Skin and nails abnormalities in a patient with ZTTK syndrome and a de novo mutation in SON

[Zhu-Tokita-Takenouchi-Kim syndrome in a neonate]

The patient is a male neonate born at term. He was admitted 16 minutes after birth due to stridor and inspiratory respiratory distress. Physical examination revealed a cleft palate, and a grade II systolic ejection murmur was audible at the left sternal border. Whole exome sequencing identified a heterozygous variant in the SON gene, c.5753-5756del (p.Val1918GlufsTer87), which was absent in either parent, indicating a de novo mutation. According to the guidelines of the American College of Medical Genetics and Genomics, this was classified as a "pathogenic variant" leading to a diagnosis of Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome. Upon admission, symptomatic supportive treatment was provided. Follow-up at the age of 8 months revealed persistent stridor; the infant could only consume small amounts of milk and was unable to sit steadily. This patient represents the youngest reported case to date, and his symptoms expand the clinical spectrum of the disease, providing valuable insights for clinical diagnosis and treatment.

Recurrent myocardial injury in a de novo SON mutation ZTTK syndrome patient: a case report

BACKGROUND

Zhu-Tokita-Takenouchi-Kim syndrome (ZTTK syndrome) is a severe multi-systemic developmental disorder, caused by variants in the SON gene. A patient diagnosed with ZTTK syndrome who carried a de novo SON mutation and exhibited recurrent myocardial injury was described in this case.

CASE PRESENTATION

A 7-year-old girl was admitted to the Cardiology Department of Beijing Children's Hospital in November 2019 due to myocardial injury following respiratory infection. She displayed elevated myocardial enzymes and severe T-wave changes on electrocardiogram. Over the past three years, she had experienced myocardial injury on three occasions. Additionally, she exhibited intellectual disability, congenital amblyopia, and dysmorphic facial features. Genetic analysis revealed a de novo heterozygous mutation c.3852_3856delGGTAT in the SON gene, which was confirmed by Sanger sequencing of her parents. She received anti-infection treatment and was administered metoprolol orally. Her condition was stable at the time of discharge. Over a 42-month follow-up period at the outpatient clinic, she complained intermittent fatigue and palpitation.

CONCLUSIONS

The identified SON mutation, which plays a crucial role in heart development and mitochondrial function, may be associated with an increased susceptibility to myocardial injury or cardiomyopathy. This case report contributes novel insights into this rare condition and suggests the expansion of the ZTTK syndrome phenotype.

A mouse model of Zhu-Tokita-Takenouchi-Kim syndrome reveals indispensable SON functions in organ development and hematopoiesis

Rare diseases are underrepresented in biomedical research, leading to insufficient awareness. Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome is a rare disease caused by genetic alterations that result in heterozygous loss of function of SON. While patients with ZTTK syndrome live with numerous symptoms, the lack of model organisms hampers our understanding of SON and this complex syndrome. Here, we developed Son haploinsufficiency (Son+/-) mice as a model of ZTTK syndrome and identified the indispensable roles of Son in organ development and hematopoiesis. Son+/- mice recapitulated clinical symptoms of ZTTK syndrome, including growth retardation, cognitive impairment, skeletal abnormalities, and kidney agenesis. Furthermore, we identified hematopoietic abnormalities in Son+/- mice, including leukopenia and immunoglobulin deficiency, similar to those observed in human patients. Surface marker analyses and single-cell transcriptome profiling of hematopoietic stem and progenitor cells revealed that Son haploinsufficiency shifted cell fate more toward the myeloid lineage but compromised lymphoid lineage development by reducing genes required for lymphoid and B cell lineage specification. Additionally, Son haploinsufficiency caused inappropriate activation of erythroid genes and impaired erythropoiesis. These findings highlight the importance of the full gene expression of Son in multiple organs. Our model serves as an invaluable research tool for this rare disease and related disorders associated with SON dysfunction.

A mouse model of ZTTK syndrome reveals indispensable SON functions in organ development and hematopoiesis

Rare diseases are underrepresented in biomedical research, leading to insufficient awareness. Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome is a rare disease caused by genetic alterations that result in heterozygous loss-of-function of SON. While ZTTK syndrome patients suffer from numerous symptoms, the lack of model organisms hamper our understanding of both SON and this complex syndrome. Here, we developed Son haploinsufficiency (Son+/-) mice as a model of ZTTK syndrome and identified the indispensable roles of Son in organ development and hematopoiesis. Son+/- mice recapitulated clinical symptoms of ZTTK syndrome, including growth retardation, cognitive impairment, skeletal abnormalities, and kidney agenesis. Furthermore, we identified hematopoietic abnormalities in Son+/- mice, similar to those observed in human patients. Surface marker analyses and single-cell transcriptome profiling of hematopoietic stem and progenitor cells revealed that Son haploinsufficiency inclines cell fate toward the myeloid lineage but compromises lymphoid lineage development by reducing key genes required for lymphoid and B cell lineage specification. Additionally, Son haploinsufficiency causes inappropriate activation of erythroid genes and impaired erythroid maturation. These findings highlight the importance of the full gene dosage of Son in organ development and hematopoiesis. Our model serves as an invaluable research tool for this rare disease and related disorders associated with SON dysfunction.

Expanding the mutational spectrum of ZTTK syndrome: A de novo variant with global developmental delay and malnutrition in a Chinese patient

BACKGROUND

Zhu-Tokita-Takenouchi-Kim (ZTTK, OMIM 617140) syndrome is a severe multisystem developmental disorder characterized by intellectual disability, developmental delay, cortical malformations, epilepsy, visual problems, musculoskeletal abnormalities, and congenital malformations. ZTTK syndrome is caused by a heterozygous pathogenic variant of the SON gene (NM_138927) at chromosome 21q22.1. The purpose of this study was to investigate the pathogenesis of a 6-month-old Chinese child who exhibited global developmental delay, muscle weakness, malnutrition, weight loss, and strabismus, brain abnormality, immunological system abnormalities.

METHODS

The little girl was tested for medical exome sequencing (MES) and mtDNA sequencing in trio. And, the mutation was validated by Sanger sequencing.

RESULTS

A novel de novo frameshift variant, c.1845_1870del26 (p.G616Sfs*61), in the SON gene was found in the proband.

CONCLUSION

We described a 6-month-old Chinese child with global developmental delay caused by pathogenic de novo mutation c.1845_1870del26 (p.G616Sfs*61) in the SON. Apart from a founder mutation, we reviewed the phenotypic abnormalities and genotypes in 79 individuals. The data showed that global developmental delay is accompanied by other system disorders. Our findings expanded the mutational spectrum of ZTTK syndrome and provide genetic counseling of baby with global developmental delay.

Case report: A novel SON mutation in a Colombian patient with ZTTK syndrome

Zhu-Tokita-Takenouchi-Kim syndrome is a multisystem disorder resulting from haploinsufficiency in the SON gene, which is characterized by developmental delay/intellectual disability, seizures, facial dysmorphism, short stature, and congenital malformations, primarily in the central nervous system, along with ophthalmic, dental, pulmonary, cardiologic, renal, gastrointestinal, and musculoskeletal anomalies. In this study, we describe the first Colombian patient with ZTT harboring a novel mutation that has not been previously reported and review the clinical and molecular features of previously reported patients in the literature.

The Expanding Phenotype of ZTTK Syndrome Due to the Heterozygous Variant of SON Gene Focusing on Liver Involvement: Patient Report and Literature Review

Zhu–Tokita–Takenouchi–Kim (ZTTK) syndrome, an intellectual disability syndrome first described in 2016, is caused by heterozygous loss-of-function variants in SON. Haploinsufficiency in SON may affect multiple genes, including those involved in the development and metabolism of multiple organs. Considering the broad spectrum of SON functions, it is to be expected that pathogenic variants in this gene can cause a wide spectrum of clinical symptoms. We present an additional ZTTK syndrome case due to a de novo heterozygous variant in the SON gene (c.5751_5754delAGTT). The clinical manifestations of our patient were similar to those present in previously reported cases; however, the diagnosis of ZTTK syndrome was delayed for a long time and was carried out during the diagnostic work-up of significant chronic liver disease (CLD). CLD has not yet been reported in any series; therefore, our report provides new information on this rare condition and suggests the expansion of the ZTTK syndrome phenotype, including possible liver involvement. Correspondingly, we recommend screening patients with SON variants specifically for liver involvement from the first years of life. Once the CLD has been diagnosed, an appropriate follow-up is mandatory, especially considering the role of SON as an emerging player in cancer development. Further studies are needed to investigate the role of SON haploinsufficiency as a downregulator of essential genes, thus potentially impairing the normal development and/or functions of multiple organs.

Novel malformations: Chiari type 1 and hydrocephalus in Zhu-Tokita-Takenouchi-Kim syndrome and novel SON variants

Zhu-Tokita-Tachenouchi-Kim syndrome (ZTTK) is a recently recognized malformation syndrome presenting with craniofacial dysmorphism, developmental delay/intellectual disability, seizures, anomalies involving brain white matter, and other body-organs. In humans, the disorder is linked to the loss-of-function variants in the SON gene (MIM# 617140). Herewith, a new case of this syndrome is reported in a 2-year-old Caucasian child who presented the classical clinical features of the ZTTK syndrome in association with hydrocephalus and Chiari malformations type 1 an anomaly previously unreported. Exome analysis showed a de novo heterozygous variant in SON gene. Literature review of similar cases is reported.

Distinctive Brain Malformations in Zhu-Tokita-Takenouchi-Kim Syndrome

BACKGROUND AND PURPOSE

Zhu-Tokita-Takenouchi-Kim syndrome is a severe multisystem malformation disorder characterized by developmental delay and a diverse array of congenital abnormalities. However, these currently identified phenotypic components provide limited guidance in diagnostic situations, due to both the nonspecificity and variability of these features. Here we report a case series of 7 individuals with a molecular diagnosis of Zhu-Tokita-Takenouchi-Kim syndrome, 5 ascertained by their presentation with the neuronal migration disorder, periventricular nodular heterotopia.

MATERIALS AND METHODS

Individuals with a molecular diagnosis of Zhu-Tokita-Takenouchi-Kim syndrome were recruited from 2 sources, a high-throughput sequencing study of individuals with periventricular nodular heterotopia or from clinical diagnostic sequencing studies. We analyzed available brain MR images of recruited individuals to characterize periventricular nodular heterotopia distribution and to identify the presence of any additional brain abnormalities.

RESULTS

Pathogenic variants in SON, causative of Zhu-Tokita-Takenouchi-Kim syndrome, were identified in 7 individuals. Brain MR images from these individuals were re-analyzed. A characteristic set of imaging anomalies in addition to periventricular nodular heterotopia was identified, including the elongation of the pituitary stalk, cerebellar enlargement with an abnormally shaped posterior fossa, rounding of the caudate nuclei, hippocampal malformations, and cortical anomalies including polymicrogyria or dysgyria.

CONCLUSIONS

The recurrent neuroradiologic changes identified here represent an opportunity to guide diagnostic formulation of Zhu-Tokita-Takenouchi-Kim syndrome on the basis of brain MR imaging evaluation.

Establishing the phenotypic spectrum of ZTTK syndrome by analysis of 52 individuals with variants in SON

Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome, an intellectual disability syndrome first described in 2016, is caused by heterozygous loss-of-function variants in SON. Its encoded protein promotes pre-mRNA splicing of many genes essential for development. Whereas individual phenotypic traits have previously been linked to erroneous splicing of SON target genes, the phenotypic spectrum and the pathogenicity of missense variants have not been further evaluated. We present the phenotypic abnormalities in 52 individuals, including 17 individuals who have not been reported before. In total, loss-of-function variants were detected in 49 individuals (de novo in 47, inheritance unknown in 2), and in 3, a missense variant was observed (2 de novo, 1 inheritance unknown). Phenotypic abnormalities, systematically collected and analyzed in Human Phenotype Ontology, were found in all organ systems. Significant inter-individual phenotypic variability was observed, even in individuals with the same recurrent variant (n = 13). SON haploinsufficiency was previously shown to lead to downregulation of downstream genes, contributing to specific phenotypic features. Similar functional analysis for one missense variant, however, suggests a different mechanism than for heterozygous loss-of-function. Although small in numbers and while pathogenicity of these variants is not certain, these data allow for speculation whether de novo missense variants cause ZTTK syndrome via another mechanism, or a separate overlapping syndrome. In conclusion, heterozygous loss-of-function variants in SON define a recognizable syndrome, ZTTK, associated with a broad, severe phenotypic spectrum, characterized by a large inter-individual variability. These observations provide essential information for affected individuals, parents, and healthcare professionals to ensure appropriate clinical management.

A Novel De Novo Frameshift Variation in the SON Gene Causing Severe Global Developmental Delay and Seizures in a Chinese Female

BACKGROUND

With the rapid development of genetic detection technology, especially next-generation sequencing, identification of the etiology of unexplained intellectual disabilities accompanied by seizures and other dysmorphic features has become possible. The purpose of our paper is to make a definitive diagnosis of a girl with neonatal hypotonia, severe global developmental delay, seizures and mild facial dysmorphism.

METHODS

The clinical data of the patient were retrospectively studied. Whole-exome sequencing was performed on a blood sample from the patient. Subsequently, Sanger sequencing was utilized for validation of variants and parental validation.

RESULTS

The patient had hypotonia since the neonatal period. She showed a significant delay in physical and psychomotor development. She did not have any speech until the age of 2 years and 6 months. She had seizures that were easy to control with levetiracetam. The craniocerebral MRI then showed mild delayed myelination, enlarged bilateral ventricles and widened frontotemporal extracerebral space. Interictal VEEG was normal. She had esotropia and mild facial abnormalities with a flat nasal bridge and a short nose. She showed no abnormalities in the heart, genitourinary or skeletal systems. Whole-exome sequencing revealed a novel de novo variant c.5334_5335delAG (p. Arg1778Serfs*11) in the SON gene.

CONCLUSION

Our paper reports a novel variant in the SON gene and provides a definitive diagnosis of a female with neonatal hypotonia, severe global developmental delay, seizures and mild facial abnormalities, which are symptoms consistent with Zhu-Tokita-Takenouchi-Kim syndrome (ZTTK syndrome).

Novel De Novo Heterozygous Variants in the SON Gene Causing ZTTK Syndrome: A Case Report of Two Patients and Review of Neurological Findings

Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome is a newly described autosomal dominant multisystem developmental disorder resulting from a mutation of the SON gene located on chromosome region 21q22.11. It is characterized by heterogeneous features such as intellectual disability, facial dysmorphisms, poor feeding, vision abnormalities, musculoskeletal anomalies, congenital heart and genitourinary system defects, as well as several unique neurological findings including seizures, tone abnormalities, autism spectrum disorder and variable brain abnormalities noted on neuroimaging. Unfortunately, we lack adequate information regarding the spectrum of these neurological symptoms. In this study, we report 2 new unrelated cases of ZTTK syndrome, and identify new pathogenic variants in the SON gene through microarray analysis and whole-exome sequencing. We also emphasize the neurological manifestations of the syndrome in our patients and discuss the significance of gathering more data regarding neurological presentation, particularly seizure characteristics and long-term developmental progression. This information will be crucial to help understand long-term neurodevelopmental prognosis in these patients.

ZTTK syndrome: Clinical and molecular findings of 15 cases and a review of the literature

Zhu-Tokita-Takenouchi-Kim (ZTTK) syndrome is caused by de novo loss-of-function variants in the SON gene (MIM #617140). This multisystemic disorder is characterized by intellectual disability, seizures, abnormal brain imaging, variable dysmorphic features, and various congenital anomalies. The wide application and increasing accessibility of whole exome sequencing (WES) has helped to identify new cases of ZTTK syndrome over the last few years. To date, there have been approximately 45 cases reported in the literature. Here, we describe 15 additional individuals with variants in the SON gene, including those with missense variants bringing the total number of known cases to 60. We have reviewed the clinical and molecular data of these new cases and all previously reported cases to further delineate the most common as well as emerging clinical findings related to this syndrome. Furthermore, we aim to delineate any genotype-phenotype correlations specifically for a recurring pathogenic four base pair deletion (c.5753_5756del) along with discussing the impact of missense variants seen in the SON gene.

A de novo heterozygous variant in the SON gene is associated with Zhu-Tokita-Takenouchi-Kim syndrome

BACKGROUND

Zhu-Tokita-Takenouchi-Kim (ZTTK, OMIM# 617140) syndrome is a rare, autosomal dominant genetic disorder caused by heterozygous variants in the SON gene (OMIM#182465, GenBank#NC_000021.9). There are only 33 cases and 26 causative SON variants reported to date since the first report in 2015. Here, we report a new case of ZTTK syndrome and a de novo disease-causing SON variant.

METHODS

We conducted whole-exome sequencing (WES) to obtain genetic data of the patient. The clinical and genetic data of the patient were analyzed.

RESULTS

The clinical features of our patient were strikingly similar to previously reported cases. Notably, our patient had unique presentations, including a bridged palmar crease in the left hand and growth hormone deficiency. The c.5297del de novo variant in SON causes an amino change (p.Ser1766Leufs*7).

CONCLUSION

Our report expands the mutant spectrum of the SON gene and refines the genotype-phenotype map of ZTTK syndrome. Our findings also highlighted the importance of WES for early diagnosis of ZTTK syndrome, which may improve diagnostic procedures for affected individuals.