Unbiased phenotype and genotype matching maximizes gene discovery and diagnostic yield.

PURPOSE: Widespread application of next-generation sequencing, combined with data exchange platforms, has provided molecular diagnoses for countless families. To maximize diagnostic yield, we implemented an unbiased semi-automated genematching algorithm based on genotype and phenotype matching. METHODS: Rare homozygous variants identified in 2 or more affected individuals, but not in healthy individuals, were extracted from our local database of ∼12,000 exomes. Phenotype similarity scores (PSS), based on human phenotype ontology terms, were assigned to each pair of individuals matched at the genotype level using HPOsim. RESULTS: 33,792 genotype-matched pairs were discovered, representing variants in 7567 unique genes. There was an enrichment of PSS ≥0.1 among pathogenic/likely pathogenic variant-level pairs (94.3% in pathogenic/likely pathogenic variant-level matches vs 34.75% in all matches). We highlighted founder or region-specific variants as an internal positive control and proceeded to identify candidate disease genes. Variant-level matches were particularly helpful in cases involving inframe indels and splice region variants beyond the canonical splice sites, which may otherwise have been disregarded, allowing for detection of candidate disease genes, such as KAT2A, RPAIN, and LAMP3. CONCLUSION: Semi-automated genotype matching combined with PSS is a powerful tool to resolve variants of uncertain significance and to identify candidate disease genes.

Eligibility for growth hormone therapy in children born small for gestational age is substantially lower than expected.

BACKGROUND: Growth hormone therapy is indicated for children who are both born 'small for gestational age' (SGA) and do not achieve adequate catch-up growth (ACUG). OBJECTIVE: To evaluate the actual incidence of infants born SGA and their actual ACUG. METHODS: Birth weight data from the newborn registry at two hospitals were analysed during four consecutive years. SGA was defined according to WHO parameters and the corresponding Israeli criteria. Follow-up measurements of height and weight were abstracted from either the Ministry of Health-child growth follow-up centres, or their paediatrician clinic. ACUG was declared when the height reached was above -2.5 or -2 standard deviations (SDS) from the mean for age and gender. RESULTS: Out of 43 307, only 524 babies in the cohort (1.2%) were SGA (52% of expected). This finding was consistent annually. Out of the 446 SGA born children with available growth data (85%) during 4-8 years, 405 children (90.8%) reached a height greater than -2SDS and 428 (96%!) reached a height greater than -2.5 SDS. Term children had higher rate of ACUG achievement as compared to preterm 97.2% vs 86.8% (P < .001). Birth week and birth weight were also related to achievement of ACUG (P < .001). CONCLUSION: This large representative, heterogeneous and Western Caucasian cohort indicates that the actual number of SGA newborns is nearly half of the expected and that the actual prevalence of ACUG is also significantly higher than previously reported. These findings may have an impact on morbidity, health cost planning and growth hormone requirements in SGA babies.

Aldosterone synthase (CYP11B2) deficiency among Palestinian infants: Three novel variants and genetic heterogeneity.

Aldosterone synthase deficiency (ASD) is a rare potentially life-threatening genetic disorder that usually presents during infancy due to pathogenic variants in the CYP11B2 gene. Knowledge about CYP11B2 variants in the Arab population is scarce. Here, we present and analyze five Palestinian patients and their different novel pathogenic variants. Data on clinical presentation, electrolytes, plasma renin activity, and steroid hormone levels of five patients diagnosed with ASD were summarized. Sequencing of the CYP11B2 gene exons was followed by evolutionary conservation analysis and structural modeling of the variants. All patients were from highly consanguineous Palestinian families. The patients presented at 1-4 months of age with recurrent vomiting, poor weight gain, hyponatremia, hyperkalemia, and low aldosterone levels. Genetic analysis of the CYP11B2 gene revealed three homozygous pathogenic variants: p.Ser344Profs*9, p.G452W in two patients from an extended family, and p.Q338stop. A previously described pathogenic variant was found in one patient: p.G288S. We described four different CYP11B2 gene pathogenic variants in a relatively small population. Our findings may contribute to the future early diagnosis and therapy for patients with ASD among Arab patients who present with failure to thrive and compatible electrolyte disturbances.

A Unique Presentation of XY Gonadal Dysgenesis in Frasier Syndrome due to WT1 Mutation and a Literature Review.

Frasier syndrome (FS), a rare disease caused by inherited or de novo mutation in Wilm's Tumor suppressor gene 1 (WT1), is characterized by slow progressive nephropathy, XY gonadal dysgenesis (XY-DSD), and increased risk for gonadal tumors. Early childhood (1-6 years) nephropathy progresses with age to refractory nephrotic syndrome, and end-stage renal failure in late adolescence, when delayed puberty and/or primary amenorrhea are clinically evident. We report a unique case of FS presenting initially with primary amenorrhea at 16 years, without previous or concomitant renal damage. Only subsequently she developed an extremely late-onset nephropathy. Genetic analysis revealed the IVS9 + 5 G>A mutation in intron 9 of the WT1 gene. This clinical presentation and review of WT1 literature highlights the importance of considering FS in the differential diagnosis of patients with 46,XY disorders of Sexual development, even without nephropathy. Furthermore, the identification WT1 gene mutation prior to evident renal dysfunction indicates an immediate and close surveillance of renal function enabling an optimal and timely medical response.

Combined mineralocorticoid and glucocorticoid deficiency is caused by a novel founder nicotinamide nucleotide transhydrogenase mutation that alters mitochondrial morphology and increases oxidative stress.

BACKGROUND: Familial glucocorticoid deficiency (FGD) reflects specific failure of adrenocortical glucocorticoid production in response to adrenocorticotropic hormone (ACTH). Most cases are caused by mutations encoding ACTH-receptor components (MC2R, MRAP) or the general steroidogenesis protein (StAR). Recently, nicotinamide nucleotide transhydrogenase (NNT) mutations were found to cause FGD through a postulated mechanism resulting from decreased detoxification of reactive oxygen species (ROS) in adrenocortical cells. METHODS AND RESULTS: In a consanguineous Palestinian family with combined mineralocorticoid and glucocorticoid deficiency, whole-exome sequencing revealed a novel homozygous NNT_c.598 G>A, p.G200S, mutation. Another affected, unrelated Palestinian child was also homozygous for NNT_p.G200S. Haplotype analysis showed this mutation is ancestral; carrier frequency in ethnically matched controls is 1/200. Assessment of patient fibroblasts for ROS production, ATP content and mitochondrial morphology showed that biallelic NNT mutations result in increased levels of ROS, lower ATP content and morphological mitochondrial defects. CONCLUSIONS: This report of a novel NNT mutation, p.G200S, expands the phenotype of NNT mutations to include mineralocorticoid deficiency. We provide the first patient-based evidence that NNT mutations can cause oxidative stress and both phenotypic and functional mitochondrial defects. These results directly demonstrate the importance of NNT to mitochondrial function in the setting of adrenocortical insufficiency.

XX ovarian dysgenesis is caused by a PSMC3IP/HOP2 mutation that abolishes coactivation of estrogen-driven transcription.

XX female gonadal dysgenesis (XX-GD) is a rare, genetically heterogeneous disorder characterized by lack of spontaneous pubertal development, primary amenorrhea, uterine hypoplasia, and hypergonadotropic hypogonadism as a result of streak gonads. Most cases are unexplained but thought to be autosomal recessive. We elucidated the genetic basis of XX-GD in a highly consanguineous Palestinian family by using homozygosity mapping and candidate-gene and whole-exome sequencing. Affected females were homozygous for a 3 bp deletion (NM_016556.2, c.600_602del) in the PSMC3IP gene, leading to deletion of a glutamic acid residue (p.Glu201del) in the highly conserved C-terminal acidic domain. Proteasome 26S subunit, ATPase, 3-Interacting Protein (PSMC3IP)/Tat Binding Protein Interacting Protein (TBPIP) is a nuclear, tissue-specific protein with multiple functions. It is critical for meiotic recombination as indicated by the known role of its yeast ortholog, Hop2. Through the C terminus (not present in yeast), PSMC3IP also coactivates ligand-driven transcription mediated by estrogen, androgen, glucocorticoid, progesterone, and thyroid nuclear receptors. In cell lines, the p.Glu201del mutation abolished PSMC3IP activation of estrogen-driven transcription. Impaired estrogenic signaling can lead to ovarian dysgenesis both by affecting the size of the follicular pool created during fetal development and by failing to counteract follicular atresia during puberty. PSMC3IP joins previous genes known to be mutated in XX-GD, the FSH receptor, and BMP15, highlighting the importance of hormonal signaling in ovarian development and maintenance and suggesting a common pathway perturbed in isolated XX-GD. By analogy to other XX-GD genes, PSMC3IP is also a candidate gene for premature ovarian failure, and its role in folliculogenesis should be further investigated.

Wolfram Syndrome-2, a Cause of Severe Gastrointestinal Bleeding: A Case Series and a Literature Review.

Background: There are very few reports of Wolfram syndrome-2 (WFS2) in the literature, and understanding of involvement of the gastrointestinal (GI) tract in the syndrome is limited. Objectives: This study aims to describe the clinical presentations of a large number of WFS2 patients with specific focus on their GI manifestations. Methods: This is a retrospective case series study. Patients who were homozygous for the CISD2 gene mutation were identified through the genetic department of Al-Makassed hospital. Their medical records were reviewed, and biometric data have been obtained. The data were collected and arranged on a data sheet, and descriptive analysis was done using SPSS. Results: Thirteen patients from 9 families were identified; diabetes mellitus was present in 6 of them, optic atrophy in 5, diabetes insipidus (DI) in 5, and deafness in 2. All of the patients had GI manifestations with abnormal findings on upper endoscopy. Dysmorphic facial features and abnormal findings on brain MRI were present in 3 of our patients. The GI manifestations including GI bleeding and severe ulcerations were the first to appear in 9 of them, while anemia in the remaining 4. Conclusion: This is the largest study to date describing patients with WFS2. This study's evidence shows the prominent presence of GI involvement, and the severe findings on endoscopy, including duodenal, gastric, and esophageal ulcerations and strictures. Unlike in the Jordanian report, some of the patients in our report also have DI.

Lessons Learned From COVID-19 Lockdown: An ASPED/MENA Study on Lifestyle Changes and Quality of Life During Ramadan Fasting in Children and Adolescents Living With Type 1 Diabetes.

Background: Lockdown was a unique experience that affected many aspects of life, particularly during the challenge of Ramadan fasting (RF). Studying this can increase understanding of the effects of lifestyle changes on quality of life (QoL) for children with type 1 diabetes (T1D) during RF. Methods: A cross-sectional study that assessed the effect of lockdown on lifestyle and QoL on fasting children living with T1D during Ramadan in the Middle East and North Africa region (2020-2021). We compared the child (self) and parent (proxy) reports using PEDQoL v3.0 disease specific questionnaire during lockdown and non-lockdown periods, and assessed correlations with lifestyle changes using regression and gap analyses. Results: A total of 998 reports from 499 children with T1D aged 8 to 18 years (study = 276, control = 223), and their parents during RF in lockdown and non-lockdown periods. Fathers were more involved in their children's care during lockdown (P = .019). Patients had better compliance with treatment (P = .002), a reversed sleep pattern (P = .033), increased food intake (P ⩽ .001), and less exercise (P < .001). Children and parents perceived better QoL during lockdown (P ⩽.001) with no differences between their reports in "Diabetes Symptoms", "Treatment Adherence," and "Communication" domains. Self and proxy reports were different in all domains during non-lockdown (P = <.001-.009). In gap analysis, although not statistically significant, the gap was approximated between children's and parents' perceptions in all domains during lockdown. Conclusion: COVID-19 lockdown had a positive impact on QoL of children living with T1D during RF, possibly due to lifestyle changes and superior psychosocial family dynamics.

RECON syndrome is a genome instability disorder caused by mutations in the DNA helicase RECQL1.

Despite being the first homolog of the bacterial RecQ helicase to be identified in humans, the function of RECQL1 remains poorly characterized. Furthermore, unlike other members of the human RECQ family of helicases, mutations in RECQL1 have not been associated with a genetic disease. Here, we identify 2 families with a genome instability disorder that we have named RECON (RECql ONe) syndrome, caused by biallelic mutations in the RECQL gene. The affected individuals had short stature, progeroid facial features, a hypoplastic nose, xeroderma, and skin photosensitivity and were homozygous for the same missense mutation in RECQL1 (p.Ala459Ser), located within its zinc binding domain. Biochemical analysis of the mutant RECQL1 protein revealed that the p.A459S missense mutation compromised its ATPase, helicase, and fork restoration activity, while its capacity to promote single-strand DNA annealing was largely unaffected. At the cellular level, this mutation in RECQL1 gave rise to a defect in the ability to repair DNA damage induced by exposure to topoisomerase poisons and a failure of DNA replication to progress efficiently in the presence of abortive topoisomerase lesions. Taken together, RECQL1 is the fourth member of the RecQ family of helicases to be associated with a human genome instability disorder.

Familial autosomal recessive renal tubular acidosis: importance of early diagnosis.

BACKGROUND AND AIMS: Untreated renal tubular acidosis (RTA) can result in severe complications. We reviewed the clinical features of patients with mutations in two genes causing RTA and evaluated their developmental expression assuming that timing, symptom severity and complications may be related to its occurrence. METHODS: Clinical data from 16 patients with RTA due to mutations in either ATP6V1B1 or CAII were retrospectively reviewed. Both genes' localization and expression pattern in the developing human kidney were analyzed by real-time polymerase chain reaction and immunostaining. RESULTS: RTA-presenting symptoms were non-specific. Patients with mutations in ATP6V1B1 had earlier presentation (4.9 vs. 11 months, p < 0.041) and longer time to diagnosis than patients with CAII mutations (5.8 vs. 57 months, p < 0.01). Patients with ATP6V1B1 mutations were more likely to develop chronic kidney disease than those with CAII mutations (follow-up GFR values: 89 vs. 110 ml/min/1.73 m2, respectively, p < 0.017), probably secondary to nephrocalcinosis. Both ATP6V1B1 and CAII were expressed early during human nephrogenesis, with relatively higher transcript levels of ATP6V1B1. CONCLUSIONS: There is considerable delay in establishing a diagnosis of both types of RTA, supporting the need for earlier biochemical investigation. RTA due to ATP6V1B1 mutations is associated with mild progressive loss of kidney function.

Access to fludrocortisone and to hydrocortisone in children with congenital adrenal hyperplasia in the WHO Eastern Mediterranean Region: it takes a village .

Congenital adrenal hyperplasia (CAH), if untreated, carries high morbidity and mortality. A higher incidence of CAH is expected in countries where consanguinity is common, such as in the countries of the WHO Eastern Mediterranean Region (EMRO). CAH is managed through lifelong treatment with fludrocortisone and hydrocortisone. In this analysis, performed in the 22 EMRO countries and territories plus Algeria, we review which countries offer a neonatal screening programme for CAH and describe the barriers and opportunities to access oral fludrocortisone and oral and injectable hydrocortisone. Neonatal CAH screening was only available nationally in Qatar, Kuwait and partially in Lebanon and Saudi Arabia. We reviewed the national lists of essential medicines (NEMLs) and found that 13/23 (57%) countries included fludrocortisone and 18/23 (78%) included oral hydrocortisone. Fludrocortisone was not included by any of the low-income countries and oral hydrocortisone was only included by one low-income country. We then contacted paediatric endocrinologists in each country to assess perceived availability of these medicines. Overall, there was a relatively good consistency between inclusion of fludrocortisone and hydrocortisone in the NEML and their actual availability in a country. We propose several mechanisms to improve access, including prequalification by the WHO, a common registration process for groups of countries, pooled procurement, working with local pharmaceutical companies, special access status for medicines not yet registered in a country and compounding. We suggest that access to medicines requires a collaboration between health professionals, families of patients, health authorities, pharmaceutical companies and the WHO.

Optimizing health care for individuals with Down syndrome in Israel.

BACKGROUND: Down syndrome is one of the most common chromosomal abnormalities. Children and adults with DS have significant medical problems and require life-long medical follow-up. OBJECTIVES: To determine the adequacy of medical surveillance of individuals with DS as recommended by the American Academy of Pediatrics. METHODS: The study was conducted at a multidisciplinary center specializing in the care of DS during the period 2004-2006. At their first visit to the Center, caregivers of individuals with DS were questioned about the medical status of their child including previous evaluations. Medical records brought in by the parents were reviewed. RESULTS: The caregivers of 150 individuals with DS (age ranging from newborn to 48-years-old, median age 5 years) were interviewed and the medical records were reviewed. The prevalence of specific medical problems differed between our population and the reported prevalence from other surveys. For example, 39.3% of our population had documented auditory deficits while the reported prevalence is 75%. For gastrointestinal and thyroid disease, the prevalence was higher in the studied population than that reported in the literature. In terms of compliance with the AAP recommendations, most children (94%) underwent echocardiography, but only 42.7% and 63.3% had been tested for auditory or visual acuity respectively. Only 36.3% over the age of 3 years had cervical spine films. DISCUSSION: Many individuals with DS are not receiving appropriate medical follow-up and the consequences of inadequate surveillance can be serious.

Combined Gestational Age- and Birth Weight-Adjusted Cutoffs for Newborn Screening of Congenital Adrenal Hyperplasia.

CONTEXT: Congenital adrenal hyperplasia (CAH) was among the first genetic disorders included in newborn screening (NBS) programs worldwide, based on 17α-hydroxyprogesterone (17-OHP) levels in dried blood spots. However, the success of NBS for CAH is hampered by high false positive (FP) rates, especially in preterm and low-birthweight infants. OBJECTIVE: To establish a set of cutoff values adjusting for both gestational age (GA) and birthweight (BW), with the aim of reducing FP rates. DESIGN: This cross-sectional, population-based study summarizes 10 years of experience of the Israeli NBS program for diagnosis of CAH. Multitiered 17-OHP cutoff values were stratified according to both BW and GA. PARTICIPANTS: A total of 1,378,132 newborns born between 2008 and 2017 were included in the NBS program. RESULTS: Eighty-eight newborns were ultimately diagnosed with CAH; in 84 of these, CAH was detected upon NBS. The combined parameters-adjusted approach significantly reduced the recall FP rate (0.03%) and increased the positive predictive value (PPV) (16.5%). Sensitivity among those referred for immediate attention increased significantly (94%). There were four false negative cases (sensitivity, 95.4%), all ultimately diagnosed as simple-virilizing. Sensitivity and specificity were 95.4% and 99.9%, respectively, and the percentage of true-positive cases from all newborns referred for evaluation following a positive NBS result was 96%. CONCLUSIONS: The use of cutoff values adjusted for both GA and BW significantly reduced FP rates (0.03%) and increased overall PPV (16.5%). Based on our 10 years of experience, we recommend the implementation of this two parameter-adjusted approach for NBS of classic CAH in NBS programs worldwide.

Generalized verrucosis and abnormal T cell activation due to homozygous TAOK2 mutation.

BACKGROUND: Generalized verrucosis (GV) is a chronic and progressive cutaneous human papillomavirus (HPV) infection resulting in multiple warts and associated with acquired or genetic immune defects. We identified a consanguineous Arab family manifesting GV and recurrent bacterial and viral infections, in association with inflammatory bowel disease (IBD). OBJECTIVE: To identify the mutated gene responsible for GV, recurrent infections and IBD, in this family. METHODS: Flow cytometry of peripheral blood mononuclear cells was performed, as well as proliferation and cell cycle assays of T cells. Whole exome sequencing was utilized to detect candidate mutated genes, assuming an autosomal recessive mode of inheritance. Skin fibroblasts from a patient, the mother and control were incubated with sorbitol to detect the phosphorylation ability of TAOK2, and a clonogenic assay was performed to assess the survival and proliferative capacity of fibroblasts' colonies. RESULTS: Despite normal immunophenotyping of T and B cells, T cell proliferation upon activation was impaired in a patient compared to a heterozygous family member and a control. Genetic analyses identified a rare homozygous missense variant, c.2098C>T (p.R700C) in the TAOK2 gene, segregating with the disease phenotype in the family. TAOK2 encodes the TAO2 kinase, a mitogen activated protein kinase kinase kinase (MAP3K) in the p38-MAPK cascade. The mutation is predicted to disrupt its normal folding and molecular interaction; however, no impairment was observed in TAOK2 kinase activity toward its downstream target, MEK3/6, in patient's fibroblasts. Despite this normal kinase activity, a noticeably higher survival/proliferation of patient's skin fibroblasts was found. CONCLUSIONS: A mutation in TAOK2 appears to cause a novel form of primary immunodeficiency, characterized by an impaired T cell proliferation upon activation. This novel cause of GV gives further support to the importance of the p38-MAPK pathway in the immune response against HPV, and possibly also in the pathogenesis of IBD.

GLP-1-RA Corrects Mitochondrial Labile Iron Accumulation and Improves ß-Cell Function in Type 2 Wolfram Syndrome.

CONTEXT: Type 2 Wolfram syndrome (T2-WFS) is a neuronal and ß-cell degenerative disorder caused by mutations in the CISD2 gene. The mechanisms underlying ß-cell dysfunction in T2-WFS are not known, and treatments that effectively improve diabetes in this context are lacking. OBJECTIVE: Unraveling the mechanisms of ß-cell dysfunction in T2-WFS and the effects of treatment with GLP-1 receptor agonist (GLP-1-RA). DESIGN AND SETTING: A case report and in vitro mechanistic studies. PATIENT AND METHODS: We treated an insulin-dependent T2-WFS patient with the GLP-1-RA exenatide for 9 weeks. An iv glucose/glucagon/arginine stimulation test was performed off-drug before and after intervention. We generated a cellular model of T2-WFS by shRNA knockdown of CISD2 (nutrient-deprivation autophagy factor-1 [NAF-1]) in rat insulinoma cells and studied the mechanisms of ß-cell dysfunction and the effects of GLP-1-RA. RESULTS: Treatment with exenatide resulted in a 70% reduction in daily insulin dose with improved glycemic control, as well as an off-drug 7-fold increase in maximal insulin secretion. NAF-1 repression in INS-1 cells decreased insulin content and glucose-stimulated insulin secretion, while maintaining the response to cAMP, and enhanced the accumulation of labile iron and reactive oxygen species in mitochondria. Remarkably, treatment with GLP-1-RA and/or the iron chelator deferiprone reversed these defects. CONCLUSION: NAF-1 deficiency leads to mitochondrial labile iron accumulation and oxidative stress, which may contribute to ß-cell dysfunction in T2-WFS. Treatment with GLP-1-RA and/or iron chelation improves mitochondrial function and restores ß-cell function. Treatment with GLP-1-RA, probably aided by iron chelation, should be considered in WFS and other forms of diabetes associated with iron dysregulation.

Propionic acidemia mimicking diabetic ketoacidosis.

Propionic acidemia manifesting with hyperglycemia is rare. Few cases have been reported mainly of the neonatal-onset form associated with high mortality. We report a 9-month-old Palestinian boy who manifested with coma, severe hyperglycemia and ketoacidosis mimicking diabetic ketoacidosis. Family history of unexplained infant deaths was helpful in reaching the correct diagnosis. In response to therapy, the patient regained consciousness without neurologic deficits and had normal examination. This is, to our knowledge, the first case report of late-onset propionic acidemia that had this presentation and survived.

Autosomal recessive familial neurohypophyseal diabetes insipidus: onset in early infancy.

BACKGROUND: Familial neurohypophyseal diabetes insipidus (FNDI), usually an autosomal dominant disorder, is caused by mutations in the arginine vasopressin (AVP)-neurophysin II preprohormone leading to aberrant preprohormone processing and gradual destruction of AVP-secreting cells. Patients typically present between 1 and 6 years of age with polyuria and polydipsia. OBJECTIVE: Clinical, biochemical, and genetic studies of three new cases of autosomal recessive FNDI presenting in early infancy. PATIENTS: Three Palestinian cousins presented with failure to thrive, vomiting, irritability, and fever. The parents were asymptomatic. Patients developed hypernatremia (154-163 mmol/l) and serum hyperosmolality (>320 mOsm/kg), while urine osmolality remained between 73 and 229 mOsm/kg. Plasma AVP levels were low, and the posterior pituitary bright spot was absent on magnetic resonance imaging (MRI). All patients responded to desmopressin. RESULTS: Patients were homozygous and parents were heterozygous for microsatellite markers flanking the AVP gene. All patients were homozygous for the P26L (proline to leucine) substitution affecting mature AVP. A founder effect with the single original kindred carrying the P26L mutation was confirmed by microsatellite analysis, but patients in that family presented only at 2 years of age. In microsatellite analysis, the new kindred patients were not homozygous and did not share a single allele at the aquaporin 2 and vasopressin receptor-2 genes locuses. CONCLUSION: This is the first description of autosomal recessive FNDI presenting in the neonatal period. The unusual early clinical and radiological (MRI) presentation argues against gradual destruction of AVP-secreting neurons as the pathophysiological mechanism. Factors beside allelism of AVP-related genes must influence the age of FNDI presentation given the founder effect demonstrated for the P26L mutation.