A new variant in the ZCCHC8 gene: diverse clinical phenotypes and expression in the lung.

Introduction: Pulmonary fibrosis is a severe disease which can be familial. A genetic cause can only be found in ∼40% of families. Searching for shared novel genetic variants may aid the discovery of new genetic causes of disease. Methods: Whole-exome sequencing was performed in 152 unrelated patients with a suspected genetic cause of pulmonary fibrosis from the St Antonius interstitial lung disease biobank. Variants of interest were selected by filtering for novel, potentially deleterious variants that were present in at least three unrelated pulmonary fibrosis patients. Results: The novel c.586G>A p.(E196K) variant in the ZCCHC8 gene was observed in three unrelated patients: two familial patients and one sporadic patient, who was later genealogically linked to one of the families. The variant was identified in nine additional relatives with pulmonary fibrosis and other telomere-related phenotypes, such as pulmonary arterial venous malformations, emphysema, myelodysplastic syndrome, acute myeloid leukaemia and dyskeratosis congenita. One family showed incomplete segregation, with absence of the variant in one pulmonary fibrosis patient who carried a PARN variant. The majority of ZCCHC8 variant carriers showed short telomeres in blood. ZCCHC8 protein was located in different lung cell types, including alveolar type 2 (AT2) pneumocytes, the culprit cells in pulmonary fibrosis. AT2 cells showed telomere shortening and increased DNA damage, which was comparable to patients with sporadic pulmonary fibrosis and those with pulmonary fibrosis carrying a telomere-related gene variant, respectively. Discussion: The ZCCHC8 c.586G>A variant confirms the involvement of ZCCHC8 in pulmonary fibrosis and short-telomere syndromes and underlines the importance of including the ZCCHC8 gene in diagnostic gene panels for these diseases.

Disruption of TUFT1, a Desmosome-Associated Protein, Causes Skin Fragility, Woolly Hair, and Palmoplantar Keratoderma.

Desmosomes are dynamic complex protein structures involved in cellular adhesion. Disruption of these structures by loss-of-function variants in desmosomal genes leads to a variety of skin- and heart-related phenotypes. In this study, we report TUFT1 as a desmosome-associated protein, implicated in epidermal integrity. In two siblings with mild skin fragility, woolly hair, and mild palmoplantar keratoderma but without a cardiac phenotype, we identified a homozygous splice-site variant in the TUFT1 gene, leading to aberrant mRNA splicing and loss of TUFT1 protein. Patients' skin and keratinocytes showed acantholysis, perinuclear retraction of intermediate filaments, and reduced mechanical stress resistance. Immunolabeling and transfection studies showed that TUFT1 is positioned within the desmosome and that its location is dependent on the presence of the desmoplakin carboxy-terminal tail. A Tuft1-knockout mouse model mimicked the patients' phenotypes. Altogether, this study reveals TUFT1 as a desmosome-associated protein, whose absence causes skin fragility, woolly hair, and palmoplantar keratoderma.

Low-Cost High-Throughput Genotyping for Diagnosing Familial Hypercholesterolemia.

BACKGROUND: Familial hypercholesterolemia (FH) is a common but underdiagnosed genetic disorder characterized by high low-density lipoprotein cholesterol levels and premature cardiovascular disease. Current sequencing methods to diagnose FH are expensive and time-consuming. In this study, we evaluated the accuracy of a low-cost, high-throughput genotyping array for diagnosing FH. METHODS: An Illumina Global Screening Array was customized to include probes for 636 variants, previously classified as FH-causing variants. First, its theoretical coverage was assessed in all FH variant carriers diagnosed through next-generation sequencing between 2016 and 2022 in the Netherlands (n=1772). Next, the performance of the array was validated in another sample of FH variant carriers previously identified in the Dutch FH cascade screening program (n=1268). RESULTS: The theoretical coverage of the array for FH-causing variants was 91.3%. Validation of the array was assessed in a sample of 1268 carriers of whom 1015 carried a variant in LDLR, 250 in APOB, and 3 in PCSK9. The overall sensitivity was 94.7% and increased to 98.2% after excluding participants with variants not included in the array design. Copy number variation analysis yielded a 89.4% sensitivity. In 18 carriers, the array identified a total of 19 additional FH-causing variants. Subsequent DNA analysis confirmed 5 of the additionally identified variants, yielding a false-positive result in 16 subjects (1.3%). CONCLUSIONS: The FH genotyping array is a promising tool for genetically diagnosing FH at low costs and has the potential to greatly increase accessibility to genetic testing for FH. Continuous customization of the array will further improve its performance.

Prevalence of Monogenic Bone Disorders in a Dutch Cohort of Atypical Femur Fracture Patients.

Atypical femur fractures (AFFs), considered rare associations of bisphosphonates, have also been reported in patients with monogenic bone disorders without bisphosphonate use. The exact association between AFFs and monogenic bone disorders remains unknown. Our aim was to determine the prevalence of monogenic bone disorders in a Dutch AFF cohort. AFF patients were recruited from two specialist bone centers in the Netherlands. Medical records of the AFF patients were reviewed for clinical features of monogenic bone disorders. Genetic variants identified by whole-exome sequencing in 37 candidate genes involved in monogenic bone disorders were classified based on the American College of Medical Genetics and Genomics (ACMG) classification guidelines. Copy number variations overlapping the candidate genes were also evaluated using DNA array genotyping data. The cohort comprises 60 AFF patients (including a pair of siblings), with 95% having received bisphosphonates. Fifteen AFF patients (25%) had clinical features of monogenic bone disorders. Eight of them (54%), including the pair of siblings, had a (likely) pathogenic variant in either PLS3, COL1A2, LRP5, or ALPL. One patient carried a likely pathogenic variant in TCIRG1 among patients not suspected of monogenic bone disorders (2%). In total, nine patients in this AFF cohort (15%) had a (likely) pathogenic variant. In one patient, we identified a 12.7 Mb deletion in chromosome 6, encompassing TENT5A. The findings indicate a strong relationship between AFFs and monogenic bone disorders, particularly osteogenesis imperfecta and hypophosphatasia, but mainly in individuals with symptoms of these disorders. The high yield of (likely) pathogenic variants in AFF patients with a clinical suspicion of these disorders stresses the importance of careful clinical evaluation of AFF patients. Although the relevance of bisphosphonate use in this relationship is currently unclear, clinicians should consider these findings in medical management of these patients. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Expanding the Phenotypic Spectrum of Kenny-Caffey Syndrome.

CONTEXT: Kenny-Caffey syndrome (KCS) is a rare hereditary disorder characterized by short stature, hypoparathyroidism, and electrolyte disturbances. KCS1 and KCS2 are caused by pathogenic variants in TBCE and FAM111A, respectively. Clinically the phenotypes are difficult to distinguish. OBJECTIVE: The objective was to determine and expand the phenotypic spectrum of KCS1 and KCS2 in order to anticipate complications that may arise in these disorders. METHODS: We clinically and genetically analyzed 10 KCS2 patients from 7 families. Because we found unusual phenotypes in our cohort, we performed a systematic review of genetically confirmed KCS cases using PubMed and Scopus. Evaluation by 3 researchers led to the inclusion of 26 papers for KCS1 and 16 for KCS2, totaling 205 patients. Data were extracted following the Cochrane guidelines and assessed by 2 independent researchers. RESULTS: Several patients in our KCS2 cohort presented with intellectual disability (3/10) and chronic kidney disease (6/10), which are not considered common findings in KCS2. Systematic review of all reported KCS cases showed that the phenotypes of KCS1 and KCS2 overlap for postnatal growth retardation (KCS1: 52/52, KCS2: 23/23), low parathyroid hormone levels (121/121, 16/20), electrolyte disturbances (139/139, 24/27), dental abnormalities (47/50, 15/16), ocular abnormalities (57/60, 22/23), and seizures/spasms (103/115, 13/16). Symptoms more prevalent in KCS1 included intellectual disability (74/80, 5/24), whereas in KCS2 bone cortical thickening (1/18, 16/20) and medullary stenosis (7/46, 27/28) were more common. CONCLUSION: Our case series established chronic kidney disease as a new feature of KCS2. In the literature, we found substantial overlap in the phenotypic spectra of KCS1 and KCS2, but identified intellectual disability and the abnormal bone phenotype as the most distinguishing features.

Withdrawn as duplicate: Expanding the phenotypic spectrum of Kenny-Caffey syndrome: a case series and systematic literature review.

This article has been withdrawn due to a publisher error that caused it to be duplicated. The definitive version of this article is published under https://doi.org/10.1210/clinem/dgad147.

A comparison of genotyping arrays.

Array technology to genotype single-nucleotide variants (SNVs) is widely used in genome-wide association studies (GWAS), clinical diagnostics, and linkage studies. Arrays have undergone a tremendous growth in both number and content over recent years making a comprehensive comparison all the more important. We have compared 28 genotyping arrays on their overall content, genome-wide coverage, imputation quality, presence of known GWAS loci, mtDNA variants and clinically relevant genes (i.e., American College of Medical Genetics (ACMG) actionable genes, pharmacogenetic genes, human leukocyte antigen (HLA) genes and SNV density). Our comparison shows that genome-wide coverage is highly correlated with the number of SNVs on the array but does not correlate with imputation quality, which is the main determinant of GWAS usability. Average imputation quality for all tested arrays was similar for European and African populations, indicating that this is not a good criterion for choosing a genotyping array. Rather, the additional content on the array, such as pharmacogenetics or HLA variants, should be the deciding factor. As the research question of a study will in large part determine which class of genes are of interest, there is not just one perfect array for all different research questions. This study can thus help as a guideline to determine which array best suits a study's requirements.

The Genetics of Atypical Femur Fractures-a Systematic Review.

PURPOSE OF REVIEW: Atypical femur fractures (AFFs) are rare subtrochanteric or diaphyseal fractures regarded as side effects of bisphosphonates (BPs), possibly with a genetic background. Here, we summarize the most recent knowledge about genetics of AFFs. RECENT FINDINGS: AFF has been reported in 57 patients with seven different monogenic bone disorders including hypophosphatasia and osteogenesis imperfecta; 56.1% had never used BPs, while 17.5% were diagnosed with the disorder only after the AFF. Gene mutation finding in familial and sporadic cases identified possible AFF-related variants in the GGPS1 and ATRAID genes respectively. Functional follow-up studies of mutant proteins showed possible roles in AFF. A recent small genome-wide association study on 51 AFF cases did not identify significant hits associated with AFF. Recent findings have strengthened the hypothesis that AFFs have underlying genetic components but more studies are needed in AFF families and larger cohorts of sporadic cases to confirm previous results and/or find novel gene variants involved in the pathogenesis of AFFs.

Underlying genetic variation in familial frontotemporal dementia: sequencing of 198 patients.

Frontotemporal dementia (FTD) presents with a wide variability in clinical syndromes, genetic etiologies, and underlying pathologies. Despite the discovery of pathogenic variants in several genes, many familial cases remain unsolved. In a large FTD cohort of 198 familial patients, we aimed to determine the types and frequencies of variants in genes related to FTD. Pathogenic or likely pathogenic variants were revealed in 74 (37%) patients, including 4 novel variants. The repeat expansion in C9orf72 was most common (21%), followed by variants in MAPT (6%), GRN (4.5%), and TARDBP (3.5%). Other pathogenic variants were found in VCP, TBK1, PSEN1, and a novel homozygous variant in OPTN. Furthermore, we identified 15 variants of uncertain significance, including a promising variant in TUBA4A and a frameshift in VCP, for which additional research is needed to confirm pathogenicity. The patients without identified genetic cause demonstrated a wide clinical and pathological variety. Our study contributes to the clinical characterization of the genetic subtypes and confirms the value of whole-exome sequencing in identifying novel genetic variants.

Congenital hypopituitarism in two brothers with a duplication of the 'acrogigantism gene' GPR101: clinical findings and review of the literature.

PURPOSE: Congenital hypopituitarism (CH) can cause significant morbidity or even mortality. In the majority of patients, the etiology of CH is unknown. Understanding the etiology of CH is important for anticipation of clinical problems and for genetic counselling. Our previous studies showed that only a small proportion of cases have mutations in the known 'CH genes'. In the current project, we present the results of SNP array based copy number variant analysis in a family with unexplained congenital hypopituitarism. METHODS: DNA samples of two affected brothers with idiopathic CH and their mother were simultaneously analyzed by SNP arrays for copy number variant analysis and Whole Exome Sequencing (WES) for mutation screening. DNA of the father was not available. RESULTS: We found a 6 Mb duplication including GPR101 and SOX3 on the X-chromosome (Xq26.2-q27.1) in the two siblings and their mother, leading to 2 copies of this region in the affected boys and 3 copies in the mother. Duplications of GPR101 are associated with X-linked acrogigantism (the phenotypic 'opposite' of the affected brothers), whereas alterations in SOX3 are associated with X-linked hypopituitarism. CONCLUSION: In our patients with hypopituitarism we found a 6 Mb duplication which includes GPR101, a gene associated with X- linked gigantism, and SOX3, a gene involved in early pituitary organogenesis that is associated with variable degrees of hypopituitarism. Our findings show that in duplications containing both GPR101 and SOX3, the growth hormone deficiency phenotype is dominant. This suggests that, if GPR101 is duplicated, it might not be expressed phenotypically when early patterning of the embryonic pituitary is affected due to SOX3 duplication. These results, together with the review of the literature, shed a new light on the role of GPR101 and SOX3 in pituitary function.

Reduced penetrance of pathogenic ACMG variants in a deeply phenotyped cohort study and evaluation of ClinVar classification over time.

PURPOSE: We studied the penetrance of pathogenically classified variants in an elderly Dutch population from the Rotterdam Study, for which deep phenotyping is available. We screened the 59 actionable genes for which reporting of known pathogenic variants was recommended by the American College of Medical Genetics and Genomics (ACMG), and demonstrate that determining what constitutes a known pathogenic variant can be quite challenging. METHODS: We defined "known pathogenic" as classified pathogenic by both ClinVar and the Human Gene Mutation Database (HGMD). In 2628 individuals, we performed exome sequencing and identified known pathogenic variants. We investigated the clinical records of carriers and evaluated clinical events during 25 years of follow-up for evidence of variant pathogenicity. RESULTS: Of 3815 variants detected in the 59 ACMG genes, 17 variants were considered known pathogenic. For 14/17 variants the ClinVar classification had changed over time. Of 24 confirmed carriers of these variants, we observed at least one clinical event possibly caused by the variant in only three participants (13%). CONCLUSION: We show that the definition of "known pathogenic" is often unclear and should be approached carefully. Additionally variants marked as known pathogenic do not always have clinical impact on their carriers. Definition and classification of true (individual) expected pathogenic impact should be defined carefully.

Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation.

OBJECTIVE: To describe the clinical and pathologic features of a novel pedigree with heterozygous STUB1 mutation causing SCA48. METHODS: We report a large pedigree of Dutch decent. Clinical and pathologic data were reviewed, and genetic analyses (whole-exome sequencing, whole-genome sequencing, and linkage analysis) were performed on multiple family members. RESULTS: Patients presented with adult-onset gait disturbance (ataxia or parkinsonism), combined with prominent cognitive decline and behavioral changes. Whole-exome sequencing identified a novel heterozygous frameshift variant c.731_732delGC (p.C244Yfs*24) in STUB1 segregating with the disease. This variant was present in a linkage peak on chromosome 16p13.3. Neuropathologic examination of 3 cases revealed a consistent pattern of ubiquitin/p62-positive neuronal inclusions in the cerebellum, neocortex, and brainstem. In addition, tau pathology was present in 1 case. CONCLUSIONS: This study confirms previous findings of heterozygous STUB1 mutations as the cause of SCA48 and highlights its prominent cognitive involvement, besides cerebellar ataxia and movement disorders as cardinal features. The presence of intranuclear inclusions is a pathologic hallmark of the disease. Future studies will provide more insight into its pathologic heterogeneity.

Unique near-complete deletion of GLI2 in a patient with combined pituitary hormone deficiency and post-axial polydactyly.

INTRODUCTION: Combined pituitary hormone deficiency (CPHD) can cause a broad spectrum of health problems, ranging from short stature only, to convulsions or even death. In the majority of patients, the cause is unknown. METHODS: The idex case had unexplained CPHD, pituitary anomalies on MRI and polydactyly. In the patients and her unaffected parents, we performed SNP array analysis and Whole Exome Sequencing, after candidate gene analysis turned out negative. RESULTS: We found a unique de novo heterozygous 229.9 kb deletion in the index case on chr. 2q14.2. This deletion covered 12 out of the 13 coding exons of the GLI2 gene, a transcription factor involved in midline formation and previously associated with CPHD. As reported GLI2 deletions and mutations show a large phenotypic variability, we performed a genotype-phenotype analysis. This revealed that GLI2 missense mutations usually present with a 'ppp-only' phenotype (pituitary anomalies ± postaxial polydactyly without brain phenotype), whereas the 'ppp-plus' phenotype (with major brain malformations and/or intellectual disabilities) is more frequent in patients with larger deletions, and those with frameshift mutations/point mutations or splice variants resulting in a stop codon (p < .001). CONCLUSION: The present case shows that a deletion of the GLI2 gene only (not affecting any of the adjacent genes) causes pituitary anomalies without brain phenotype. This suggests that brain phenotype only occurs when additional genes adjacent to GLI2 are deleted, or when mutations result in truncated GLI2 mRNA/protein. However, due to the lack of functional data for many GLI2 mutations and based on the available information regarding variable penetrance, phenotype-genotype correlations need to be made with caution.

Linkage analysis and whole exome sequencing identify a novel candidate gene in a Dutch multiple sclerosis family.

BACKGROUND: Multiple sclerosis (MS) is a complex disease resulting from the joint effect of many genes. It has been speculated that rare variants might explain part of the missing heritability of MS. OBJECTIVE: To identify rare coding genetic variants by analyzing a large MS pedigree with 11 affected individuals in several generations. METHODS: Genome-wide linkage screen and whole exome sequencing (WES) were performed to identify novel coding variants in the shared region(s) and in the known 110 MS risk loci. The candidate variants were then assessed in 591 MS patients and 3169 controls. RESULTS: Suggestive evidence for linkage was obtained to 7q11.22-q11.23. In WES data, a rare missense variant p.R183C in FKBP6 was identified that segregated with the disease in this family. The minor allele frequency was higher in an independent cohort of MS patients than in healthy controls (1.27% vs 0.95%), but not significant (odds ratio (OR) = 1.33 (95% confidence interval (CI): 0.8-2.4), p = 0.31). CONCLUSION: The rare missense variant in FKBP6 was identified in a large Dutch MS family segregating with the disease. This association to MS was not found in an independent MS cohort. Overall, genome-wide studies in larger cohorts are needed to adequately investigate the role of rare variants in MS risk.

Genetic Risk Factors for Atypical Femoral Fractures (AFFs): A Systematic Review.

Atypical femoral fractures (AFFs) are uncommon and have been associated particularly with long-term antiresorptive therapy, including bisphosphonates. Although the pathogenesis of AFFs is unknown, their identification in bisphosphonate-naïve individuals and in monogenetic bone disorders has led to the hypothesis that genetic factors predispose to AFF. Our aim was to review and summarize the evidence for genetic factors in individuals with AFF. We conducted structured literature searches and hand-searching of conference abstracts/reference lists for key words relating to AFF and identified 2566 citations. Two individuals independently reviewed citations for (i) cases of AFF in monogenetic bone diseases and (ii) genetic studies in individuals with AFF. AFFs were reported in 23 individuals with the following 7 monogenetic bone disorders (gene): osteogenesis imperfecta (COL1A1/COL1A2), pycnodysostosis (CTSK), hypophosphatasia (ALPL), X-linked osteoporosis (PLS3), osteopetrosis, X-linked hypophosphatemia (PHEX), and osteoporosis pseudoglioma syndrome (LRP5). In 8 cases (35%), the monogenetic bone disorder was uncovered after the AFF occurred. Cases of bisphosphonate-naïve AFF were reported in pycnodysostosis, hypophosphatasia, osteopetrosis, X-linked hypophosphatemia, and osteoporosis pseudoglioma syndrome. A pilot study in 13 AFF patients and 268 controls identified a greater number of rare variants in AFF cases using exon array analysis. A whole-exome sequencing study in 3 sisters with AFFs showed, among 37 shared genetic variants, a p.Asp188Tyr mutation in the GGPS1 gene in the mevalonate pathway, critical to osteoclast function, which is also inhibited by bisphosphonates. Two studies completed targeted ALPL gene sequencing, an ALPL heterozygous mutation was found in 1 case of a cohort of 11 AFFs, whereas the second study comprising 10 AFF cases did not find mutations in ALPL. Targeted sequencing of ALPL, COL1A1, COL1A2, and SOX9 genes in 5 cases of AFF identified a variant in COL1A2 in 1 case. These findings suggest a genetic susceptibility for AFFs. A large multicenter collaborative study of well-phenotyped AFF cases and controls is needed to understand the role of genetics in this uncommon condition.

CXorf56, a dendritic neuronal protein, identified as a new candidate gene for X-linked intellectual disability.

Intellectual disability (ID) comprises a large group of heterogeneous disorders, often without a known molecular cause. X-linked ID accounts for 5-10% of male ID cases. We investigated a large, three-generation family with mild ID and behavior problems in five males and one female, with a segregation suggestive for X-linked inheritance. Linkage analysis mapped a disease locus to a 7.6 Mb candidate region on the X-chromosome (LOD score 3.3). Whole-genome sequencing identified a 2 bp insertion in exon 2 of the chromosome X open reading frame 56 gene (CXorf56), resulting in a premature stop codon. This insertion was present in all intellectually impaired individuals and carrier females. Additionally, X-inactivation status showed skewed methylation patterns favoring the inactivation of the mutated allele in the unaffected carrier females. We demonstrate that the insertion leads to nonsense-mediated decay and that CXorf56 mRNA expression is reduced in the impaired males and female. In murine brain slices and primary hippocampal neuronal cultures, CXorf56 protein was present and localized in the nucleus, cell soma, dendrites, and dendritic spines. Although no other families have been identified with pathogenic variants in CXorf56, these results suggest that CXorf56 is the causative gene in this family, and thus a novel candidate gene for X-linked ID with behavior problems.

Population-specific genetic variation in large sequencing data sets: why more data is still better.

We have generated a next-generation whole-exome sequencing data set of 2628 participants of the population-based Rotterdam Study cohort, comprising 669 737 single-nucleotide variants and 24 019 short insertions and deletions. Because of broad and deep longitudinal phenotyping of the Rotterdam Study, this data set permits extensive interpretation of genetic variants on a range of clinically relevant outcomes, and is accessible as a control data set. We show that next-generation sequencing data sets yield a large degree of population-specific variants, which are not captured by other available large sequencing efforts, being ExAC, ESP, 1000G, UK10K, GoNL and DECODE.

Successful Growth Hormone Therapy in Cornelia de Lange Syndrome.

Cornelia de Lange syndrome (CdLS) is a both clinically and genetically heterogeneous syndrome. In its classical form, it is characterised by distinctive facial features, intra-uterine growth retardation, short stature, developmental delay, and anomalies in multiple organ systems. NIPBL, SMC1A, SMC3, RAD21 and HDAC8, all involved in the cohesin pathway, have been identified to cause CdLS. Growth hormone (GH) secretion has been reported as normal, and to our knowledge, there are no reports on the effect of recombinant human GH treatment in CdLS patients. We present a patient born small for gestational age with persistent severe growth retardation [height -3.4 standard deviation score (SDS)] and mild dysmorphic features, who was treated with GH from 4.3 years of age onward and was diagnosed 6 years later with CdLS using whole-exome sequencing. Treatment led to a height gain of 1.6 SDS over 8 years. Treatment was interrupted shortly due to high serum insulin-like growth factor-1 serum values. In conclusion, GH therapy may be effective and safe for short children with CdLS.

Novel Leptin Receptor Mutations Identified in Two Girls with Severe Obesity Are Associated with Increased Bone Mineral Density.

BACKGROUND: Recessive mutations in the leptin receptor (LEPR) are a rare cause of hyperphagia and severe early-onset obesity. To date, the phenotype has only been described in 25 obese children, some of whom also had altered immune function, hypogonadotropic hypogonadism, reduced growth hormone secretion, hypothalamic hypothyroidism or reduced adult height. We provide a detailed description of the phenotype of 2 affected girls to add to this knowledge. METHODS: Whole-exome sequencing and targeted sequencing were used to detect the LEPR mutations. RNA analysis was performed to assess the effect of splice-site mutations. RESULTS: In 2 unrelated girls with severe obesity, three novel LEPR mutations were detected. Longitudinal growth data show normal childhood growth, and in the older girl, a normal adult height despite hypogonadotropic hypogonadism and the lack of an obvious pubertal growth spurt. Bone age is remarkably advanced in the younger (prepubertal) girl, and bone mineral density (BMD) is high in both girls, which might be directly or indirectly related to leptin resistance. CONCLUSION: The spectrum of clinical features of LEPR deficiency may be expanded with increased BMD. Future observations in LEPR-deficient subjects should help further unravel the role of leptin in human bone biology.

A novel variant of FGFR3 causes proportionate short stature.

OBJECTIVE: Mutations of the fibroblast growth factor receptor 3 (FGFR3) cause various forms of short stature, of which the least severe phenotype is hypochondroplasia, mainly characterized by disproportionate short stature. Testing for an FGFR3 mutation is currently not part of routine diagnostic testing in children with short stature without disproportion. DESIGN: A three-generation family A with dominantly transmitted proportionate short stature was studied by whole-exome sequencing to identify the causal gene mutation. Functional studies and protein modeling studies were performed to confirm the pathogenicity of the mutation found in FGFR3. We performed Sanger sequencing in a second family B with dominant proportionate short stature and identified a rare variant in FGFR3. METHODS: Exome sequencing and/or Sanger sequencing was performed, followed by functional studies using transfection of the mutant FGFR3 into cultured cells; homology modeling was used to construct a three-dimensional model of the two FGFR3 variants. RESULTS: A novel p.M528I mutation in FGFR3 was detected in family A, which segregates with short stature and proved to be activating in vitro. In family B, a rare variant (p.F384L) was found in FGFR3, which did not segregate with short stature and showed normal functionality in vitro compared with WT. CONCLUSIONS: Proportionate short stature can be caused by a mutation in FGFR3. Sequencing of this gene can be considered in patients with short stature, especially when there is an autosomal dominant pattern of inheritance. However, functional studies and segregation studies should be performed before concluding that a variant is pathogenic.