Partial duplication of DHH causes minifascicular neuropathy: A novel mutation detection of DHH

New observations on minifascicular neuropathy with sex-dependent gonadal dysgenesis: a case series with nerve ultrasound assessment

BACKGROUND

Gonadal dysgenesis with minifascicular neuropathy (GDMN) is a rare autosomal recessive condition associated with biallelic DHH pathogenic variants. In 46, XY individuals, this disorder is characterized by an association of minifascicular neuropathy (MFN) and gonadal dysgenesis, while in 46, XX subjects only the neuropathic phenotype is present. Very few patients with GDMN have been reported so far. We describe four patients with MFN due to a novel DHH likely pathogenic homozygous variant and the results of nerve ultrasound assessment.

METHODS

This retrospective observational study included 4 individuals from 2 unrelated Brazilian families evaluated for severe peripheral neuropathy. Genetic diagnosis was performed with a peripheral neuropathy next-generation sequencing (NGS) panel based on whole exome sequencing focused analysis that included a control SRY probe to confirm genetic sex. Clinical characterization, nerve conduction velocity studies, and high-resolution ultrasound nerve evaluation were performed in all subjects.

RESULTS

Molecular analysis disclosed in all subjects the homozygous DHH variant p.(Leu335Pro). Patients had a striking phenotype, with marked trophic changes of extremities, sensory ataxia, and distal anesthesia due to a sensory-motor demyelinating polyneuropathy. One 46, XY phenotypically female individual had gonadal dysgenesis. High-resolution nerve ultrasound showed typical minifascicular formation and increased nerve area in at least one of the nerves assessed in all patients.

CONCLUSION

Gonadal dysgenesis with minifascicular neuropathy is a severe autosomal recessive neuropathy characterized by trophic alterations in limbs, sensory ataxia, and distal anesthesia. Nerve ultrasound studies are very suggestive of this condition and may help to avoid invasive nerve biopsies.

Hedgehog Signaling in Gonadal Development and Function

Three distinct hedgehog (HH) molecules, (sonic, desert, and indian), two HH receptors (PTCH1 and PTCH2), a membrane bound activator (SMO), and downstream three transcription factors (GLI1, GLI2, and GLI3) are the major components of the HH signaling. These signaling molecules were initially identified in Drosophila melanogaster. Later, it has been found that the HH system is highly conserved across species and essential for organogenesis. HH signaling pathways play key roles in the development of the brain, face, skeleton, musculature, lungs, and gastrointestinal tract. While the sonic HH (SHH) pathway plays a major role in the development of the central nervous system, the desert HH (DHH) regulates the development of the gonads, and the indian HH (IHH) acts on the development of bones and joints. There are also overlapping roles among the HH molecules. In addition to the developmental role of HH signaling in embryonic life, the pathways possess vital physiological roles in testes and ovaries during adult life. Disruption of DHH and/or IHH signaling results in ineffective gonadal steroidogenesis and gametogenesis. While DHH regulates the male gonadal functions, ovarian functions are regulated by both DHH and IHH. This review article focuses on the roles of HH signaling in gonadal development and reproductive functions with an emphasis on ovarian functions. We have acknowledged the original research work that initially reported the findings and discussed the subsequent studies that have further analyzed the role of HH signaling in testes and ovaries.

Peripheral glia diversity

Recent years have seen an evolving appreciation for the role of glial cells in the nervous system. As we move away from the typical neurocentric view of neuroscience, the complexity and variability of central nervous system glia is emerging, far beyond the three main subtypes: astrocytes, oligodendrocytes, and microglia. Yet the diversity of the glia found in the peripheral nervous system remains rarely discussed. In this review, we discuss the developmental origin, morphology, and function of the different populations of glia found in the peripheral nervous system, including: myelinating Schwann cells, Remak Schwann cells, repair Schwann cells, satellite glia, boundary cap-derived glia, perineurial glia, terminal Schwann cells, glia found in the skin, olfactory ensheathing cells, and enteric glia. The morphological and functional heterogeneity of glia found in the periphery reflects the diverse roles the nervous system performs throughout the body. Further, it highlights a complexity that should be appreciated and considered when it comes to a complete understanding of the peripheral nervous system in health and disease.

Case Report: Long-term follow-up of desert hedgehog variant caused 46, XY gonadal dysgenesis with multiple complications in a Chinese child

Background: Desert hedgehog (DHH), as a member of the Hedgehog (HH) family, is mainly involved in testicular development and peripheral nerve sheath formation. A DHH variant has been identified in patients with 46, XY gonadal dysgenesis (46, XY GD) with or without neuropathy, but few reports mention the involvement of other complications.

Case presentation: Here, we report a Chinese female patient who was hospitalized at 14.3 years old due to slow breast development for more than 1 year. She had a female genitalia phenotype and breast development started at 13 years old but progressed slowly. She was not yet menarche on admission, and she had intermittent muscle cramps in her hands and feet. Her karyotype analysis was 46, XY and the SRY gene was positive. Surgical exploration revealed no uterus or ovaries, and the pathology of bilateral gonads was dysplastic testis tissue, which was consistent with partial gonadal dysgenesis (PGD). Genetic analysis identified a homozygous pathogenic variant in DHH exon 3 (c.1027T>C, p. Cys343Arg). During the 6-year follow-up, she received estrogen replacement therapy, resulting in breast development progression without gender dysphoria. However, her peripheral neuropathy became more obvious, and a nerve conduction study (NCS) indicated decreased nerve conduction velocity and action potential. In addition, she also suffered complications such as obesity, insulin resistance, fatty liver, and gastric ulcers.

Conclusion: In the present study, we reported a case of 46, XY GD with minifascicular neuropathy caused by a DHH homozygous variant, and we summarized the reported cases worldwide. For the first time in such patients, we showed a comparison of NCS changes with age as well as the presence of multiple complications not previously reported.

Novel compound heterozygous mutations in the desert hedgehog (DHH) gene in cases of siblings with 46,XY disorders of sexual development

Background

Disorders of sex development (DSD) are congenital disorders in which the development of the chromosomal, gonadal, or anatomical sex is atypical. Mutations in various genes can impede gonadal development, hormone synthesis, or hormone function and cause DSD.

Methods

Exome sequencing was performed for two siblings with 46,XY DSD. All mutations identified by exome sequencing were confirmed by Sanger sequencing.

Results

The 13-month-old younger sibling had a female appearance of the external genital with a clitoris that was assessed as Prader III and scored 2 in the external masculinization score evaluative test. The 16-year-old elder sibling had severe hypospadias. Exome sequencing revealed compound heterozygous mutations in exon 3 of DHH in the siblings with 46,XY DSD. The frameshift mutation (NM_021044.3: c.602delC) was derived from the father and was predicted to be deleterious. The (c.937G > T) substitution mutation was derived from the mother.

Conclusions

Novel compound heterozygous mutations of DHH led to 46,XY DSD in two siblings. This study expands the phenotypic mutation spectra of DHH in patients with 46,XY DSD.

The Desert Hedgehog Signalling Pathway in Human Gonadal Development and Differences of Sex Development

While the Hedgehog signalling pathway is implicated in numerous developmental processes and maladies, variants in the Desert Hedgehog (DHH) ligand underlie a condition characterised by 46,XY gonadal dysgenesis with or without peripheral neuropathy. We discuss here the role and regulation of DHH and its signalling pathway in the developing gonads and examine the current understanding of how disruption to this pathway causes this difference of sex development (DSD) in humans.

Mutations in the desert hedgehog (DHH) gene in the disorders of sexual differentiation and male infertility

PURPOSE

To identify the contribution of mutations in the Desert Hedgehog (DHH) gene to the disorders of sexual differentiation (DSD) and male infertility.

METHODS

The study included a total 430 subjects, including 47 gonadal dysgenesis cases, 6 patients with undescended testis and infertility characterized by azoospermia, 125 infertile male patients characterized by oligoasthenozoospermia, 24 patients with oligoasthenoteratozoospermia, and 200 ethnically matched normozoospermic fertile men who had fathered a child in the last two years. Sequencing of the complete coding region of the DHH gene was undertaken to find its contribution to the DSD and male infertility.

RESULTS

We observed four novel mutations in the DHH gene in the cases with different reproductive anomalies. A synonymous substitution, c. 543C>T (p.His181His) was observed in 6.6% oligoasthenozoospermic infertile males and 1.5% normozoospermic fertile control samples (RR = 4.4077, 95%CI 1.19-16.29). Another synonymous substitution, c.990G>A (p.Ala330Ala) was observed in an infertile patient with unilateral undescended testis (case #12). Insertion of G at c.1156insG (p.Arg385fs) was observed in a case with bilateral undescended testis and azoospermia (case #23). In gonadal dysgenesis category, two mutations, insertion of G at c.1156insG (p.Arg385fs) and c.997A>G (p.Thr333Ala) substitution were observed in one case (case #34). These mutations were completely absent in control samples.

CONCLUSION

Mutations in the DHH gene impact reproduction with mild mutations affecting fertility, and severe or multiple mutations resulting in gonadal dysgenesis.

Convergent pathological and ultrasound features in hereditary syndromic and non-syndromic minifascicular neuropathy related to DHH

Minifascicular neuropathy (MN) is a rare, autosomal recessive disease with prominent structural changes of peripheral nerves. So far, it has been observed in females with a 46,XY karyotype and mutations of the Desert Hedgehog (DHH) gene, thus linking MN to gonadal dysgenesis (GD) and disorders of sex development (DSD). However, a 46,XX proband with normal female sex and gender development underwent clinical evaluations, nerve conduction studies and genetic screening for a severe motor-sensory neuropathy with a pathological phenotype that hinted at MN. Indeed, sural nerve biopsy revealed a profound disturbance of perineurium development with a thin and loose structure. High-resolution ultrasound (HRUS) also disclosed diffuse changes of nerve echotexture that visibly correlated with the pathological features. After extensive genetic testing, a novel homozygous DHH null mutation (p.Ser185*) was identified in the proband and in her sister, who was affected by a similar motor-sensory neuropathy, but was eventually found to be a 46,XY patient according to a late diagnosis of DSD with complete GD. DHH should therefore be considered as a possible cause of rare non-syndromic hereditary motor-sensory neuropathies, regardless of DSD. Furthermore, HRUS could effectively smooth the complex diagnostic workup as it demonstrated a high predictive power to detect MN, providing the same detailed correlations to the pathologic features of the nerve biopsy and Dhh-/- mice in both sisters. Hence, HRUS may assume a pivotal role in guiding molecular analysis in individuals with or without DSD.

Functional analysis of novel desert hedgehog gene variants improves the clinical interpretation of genomic data and provides a more accurate diagnosis for patients with 46,XY differences of sex development

BACKGROUND

Desert hedgehog (DHH) gene variants are known to cause 46,XY differences/disorders of sex development (DSD). We have identified six patients with 46,XY DSD with seven novel DHH gene variants. Many of these variants were classified as variants of uncertain significance due to their heterozygosity or associated milder phenotype. To assess variant pathogenicity and to refine the spectrum of DSDs associated with this gene, we have carried out the first reported functional testing of DHH gene variant activity.

METHODS

A cell co-culture method was used to assess DHH variant induction of Hedgehog signalling in cultured Leydig cells. Protein expression and subcellular localisation were also assessed for DHH variants using western blot and immunofluorescence.

RESULTS

Our co-culture method provided a robust read-out of DHH gene variant activity, which correlated closely with patient phenotype severity. While biallelic DHH variants from patients with gonadal dysgenesis showed significant loss of activity, variants found as heterozygous in patients with milder phenotypes had no loss of activity when tested with a wild type allele. Taking these functional results into account improved clinical interpretation.

CONCLUSION

Our findings suggest heterozygous DHH gene variants are unlikely to cause DSD, reaffirming that DHH is an autosomal recessive cause of 46,XY gonadal dysgenesis. Functional characterisation of novel DHH variants improves variant interpretation, leading to greater confidence in patient reporting and clinical management.

In vitro functional characterization of the novel DHH mutations p.(Asn337Lysfs*24) and p.(Glu212Lys) associated with gonadal dysgenesis

In humans, mutations of Desert Hedgehog gene (DHH) have been described in patients with 46,XY gonadal dysgenesis (GD), associated or not with polyneuropathy. In this study, we describe two patients diagnosed with GD, both harboring novel DHH compound heterozygous mutations p.[Tyr176*];[Asn337Lysfs*24] and p.[Tyr176*];[Glu212Lys]. To investigate the functional consequences of p.(Asn337Lysfs*24) and p.(Glu212Lys) mutations, located within the C-terminal part of DHh on auto-processing, we performed in vitro cleavage assays of these proteins in comparison with Drosophila melanogaster Hedgehog (Hh). We found that p.(Glu212Lys) mutation retained 50% of its activity and led to a partially abolished DHh auto-processing. In contrast, p.(Asn337Lysfs*24) mutation resulted in a complete absence of auto-proteolysis. Furthermore, we found a different auto-processing profile between Drosophila Hh and human DHh, which suggests differences in the processing mechanism between the two species. Review of the literature shows that proven polyneuropathy and GD is associated with complete disruption of DHh-N, whereas disruption of the DHh auto-processing is only described with GD. We propose a model that may explain the differences between Schwann and Leydig cell development by autocrine versus paracrine DHh signaling. To our knowledge, this is the first study investigating the effect of DHH mutations on DHh in vitro auto-processing.

Novel Familial Variant of the Desert Hedgehog Gene: Clinical Findings in Two Sisters with 46,XY Gonadal Dysgenesis or 46,XX Karyotype and Literature Review

BACKGROUND

In humans, Desert Hedgehog (DHH) gene mutations are a very rare cause of 46,XY gonadal dysgenesis (GD), eventually associated with peripheral neuropathy.

PATIENTS AND METHODS

Clinical records of 12 patients with 46,XY GD and unknown genetic background were reviewed and a 46,XY woman with peripheral neuropathy was individuated. Her 46,XX sister affected by similar neuropathy was also investigated. Genomic DNA was extracted and DHH exons sequenced and analyzed. A comparative genomic hybridization array was also performed.

RESULTS

In both the 46,XY and 46,XX sisters, a homozygous c.554C>A mutation in exon 2 of the DHH gene was found, determining a premature termination codon (p.Ser 185*). Heterozygous consanguineous carrier parents showed neither reproductive problems nor peripheral neuropathy. In the proband and her sister, a 499-kb duplication in 9p22.1 was also found.

CONCLUSION

A 46,XY European woman with 46,XY GD and a novel homozygous DHH pathogenic variant is reported, confirming that this gene plays a key role in male gonadal development. Her 46,XX sister, harboring the same mutation, showed normal internal and external female phenotype. Thus, DHH seems not to be involved in the ovarian development pathway or its postpubertal function. Homozygous DHH mutations cause a specific peripheral neuropathy in humans with both 46,XY and 46,XX karyotypes.

Genetic testing of XY newborns with a suspected disorder of sex development

PURPOSE OF REVIEW

The current review focuses on the neonatal presentation of disorders of sex development, summarize the current approach to the evaluation of newborns and describes recent advances in understanding of underlying genetic aetiology of these conditions.

RECENT FINDINGS

Several possible candidate genes as well as other adverse environmental factors have been described as contributing to several clinical subgroups of 46,XY DSDs. Moreover, registry-based studies showed that infants with suspected DSD may have extragenital anomalies and in 46,XY cases, being small for gestational age (SGA), cardiac and neurological malformations are the commonest concomitant conditions.

SUMMARY

Considering that children and adults with DSD may be at risk of several comorbidities a clear aetiological diagnosis will guide further management. To date, a firm diagnosis is not reached in over half of the cases of 46,XY DSD. Whilst it is likely that improved diagnostic resources will bridge this gap in the future, the next challenge to the clinical community will be to show that such advances will result in an improvement in clinical care.

A novel, homozygous mutation in desert hedgehog (DHH) in a 46, XY patient with dysgenetic testes presenting with primary amenorrhoea: a case report

Background

Desert hedgehog (DHH) mutations have been described in only a limited number of individuals with 46, XY disorders of sex development (DSD) presenting as either partial or complete gonadal dysgenesis. Gonadal tumours and peripheral neuropathy have been associated with DHH mutations. Herein we report a novel, homozygous mutation of DHH identified through a targeted, massively parallel sequencing (MPS) DSD panel, in a patient presenting with partial gonadal dysgenesis. This novel mutation is two amino acids away from a previously described mutation in a patient who presented with complete gonadal dysgenesis. Adding to the complexity of work-up, our patient also expressed gender identity concern.

Case presentation

A 14-year-old, phenotypic female presented with primary amenorrhoea and absent secondary sex characteristics. Investigations revealed elevated gonadotrophins with low oestradiol, testosterone of 0.6 nmol/L and a 46, XY karyotype. Müllerian structures were not seen on pelvic ultrasound or laparoscopically and gonadal biopsies demonstrated dysgenetic testes without neoplasia (partial gonadal dysgenesis). The patient expressed gender identity confusion upon initial notification of investigation findings. Formal psychiatric evaluation excluded gender dysphoria. Genetic analysis was performed using a targeted, MPS DSD panel of 64 diagnostic and 927 research candidate genes. This identified a novel, homozygous mutation in exon 2 of DHH (DHH:NM_021044:exon2:c.G491C:p.R164P). With this finding our patient was screened for the possibility of peripheral neuropathy which was not evident clinically nor on investigation. She was commenced on oestrogen for pubertal induction.

Conclusion

The evaluation of patients with DSD is associated with considerable psychological distress. Targeted MPS enables an affordable and efficient method for diagnosis of 46, XY DSD cases. Identifying a genetic diagnosis may inform clinical management and in this case directed screening for peripheral neuropathy. In addition to the structural location of the mutation other interacting factors may influence phenotypic expression in homozygous DHH mutations.