Chromosomal microdeletion leading to pituitary gigantism through hormone-gene overexpression.

Pituitary gigantism is a rare endocrinopathy characterized by tall stature due to growth hormone (GH) hypersecretion. This condition is generally linked to a genetic predisposition to tumors that produce GH or GH-releasing hormone (GHRH). Here, we report a Japanese woman who exhibited prominent body growth from infancy to reach an adult height of 197.4 cm (+7.4 standard deviation). Her blood GH levels were markedly elevated. She carried no pathogenic variants in known growth-controlling genes but had a hitherto unreported 752 kb heterozygous deletion at 20q11.23. The microdeletion was located 8.9 kb upstream of GHRH and encompassed exons 2-9 of a ubiquitously expressed gene TTI1 together with 12 other genes, pseudogenes and non-coding RNAs. Transcript analyses of the patient's leukocytes showed that the microdeletion produced chimeric mRNAs consisting of exon 1 of TTI1 and all coding exons of GHRH. In silico analysis detected promoter-associated genomic features around TTI1 exon 1. Genome-edited mice carrying the same microdeletion recapitulated accelerated body growth from a few weeks after birth. The mutant mice developed pituitary hyperplasia and exhibited ectopic Ghrh expression in all tissues examined. Thus, the extreme phenotype of pituitary gigantism in the patient likely reflects GHRH overexpression driven by an acquired promoter. The results of this study indicate that germline submicroscopic deletions have the potential to cause conspicuous developmental abnormalities due to gene overexpression. Furthermore, this study provides evidence that constitutive expression of a hormone-encoding gene can result in congenital disease.

Isodicentric Y chromosome with multiple breakpoints in the pseudoautosomal region 1.

INTRODUCTION: Isodicentric Y chromosomes are relatively common structural variants of the human genome. The underlying mechanism of isodicentric Y chromosomes with short arm breakpoints [idic(Yq)] remains to be clarified. CASE PRESENTATION: We encountered a Japanese man with azoospermia and mild short stature. G-banding and array-based comparative genomic hybridization indicated that his karyotype was 45,X/46,X,idic(Y)(qter→p11.32::p11.32→qter) with a ~1.8 Mb terminal deletion. Whole genome sequencing suggested that the Y chromosome had four breakpoints in a ~7 kb region of the pseudoautosomal region 1 (PAR1). CONCLUSION: This case was assumed to have an idic(Yq) resulting from multiple DNA double-strand breaks in PAR1. This rearrangement may have been facilitated by the PAR1-specific chromatin architecture. The clinical features of the patient can be ascribed to SHOX haploinsufficiency and the presence of a 45,X cell line, although copy-number gains of some Yq genes and the size reduction of PAR1 may also contribute to his spermatogenic failure.

Systematic molecular analyses for 115 karyotypically normal men with isolated non-obstructive azoospermia.

STUDY QUESTION: Do copy-number variations (CNVs) in the azoospermia factor (AZF) regions and monogenic mutations play a major role in the development of isolated (non-syndromic) non-obstructive azoospermia (NOA) in Japanese men with a normal 46, XY karyotype? SUMMARY ANSWER: Deleterious CNVs in the AZF regions and damaging sequence variants in eight genes likely constitute at least 8% and approximately 8% of the genetic causes, respectively, while variants in other genes play only a minor role. WHAT IS KNOWN ALREADY: Sex chromosomal abnormalities, AZF-linked microdeletions, and monogenic mutations have been implicated in isolated NOA. More than 160 genes have been reported as causative/susceptibility/candidate genes for NOA. STUDY DESIGN, SIZE, DURATION: Systematic molecular analyses were conducted for 115 patients with isolated NOA and a normal 46, XY karyotype, who visited our hospital between 2017 and 2021. PARTICIPANTS/MATERIALS, SETTING, METHODS: We studied 115 unrelated Japanese patients. AZF-linked CNVs were examined using sequence-tagged PCR and multiplex ligation-dependent probe amplification, and nucleotide variants were screened using whole exome sequencing (WES). An optimized sequence kernel association test (SKAT-O), a gene-based association study using WES data, was performed to identify novel disease-associated genes in the genome. The results were compared to those of previous studies and our in-house control data. MAIN RESULTS AND THE ROLE OF CHANCE: Thirteen types of AZF-linked CNVs, including the hitherto unreported gr/gr triplication and partial AZFb deletion, were identified in 63 (54.8%) cases. When the gr/gr deletion, a common polymorphism in Japan, was excluded from data analyses, the total frequency of CNVs was 23/75 (30.7%). This frequency is higher than that of the reference data in Japan and China (11.1% and 14.7%, respectively). Known NOA-causative AZF-linked CNVs were found in nine (7.8%) cases. Rare damaging variants in known causative genes (DMRT1, PLK4, SYCP2, TEX11, and USP26) and hemizygous/multiple-heterozygous damaging variants in known spermatogenesis-associated genes (TAF7L, DNAH2, and DNAH17) were identified in nine cases (7.8% in total). Some patients carried rare damaging variants in multiple genes. SKAT-O detected no genes whose rare damaging variants were significantly accumulated in the patient group. LIMITATIONS, REASONS FOR CAUTION: The number of participants was relatively small, and the clinical information of each patient was fragmentary. Moreover, the pathogenicity of identified variants was assessed only by in silico analyses. WIDER IMPLICATIONS OF THE FINDINGS: This study showed that various AZF-linked CNVs are present in more than half of Japanese NOA patients. These results broadened the structural variations of AZF-linked CNVs, which should be considered for the molecular diagnosis of spermatogenic failure. Furthermore, the results of this study highlight the etiological heterogeneity and possible oligogenicity of isolated NOA. STUDY FUNDING/COMPETING INTEREST(S): This study was supported by Grants from the Japan Society for the Promotion of Science (21K19283 and 21H0246), the Japan Agency for Medical Research and Development (22ek0109464h0003), the National Center for Child Health and Development, the Canon Foundation, the Japan Endocrine Society, and the Takeda Science Foundation. The results of this study were based on samples and patient data obtained from the International Center for Reproductive Medicine, Dokkyo Medical University Saitama Medical Center, Koshigaya, Japan. The authors have no conflicts of interest to disclose. TRIAL REGISTRATION NUMBER: N/A.

SHOX and sex difference in height: a hypothesis.

The mean height is taller in males than in females, except for early teens. In this regard, previous studies have revealed that (1) distribution of the mean adult heights in subjects with disorders accompanied by discordance between sex chromosome complement and bioactive sex steroids and in control subjects (the British height standards) indicates that, of the ~12.5 cm of sex difference in the mean adult height, ~9 cm is accounted for by the difference in the sex chromosome complement and the remaining ~3.5 cm is explained by the dimorphism in sex steroids (primarily due to the growth-promoting effect of gonadal androgens); (2) according to the infancy-childhood-puberty growth model, the sex difference in the childhood growth function produces height differences of ~1 cm in childhood and 8-10 cm at 18-20 years of age, whereas the sex difference in the pubertal growth function yields height difference of ~4.5 cm at 18-20 years of age; and (3) SHOX expression and methylation analyses using knee cartilage tissues and cultured chondrocytes have shown lower SHOX expression levels in female samples than in male samples and methylation patterns consistent with partial spreading of X-inactivation affecting SHOX in female samples. These findings suggest that small but persistent sex difference in SHOX expression dosage leads to the variation in the sex steroid independent childhood growth function, thereby yielding the sex difference in height which remains small in childhood but becomes obvious in adulthood.

Optical Genome Mapping for a Patient with a Congenital Disorder and Chromosomal Translocation.

We performed optical genome mapping (OGM), a newly developed cytogenetic technique, for a patient with a disorder of sex development (DSD) and a 46,XX,t(9;11)(p22;p13) karyotype. The results of OGM were validated using other methods. OGM detected a 9;11 reciprocal translocation and successfully mapped its breakpoints to small regions of 0.9-12.3 kb. OGM identified 46 additional small structural variants, only three of which were detected by array-based comparative genomic hybridization. OGM suggested the presence of complex rearrangements on chromosome 10; however, these variants appeared to be artifacts. The 9;11 translocation was unlikely to be associated with DSD, while the pathogenicity of the other structural variants remained unknown. These results indicate that OGM is a powerful tool for detecting and characterizing chromosomal structural variations, although the current methods of OGM data analyses need to be improved.

Quantification of Maternal Microchimeric Cells in the Liver of Children With Biliary Atresia.

ABSTRACT: Biliary atresia (BA) is a rare disorder of unknown etiology. There is a debate as to whether maternal microchimerism plays a significant role in the development of BA or in graft tolerance after liver transplantation. Here, we performed quantitative-PCR-based assays for liver tissues of children with BA and other diseases. Maternal cells were detected in 4/13 and 1/3 of the BA and control groups, respectively. The estimated number of maternal cells ranged between 0 and 34.7 per 106 total cells. The frequency and severity of maternal microchimerism were similar between the BA and control groups, and between patients with and without acute rejection of maternal grafts. These results highlight the high frequency of maternal microchimerism in the liver. This study provides no evidence for roles of microchimerism in the etiology of BA or in graft tolerance. Thus, the biological consequences of maternal microchimerism need to be clarified in future studies.

Lupus anticoagulant hypoprothrombinemia syndrome associated with bilateral adrenal haemorrhage in a child: early diagnosis and intervention.

BACKGROUND: Lupus anticoagulant-hypoprothrombinemia syndrome (LAHPS) is characterized by bleeding and thrombosis in patients with autoimmune diseases or infections. Paediatric LAHPS exhibits various degrees of bleeding, ranging from mild to severe; however, adrenal haemorrhage due to LAHPS and its long-term clinical course have not been sufficiently described. CASE PRESENTATION: A 9-year-old boy presented with prolonged abdominal pain and abnormal coagulation screening tests. The laboratory tests showed prolonged activated partial thromboplastin time and subsequently revealed the presence of lupus anticoagulant, anti-nuclear antibodies, and hypoprothrombinemia, leading to diagnosis of LAHPS. An enhanced computed tomogram demonstrated nodular lesions in the adrenal glands bilaterally, suggestive of adrenal haemorrhage. Laboratory and clinical manifestations exhibited life-threatening adrenal insufficiency that required hydrocortisone administration. The patient developed systemic lupus erythematosus, diagnosed 12 months later. CONCLUSIONS: This patient with LAHPS developed rare adrenal failure due to adrenal haemorrhage, a life-threatening event that should be recognized and treated early. In our case, renal dysfunction was also observed when systemic lupus erythematosus was diagnosed 1 year after LAHPS. Our case emphasizes that early recognition of adrenal failure and careful long-term observation is required in patients with autoantibodies.

Established and Novel Mechanisms Leading to de novo Genomic Rearrangements in the Human Germline.

During gametogenesis, the human genome can acquire various de novo rearrangements. Most constitutional genomic rearrangements are created through 1 of the 4 well-known mechanisms, i.e., nonallelic homologous recombination, erroneous repair after double-strand DNA breaks, replication errors, and retrotransposition. However, recent studies have identified 2 types of extremely complex rearrangements that cannot be simply explained by these mechanisms. The first type consists of chaotic structural changes in 1 or a few chromosomes that result from "chromoanagenesis (an umbrella term that covers chromothripsis, chromoanasynthesis, and chromoplexy)." The other type is large independent rearrangements in multiple chromosomes indicative of "transient multifocal genomic crisis." Germline chromoanagenesis (chromothripsis) likely occurs predominantly during spermatogenesis or postzygotic embryogenesis, while multifocal genomic crisis appears to be limited to a specific time window during oogenesis and early embryogenesis or during spermatogenesis. This review article introduces the current understanding of the molecular basis of de novo rearrangements in the germline.

Unbalanced Y;7 Translocation between Two Low-Similarity Sequences Leading to SRY-Positive 45,X Testicular Disorders of Sex Development.

Unbalanced translocations of Y-chromosomal fragments harboring the sex-determining region Y gene (SRY) to the X chromosome or an autosome result in 46,XX and 45,X testicular disorders of sex development (DSD), respectively. Of these, Y;autosome translocation is an extremely rare condition. Here, we identified a 20-year-old man with a 45,X,t(Y;7)(q11.21;q35) karyotype, who exhibited unilateral cryptorchidism, small testis, intellectual disability, and various congenital anomalies. The fusion junction of the translocation was blunt, and the breakpoint-flanking regions shared only 50% similarity. These results indicate that Y;autosome translocations can occur between 2 low-similarity sequences, probably via nonhomologous end joining. Furthermore, translocations of a Ypterq11.21 fragment to 7q35 likely result in normal or only mildly impaired male-type sexual development, along with various clinical features of 7q deletion syndrome, although their effects on adult testicular function remain to be studied.

DNA Methylation Status of SHOX-Flanking CpG Islands in Healthy Individuals and Short Stature Patients with Pseudoautosomal Copy Number Variations.

SHOX resides in the short arm pseudoautosomal region (PAR1) of the sex chromosomes and escapes X inactivation. SHOX haploinsufficiency underlies idiopathic short stature (ISS) and Leri-Weill dyschondrosteosis (LWD). A substantial percentage of cases with SHOX haploinsufficiency arise from pseudoautosomal copy number variations (CNVs) involving putative enhancer regions of SHOX. Our previous study using peripheral blood samples showed that some CpG dinucleotides adjacent to SHOX exon 1 were hypomethylated in a healthy woman and methylated in a woman with gross X chromosomal rearrangements. However, it remains unknown whether submicroscopic pseudoautosomal CNVs cause aberrant DNA methylation of SHOX-flanking CpG islands. In this study, we examined the DNA methylation status of SHOX-flanking CpG islands in 50 healthy individuals and 10 ISS/LWD patients with pseudoautosomal CNVs. In silico analysis detected 3 CpG islands within the 20-kb region from the translation start site of SHOX. Pyrosequencing and bisulfite sequencing of genomic DNA samples revealed that these CpG islands were barely methylated in peripheral blood cells and cultured chondrocytes of healthy individuals, as well as in peripheral blood cells of ISS/LWD patients with pseudoautosomal CNVs. These results, in conjunction with our previous findings, indicate that the DNA methylation status of SHOX-flanking CpG islands can be affected by gross X-chromosomal abnormalities, but not by submicroscopic CNVs in PAR1. Such CNVs likely disturb SHOX expression through DNA methylation-independent mechanisms, which need to be determined in future studies.

Next generation sequencing-based mutation screening of 86 patients with idiopathic short stature.

Although mutations in ACAN, FGFR3, NPR2, and SHOX typically lead to skeletal dysplasia, and mutations in GHRHR, GH1, GHR, STAT5B, IGF1, IGFALS, and IGF1R usually underlie hormonal defects of the growth hormone (GH)-insulin-like growth factor 1 (IGF1) axis, such mutations have also been identified in patients with idiopathic short stature (ISS). Of these, SHOX abnormalities are known to account for a certain percentage of ISS cases, whereas the frequency of mutations in the other 10 genes in ISS cohorts remains unknown. Here, we performed next-generation sequencing-based mutation screening of the 10 genes in 86 unrelated Japanese ISS patients without SHOX abnormalities. We searched for rare protein-altering variants. The functional significance of the identified variants was assessed by in silico analyses. Consequently, we identified 18 heterozygous rare variants in 19 patients, including four probable damaging variants in ACAN, six pathogenicity-unknown variants in FGFR3, GHRHR, GHR, and IGFALS, and eight possible benign variants. Pathogenic variants in NPR2, GH1, and IGF1 were absent from our cohort. Unlike previously reported patients with ACAN mutations, our four patients with ACAN variants manifested non-specific short stature with age-appropriate or mildly delayed bone ages, and had parents of normal stature. These results indicate that ACAN mutations can underlie ISS without characteristic skeletal features, and that such mutations are possibly associated with de novo occurrence or low penetrance. In addition, our data imply that mutations in FGFR3, NPR2, and GH-IGF1 axis genes play only limited roles in the etiology of ISS.

Long-read next-generation sequencing for molecular diagnosis of pediatric endocrine disorders.

Recent advances in long-read next-generation sequencing (NGS) have enabled researchers to identify several pathogenic variants overlooked by short-read NGS, array-based comparative genomic hybridization, and other conventional methods. Long-read NGS is particularly useful in the detection of structural variants and repeat expansions. Furthermore, it can be used for mutation screening in difficultto- sequence regions, as well as for DNA-methylation analyses and haplotype phasing. This mini-review introduces the usefulness of long-read NGS in the molecular diagnosis of pediatric endocrine disorders.

Homozygous 6-bp deletion of IGFALS in a prepubertal boy with short stature.

Biallelic IGFALS variants lead to acid‒labile subunit (ALS) deficiency characterized by growth hormone resistance with or without delayed puberty. Here, we report a prepubertal boy with a homozygous 2-amino acid deletion within the fourth N-glycosylation motif (c.1103_1108del, p.N368_S370delinsT) associated with parental consanguinity. He showed short stature consistent with ALS deficiency. This case expands the mutation spectrum of IGFALS to include the elimination of only one N-glycosylation motif of ALS.

Molecular and Clinical Features of Congenital Hypothyroidism Due to Multiple DUOX2 Variants.

Background: DUOX2 is one of the major causative genes of congenital hypothyroidism (CH). Still, the mutation spectrum and clinical outcomes of biallelic DUOX2 variants are not fully understood. This study aimed to elucidate the molecular features and long-term clinical manifestations of CH caused by multiple pathogenic DUOX2 variants. Methods: A total of 255 patients with CH were screened for rare variants of 11 known causative genes. DUOX2 variants were classified according to their protein structure and residual activity. In vitro assays were performed for several variants of unknown functions. Clinical analyses were conducted for patients with multiple pathogenic variants of DUOX2 but not of other genes. Results: We identified 24 pathogenic variants of DUOX2, together with two benign variants and seven variants of uncertain significance, in 63 patients. The pathogenic variants included three missense substitutions and one frameshift variant that have not yet been linked to CH. Twenty-one patients carried multiple pathogenic DUOX2 variants without any other pathogenic gene variants. Three of the 21 patients harbored homozygous variants. Family analysis, long-read amplicon sequencing, and haplotype phasing confirmed compound heterozygosity of the DUOX2 variants in 14 patients, whereas the allelic positions of the variants in the remaining four patients could not be determined. Of the 21 patients, 19 were treated with levothyroxine; their ages at drug withdrawal ranged from 9 months to 21.4 years. Three patients required retreatment after drug-free intervals of 6 months, 8 months, and 10 years. There were no differences in clinical severity among patients with DUOX2 amorphic/amorphic, amorphic/hypomorphic, and hypomorphic/hypomorphic variants. Conclusions: These results broaden the mutational spectrum of DUOX2. Furthermore, our data imply that patients with multiple pathogenic DUOX2 variants typically exhibit transient CH without significant genotype-phenotype correlations. Most importantly, this study demonstrated for the first time that these patients are at risk of developing recurrent hypothyroidism after a long drug-free interval.

PTPN11 and FLNA variants in a boy with ambiguous genitalia, short stature, and non-specific dysmorphic features.

Noonan syndrome is a congenital disorder characterized by distinctive facial appearance, congenital heart defects, short stature, and skeletal dysplasia. Although boys with Noonan syndrome frequently exhibit cryptorchidism, a mild form of 46,XY disorders of sex development (DSD), they barely manifest more severe genital abnormalities. Here, we report a boy with ambiguous genitalia, short stature, and non-specific dysmorphic features. He had no cardiac abnormalities or skeletal dysplasia. His score in the Noonan syndrome diagnostic criteria (36 of 157 points, 23%) was lower than the cutoff for diagnosis (50%). Whole-exome sequencing identified a de novo heterozygous variant (c.922A>G: p.Asn308Asp) in PTPN11 and a maternally inherited hemizygous variant (c.1439C>T: p.Pro480Leu) in FLNA. The PTPN11 variant was a known causative mutation for Noonan syndrome. FLNA is a causative gene for neurodevelopmental and skeletal abnormalities and has also been implicated in 46,XY DSD. The p.Pro480Leu variant of FLNA was assessed as deleterious by in silico analyses. These results provide evidence that whole-exome sequencing is a powerful tool for diagnosing patients with atypical disease manifestations. Furthermore, our data suggest a possible role of digenic mutations as phenotypic modifiers of Noonan syndrome.

Expression levels and DNA methylation profiles of the growth gene SHOX in cartilage tissues and chondrocytes.

All attempts to identify male-specific growth genes in humans have failed. This study aimed to clarify why men are taller than women. Microarray-based transcriptome analysis of the cartilage tissues of four adults and chondrocytes of 12 children showed that the median expression levels of SHOX, a growth gene in the pseudoautosomal region (PAR), were higher in male samples than in female samples. Male-dominant SHOX expression was confirmed by quantitative RT-PCR for 36 cartilage samples. Reduced representation bisulfite sequencing of four cartilage samples revealed sex-biased DNA methylation in the SHOX-flanking regions, and pyrosequencing of 22 cartilage samples confirmed male-dominant DNA methylation at the CpG sites in the SHOX upstream region and exon 6a. DNA methylation indexes of these regions were positively correlated with SHOX expression levels. These results, together with prior findings that PAR genes often exhibit male-dominant expression, imply that the relatively low SHOX expression in female cartilage tissues reflects the partial spread of X chromosome inactivation into PAR. Altogether, this study provides the first indication that sex differences in height are ascribed, at least in part, to the sex-dependent epigenetic regulation of SHOX. Our findings deserve further validation.

Nuclear Receptor Gene Variants Underlying Disorders/Differences of Sex Development through Abnormal Testicular Development.

Gonadal development is the first step in human reproduction. Aberrant gonadal development during the fetal period is a major cause of disorders/differences of sex development (DSD). To date, pathogenic variants of three nuclear receptor genes (NR5A1, NR0B1, and NR2F2) have been reported to cause DSD via atypical testicular development. In this review article, we describe the clinical significance of the NR5A1 variants as the cause of DSD and introduce novel findings from recent studies. NR5A1 variants are associated with 46,XY DSD and 46,XX testicular/ovotesticular DSD. Notably, both 46,XX DSD and 46,XY DSD caused by the NR5A1 variants show remarkable phenotypic variability, to which digenic/oligogenic inheritances potentially contribute. Additionally, we discuss the roles of NR0B1 and NR2F2 in the etiology of DSD. NR0B1 acts as an anti-testicular gene. Duplications containing NR0B1 result in 46,XY DSD, whereas deletions encompassing NR0B1 can underlie 46,XX testicular/ovotesticular DSD. NR2F2 has recently been reported as a causative gene for 46,XX testicular/ovotesticular DSD and possibly for 46,XY DSD, although the role of NR2F2 in gonadal development is unclear. The knowledge about these three nuclear receptors provides novel insights into the molecular networks involved in the gonadal development in human fetuses.

Inhibitory effects of water-soluble low-molecular-weight ß-(1,3-1,6) D-glucan isolated from Aureobasidium pullulans 1A1 strain black yeast on mast cell degranulation and passive cutaneous anaphylaxis.

We investigated the effects of water-soluble low-molecular-weight ß-(1,3-1,6) D-glucan isolated from Aureobasidium pullulans 1A1 strain black yeast (LMW-ß-glucan) on mast cell-mediated anaphylactic reactions. Although it is known that LMW-ß-glucan has anti-tumor, anti-metastatic and anti-stress effects, the roles of LMW-ß-glucan in immediate-type allergic reactions have not been fully investigated. We examined whether LMW-ß-glucan could inhibit mast cell degranulation and passive cutaneous anaphylaxis (PCA). LMW-ß-glucan dose-dependently inhibited the degranulation of both rat basophilic leukemia (RBL-2H3) and cultured mast cells (CMCs) activated by calcium ionophore A23187 or IgE. However, LMW-ß-glucan had no cytotoxicity towards RBL-2H3 cells and CMCs. Furthermore, orally administered LMW-ß-glucan inhibited the IgE-induced PCA reaction in mice. These results show LMW-ß-glucan to be a possible compound for the effective therapeutic treatment of allergic diseases.

Maternal uniparental disomy of chromosome 7 underlying argininosuccinic aciduria and Silver-Russell syndrome.

We describe a patient presenting with argininosuccinic aciduria and Silver-Russell syndrome (SRS). SRS was caused by maternal uniparental disomy of chromosome 7 (UPD(7)mat). UPD(7)mat also unmasked a maternally inherited splicing variant in ASL on chromosome 7, leading to the onset of argininosuccinic aciduria. The phenotype of the present case was more severe than that of a previous case, demonstrating a phenotypic variation in the combination of argininosuccinic aciduria and SRS.

NDNF variants are rare in patients with congenital hypogonadotropic hypogonadism.

Although NDNF was recently reported as a novel causative gene for congenital hypogonadotropic hypogonadism (CHH), this conclusion has yet to be validated. In this study, we sequenced NDNF in 61 Japanese CHH patients. No variants, except for nine synonymous substitutions that appear to have no effect on splice-site recognition, were identified in NDNF coding exons or flanking intronic sequences. These results indicate the rarity of NDNF variants in CHH patients and highlight the genetic heterogeneity of CHH.