A novel pathogenic mitochondrial DNA variant m.4344T>C in tRNAGln causes developmental delay.

Mitochondrial diseases are a group of genetic diseases caused by mutations in mitochondrial DNA and nuclear DNA. However, the genetic spectrum of this disease is not yet complete. In this study, we identified a novel variant m.4344T>C in mitochondrial tRNAGln from a patient with developmental delay. The mutant loads of m.4344T>C were 95% and 89% in the patient's blood and oral epithelial cells, respectively. Multialignment analysis showed high evolutionary conservation of this nucleotide. TrRosettaRNA predicted that m.4344T>C variant would introduce an additional hydrogen bond and alter the conformation of the T-loop. The transmitochondrial cybrid-based study demonstrated that m.4344T>C variant impaired the steady-state level of mitochondrial tRNAGln and decreased the contents of mitochondrial OXPHOS complexes I, III, and IV, resulting in defective mitochondrial respiration, elevated mitochondrial ROS production, reduced mitochondrial membrane potential and decreased mitochondrial ATP levels. Altogether, this is the first report in patient carrying the m.4344T>C variant. Our data uncover the pathogenesis of the m.4344T>C variant and expand the genetic mutation spectrum of mitochondrial diseases, thus contributing to the clinical diagnosis of mitochondrial tRNAGln gene variants-associated mitochondrial diseases.

KaryoXpert: An accurate chromosome segmentation and classification framework for karyotyping analysis without training with manually labeled metaphase-image mask annotations.

Automated karyotyping is of great importance for cytogenetic research, as it speeds up the process for cytogeneticists through incorporating AI-driven automated segmentation and classification techniques. Existing frameworks confront two primary issues: Firstly the necessity for instance-level data annotation with either detection bounding boxes or semantic masks for training, and secondly, its poor robustness particularly when confronted with domain shifts. In this work, we first propose an accurate segmentation framework, namely KaryoXpert. This framework leverages the strengths of both morphology algorithms and deep learning models, allowing for efficient training that breaks the limit for the acquirement of manually labeled ground-truth mask annotations. Additionally, we present an accurate classification model based on metric learning, designed to overcome the challenges posed by inter-class similarity and batch effects. Our framework exhibits state-of-the-art performance with exceptional robustness in both chromosome segmentation and classification. The proposed KaryoXpert framework showcases its capacity for instance-level chromosome segmentation even in the absence of annotated data, offering novel insights into the research for automated chromosome segmentation. The proposed method has been successfully deployed to support clinical karyotype diagnosis.

Genome-wide epigenetic signatures facilitated the variant classification of PURA gene and uncovered the pathomechanism of PURA-related neurodevelopmental disorders.

PURPOSE: Rare genetic variants in the PURA gene cause PURA-related neurodevelopmental disorder (PURA-NDD), characterized by neonatal abnormalities and developmental delay. Using genome-wide DNA methylation analysis on patients with PURA variants, we aim to establish PURA-NDD-specific methylation profile and provide further insights on the molecular basis of the PURA-NDD. METHODS: 23 individuals (including 12 unpublished) carrying PURA variants were enrolled. We conducted the Illumina Infinium EPIC microarray analysis in 17 PURA-NDD individuals. In vitro experiments were performed to examine how PURA variants affect Pur-α expression. RESULTS: Additional phenotypes in 12 newly identified patients were described in this study. Genome-wide DNA methylation analysis unveiled distinctive methylation profiles to PURA-NDD, and the established classifier can reclassify PURA variants of uncertain significance. Patients bearing PURA hapoloinsufficient and missense variants have comparable DNA methylation profiles, and cells expressing these PURA variants showed consistent Pur-α downregulation suggesting a haploinsufficiency mechanism. CONCLUSION: Patients with PURA-NDD exhibit a specific epi-signature, which has potential to aid identification and diagnosis of PURA-NDD patients and offer implications for further functional investigations.

[Expert consensus on the genetic diagnosis for Dystrophinopathies].

Dystrophinopathies, including Duchenne muscular dystrophy, Becker muscular dystrophy and dilated cardiomyopathy, are X-linked recessive genetic disorders due to variants of the dystrophin gene, which can seriously affect quality of life and health. Genetic diagnosis plays a crucial role in their diagnosis, treatment, and prevention. How to rationally select and standardize the use of various genetic techniques is a skill that clinicians must acquire. By compiling expertise of experts from the relevant areas and guidelines published home and abroad, this consensus has provided a guidance from the perspective of genetic diagnosis for the selection of genetic techniques, testing strategies, and detection process for dystrophinopathies.

Genetic and phenotypic spectrum of non-21-hydroxylase-deficiency primary adrenal insufficiency in childhood: data from 111 Chinese patients.

BACKGROUND: Primary adrenal insufficiency (PAI) is a rare but life-threatening condition. Differential diagnosis of numerous causes of PAI requires a thorough understanding of the condition. METHODS: To describe the genetic composition and presentations of PAI. The following data were collected retrospectively from 111 patients with non-21OHD with defined genetic diagnoses: demographic information, onset age, clinical manifestations, laboratory findings and genetic results. Patients were divided into four groups based on the underlying pathogenesis: (1) impaired steroidogenesis, (2) adrenal hypoplasia, (3) resistance to adrenocorticotropic hormone (ACTH) and (4) adrenal destruction. The age of onset was compared within the groups. RESULTS: Mutations in the following genes were identified: NR0B1 (n=39), STAR (n=33), CYP11B1 (n=12), ABCD1 (n=8), CYP17A1 (n=5), HSD3B2 (n=4), POR (n=4), MRAP (n=2), MC2R (n=1), CYP11A1 (n=1), LIPA (n=1) and SAMD9 (n=1). Frequent clinical manifestations included hyperpigmentation (73.0%), dehydration (49.5%), vomiting (37.8%) and abnormal external genitalia (23.4%). Patients with adrenal hypoplasia typically presented manifestations earlier than those with adrenal destruction but later than those with impaired steroidogenesis (both p<0.01). The elevated ACTH (92.6%) and decreased cortisol (73.5%) were the most common laboratory findings. We generated a differential diagnosis flowchart for PAI using the following clinical features: 17-hydroxyprogesterone, very-long-chain fatty acid, external genitalia, hypertension and skeletal malformation. This flowchart identified 84.8% of patients with PAI before next-generation DNA sequencing. CONCLUSIONS: STAR and NR0B1 were the most frequently mutated genes in patients with non-21OHD PAI. Age of onset and clinical characteristics were dependent on aetiology. Combining clinical features and molecular tests facilitates accurate diagnosis.

CCNK Gene Deficiency Influences Neural Progenitor Cells Via Wnt5a Signaling in CCNK-Related Syndrome.

OBJECTIVE: Rare variants of CCNK (cyclin K) give rise to a syndrome with intellectual disability. The purpose of this study was to describe the genotype-phenotype spectrum of CCNK-related syndrome and the underlying molecular mechanisms of pathogenesis. METHODS: We identified a number of de novo CCNK variants in unrelated patients. We generated patient-induced pluripotent stem cells (iPSCs) and neural progenitor cells (NPCs) as disease models. In addition, we constructed NPC-specific Ccnk knockout (KO) mice and performed molecular and morphological analyses. RESULTS: We identified 2 new patients harboring CCNK missense variants and followed-up 3 previous reported patients, which constitute the largest patient population analysis of the disease. We demonstrate that both the patient-derived NPC models and the Ccnk KO mouse displayed deficient NPC proliferation and enhanced apoptotic cell death. RNA sequencing analyses of these NPC models uncovered transcriptomic signatures unique to CCNK-related syndrome, revealing significant changes in genes, including WNT5A, critical for progenitor proliferation and cell death. Further, to confirm WNT5A's role, we conducted rescue experiments using NPC and mouse models. We found that a Wnt5a inhibitor significantly increased proliferation and reduced apoptosis in NPCs derived from patients with CCNK-related syndrome and NPCs in the developing cortex of Ccnk KO mice. INTERPRETATION: We discussed the genotype-phenotype relationship of CCNK-related syndrome. Importantly, we demonstrated that CCNK plays critical roles in NPC proliferation and NPC apoptosis in vivo and in vitro. Together, our study highlights that Wnt5a may serve as a promising therapeutic target for the disease intervention. ANN NEUROL 2023;94:1136-1154.

[Consensus on laboratory diagnosis of congenital adrenal hyperplasia due to 21 hydroxylase deficiency].

21 hydroxylase deficiency (21-OHD), the most common form of congenital adrenal hyperplasia, is caused by defects in CYP21A2 gene, which encodes the cytochrome P450 oxidase (P450C21) involved in glucocorticoid and mineralocorticoid synthesis. The diagnosis of 21-OHD is based on the comprehensive evaluation of clinical manifestation, biochemical alteration and molecular genetics results. Due to the complex structure of CYP21A2, special techniques are required to perform delicate analysis to avoid the interference of its pseudogene. Recently, the state-of-the-art diagnostic methods were applied to the clinic gradually, including the steroid hormone profiling and third generation sequencing. To standardize the laboratory diagnosis of 21-OHD, this consensus was drafted on the basis of the extensive knowledge, the updated progress and the published consensuses and guidelines worldwide by expert discussion organized by Rare Diseases Group of Pediatric Branch of Chinese Medical Association, Medical Genetics Branch of Chinese Medical Doctor Association, Birth Defect Prevention and Molecular Genetics Branch of China Maternal and Child Health Association. and Molecular Diagnosis Branch of Shanghai Medical Association.

Deep Intronic PAH Variants Explain Missing Heritability in Hyperphenylalaninemia.

Phenylalanine hydroxylase (PAH) deficiency or phenylketonuria (PKU) is the most common cause of hyperphenylalaninemia (HPA), and approximately 5% of patients remain genetically unsolved. Identifying deep intronic PAH variants may help improve their molecular diagnostic rate. Next-generation sequencing was utilized to detect the whole PAH gene in 96 patients with genetically unsolved HPA from 2013 to 2022. The effects of deep intronic variants on pre-mRNA splicing were investigated by minigene-based assay. The allelic phenotype values of recurrent deep intronic variants were calculated. Twelve deep intronic PAH variants, located in intron 5 (c.509+434C>T), intron 6 (c.706+288T>G, c.706+519T>C, c.706+531T>C, c.706+535G>T, c.706+600A>C, c.706+603T>G, and c.706+608A>C), intron 10 (c.1065+241C>A and c.1065+258C>A), and intron 11 (c.1199+502A>T and c.1199+745T>A) were identified in 80.2% (77/96) patients. Ten of the 12 variants were novel, and they all generated pseudoexons in mRNA, leading to frameshift or lengthened proteins. The most prevalent deep intronic variant was c.1199+502A>T, followed by c.1065+241C>A, c.1065+258C>A, and c.706+531T>C. The metabolic phenotypes of the four variants were assigned as classic PKU, mild HPA, mild HPA, and mild PKU, respectively. The results suggest that deep intronic PAH variants improved the diagnostic rate from 95.3% to 99.3% in the overall patients with HPA. Our data demonstrate the importance of assessing noncoding variants in genetic diseases. Pseudoexon inclusion caused by deep intronic variants may represent a recurrent mechanism.

A 25 Mainland Chinese cohort of patients with PURA-related neurodevelopmental disorders: clinical delineation and genotype-phenotype correlations.

PURA-related neurodevelopmental disorders (PURA-NDDs) include 5q31.3 microdeletion syndrome and PURA syndrome. PURA has been proposed as a candidate gene responsible for 5q31.3 microdeletion syndrome. Phenotype comparisons between patients with PURA mutations and 5q31.3 microdeletions encompassing more than PURA gene are lacking. A total of 25 previously undescribed Mainland China patients were evaluated. Clinical data were obtained from medical record review and standardized medical history questionnaire. Clinical profile and genetic spectrum of the patients with PURA syndrome and genotype-phenotype correlations between PURA mutations group and 5q31.3 microdeletions group were analyzed. Our identified seventeen de nove PURA variants were novel, and two recurrent frameshift variants, c.697_699del (p.F233del) and c.159dup (p.L54Afs*147) were detected in the four independent pedigrees. One patient with 5q31.3 microdeletion further supported the shortest overlapping region only contains PURA and IGIP gene. Developmental delay/intellectual disability, neonatal hypotonia, neonatal feeding difficulties, hypersomnolence and dysmorphic features were prominent clinical features in PURA syndrome. There was no significant difference between two groups in incidence of neonatal problems, developmental delay and common medical comorbidities. We observed a higher frequency of abnormal brain MRI and specific facial dysmorphism in 5q31.3 microdeletion group. This is the first work describing a largest cohort of Mainland China patients broaden the clinical and molecular spectrum of PURA-NDDs. Our findings not only demonstrated that PURA haploinsufficiency was a major contributor to the important phenotypes of 5q31.3 microdeletion, but also implied that additional genes still played a role in the 5q31.3 microdeletion.

Improving variant prioritization in exome analysis by entropy-weighted ensemble of multiple tools.

Variant prioritization is a crucial step in the analysis of exome and genome sequencing. Multiple phenotype-driven tools have been developed to automate the variant prioritization process, but the efficacy of these tools in clinical setting with fuzzy phenotypic information and whether ensemble of these tools could outperform single algorithm remains to be assessed. A large rare disease cohort with heterogeneous phenotypic information, including a primary cohort of 1614 patients and a replication cohort of 1904 patients referred to exome sequencing, were recruited to assess the efficacy of variant prioritization and their ensemble. Three freely available tools-Exomiser, Xrare, and DeepPVP-and their ensemble were evaluated. The performance of all three tools was influenced by the attributes of phenotypic input. When combining these three tools by weighted-sum entropy method (EWE3), the ensemble outperformed any single algorithm, achieving a rate of 78% diagnostic variants in top 3 (13% improvement over current best performer, compared to Exomiser: 63%, Xrare: 65%, and DeepPVP: 51%), 88% in top 10 and 96% in top 30. The results were replicated in another independent cohort. Our study supports using entropy-weighted ensemble of multiple tools to improve variant prioritization and accelerate molecular diagnosis in exome/genome sequencing.

Genetic and clinical characteristics of 24 mainland Chinese patients with CTNNB1 loss-of-function variants.

BACKGROUND: Neurodevelopmental disorder with spastic diplegia and visual defects (NEDSDV) is a rare autosomal dominant syndrome, which is caused by the heterozygous germline loss-of-function variants in CTNNB1. METHODS: We evaluated the clinical and genetic findings of 24 previously undescribed Chinese patients affected by CTNNB1-related disorders and explored the possible ethnicity-related phenotypic variations. RESULTS: Twenty-one loss-of-function variants were identified within these 24 NEDSDV patients, including 14 novel CTNNB1 variants and 7 recurrent ones. The prominent clinical manifestations in our cohort are developmental delay/intellectual disability (100%), motor delay (100%), speech impairment (100%), dystonia (87.5%) and microcephaly (69.6%). The common facial dysmorphisms were consistent with previous reports, including wide nasal bridge (58.3%), bulbous nose (45.8%), long philtrum (45.8%) and thin upper lip (45.8%). In addition, 19 patients (79.2%) in our cohort had mild visual defects, while one affected individual (4.2%) had familial exudative vitreoretinopathy. Notably, we discovered that 20 patients (83.3%) exhibited various behavioral abnormalities, which is described in Chinese patients for the first time. CONCLUSION: We provided the largest known Chinese cohort with pathogenic CTNNB1 variants, which not only helps to expand the variant spectrum of CTNNB1 gene, but further delineates the typical phenotype of this disorder in Chinese population.

Genome sequencing demonstrates high diagnostic yield in children with undiagnosed global developmental delay/intellectual disability: A prospective study.

Genome sequencing (GS) has been used in the diagnosis of global developmental delay (GDD)/intellectual disability (ID). However, the performance of GS in patients with inconclusive results from chromosomal microarray analysis (CMA) and exome sequencing (ES) is unknown. We recruited 100 pediatric GDD/ID patients from multiple sites in China from February 2018 to August 2020 for GS. Patients have received at least one genomic diagnostic test before enrollment. Reanalysis of their CMA/ES data was performed. The yield of GS was calculated and explanations for missed diagnoses by CMA/ES were investigated. Clinical utility was assessed by interviewing the parents by phone. The overall diagnostic yield of GS was 21%. Seven cases could have been solved with reanalysis of ES data. Thirteen families were missed by previous CMA/ES due to improper methodology. Two remained unsolved after ES reanalysis due to complex variants missed by ES, and a CNV in untranslated regions. Follow-up of the diagnosed families revealed that nine families experienced changes in clinical management, including identification of targeted treatments, cessation of unnecessary treatment, and considerations for family planning. GS demonstrated high diagnostic yield and clinical utility in this undiagnosed GDD/ID cohort, detecting a wide range of variant types of different sizes in a single workflow.

Diagnosis and follow-up of glycogen storage disease (GSD) type VI from the largest GSD center in China.

Glycogen storage disease (GSD) Type VI is a glycogenolysis disorder caused by variants of PYGL. Knowledge about this disease is limited because only approximately 50 cases have been reported. We investigated the clinical profiles, molecular diagnosis, and treatment outcomes in patients with GSD VI from 2000 to 2021. The main initial clinical features of this cohort include hepatomegaly, short stature, elevated liver transaminases, hypertriglyceridemia, fasting hypoglycemia, and hyperuricemia. After uncooked cornstarch treatment, the stature and biochemical parameters improved significantly (p < 0.05). However, hyperuricemia recurred in most patients during adolescence. Among the 56 GSD VI patients, 54 biallelic variants and two single allelic variants of PYGL were identified, of which 43 were novel. There were two hotspot variants, c.1621-258_2178-23del and c.2467C>T p.(Gln823*), mainly in patients from Southwest and South China. c.1621-258_2178-23del is a 3.6 kb deletion that results in an out-of-frame deletion r.1621_2177del and an in-frame deletion r.1621_2265del. Our data show for the first time that long-term monitoring of uric acid is recommended for older GSD VI patients. This study also broadens the variant spectrum of PYGL and indicates that there are two hot-spot variants in China.

A comparison of the clinical characteristics of pediatric urolithiasis patients with positive and negative molecular diagnoses.

PURPOSE: To compare the clinical characteristics of pediatric urolithiasis patients with positive and negative molecular diagnoses. METHODS: The clinical characteristics corresponding to pediatric urolithiasis patients that had undergone exome sequencing at our hospital between January 2016 and May 2021 were collected. Genetic analysis results were used to separate patients into positive and negative molecular diagnosis groups. Multivariate logistic regression analyses adjusted for visiting age, sex, ethnicity, province, and body mass index were used to compare differences in medical history, diagnostic imaging findings, and renal function between individuals with and without molecular diagnoses. RESULTS: In total, 194 patients with pediatric urolithiasis of unknown etiology underwent exome sequencing and were included in the present study, of whom 63 obtained urolithiasis-related molecular diagnoses. Relative to cases without a molecular diagnosis, those with a positive molecular diagnosis were more likely to be associated with a positive family history (OR 2.84, 95% CI 1.29-6.29, p = 0.008), consanguineous parents (OR 24.7, 95% CI 1.34-454, p = 0.002), early onset (OR 1.26, 95% CI 1.09-1.45, p < 0.001), nephrocalcinosis (OR 10.6, 95% CI 3.06-36.6, p < 0.001), cast stone (OR 18.9, 95% CI 4.40-81.1, p < 0.001), multiple stones (OR 13.9, 95% CI 6.39-30.2, p < 0.001), bilateral stones (OR 7.04, 95% CI 3.47-14.2, p < 0.001), a lower estimated glomerular filtration rate (OR 1.17, 95% CI 1.07-1.28, p < 0.001), and chronic kidney disease (OR 26.9, 95% CI 1.42-526, p < 0.001). CONCLUSION: A positive family history, consanguineous parents, early onset, nephrocalcinosis, severe stone burden, and impaired renal function are signals of concern that are suggestive of inherited urolithiasis.

Enhanced genome editing to ameliorate a genetic metabolic liver disease through co-delivery of adeno-associated virus receptor.

Genome editing through adeno-associated viral (AAV) vectors is a promising gene therapy strategy for various diseases, especially genetic disorders. However, homologous recombination (HR) efficiency is extremely low in adult animal models. We assumed that increasing AAV transduction efficiency could increase genome editing activity, especially HR efficiency, for in vivo gene therapy. Firstly, a mouse phenylketonuria (PKU) model carrying a pathogenic R408W mutation in phenylalanine hydroxylase (Pah) was generated. Through co-delivery of the general AAV receptor (AAVR), we found that AAVR could dramatically increase AAV transduction efficiency in vitro and in vivo. Furthermore, co-delivery of SaCas9/sgRNA/donor templates with AAVR via AAV8 vectors increased indel rate over 2-fold and HR rate over 15-fold for the correction of the single mutation in PahR408W mice. Moreover, AAVR co-injection successfully increased the site-specific insertion rate of a 1.4 kb Pah cDNA by 11-fold, bringing the HR rate up to 7.3% without detectable global off-target effects. Insertion of Pah cDNA significantly decreased the Phe level and ameliorated PKU symptoms. This study demonstrates a novel strategy to dramatically increase AAV transduction which substantially enhanced in vivo genome editing efficiency in adult animal models, showing clinical potential for both conventional and genome editing-based gene therapy.

A retrospective study of nine patients with progressive pseudorheumatoid dysplasia: to explore early diagnosis and further treatment.

OBJECTIVES: Most patients with progressive pseudorheumatoid dysplasia (PPRD) are initially misdiagnosed because of disease rarity and lack of awareness by most clinicians. The purpose of this study was to provide further early diagnostic options and potential treatment to patients with PPRD. METHODS: A retrospective study was performed by collecting and organizing clinical manifestations, radiographic features, laboratory test results, genetic test outcome, treatment, and follow-up records of the patients with PPRD. Age of diagnosis and genotype-phenotype correlation were further analyzed. RESULTS: Nine PPRD children with causative CCN6 mutation were included. There were 3 pairs of siblings and 1 patient from inbred family. Five patients were primarily misdiagnosed as juvenile idiopathic arthritis (JIA). The interval between onset of symptoms and definite diagnosis of 8 patients varied from 3.6 to 20 years. Symptoms at the onset included enlarged and stiff interphalangeal joints of the fingers, gait disturbance, or joint pain. Laboratory tests revealed normal range of inflammatory parameters. Radiographic findings disclosed different degrees of abnormal vertebral bodies and epiphyseal enlargement of the interphalangeal joints. After the treatment of calcitriol in 5 patients with low level 25-hydroxyvitamin D3 for around 1.25 years to 1.75 years, 2 patients kept stable, while 3 of them improved gradually. CONCLUSIONS: Combining the patient's family history, clinical features, normal inflammatory markers, and the characteristic radiographic findings, the clinical diagnosis of PPRD for the patients could be obtained at very early stage of the disease. The patients with PPRD carrying c.624dupA variant in CCN6 may have delayed onset. Underlying vitamin D deficiency should be sought and corrected in patients with PPRD.

Copy number variation analysis in Chinese children with complete atrioventricular canal and single ventricle.

BACKGROUND: Congenital heart disease (CHD) is one of the most common birth defects. Copy number variations (CNVs) have been proved to be important genetic factors that contribute to CHD. Here we screened genome-wide CNVs in Chinese children with complete atrioventricular canal (CAVC) and single ventricle (SV), since there were scarce researches dedicated to these two types of CHD. METHODS: We screened CNVs in 262 sporadic CAVC cases and 259 sporadic SV cases respectively, using a customized SNP array. The detected CNVs were annotated and filtered using available databases. RESULTS: Among 262 CAVC patients, we identified 6 potentially-causative CNVs in 43 individuals (16.41%, 43/262), including 2 syndrome-related CNVs (7q11.23 and 8q24.3 deletion). Surprisingly, 90.70% CAVC patients with detected CNVs (39/43) were found to carry duplications of 21q11.2-21q22.3, which were recognized as trisomy 21 (Down syndrome, DS). In CAVC with DS patients, the female to male ratio was 1.6:1.0 (24:15), and the rate of pulmonary hypertension (PH) was 41.03% (16/39). Additionally, 6 potentially-causative CNVs were identified in the SV patients (2.32%, 6/259), and none of them was trisomy 21. Most CNVs identified in our cohort were classified as rare (< 1%), occurring just once among CAVC or SV individuals except the 21q11.2-21q22.3 duplication (14.89%) in CAVC cohort. CONCLUSIONS: Our study identified 12 potentially-causative CNVs in 262 CAVC and 259 SV patients, representing the largest cohort of these two CHD types in Chinese population. The results provided strong correlation between CAVC and DS, which also showed sex difference and high incidence of PH. The presence of potentially-causative CNVs suggests the etiology of complex CHD is incredibly diverse, and CHD candidate genes remain to be discovered.

One-year follow-up of thyroid function in 23 infants with Prader- Willi syndrome at a single center in China.

Endocrine disorders are common in patients with Prader-Willi syndrome (PWS). Whether hypothyroidism is present in patients with PWS, and especially infants and young children, remains unclear. The aims of this study were to evaluate thyroid function in patients with PWS, to assess the prevalence of thyroid dysfunction, and to evaluate the effect of growth hormone on thyroid function. Subjects were 23 patients with PWS ages 3 months to 3 years who were followed for up to one year. Four patients were lost to follow-up after the first visit. The remaining 19 patients were treated with recombinant human growth hormone (rhGH). PWS was diagnosed based on a genetic analysis. Free thyroxine (FT4), free triiodothyronine (FT3), and thyroid-stimulating hormone (TSH) levels were evaluated before and after growth hormone treatment. A total of 9 patients (9/23 = 39.1%) developed abnormal thyroid function. Five out of 23 patients (21.7%) had abnormal thyroid function before growth hormone treatment. Four patients developed thyroid dysfunction during the 3- to 9-month period of rhGH treatment. Of the 9 patients with abnormal thyroid function, 7 (5 boys, 2 girls) had central hypothyroidism, and the other 2 patients had subclinical hypothyroidism. TSH levels were higher in patients with PWS due to maternal uniparental disomy (UPD) than in patients with PWS due to a 15q11-q13 deletion. The prevalence of hypothyroidism was high in infants and young children with PWS. Thyroid function should be regularly monitored in patients with PWS at both diagnosis and follow-up.