanding of COD.

Genetics of congenital central hypogonadism

The diagnostic suspicion of congenital central hypogonadism is based on clinical signs. Biochemical confirmation is challenging, especially after the postnatal activation stage of the hypothalamic-pituitary-testicular axis. Sertoli cell markers, like AMH and inhibin B, have become useful tools for the diagnosis of male central hypogonadism during childhood. Different mechanisms can participate in the aetiopathogenesis of central hypogonadism, leading to a deficiency in the production of gonadotrophins. Advances in genetic studies, mainly next generation sequencing techniques, have allowed the discovery of a large number of genes related to central hypogonadism. However, a causal variant is found in approximately half of the patients. Central hypogonadism has been classically described as a pathology with variable expressivity and incomplete penetrance. Currently, these characteristics are known to be partially explained by the presence of oligogenicity, that is the participation of variants in more than one gene in the aetiology of central hypogonadism in the same patient.

Defects in GnRH Neuron Migration/Development and Hypothalamic-Pituitary Signaling Impact Clinical Variability of Kallmann Syndrome

Kallmann syndrome (KS) is a combination of isolated hypogonadotropic hypogonadism (IHH) with olfactory dysfunction, representing a heterogeneous disorder with a broad phenotypic spectrum. The genetic background of KS has not yet been fully established. This study was conducted on 46 Polish KS subjects (41 males, 5 females; average age: 29 years old). The studied KS patients were screened for defects in a 38-gene panel with next-generation sequencing (NGS) technology. The analysis revealed 27 pathogenic and likely pathogenic (P/LP) variants, and 21 variants of uncertain significance (VUS). The P/LP variants were detected in 20 patients (43.5%). The prevalence of oligogenic P/LP defects in selected genes among KS patients was 26% (12/46), whereas the co-occurrence of other variants was detected in 43% (20 probands). The examined KS patients showed substantial genotypic and phenotypic variability. A marked difference in non-reproductive phenotypes, involving defects in genes responsible for GnRH neuron development/migration and genes contributing to pituitary development and signaling, was observed. A comprehensive gene panel for IHH testing enabled the detection of clinically relevant variants in the majority of KS patients, which makes targeted NGS an effective molecular tool. The significance of oligogenicity and the high incidence of alterations in selected genes should be further elucidated.

Congenital Hypogonadotropic Hypogonadism with Anosmia and Gorlin Features Caused by a PTCH1 Mutation Reveals a New Candidate Gene for Kallmann Syndrome

BACKGROUND

Two loci (CHD7 and SOX10) underlying Kallmann syndrome (KS) were discovered through clinical and genetic analysis of CHARGE and Waardenburg syndromes, conditions that include congenital anosmia caused by olfactory bulb (CA/OBs) defects and congenital hypogonadotropic hypogonadism (CHH). We hypothesized that other candidate genes for KS could be discovered by analyzing rare syndromes presenting with these signs. Study Design, Size, Duration: We first investigated a family with Gorlin-Goltz syndrome (GGS) in which affected members exhibited clinical signs suggesting KS. Participants/Materials, Methods: Proband and family members underwent detailed clinical assessment. The proband received detailed neuroendocrine evaluation. Genetic analyses included sequencing the PTCH1 gene at diagnosis, followed by exome analyses of causative or candidate KS/CHH genes, in order to exclude contribution to the phenotypes of additional mutations. Exome analyses in additional 124 patients with KS/CHH probands with no additional GGS signs.

RESULTS

The proband exhibited CA, absent OBs on magnetic resonance imaging, and had CHH with unilateral cryptorchidism, consistent with KS. Pulsatile Gonadotropin-releasing hormone (GnRH) therapy normalized serum gonadotropins and increased testosterone levels, supporting GnRH deficiency. Genetic studies revealed 3 affected family members harbor a novel mutation of PTCH1 (c.838G> T; p.Glu280*). This unreported nonsense deleterious mutation results in either a putative truncated Ptch1 protein or in an absence of translated Ptch1 protein related to nonsense mediated messenger RNA decay. This heterozygous mutation cosegregates in the pedigree with GGS and CA with OBs aplasia/hypoplasia and with CHH in the proband suggesting a genetic linkage and an autosomal dominant mode of inheritance. No pathogenic rare variants in other KS/CHH genes cosegregated with these phenotypes. In additional 124 KS/CHH patients, 3 additional heterozygous, rare missense variants were found and predicted in silico to be damaging: p.Ser1203Arg, p.Arg1192Ser, and p.Ile108Met.

CONCLUSION

This family suggests that the 2 main signs of KS can be included in GGS associated with PTCH1 mutations. Our data combined with mice models suggest that PTCH1 could be a novel candidate gene for KS/CHH and reinforce the role of the Hedgehog signaling pathway in pathophysiology of KS and GnRH neuron migration.

A novel GLI2 mutation responsible for congenital hypopituitarism and polymalformation syndrome

OBJECTIVE

We report a novel GLI2 frameshift mutation and describe the phenotypic spectrum of mutations within this gene.

PATIENTS AND METHODS

A male with congenital hypopituitarism and polymalformation syndrome was clinically, biochemically and neuroradiologically characterized. Genetic analysis for congenital hypopituitarism was performed using a targeted NGS custom gene panel.

RESULTS

A heterozygous frameshift mutation, NM_005270.4:c.2125del, p.(Leu709Trpfs*15), was identified in GLI2 exon 12. This mutation has not been previously reported and confirms the diagnosis of Culler-Jones syndrome (MIM #615849).

CONCLUSION

GLI2 mutations should be suspected in the presence of congenital hypopitutarism, characteristic facial abnormalities and polydactyly.

WDR11-mediated Hedgehog signalling defects underlie a new ciliopathy related to Kallmann syndrome

WDR11 has been implicated in congenital hypogonadotropic hypogonadism (CHH) and Kallmann syndrome (KS), human developmental genetic disorders defined by delayed puberty and infertility. However, WDR11's role in development is poorly understood. Here, we report that WDR11 modulates the Hedgehog (Hh) signalling pathway and is essential for ciliogenesis. Disruption of WDR11 expression in mouse and zebrafish results in phenotypic characteristics associated with defective Hh signalling, accompanied by dysgenesis of ciliated tissues. Wdr11-null mice also exhibit early-onset obesity. We find that WDR11 shuttles from the cilium to the nucleus in response to Hh signalling. WDR11 regulates the proteolytic processing of GLI3 and cooperates with the transcription factor EMX1 in the induction of downstream Hh pathway gene expression and gonadotrophin-releasing hormone production. The CHH/KS-associated human mutations result in loss of function of WDR11. Treatment with the Hh agonist purmorphamine partially rescues the WDR11 haploinsufficiency phenotypes. Our study reveals a novel class of ciliopathy caused by WDR11 mutations and suggests that CHH/KS may be a part of the human ciliopathy spectrum.

Six3 regulates optic nerve development via multiple mechanisms

Malformations of the optic nerve lead to reduced vision or even blindness. During optic nerve development, retinal ganglion cell (RGC) axons navigate across the retina, exit the eye to the optic stalk (OS), and cross the diencephalon midline at the optic chiasm en route to their brain targets. Many signalling molecules have been implicated in guiding various steps of optic nerve pathfinding, however much less is known about transcription factors regulating this process. Here we show that in zebrafish, reduced function of transcription factor Six3 results in optic nerve hypoplasia and a wide repertoire of RGC axon pathfinding errors. These abnormalities are caused by multiple mechanisms, including abnormal eye and OS patterning and morphogenesis, abnormal expression of signalling molecules both in RGCs and in their environment and anatomical deficiency in the diencephalic preoptic area, where the optic chiasm normally forms. Our findings reveal new roles for Six3 in eye development and are consistent with known phenotypes of reduced SIX3 function in humans. Hence, the new zebrafish model for Six3 loss of function furthers our understanding of the mechanisms governing optic nerve development and Six3-mediated eye and forebrain malformations.

Novel application of luciferase assay for the in vitro functional assessment of KAL1 variants in three females with septo-optic dysplasia (SOD)

KAL1 is implicated in 5% of Kallmann syndrome cases, a disorder which genotypically overlaps with septo-optic dysplasia (SOD). To date, a reporter-based assay to assess the functional consequences of KAL1 mutations is lacking. We aimed to develop a luciferase assay for novel application to functional assessment of rare KAL1 mutations detected in a screen of 422 patients with SOD. Quantitative analysis was performed using L6-myoblasts stably expressing FGFR1, transfected with a luciferase-reporter vector containing elements of the FGF-responsive osteocalcin promoter. The two variants assayed [p.K185N, p.P291T], were detected in three females with SOD (presenting with optic nerve hypoplasia, midline and pituitary defects). Our novel assay revealed significant decreases in transcriptional activity [p.K185N: 21% (p < 0.01); p.P291T: 40% (p < 0.001)]. Our luciferase-reporter assay, developed for assessment of KAL1 mutations, determined that two variants in females with hypopituitarism/SOD are loss-of-function; demonstrating that this assay is suitable for quantitative assessment of mutations in this gene.

Role of GLI2 in hypopituitarism phenotype

GLI2 is a zinc-finger transcription factor involved in the Sonic Hedgehog pathway. Gli2 mutant mice have hypoplastic anterior and absent posterior pituitary glands. We reviewed the literature for patients with hypopituitarism and alterations in GLI2. Twenty-five patients (16 families) had heterozygous truncating mutations, and the phenotype frequently included GH deficiency, a small anterior pituitary lobe and an ectopic/undescended posterior pituitary lobe on magnetic resonance imaging and postaxial polydactyly. The inheritance pattern was autosomal dominant with incomplete penetrance and variable expressivity. The mutation was frequently inherited from an asymptomatic parent. Eleven patients had heterozygous non-synonymous GLI2 variants that were classified as variants of unknown significance, because they were either absent from or had a frequency lower than 0.001 in the databases. In these patients, the posterior pituitary was also ectopic, but none had polydactyly. A third group of variants found in patients with hypopituitarism were considered benign because their frequency was ≥ 0.001 in the databases. GLI2 is a large and polymorphic gene, and sequencing may identify variants whose interpretation may be difficult. Incomplete penetrance implies in the participation of other genetic and/or environmental factors. An interaction between Gli2 mutations and prenatal ethanol exposure has been demonstrated in mice dysmorphology. In conclusion, a relatively high frequency of GLI2 mutations and variants were identified in patients with congenital GH deficiency without other brain defects, and most of these patients presented with combined pituitary hormone deficiency and an ectopic posterior pituitary lobe. Future studies may clarify the relative role and frequency of GLI2 alterations in the aetiology of hypopituitarism.

Silencing of TGIF1 in bone mesenchymal stem cells applied to the post-operative rotator cuff improves both functional and histologic outcomes

Stem cells have long been hypothesized to improve outcomes following rotator cuff repair. However, these cells must be signaled in order to do so. TGIF1 is a transcription factor that has been found to be down-regulated in cells involved in chondrogenesis. We therefore wished to examine whether stem cells expressing lower levels of TGIF1 could better improve outcomes following rotator cuff repair than stem cells expressing normal levels of TGIF1. Bone mesenchymal stem cells (BMSCs) were transduced with TGIF1 siRNA to suppress native TGIF1. Nontransduced BMSCs were also obtained for the control group. Following suprapinatus tendon repair, rats were either treated with transduced BMSCs or nontransduced BMSCs. Histologic and functional testing were performed on both groups. Rats treated with transduced TGIF1 siRNA BMSCs following suprapinatus repair expressed significantly higher levels of chondrogenic proteins at 4 weeks than rats treated with nontransduced BMSCs. Further, rats treated with BMSCs transduced with TGIF1 siRNA had both a significantly greater maximum load at failure and stiffness. Rats treated with transduced TGIF1 siRNA BMSCs following supraspinatus repair perform better both histologically and functionally at 4 weeks.

Renal agenesis in Kallmann syndrome: a network approach

Kallmann syndrome (KS) is defined by the combination of isolated hypogonadotrophic hypogonadism (IHH) and anosmia, with renal agenesis occurring in 30% of KS cases with KAL1 gene mutations. Unlike other KS-related disorders, renal agenesis cannot be directly associated with mutations in the KAL1 gene. We hypothesized that protein interaction networks may suggest a link between genes currently known to be associated with KS on the one hand and those associated with renal agenesis on the other hand. We created a STRING protein interaction network from KS-related genes and renal-agenesis-associated genes and analyzed it with Cytoscape 3.0.1 network software. The STRING protein interaction network provided a conceptual framework for current knowledge on the subject of renal morphogenesis in Kallmann syndrome. In addition, STRING and Cytoscape 3.0.1 software identified new potential KS renal-aplasia-associated genes (PAX2, BMP4, and SOX10). The use of protein-protein interaction networks and network analysis tools provided interesting insights and possible directions for future studies on the subject of renal aplasia in Kallmann syndrome.

Pathogenic mutations in GLI2 cause a specific phenotype that is distinct from holoprosencephaly

BACKGROUND

Mutations in GLI2 have been associated with holoprosencephaly (HPE), a neuroanatomic anomaly resulting from incomplete cleavage of the developing forebrain, and an HPE-like phenotype involving pituitary anomalies and polydactyly.

OBJECTIVE

To characterise the genotypic and phenotypic findings in individuals with GLI2 variants and clarify clinical findings in individuals with loss-of-function mutations.

METHODS

Through the National Institutes of Health and collaborating centres, ∼400 individuals with HPE spectrum disorders, endocrine disorders or craniofacial anomalies were screened for GLI2 mutations. Results were combined with all published cases. We compared the clinical and molecular features of individuals with truncating mutations to individuals with variants of unknown significance (defined as not resulting in protein truncation, reported in normal controls and/or deemed unlikely to be pathogenic by functional prediction software).

RESULTS

112 individuals with variants in GLI2 were identified, with 43 having truncating mutations. Individuals with truncating mutations were more likely to have both pituitary anomalies and polydactyly versus those with variants of unknown significance (p<0.0001 by Fisher's exact test); only 1 of 43 had frank HPE. These individuals were more likely to have recognised penetrance (polydactyly or pituitary anomalies or both) than those without truncating mutations (p=0.0036 by Fisher's exact test). A common facial phenotype was seen in individuals (with midface hypoplasia, cleft lip/palate and hypotelorism) with truncating mutations.

CONCLUSIONS

Individuals with truncating mutations in GLI2 typically present with pituitary anomalies, polydactyly and subtle facial features rather than HPE. This will be helpful in screening populations for GLI2 mutations and for counselling affected patients.

TRIAL REGISTRATION

98-HG-0249/04-HG-0093.

Clinical, genetic and imaging findings identify new causes for corpus callosum development syndromes

The corpus callosum is the largest fibre tract in the brain, connecting the two cerebral hemispheres, and thereby facilitating the integration of motor and sensory information from the two sides of the body as well as influencing higher cognition associated with executive function, social interaction and language. Agenesis of the corpus callosum is a common brain malformation that can occur either in isolation or in association with congenital syndromes. Understanding the causes of this condition will help improve our knowledge of the critical brain developmental mechanisms required for wiring the brain and provide potential avenues for therapies for callosal agenesis or related neurodevelopmental disorders. Improved genetic studies combined with mouse models and neuroimaging have rapidly expanded the diverse collection of copy number variations and single gene mutations associated with callosal agenesis. At the same time, advances in our understanding of the developmental mechanisms involved in corpus callosum formation have provided insights into the possible causes of these disorders. This review provides the first comprehensive classification of the clinical and genetic features of syndromes associated with callosal agenesis, and provides a genetic and developmental framework for the interpretation of future research that will guide the next advances in the field.

Whole-exome sequencing: opportunities in pediatric endocrinology

Pediatric endocrinology services see a wide variety of patients with diverse clinical symptoms, including disorders of growth, metabolism, bone and sexual development. Molecular diagnosis plays an important role in this branch of medicine. Traditional PCR-based Sanger sequencing is a mainstay format for molecular testing in pediatric cases despite its relatively high cost, but the large number of gene defects associated with the various endocrine disorders renders gene-by-gene testing increasingly unattractive. Using new high-throughput sequencing technologies, whole genomes, whole exomes or candidate-gene panels (targeted gene sequencing) can now be cost-effectively sequenced for endocrine patients. Based on our own recent experiences with exome sequencing in a research context, we describe the general clinical ascertainment of relevant pediatric endocrine patients, compare different formats for next-generation sequencing and provide examples. Our view is that protocols involving next-generation sequencing should now be considered as an appropriate component of routine clinical diagnosis for relevant patients.

FGFR1 mutations cause Hartsfield syndrome, the unique association of holoprosencephaly and ectrodactyly

Background

Harstfield syndrome is the rare and unique association of holoprosencephaly (HPE) and ectrodactyly, with or without cleft lip and palate, and variable additional features. All the reported cases occurred sporadically. Although several causal genes of HPE and ectrodactyly have been identified, the genetic cause of Hartsfield syndrome remains unknown. We hypothesised that a single key developmental gene may underlie the co-occurrence of HPE and ectrodactyly.

Methods

We used whole exome sequencing in four isolated cases including one case-parents trio, and direct Sanger sequencing of three additional cases, to investigate the causative variants in Hartsfield syndrome.

Results

We identified a novel FGFR1 mutation in six out of seven patients. Affected residues are highly conserved and are located in the extracellular binding domain of the receptor (two homozygous mutations) or the intracellular tyrosine kinase domain (four heterozygous de novo variants). Strikingly, among the six novel mutations, three are located in close proximity to the ATP's phosphates or the coordinating magnesium, with one position required for kinase activity, and three are adjacent to known mutations involved in Kallmann syndrome plus other developmental anomalies.

Conclusions

Dominant or recessive FGFR1 mutations are responsible for Hartsfield syndrome, consistent with the known roles of FGFR1 in vertebrate ontogeny and conditional Fgfr1-deficient mice. Our study shows that, in humans, lack of accurate FGFR1 activation can disrupt both brain and hand/foot midline development, and that FGFR1 loss-of-function mutations are responsible for a wider spectrum of clinical anomalies than previously thought, ranging in severity from seemingly isolated hypogonadotropic hypogonadism, through Kallmann syndrome with or without additional features, to Hartsfield syndrome at its most severe end.