A patient with novel MBOAT7 variant: The cerebellar atrophy is progressive and displays a peculiar neurometabolic profile.

Mutations in the MBOAT7 gene have been described in 43 patients, belonging to 18 families, showing nonspecific clinical features (intellectual disability [ID], seizures, microcephaly or macrocephaly, and mild to moderate cerebellar atrophy) that make the clinical diagnosis difficult. Here we report the first Italian patient, a 22.5-year-old female, one of the oldest reported, born to apparently consanguineous parents. She shows severe ID, macrocephaly, seizures, aggressive outbursts, hyperphagia. We also documented progressive atrophy of the cerebellar vermis, that appeared not before the age of 7. The whole-exome sequencing of the trio identified a novel homozygous variant c.1057_1058delGCinsCA (p.Ala353His) in the MBOAT7 gene. The variant is considered to be likely pathogenic, since it is absent from population database and it lies in a highly conserved amino acid residue. This disorder has a neurometabolic pathogenesis, implicating a phospholipid remodeling abnormalities. A brain hydrogen-magnetic resonance spectroscopy (H-MRS) examination in our patient disclosed a peculiar neurometabolic profile in the cerebellar hemispheric region. This new finding could address the clinical suspicion of MBOAT7-related disorder, among the wide range of genetic conditions associated with ID and cerebellar atrophy. Moreover, the documented progression of cerebellar atrophy and the worsening of the disease only after some years open to the possibility of a therapeutic window after birth.

Imerslund-Gräsbeck Syndrome in an Infant with a Novel Intronic Variant in the AMN Gene: A Case Report.

Imerslund-Gräsbeck syndrome (IGS) is a rare autosomal recessive disorder clinically characterized by megaloblastic anemia, benign mild proteinuria, and other nonspecific symptoms. Several pathogenetic variants in the amnionless (AMN) or cubilin (CUBN) genes have been described in IGS. We describe a case of IGS with urinary tract infection and mild but persistent proteinuria at onset in an 11-month-old female child. With the appearance of macrocytic anemia, aphthous stomatitis, and neurological signs, IGS was clinically suspected, and vitamin B12 parenteral therapy was started. Sequence analysis showed the presence of a novel intronic variant c.513+5G>A of AMN, never before described in the literature, that was in compound heterozygosity with the known pathogenetic variant c.1006+34_1007-31del. Analysis extension to the parents revealed the presence of variant c.1006+34_1007-31 in the father and c.513+5G>A in the mother. In the present case with IGS, the novel intronic variant of AMN was identified in "trans" with a known pathogenic variant (c.1006-31 del) and the new variant was interpreted to be pathogenetic since it was not found in the public database of polymorphisms and because it was predicted to alter a donor splicing site. Our case underlines the relevance in detecting certain subtle symptoms, such as mild but persistent proteinuria associated with megaloblastic anemia, to reach a correct diagnosis of a rare but treatable disorder.

Expanding the Clinical Spectrum of Sotos Syndrome in a Patient with the New "c.[5867T>A]+[=]"; "p.[Leu1956Gln]+[=]" NSD1 Missense Mutation and Complex Skin Hamartoma.

Sotos syndrome is one of the most common overgrowth diseases and it predisposes patients to cancer, generally in childhood. The prevalence of this genetic disorder is 1:10,000⁻1:50,000, and it is characterized by wide allelic heterogeneity, with more than 100 different known mutations in the nuclear receptor-binding SET domain containing protein 1 (NSD1) gene. Most of these alterations are deletions and common micro-deletions with haploinsufficiency. Singular variants are missense mutations. The present study reports a case of a 4-year-old boy with specific clinical features of Sotos syndrome and a particular complex skin hamartoma on the right femoral side, in addition to other minor findings, such as a "café-au-lait" spot on the right hemithorax and syndactyly of the second and third right toes. NSD1 gene analysis identified a de novo missense mutation, "c.[5867T>A]+[=]"; "p.[Leu1956Gln]+[=]", that was not previously described in the literature. This mutation was localized to the functional domain of the gene and was likely the cause of Sotos syndrome in our patient. We also compared aspects of our patient's condition with the clinical features of tuberous sclerosis (TSC), which is an autosomal neurocutaneous syndrome caused by mutations in the TSC1/TSC2 genes. These genes control cell growth and cell survival. This disorder is characterized by hamartomas in multiple organ systems, several coetaneous abnormalities, epilepsy, and increased risk of several types of tumors.

Epileptogenic Brain Malformations and Mutations in Tubulin Genes: A Case Report and Review of the Literature.

Malformations of the cerebral cortex are an important cause of developmental disabilities and epilepsy. Neurological disorders caused by abnormal neuronal migration have been observed to occur with mutations in tubulin genes. The α- and ß-tubulin genes encode cytoskeletal proteins, which play a role in the developing brain. TUBA1A mutations are associated with a wide spectrum of neurological problems, which are characterized by peculiar clinical details and neuroradiologic patterns. This manuscript describes the case of a nine-year-old girl with microcephaly, mild facial dysmorphisms, epileptic seizures, and severe developmental delay, with a de novo heterozygous c.320A>G [p.(His 107 Arg)] mutation in TUBA1A gene, and the clinical aspects and neuroimaging features of "lissencephaly syndrome" are summarized. This case shows that TUBA1A mutations lead to a variety of brain malformations ranging from lissencephaly with perisylvian pachygyria to diffuse posteriorly predominant pachygyria, combined with internal capsule dysgenesis, cerebellar dysplasia, and callosal hypotrophy. This peculiar neuroradiological pattern, in combination with the usually severe clinical presentation, suggests the need for future molecular studies to address the mechanisms of TUBA1A mutation-induced neuropathology.

Juvenile Moyamoya and Craniosynostosis in a Child with Deletion 1p32p31: Expanding the Clinical Spectrum of 1p32p31 Deletion Syndrome and a Review of the Literature.

Moyamoya angiopathy (MA) is a rare cerebrovascular disorder characterised by the progressive occlusion of the internal carotid artery. Its aetiology is uncertain, but a genetic background seems likely, given the high MA familial rate. To investigate the aetiology of craniosynostosis and juvenile moyamoya in a 14-year-old male patient, we performed an array-comparative genomic hybridisation revealing a de novo interstitial deletion of 8.5 Mb in chromosome region 1p32p31. The deletion involved 34 protein coding genes, including NF1A, whose haploinsufficiency is indicated as being mainly responsible for the 1p32-p31 chromosome deletion syndrome phenotype (OMIM 613735). Our patient also has a deleted FOXD3 of the FOX gene family of transcription factors, which plays an important role in neural crest cell growth and differentiation. As the murine FOXD3-/- model shows craniofacial anomalies and abnormal common carotid artery morphology, it can be hypothesised that FOXD3 is involved in the pathogenesis of the craniofacial and vascular defects observed in our patient. In support of our assumption, we found in the literature another patient with a syndromic form of MA who had a deletion involving another FOX gene (FOXC1). In addition to describing the clinical history of our patient, we have reviewed all of the available literature concerning other patients with a 1p32p31 deletion, including cases from the Decipher database, and we have also reviewed the genetic disorders associated with MA, which is a useful guide for the diagnosis of syndromic form of MA.

A novel MED12 mutation: Evidence for a fourth phenotype.

Mutations of the MED12 gene have been reported mainly in males with FG (Opitz-Kaveggia), Lujan-Fryns, or X-linked Ohdo syndromes. Recently, a different phenotype characterized by minor anomalies, severe intellectual disability (ID), and absent language was reported in female and male patients belonging to the same family and carrying a frameshift MED12 mutation (c.5898dupC). Here, we report on two brothers and their niece affected by severe and mild ID, respectively, where whole exome sequencing combined with variant analysis within a panel of ID-related genes, disclosed a novel c.2312T>C (p.Ile771Thr) MED12 mutation. This variant, which has not been reported as a polymorphism, was not present in a third unaffected brother, and was predicted to be deleterious by five bioinformatic databases. This finding together with the phenotypic analogies shared with the carriers of c.5898dupC mutation suggests the existence of a fourth MED12-related disorder, characterized by severe ID, absent or deficient language and, milder, clinical manifestation in heterozygotes. We have reviewed the literature on MED12 heterozygotes, their clinical manifestations, and discuss the possible biological causes of this condition. © 2016 Wiley Periodicals, Inc.

Succinate-CoA ligase deficiency due to mutations in SUCLA2 and SUCLG1: phenotype and genotype correlations in 71 patients.

BACKGROUND: The encephalomyopathic mtDNA depletion syndrome with methylmalonic aciduria is associated with deficiency of succinate-CoA ligase, caused by mutations in SUCLA2 or SUCLG1. We report here 25 new patients with succinate-CoA ligase deficiency, and review the clinical and molecular findings in these and 46 previously reported patients. PATIENTS AND RESULTS: Of the 71 patients, 50 had SUCLA2 mutations and 21 had SUCLG1 mutations. In the newly-reported 20 SUCLA2 patients we found 16 different mutations, of which nine were novel: two large gene deletions, a 1 bp duplication, two 1 bp deletions, a 3 bp insertion, a nonsense mutation and two missense mutations. In the newly-reported SUCLG1 patients, five missense mutations were identified, of which two were novel. The median onset of symptoms was two months for patients with SUCLA2 mutations and at birth for SUCLG1 patients. Median survival was 20 years for SUCLA2 and 20 months for SUCLG1. Notable clinical differences between the two groups were hepatopathy, found in 38% of SUCLG1 cases but not in SUCLA2 cases, and hypertrophic cardiomyopathy which was not reported in SUCLA2 patients, but documented in 14% of cases with SUCLG1 mutations. Long survival, to age 20 years or older, was reported in 12% of SUCLA2 and in 10% of SUCLG1 patients. The most frequent abnormality on neuroimaging was basal ganglia involvement, found in 69% of SUCLA2 and 80% of SUCLG1 patients. Analysis of respiratory chain enzyme activities in muscle generally showed a combined deficiency of complexes I and IV, but normal histological and biochemical findings in muscle did not preclude a diagnosis of succinate-CoA ligase deficiency. In five patients, the urinary excretion of methylmalonic acid was only marginally elevated, whereas elevated plasma methylmalonic acid was consistently found. CONCLUSIONS: To our knowledge, this is the largest study of patients with SUCLA2 and SUCLG1 deficiency. The most important findings were a significantly longer survival in patients with SUCLA2 mutations compared to SUCLG1 mutations and a trend towards longer survival in patients with missense mutations compared to loss-of-function mutations. Hypertrophic cardiomyopathy and liver involvement was exclusively found in patients with SUCLG1 mutations, whereas epilepsy was much more frequent in patients with SUCLA2 mutations compared to patients with SUCLG1 mutations. The mutation analysis revealed a number of novel mutations, including a homozygous deletion of the entire SUCLA2 gene, and we found evidence of two founder mutations in the Scandinavian population, in addition to the known SUCLA2 founder mutation in the Faroe Islands.

A New Homozygous IGF1R Variant Defines a Clinically Recognizable Incomplete Dominant form of SHORT Syndrome.

Here, we describe a child, born from consanguineous parents, with clinical features of SHORT syndrome, high IGF1 levels, developmental delay, CNS defects, and marked progeroid appearance. By exome sequencing, we identified a new homozygous c.2201G>T missense mutation in the IGF1R gene. Proband's parents and other relatives, all heterozygous carriers of the mutation, presented with milder phenotype including high IGFI levels, short stature, and type 2 diabetes. Functional studies using patient's cell lines showed a lower IGF1R expression that leads to the alteration of IGF1R-mediated PI3K/AKT/mTOR downstream pathways, including autophagy. This study defines a clinically recognizable incomplete dominant form of SHORT syndrome, and provides relevant insights into the pathophysiological and phenotypical consequences of IGF1R mutations.

Characterization of 14 novel deletions underlying Rubinstein-Taybi syndrome: an update of the CREBBP deletion repertoire.

Rubinstein-Taybi syndrome (RSTS) is a rare, clinically heterogeneous disorder characterized by cognitive impairment and several multiple congenital anomalies. The syndrome is caused by almost private point mutations in the CREBBP (~55% of cases) and EP300 (~8%) genes. The CREBBP mutational spectrum is variegated and characterized by point mutations (30-50 %) and deletions (~10%). The latter are diverse in size and genomic position and remove either the whole CREBBP gene and its flanking regions or only an intragenic portion. Here, we report 14 novel CREBBP deletions ranging from single exons to the whole gene and flanking regions which were identified by applying complementary cytomolecular techniques: fluorescence in situ hybridization, multiplex ligation-dependent probe amplification and array comparative genome hybridization, to a large cohort of RSTS patients. Deletions involving CREBBP account for 23% of our detected CREBBP mutations, making an important contribution to the mutational spectrum. Genotype-phenotype correlations revealed that patients with CREBBP deletions extending beyond this gene did not always have a more severe phenotype than patients harboring CREBBP point mutations, suggesting that neighboring genes play only a limited role in the etiopathogenesis of CREBBP-centerd contiguous gene syndrome. Accordingly, the extent of the deletion is not predictive of the severity of the clinical phenotype.

Recurrent ∼100 Kb microdeletion in the chromosomal region 14q11.2, involving CHD8 gene, is associated with autism and macrocephaly.

The most frequent causes of Intellectual Disability (ID)/Autism Spectrum Disorders (ASDs) are chromosomal abnormalities, genomic rearrangements and submicroscopic deletions coupled with duplications. We report here on an 11-year-old girl showing autism, macrocephaly, and facial dysmorphism, in which array-CGH showed a de novo microdeletion of ∼114 Kb in the 14q11.2 chromosomal region, involving the SUPT16H, CHD8, and RAB2B genes. Four patients with ID and/or ASD and/or macrocephaly with overlapping deletions have been previously described: three showed very large rearrangements (>1 Mb), while one had a microdeletion of ∼101 Kb, largely overlapping the one reported herein. The minimal critical region, considering present and previous cases, contains the SUPT16H and CHD8 genes. Notably, recent studies also disclosed CHD8 heterozygous loss-of-function mutations in patients with ASD and macrocephaly. Our finding shows the presence of a recurrent microdeletion associated with a clinically recognizable phenotype, and further on underlines the pivotal role of CHD8 gene in the pathogenesis of the disorder.

Deletion 2p15-16.1 syndrome: case report and review.

We report on a 9-year-old female patient with facial anomalies and developmental delay, heterozygous for three de novo rearrangements: a paracentric inversion of chromosome 7, an apparently balanced translocation between chromosome 1 and 7, involving the same inverted chromosome 7, detected by standard cytogenetic analysis [46,XX, der(7) inv(7)(q21.1q32.1)t(1;7)(q23q32.1)]; and a 2p16.1 deletion, spanning about 3.5 Mb of genomic DNA, shown by SNP-array analysis [arr 2p16.1 (56,706,666-60,234,485)x1 dn]. Clinical features and cytogenetic imbalance in our patient were similar to those reported in five published cases, suggesting that this genomic region is prone to recombination and its hemizygosity results in a distinct although variable spectrum of clinical manifestations.

Porencephaly in an Italian neonate with foetal alcohol spectrum disorder: A case report.

INTRODUCTION: Foetal alcohol spectrum disorder (FASD) is a complex malformative disease caused by the teratogenic effect of alcohol consumed during pregnancy. Mothers are frequently reluctant to admit alcohol consumption during pregnancy. During infancy and particularly during neonatal period, differential diagnosis is difficult. PATIENT CONCERNS: This case is represented by an Italian neonate boy small for gestational age, born by caesarean section at a gestational age of 37 weeks + 6 days by neglect and single-parent pregnancy. On physical examination, he presented particular facial features: microcephaly, epicanthal folds, flat midface, low nasal bridge, indistinct philtrum, and thin upper lip; moreover, examination revealed a macro-penis and recurvation without evidence of glans. DIAGNOSIS: Echocardiogram showed an inter-ventricular defect of medium-muscular type and brain magnetic resonance imaging showed asymmetry of the cerebral hemispheres with hypoplasia of the left cerebral hemisphere, dilatation of the left ventricle, cerebrospinal fluid cavity, and porencephaly. INTERVENTIONS: We investigated the ethylglucuronide (EtG) concentration in the neonate's hair by liquid chromatography-tandem mass spectrometry and we detected EtG in the infant's hair (normal value, 30 pg/mg), demonstrating prenatal alcohol exposure. OUTCOMES: In this neonate, EtG measure in hairs permitted the diagnosis of FASD, so allowing to exclude genetic diseases associated with similar clinical findings. After this result the mother admitted that she drunk alcohol during pregnancy (she declared 3 glasses of wine every day). At the age of 6 months, the child showed a moderate neurodevelopmental delay. CONCLUSION: This case shows that FAD should be considered in neonates with rare neurological diseases as porencephaly. In neonates and infants born to a mother who did not report alcohol use, EtG measure in hairs can significantly improve diagnosis of FASD, so allowing to exclude genetic diseases associated with similar clinical findings.

Intestinal lymphangiectasia in a 3-month-old girl: A case report of Hennekam syndrome caused by CCBE1 mutation.

RATIONAL: Intestinal lymphangiectasia (IL) is a rare disease characterized by dilatation and rupture of intestinal lymphatic channels leading to protein-losing enteropathy. IL is classified as primary and secondary types. PATIENT CONCERNS: A 3-month-old girl born at term from vaginal delivery with an APGAR score of 10/10 and birth weight of 4.310 g (>97° percentile) was admitted to our hospital because of increasing abdominal tenderness and diarrhea. At first examination, she presented an abdominal circumference of 60 cm, edema of the lower extremities and vulva, and facial dysmorphisms (hypertelorism, flat nasal bridge, flat mid-face). DIAGNOSIS: Once admitted, ultrasonography showed a large amount of ascites, while blood laboratory investigations revealed severe hypoproteinemia, hypoalbuminemia and hypogammaglobulinemia. Lymphoscintigraphy with 99m-Tc-nanocolloid demonstrated abnormal leakage of the tracer in the abdomen as evidence of IL. To detect a possible secondary, exams were performed and demonstrated positive antibody titres for CMV-IgM and IgG in blood and CMV-DNA positivity in blood, urine, saliva, maternal milk, and gastric and duodenal biopsies. Genetic investigations identified the genomic variant c.472C>T of the CCBE1 gene, coding for a protein variant (p.Arg158Cys), in homozygosity. INTERVENTIONS: Total parenteral nutrition was started and continued for a total of 18 days, then gradually bridged by enteral nutrition with a special formula. In addition, antiviral therapy for CMV infection was added first with intravenous ganciclovir for 14 days, resulting in the disappearance of blood viral load after 7 days of therapy and then with valganciclovir per os for another 30 days. OUTCOMES: The clinical course of the child gradually improved. A few days after starting treatments, lower extremities and vulvar edema disappeared, and abdominal circumference gradually decreased to a stable value of 38 cm, without any ultrasonographic signs of ascites left. Moreover, serum albumin and IgG rose to normal values after 3 months (4.3 g/dL and 501 mg/dL, respectively). LESSONS: This case suggests that in presence of IL both primary and secondary causes should be evaluated. On the other hand, genetic diagnosis is crucial not only for diagnosis but also for prognosis in HS. Life expectancy and quality could deeply vary among different gene mutations and protein variants of the same gene. Further studies and case reports are needed to better understand the clinical meaning of these genetic results and the role of CMV as trigger of IL.

2q31.2q32.3 deletion syndrome: report of an adult patient.

A 36-year-old patient with a disorder characterized by severe mental retardation, behavioral problems, dysmorphic face, "muscular build," and hand/foot anomalies, is reported. Following a diagnosis of de novo pericentric inversion of chromosome 8 based on standard cytogenetic analysis, a subsequent 75 kb array-CGH investigation disclosed a deletion spanning for about 13.7 Mb in the 2q31.2q32.3 region. Whole painting of chromosome 8 established the intrachromosomal nature of the rearrangement and FISH analysis with locus-specific probes confirmed the deletion on the long arm of chromosome 2. The deleted region, clinical outcome, and medical history in this patient are mainly superimposable to those reported in a published 8-year-old boy, suggesting that this genomic segment is prone to rearrangements and its hemizygosity gives rise to a clinically recognizable syndrome. The role of some genes mapping in the deleted region and related with distinct disorders is discussed. Interestingly, deletion of MSTN gene, a negative regulator of muscle growth, was associated in our patient with a "muscular build," a feature which could be regarded as a handle for clinical recognition of this syndrome.

Schilbach-Rott syndrome associated with 9q22.32q22.33 duplication, involving the PTCH1 gene.

Schilbach-Rott syndrome (SRS, OMIM%164220) is a disorder of unknown aetiology that is characterised by hypotelorism, epichantal folds, cleft palate, dysmorphic face, hypospadia in males and mild mental retardation in some patients. To date, 5 families and 17 patients have exhibited this phenotype, and recurrence in two of these families suggests an autosomal dominant inheritance. SRS overlaps with a mild form of holoprosencephaly (HPE), but array-CGH analysis and sequencing of some HPE-related genes (SEPT9, SHH and TWIST) did not reveal any variants in at least one family. Herein, we investigated by array-CGH analysis a 11-year-old female patient and her father, both exhibiting the typical SRS phenotype, disclosing in the daughter-father couple the same microduplication of chromosome 9q22.32q22.33 [arr[hg19]9q22.32(98,049,611_98,049,636)x3,9q22.33 (99,301,483_99,301,508)x3], involving eight genes, including PTCH1. The duplication segregated with the disease, since it was not found in the healthy paternal grandparents of the proband. The gain-of-function variants of the PTCH1 gene are responsible for a mild form of HPE. This is the first genetic variant found in SRS. This finding reinforces the hypothesis that SRS belongs to the HPE clinical spectrum and suggests to perform array-CGH in patients with SRS phenotype and, if negative, to consider a potential benefit from sequencing of HPE-related genes.

Report of a Novel SHOX Missense Variant in a Boy With Short Stature and His Mother With Leri-Weill Dyschondrosteosis.

Heterozygous mutations in the SHOX gene or in the upstream and downstream enhancer elements are associated with 2-22% of cases of idiopathic short stature (OMIM #300582) and with 60% of cases of Leri-Weill dyschondrosteosis (OMIM #127300) with which female subjects are generally more severely affected. Approximately 80-90% of SHOX pathogenic variants are deletions or duplications, and the remaining 10-20% are point mutations that primarily give rise to missense variants. The clinical interpretation of novel variants, particularly missense variants, can be challenging and can remain of uncertain significance. Here, we describe a novel missense variant (c.1044 G>T, p.Arg118Met) in a Moroccan boy with a disproportionately short stature and without any radiological traits or bone deformities and in his mother, who had a disproportionately short stature and a Madelung deformity. This variant has not been reported to date in the updated SHOX allelic variant or Human Gene Mutation Databases nor is it listed as a polymorphism in the ExAC browser, dbSNP, or 1000G. This mutation was predicted to be deleterious by three different bioinformatics tools since it modifies an amino acid in a highly conserved DNA-binding domain of the SHOX protein. Based on this evidence, the patient was treated with recombinant human growth hormone.

Mutations in the Neuroblastoma Amplified Sequence gene in a family affected by Acrofrontofacionasal Dysostosis type 1.

Acrofrontofacionasal Dysostosis type 1 (AFFND1) is an extremely rare, autosomal recessive syndrome, comprising facial and skeletal abnormalities, short stature and intellectual disability. We analyzed an Indian family with two affected siblings by exome sequencing and identified a novel homozygous truncating mutation in the Neuroblastoma-Amplified Sequence (NBAS) gene in the patients' genome. Mutations in the NBAS gene have recently been associated with different phenotypes mainly involving skeletal formation, liver and cognitive development. The NBAS protein has been implicated in two key cellular processes, namely the non-sense mediated decay and the Golgi-to-Endoplasmic Reticulum retrograde traffic. Both functions were impaired in HEK293T cells overexpressing the truncated NBAS protein, as assessed by Real-Time PCR, Western blot analysis, co-immunoprecipitation, and immunofluorescence analysis. We examined the expression of NBAS protein in mouse embryos at various developmental stages by immunohistochemistry, and detected expression in developing chondrogenic and osteogenic structures of the skeleton as well as in the cortex, hippocampus and cerebellum, which is compatible with a role in bone and brain development. Functional genetics in the zebrafish model showed that depletion of endogenous z-nbas in fish embryos results in defective morphogenesis of chondrogenic cranial skeletal elements. Overall, our data point to a conserved function of NBAS in skeletal morphogenesis during development, support the hypothesis of a causative role of the mutated NBAS gene in the pathogenesis of AFFND1 and extend the spectrum of phenotypes associated with defects in this gene.

Autosomal Dominant PTH Gene Signal Sequence Mutation in a Family With Familial Isolated Hypoparathyroidism.

Context: Familial isolated hypoparathyroidism (FIH) is a genetically heterogeneous disorder due to mutations of the calcium-sensing receptor (CASR), glial cells missing-2 (GCM2), guanine nucleotide binding protein α11 (GNA11), or parathyroid hormone (PTH) genes. Thus far, only four cases with homozygous and two cases with heterozygous mutations in the PTH gene have been reported. Objective: To clinically describe an FIH family and identify and characterize the causal gene mutation. Design: Genomic DNA of the family members was subjected to CASR, GCM2, GNA11, and PTH gene mutational analysis. Functional assays were performed on the variant identified. Participants: Six subjects of a three-generation FIH family with three affected individuals having severe hypocalcemia and inappropriately low serum PTH. Results: No mutations were detected in the CASR, GCM2, and GNA11 genes. A heterozygous variant that segregated with the disease was identified in PTH gene exon 2 (c.41T>A; p.M14K). This missense variant, in the hydrophobic core of the signal sequence, was predicted in silico to impair cleavage of preproPTH to proPTH. Functional assays in HEK293 cells demonstrated much greater retention intracellularly but impaired secretion into the medium of the M14K mutant relative to wild type. The addition of the pharmacological chaperone, 4-phenylbutyric acid, led to a reduction of cellular retention and increased accumulation in the cell medium of the M14K mutant. Conclusions: We report a heterozygous PTH mutation in an FIH family and demonstrate accumulation of the mutant intracellularly and its impaired secretion. An accurate genetic diagnosis in such hypoparathyroid patients is critical for appropriate treatment and genetic counseling.