SEMA6B variants cause intellectual disability and alter dendritic spine density and axon guidance

Intellectual disability is a neurodevelopmental disorder frequently caused by monogenic defects. In this study, we collected 14 SEMA6B heterozygous variants in 16 unrelated patients referred for intellectual disability to different centres. Whereas until now SEMA6B variants have mainly been reported in patients with progressive myoclonic epilepsy, our study indicates that the clinical spectrum is wider, and also includes non-syndromic intellectual disability without epilepsy or myoclonus. To assess the pathogenicity of these variants, selected mutated forms of Sema6b were overexpressed in HEK293T cells and in primary neuronal cultures. shRNAs targeting Sema6b were also used in neuronal cultures to measure the impact of the decreased Sema6b expression on morphogenesis and synaptogenesis. The overexpression of some variants leads to a subcellular mislocalisation of SEMA6B protein in HEK293T cells and to a reduced spine density due to loss of mature spines in neuronal cultures. Sema6b knock-down also impairs spine density and spine maturation. In addition, we conducted in vivo rescue experiments in chicken embryos with the selected mutated forms of Sema6b expressed in commissural neurons after knock-down of endogenous SEMA6B. We observed that expression of these variants in commissural neurons fails to rescue the normal axon pathway. In conclusion, identification of SEMA6B variants in patients presenting with an overlapping phenotype with intellectual disability, and functional studies highlight the important role of SEMA6B in neuronal development, notably in spine formation and maturation, and in axon guidance. This study adds SEMA6B to the list of intellectual disability-related genes.

Partners in care

This festschrift contribution, written for my colleague and mentor John Graham, reflects on geneticist-genetic counselor interactions in clinical care, samples of alternative models of care for pediatric and general genetic counselors, and avenues for expanding access to genetic healthcare services utilizing genetic counselors.

Evaluating co-created patient-facing materials to increase understanding of genetic test results

Patients often have difficulty understanding genetic test reports. Technical language and jargon can impede comprehension and limit patients using results to act on findings. One potential way to improve patient understanding of genetic test reports is to provide patient-facing materials. This study aimed to examine understandability and actionability of co-created patient-facing materials for genetic test results in a research context. We combined interprofessional perspectives and patient engagement to co-create patient-facing materials for patients undergoing research genetic testing for congenital hypogonadotropic hypogonadism (Kallmann syndrome). The iterative development process was guided by principles of health literacy and human-centered design (i.e., design thinking). Readability was assessed using eight validated algorithms. Patients and parents evaluated materials using a web-based survey. The gold standard Patient Education Materials Assessment Tool for print materials (PEMAT-P) was employed to measure understandability (content, style, use of numbers, organization, design, use of visual aids) and actionability. PEMAT-P scores >80% were considered high quality. Results were analyzed descriptively and correlations performed to identify relationships between education/health literacy and PEMAT-P ratings. A consensus score of eight algorithms indicated the materials were an 8^th -9th grade reading level. Our findings are consistent with the U.S. Department of Health and Human Services 'average difficulty' classification (i.e., 7th-9th grade). In total, 61 patients/parents evaluated the materials. 'Visual Aids' received the lowest mean PEMAT-P rating (89%). All other parameters scored 90%-97%. PEMAT-P scores did not differ according to educational attainment (less than college vs. college or more, p = 0.28). Participants with adequate health literacy were more likely to approve of the 'organization' of information (p < 0.05). Respondents with low health literacy had more favorable views of 'visual aids' (p < 0.01). Involving patients in a co-creation process can produce high-quality patient-facing materials that are easier to understand.

Novel pathogenic COX20 variants causing dysarthria, ataxia, and sensory neuropathy

COX20/FAM36A encodes a mitochondrial complex IV assembly factor important for COX2 activation. Only one homozygous COX20 missense mutation has been previously described in two separate consanguineous families. We report four subjects with features that include childhood hypotonia, areflexia, ataxia, dysarthria, dystonia, and sensory neuropathy. Exome sequencing in all four subjects identified the same novel COX20 variants. One variant affected the splice donor site of intron‐one (c.41A>G), while the other variant (c.157+3G>C) affected the splice donor site of intron‐two. cDNA and protein analysis indicated that no full‐length cDNA or protein was generated. These subjects expand the phenotype associated with COX20 deficiency.

FARS2 mutations presenting with pure spastic paraplegia and lesions of the dentate nuclei

Mutations in FARS2, the gene encoding the mitochondrial phenylalanine‐tRNA synthetase (mtPheRS), have been linked to a range of phenotypes including epileptic encephalopathy, developmental delay, and motor dysfunction. We report a 9‐year‐old boy with novel compound heterozygous variants of FARS2, presenting with a pure spastic paraplegia syndrome associated with bilateral signal abnormalities in the dentate nuclei. Exome sequencing identified a paternal nonsense variant (Q216X) lacking the catalytic core and anticodon‐binding regions, and a maternal missense variant (P136H) possessing partial enzymatic activity. This case confirms and expands the phenotype related to FARS2 mutations with regards to clinical presentation and neuroimaging findings.

Biallelic Mutations in TBCD, Encoding the Tubulin Folding Cofactor D, Perturb Microtubule Dynamics and Cause Early-Onset Encephalopathy

Microtubules are dynamic cytoskeletal elements coordinating and supporting a variety of neuronal processes, including cell division, migration, polarity, intracellular trafficking, and signal transduction. Mutations in genes encoding tubulins and microtubule-associated proteins are known to cause neurodevelopmental and neurodegenerative disorders. Growing evidence suggests that altered microtubule dynamics may also underlie or contribute to neurodevelopmental disorders and neurodegeneration. We report that biallelic mutations in TBCD, encoding one of the five co-chaperones required for assembly and disassembly of the αβ-tubulin heterodimer, the structural unit of microtubules, cause a disease with neurodevelopmental and neurodegenerative features characterized by early-onset cortical atrophy, secondary hypomyelination, microcephaly, thin corpus callosum, developmental delay, intellectual disability, seizures, optic atrophy, and spastic quadriplegia. Molecular dynamics simulations predicted long-range and/or local structural perturbations associated with the disease-causing mutations. Biochemical analyses documented variably reduced levels of TBCD, indicating relative instability of mutant proteins, and defective β-tubulin binding in a subset of the tested mutants. Reduced or defective TBCD function resulted in decreased soluble α/β-tubulin levels and accelerated microtubule polymerization in fibroblasts from affected subjects, demonstrating an overall shift toward a more rapidly growing and stable microtubule population. These cells displayed an aberrant mitotic spindle with disorganized, tangle-shaped microtubules and reduced aster formation, which however did not alter appreciably the rate of cell proliferation. Our findings establish that defective TBCD function underlies a recognizable encephalopathy and drives accelerated microtubule polymerization and enhanced microtubule stability, underscoring an additional cause of altered microtubule dynamics with impact on neuronal function and survival in the developing brain.

When genetic load does not correlate with phenotypic spectrum: lessons from the GnRH receptor (GNRHR)

CONTEXT

A broad spectrum of GnRH-deficient phenotypes has been identified in individuals with both mono- and biallelic GNRHR mutations.

OBJECTIVE

The objective of the study was to determine the correlation between the severity of the reproductive phenotype(s) and the number and functional severity of rare sequence variants in GNRHR.

SUBJECTS

Eight hundred sixty-three probands with different forms of GnRH deficiency, 46 family members and 422 controls were screened for GNRHR mutations. The 70 subjects (32 patients and 38 family members) harboring mutations were divided into four groups (G1-G4) based on the functional severity of the mutations (complete or partial loss of function) and the number of affected alleles (monoallelic or biallelic) with mutations, and these classes were mapped on their clinical phenotypes.

RESULTS

The prevalence of heterozygous rare sequence variants in GNRHR was significantly higher in probands vs. controls (P < 0.01). Among the G1-G3 groups (homozygous subjects with successively decreasing severity and number of mutations), the hypogonadotropic phenotype related to their genetic load. In contrast, subjects in G4, with only monoallelic mutations, demonstrated a greater diversity of clinical phenotypes.

CONCLUSIONS

In patients with GnRH deficiency and biallelic mutations in GNRHR, genetic burden defined by severity and dose is associated with clinical phenotype. In contrast, for patients with monoallelic GNRHR mutations this correlation does not hold. Taken together, these data indicate that as-yet-unidentified genetic and/or environmental factors may combine with singly mutated GNRHR alleles to produce reproductive phenotypes.

An ancient founder mutation in PROKR2 impairs human reproduction

Congenital gonadotropin-releasing hormone (GnRH) deficiency manifests as absent or incomplete sexual maturation and infertility. Although the disease exhibits marked locus and allelic heterogeneity, with the causal mutations being both rare and private, one causal mutation in the prokineticin receptor, PROKR2 L173R, appears unusually prevalent among GnRH-deficient patients of diverse geographic and ethnic origins. To track the genetic ancestry of PROKR2 L173R, haplotype mapping was performed in 22 unrelated patients with GnRH deficiency carrying L173R and their 30 first-degree relatives. The mutation's age was estimated using a haplotype-decay model. Thirteen subjects were informative and in all of them the mutation was present on the same ~123 kb haplotype whose population frequency is ≤10%. Thus, PROKR2 L173R represents a founder mutation whose age is estimated at approximately 9000 years. Inheritance of PROKR2 L173R-associated GnRH deficiency was complex with highly variable penetrance among carriers, influenced by additional mutations in the other PROKR2 allele (recessive inheritance) or another gene (digenicity). The paradoxical identification of an ancient founder mutation that impairs reproduction has intriguing implications for the inheritance mechanisms of PROKR2 L173R-associated GnRH deficiency and for the relevant processes of evolutionary selection, including potential selective advantages of mutation carriers in genes affecting reproduction.

Olfactory phenotypic spectrum in idiopathic hypogonadotropic hypogonadism: pathophysiological and genetic implications

CONTEXT

The olfactory phenotype in patients with idiopathic hypogonadotropic hypogonadism (IHH) ranges from complete anosmia (Kallmann syndrome) to normosmia (normosmic IHH). However, the true prevalence of intermediary olfactory phenotypes (hyposmia) in IHH patients has not yet been assessed, and systematic correlations with anatomical and genetic abnormalities have not been reported.

OBJECTIVE

The objective of this study was to evaluate olfactory function in a large IHH cohort and correlate these findings with olfactory magnetic resonance imaging (MRI) and underlying genetic etiology.

DESIGN AND SETTING

We conducted a cross-sectional case-control study at an academic referral center.

PATIENTS

A total of 286 IHH patients (201 males and 85 females) and 2183 healthy historic controls (1011 males and 1172 females) were studied.

MAIN OUTCOME MEASURES

We measured olfactory function using the University of Pennsylvania Smell Identification Test; in 208 subjects, the genetic etiology of IHH was ascertained by DNA sequencing; in a minor subset [39 of 286 subjects (13%)], olfactory structures were determined by MRI.

RESULTS

In the IHH cohort, 31.5% were anosmic, 33.6% were hyposmic, and 34.9% were normosmic. Most hyposmic (seven of 11) subjects with MRI data exhibited olfactory structure abnormalities. Of hyposmic subjects, 39.5% harbored mutations in genes involved in either GnRH neuronal migration or GnRH secretion.

CONCLUSIONS

IHH subjects display a broad spectrum of olfactory function, with a significant hyposmic phenotype in nearly one third of subjects. The hyposmic subjects harbor mutations in genes affecting GnRH neuronal migration and its secretion, suggesting a pathophysiological overlap between Kallmann syndrome and normosmic IHH. Accurate olfactory phenotyping in IHH subjects will inform the pathophysiology of this condition and guide genetic testing.

Genetic counseling for isolated GnRH deficiency

As our understanding of the complexities of the various etiologies and complex genetic architecture of GnRH deficiency grows, so too does the need to apply newly-developed genetic tools in a way that: (a) is meaningful to individuals and their families; (b) integrates all of the phenotypic features of this syndrome into a rationale; and (c) provides up-to-date diagnostic technologies in a cost-effective algorithm of genetic testing. Genetic counseling aims to accomplish these goals through ascertainment of detailed family histories, targeted comprehensive phenotypic evaluations, informed selection of genetic testing, interpretation of genetic test results, and the provision of highly specific risk assessments and psychological support to individuals diagnosed with this reproductive condition. This chapter offers a guide to incorporating this rapidly evolving state of knowledge of the pedigree and phenotypes into the process of selecting and prioritizing genetic testing. In addition, the provision of risk assessment that accounts for nuanced genetic concepts such as variable expressivity, incomplete penetrance, and oligogenicity, all of which are emerging features of the genetics of this clinical syndrome, is considered. Beyond translating genetic information, genetic counseling should address the psychological impact of embarrassment, shame, anxiety, and guilt that are often seen among individuals with reproductive disorders.

The role of the prokineticin 2 pathway in human reproduction: evidence from the study of human and murine gene mutations

A widely dispersed network of hypothalamic GnRH neurons controls the reproductive axis in mammals. Genetic investigation of the human disease model of isolated GnRH deficiency has revealed several key genes crucial for GnRH neuronal ontogeny and GnRH secretion. Among these genes, prokineticin 2 (PROK2), and PROK2 receptor (PROKR2) have recently emerged as critical regulators of reproduction in both mice and humans. Both prok2- and prokr2-deficient mice recapitulate the human Kallmann syndrome phenotype. Additionally, PROK2 and PROKR2 mutations are seen in humans with Kallmann syndrome, thus implicating this pathway in GnRH neuronal migration. However, PROK2/PROKR2 mutations are also seen in normosmic GnRH deficiency, suggesting a role for the prokineticin signaling system in GnRH biology that is beyond neuronal migration. This observation is particularly surprising because mature GnRH neurons do not express PROKR2. Moreover, mutations in both PROK2 and PROKR2 are predominantly detected in the heterozygous state with incomplete penetrance or variable expressivity frequently seen within and across pedigrees. In some of these pedigrees, a "second hit" or oligogenicity has been documented. Besides reproduction, a pleiotropic physiological role for PROK2 is now recognized, including regulation of pain perception, circadian rhythms, hematopoiesis, and immune response. Therefore, further detailed clinical studies of patients with PROK2/PROKR2 mutations will help to map the broader biological role of the PROK2/PROKR2 pathway and identify other interacting genes/proteins that mediate its molecular effects in humans.

Expanding the phenotype and genotype of female GnRH deficiency

CONTEXT

GnRH deficiency is a rare genetic disorder of absent or partial pubertal development. The clinical and genetic characteristics of GnRH-deficient women have not been well-described.

OBJECTIVE

To determine the phenotypic and genotypic spectrum of a large series of GnRH-deficient women.

DESIGN, SETTING, AND SUBJECTS

Retrospective study of 248 females with GnRH deficiency evaluated at an academic medical center between 1980 and 2010.

MAIN OUTCOME MEASURES

Clinical presentation, baseline endogenous GnRH secretory activity, and DNA sequence variants in 11 genes associated with GnRH deficiency.

RESULTS

Eighty-eight percent had undergone pubarche, 51% had spontaneous thelarche, and 10% had 1-2 menses. Women with spontaneous thelarche were more likely to demonstrate normal pubarche (P = 0.04). In 27% of women, neuroendocrine studies demonstrated evidence of some endogenous GnRH secretory activity. Thirty-six percent (a large excess relative to controls) harbored a rare sequence variant in a gene associated with GnRH deficiency (87% heterozygous and 13% biallelic), with variants in FGFR1 (15%), GNRHR (6.6%), and PROKR2 (6.6%) being most prevalent. One woman had a biallelic variant in the X-linked gene, KAL1, and nine women had heterozygous variants.

CONCLUSIONS

The clinical presentation of female GnRH deficiency varies from primary amenorrhea and absence of any secondary sexual characteristics to spontaneous breast development and occasional menses. In this cohort, rare sequence variants were present in all of the known genes associated with GnRH deficiency, including the novel identification of GnRH-deficient women with KAL1 variants. The pathogenic mechanism through which KAL1 variants disrupt female reproductive development requires further investigation.

TAC3/TACR3 mutations reveal preferential activation of gonadotropin-releasing hormone release by neurokinin B in neonatal life followed by reversal in adulthood

CONTEXT

Mutations in TAC3 and TACR3 (encoding neurokinin B and its receptor) have been identified in Turkish patients with idiopathic hypogonadotropic hypogonadism (IHH), but broader populations have not yet been tested and genotype-phenotype correlations have not been established.

OBJECTIVE

A broad cohort of normosmic IHH probands was screened for mutations in TAC3/TACR3 to evaluate the prevalence of such mutations and define the genotype/phenotype relationships.

DESIGN AND SETTING

The study consisted of sequencing of TAC3/TACR3, in vitro functional assays, and neuroendocrine phenotyping conducted in tertiary care centers worldwide.

PATIENTS OR OTHER PARTICIPANTS

345 probands, 18 family members, and 292 controls were studied.

INTERVENTION

Reproductive phenotypes throughout reproductive life and before and after therapy were examined.

MAIN OUTCOME MEASURE

Rare sequence variants in TAC3/TACR3 were detected.

RESULTS

In TACR3, 19 probands harbored 13 distinct coding sequence rare nucleotide variants [three nonsense mutations, six nonsynonymous, four synonymous (one predicted to affect splicing)]. In TAC3, one homozygous single base pair deletion was identified, resulting in complete loss of the neurokinin B decapeptide. Phenotypic information was available on 16 males and seven females with coding sequence variants in TACR3/TAC3. Of the 16 males, 15 had microphallus; none of the females had spontaneous thelarche. Seven of the 16 males and five of the seven females were assessed after discontinuation of therapy; six of the seven males and four of the five females demonstrated evidence for reversibility of their hypogonadotropism.

CONCLUSIONS

Mutations in the neurokinin B pathway are relatively common as causes of hypogonadism. Although the neurokinin B pathway appears essential during early sexual development, its importance in sustaining the integrity of the hypothalamic-pituitary-gonadal axis appears attenuated over time.

Familial risk for chronic disease and intent to share family history with a health care provider among urban Appalachian women, southwestern Ohio, 2007

INTRODUCTION

Family history of certain chronic diseases is a risk factor for those diseases. We assessed demographic characteristics associated with familial risk for common diseases and whether familial risk was associated with intent to share family history with a health care provider among urban Appalachian women.

METHODS

Urban Appalachian women (N = 88) with less than a college education participated in education sessions about family history in health promotion in southwest Ohio. Participants used My Family Health Portrait, electronically or on paper, to document their level of familial risk. Evaluations completed after each session gauged intent to share family history with a health care provider.

RESULTS

Participants who used the paper version of My Family Health Portrait had lower odds of high familial risk for diabetes, heart disease, and stroke. Most participants (n = 62, 77%) reported that they intended to share their family history with a health care provider. Factors associated with intent to share family history included younger age, use of the electronic family history tool, and high familial risk of heart disease.

CONCLUSION

The large proportion of women who intended to share family history with a health care provider may reflect the success of the educational component. Since familial risk for chronic disease is high among these urban Appalachian women, the need to share family history should continue to be promoted.

Decisions to seek healthcare based on family health history among urban Appalachian women

Family health history (FHH) is a valuable health promotion tool that can be used to assess disease risk and make lifestyle and screening recommendations. However, few FHH resources exist for medically underserved populations such as the urban Appalachian community in Cincinnati Ohio. Women of Appalachian heritage with less than a college education who did and did not participate in a prior FHH education session were interviewed by phone in a semi-structured format. Interviewees were asked to discuss their understanding of FHH and the role FHH played in seeking (or not seeking) medical care. Analysis of their discussion identified four overarching themes as well as a model identifying conditions that facilitated or impeded the choice to seek medical care based on FHH. Findings from this study may be used to develop targeted FHH educational interventions in the urban Appalachian and other communities.

A family history demonstration project among women in an urban Appalachian community

BACKGROUND

Family health history (FHH) is promoted to consumers by the Surgeon General as a tool to improve health and prevent disease. However, few FHH resources exist for medically underserved populations such as the urban Appalachian community in Southwest Ohio.

OBJECTIVES

To engage and educate urban Appalachian women about the importance and collection of their own FHH.

METHODS

Researchers partnered with six community organizations to develop a model Family History Demonstration Project. Focus groups were held with urban Appalachian women to determine how they would like to learn about their FHH. Resources and an educational intervention were developed based on focus group findings with input from the academic and community partners. Participants in the project recorded their family history and evaluated the education sessions and materials.

RESULTS

Eleven fact sheets and four educational presentations were developed based on feedback from the target community. One hundred women participated in two family history education sessions. Learning objectives for both education sessions were met. All participants recorded their family history electronically or on paper and 91% of participants found the first education session (ES1) very helpful at teaching the importance of FHH.

CONCLUSIONS

Community organizations and university researchers partnered to develop a model Family History Demonstration Project with input from community members. Evaluations of the project were positive. Future efforts should focus on sustainable dissemination of the educational programs and resulting health outcomes.