Noncoding deletions reveal a gene that is critical for intestinal function.

Large-scale genome sequencing is poised to provide a substantial increase in the rate of discovery of disease-associated mutations, but the functional interpretation of such mutations remains challenging. Here we show that deletions of a sequence on human chromosome 16 that we term the intestine-critical region (ICR) cause intractable congenital diarrhoea in infants1,2. Reporter assays in transgenic mice show that the ICR contains a regulatory sequence that activates transcription during the development of the gastrointestinal system. Targeted deletion of the ICR in mice caused symptoms that recapitulated the human condition. Transcriptome analysis revealed that an unannotated open reading frame (Percc1) flanks the regulatory sequence, and the expression of this gene was lost in the developing gut of mice that lacked the ICR. Percc1-knockout mice displayed phenotypes similar to those observed upon ICR deletion in mice and patients, whereas an ICR-driven Percc1 transgene was sufficient to rescue the phenotypes found in mice that lacked the ICR. Together, our results identify a gene that is critical for intestinal function and underscore the need for targeted in vivo studies to interpret the growing number of clinical genetic findings that do not affect known protein-coding genes.

Expanded targeted preconception screening panel in Israel: findings and insights.

BACKGROUND: We aimed to analyse the efficacy and added value of a targeted Israeli expanded carrier screening panel (IL-ECSP), beyond the first-tier test covered by the Israeli Ministry of Health (IMOH) and the second-tier covered by the Health Maintenance Organisations (HMOs). METHODS: A curated variant-based IL-ECSP, tailored to the uniquely diverse Israeli population, was offered at two tertiary hospitals and a major genetics laboratory. The panel includes 1487 variants in 357 autosomal recessive and X-linked genes. RESULTS: We analysed 10 115 Israeli samples during an 18-month period. Of these, 6036 (59.7%) were tested as couples and 4079 (40.3%) were singles. Carriers were most frequently identified with mutations in the following genes: GJB2/GJB6 (1:22 allele frequency), CFTR (1:28), GBA (1:34), TYR (1:39), PAH (1:50), SMN1 (1:52) and HEXA (1:56). Of 3018 couples tested, 753 (25%) had no findings, in 1464 (48.5%) only one partner was a carrier, and in 733 (24.3%) both were carriers of different diseases. We identified 79 (2.6%) at-risk couples, where both partners are carriers of the same autosomal recessive condition, or the female carries an X-linked disease. Importantly, 48.1% of these would not have been detected by ethnically-based screening tests currently provided by the IMOH and HMOs, for example, variants in GBA, TYR, PAH and GJB2/GJB6. CONCLUSION: This is the largest cohort of targeted ECSP testing, tailored to the diverse Israeli population. The IL-ECSP expands the identification of couples at risk and empowers their reproductive choices. We recommend endorsing an expanded targeted panel to the National Genetic Carrier Screening programme.

The role of orotic acid measurement in routine newborn screening for urea cycle disorders.

Urea cycle disorders (UCDs), including OTC deficiency (OTCD), are life-threatening diseases with a broad clinical spectrum. Early diagnosis and initiation of treatment based on a newborn screening (NBS) test for OTCD with high specificity and sensitivity may contribute to reduction of the significant complications and high mortality. The efficacy of incorporating orotic acid determination into routine NBS was evaluated. Combined measurement of orotic acid and citrulline in archived dried blood spots from newborns with urea cycle disorders and normal controls was used to develop an algorithm for routine NBS for OTCD in Israel. Clinical information and genetic confirmation results were obtained from the follow-up care providers. About 1147986 newborns underwent routine NBS including orotic acid determination, 25 of whom were ultimately diagnosed with a UCD. Of 11 newborns with OTCD, orotate was elevated in seven but normal in two males with early-onset and two males with late-onset disease. Orotate was also elevated in archived dried blood spots of all seven retrospectively tested historical OTCD patients, only three of whom had originally been identified by NBS with low citrulline and elevated glutamine. Among the other UCDs emerge, three CPS1D cases and additional three retrospective CPS1D cases otherwise reported as a very rare condition. Combined levels of orotic acid and citrulline in routine NBS can enhance the detection of UCD, especially increasing the screening sensitivity for OTCD and differentiate it from CPS1D. Our data and the negligible extra cost for orotic acid determination might contribute to the discussion on screening for proximal UCDs in routine NBS.

Identification of a homozygous VRK1 mutation in two patients with adult-onset distal hereditary motor neuropathy.

BACKGROUND: Adult-onset hereditary motor neuropathies are caused by mutations in multiple genes. Mutations within the vaccinia-related kinase 1 (VRK1) gene were associated with a wide spectrum of recessively inherited motor neuropathies, characterized by childhood to early adulthood age of onset and an occasionally non-lower motor neuron involvement. METHODS: We describe two patients with adult-onset (aged 48 and 40 years) length-dependent motor neuropathy from unrelated consanguineous families of Moroccan Jewish descent. One also demonstrated mild nocturnal respiratory difficulty and sensory symptoms. Whole-exome sequencing (WES) was performed. RESULTS: A homozygous mutation in VRK1 (c.1160G>A (p.Arg387His)), shared by both patients, was identified. This rare mutation segregated with the disease in the two families, and was absent in 120 controls of Jewish Moroccan origin. CONCLUSIONS: Our findings support VRK1 as a causative gene for adult-onset distal hereditary motor neuropathy, and indicate its relevance for evaluation of individuals with similar motor impairment.

A high and equal prevalence of the Q703K variant in NLRP3 patients with autoinflammatory symptoms and ethnically matched controls.

OBJECTIVES: Cryopyrin associated periodic syndromes (CAPS) comprise a spectrum of autoinflammatory disorders of varying severity caused by mutations in the NLRP3 gene. The NLRP3-Q703K allele has been reported both as a functional polymorphism and as a low penetrance mutation. METHODS: To describe the clinical phenotype of subjects with the Q703K allele and to report the frequency of this allele among patients with autoinflammatory symptoms and healthy controls. To this end, a cohort of 10 ethnically-matched controls per each Q703K-carrying patient, was composed. RESULTS: Ninety patients suspected of harboring a systemic autoinflammatory disease (SAID), exclusive of FMF, were referred to our center for genotyping between 2012 and 2015. Fourteen of them (15.5%) were found to carry the Q703K allele, compared to 22 of 130 (16.9%) healthy, ethnically matched controls. CONCLUSIONS: The similar carrier rate of the NLRP3-Q703K allele among patients with manifestations of a SAID and an ethnically matched control group suggest that this variant, does not determine the clinical phenotype. This reiterates the importance of testing a control group to avoid erroneously attributing a causative role to a gene polymorphism.

Mutation in TECPR2 reveals a role for autophagy in hereditary spastic paraparesis.

We studied five individuals from three Jewish Bukharian families affected by an apparently autosomal-recessive form of hereditary spastic paraparesis accompanied by severe intellectual disability, fluctuating central hypoventilation, gastresophageal reflux disease, wake apnea, areflexia, and unique dysmorphic features. Exome sequencing identified one homozygous variant shared among all affected individuals and absent in controls: a 1 bp frameshift TECPR2 deletion leading to a premature stop codon and predicting significant degradation of the protein. TECPR2 has been reported as a positive regulator of autophagy. We thus examined the autophagy-related fate of two key autophagic proteins, SQSTM1 (p62) and MAP1LC3B (LC3), in skin fibroblasts of an affected individual, as compared to a healthy control, and found that both protein levels were decreased and that there was a more pronounced decrease in the lipidated form of LC3 (LC3II). siRNA knockdown of TECPR2 showed similar changes, consistent with aberrant autophagy. Our results are strengthened by the fact that autophagy dysfunction has been implicated in a number of other neurodegenerative diseases. The discovered TECPR2 mutation implicates autophagy, a central intracellular mechanism, in spastic paraparesis.

The yield of genetic workup for middle-aged and elderly patients with neurological disorders in a real-world setting.

Genetic workup is becoming increasingly common in the clinical assessment of neurological disorders. We evaluated its yield among middle-aged and elderly neurological patients, in a real-world context. This retrospective study included 368 consecutive Israeli patients aged 50 years and older (202 [54.9%] males), who were referred to a single neurogenetics clinic between 2017 and mid-2023. All had neurological disorders, without a previous molecular diagnosis. Demographic, clinical and genetic data were collected from medical records. The mean age at first genetic counseling at the clinic was 62.3 ± 7.8 years (range 50-85 years), and the main indications for referral were neuromuscular, movement and cerebrovascular disorders, as well as cognitive impairment and dementia. Out of the 368 patients, 245 (66.6%) underwent genetic testing that included exome sequencing (ES), analysis of nucleotide repeat expansions, detection of specific mutations, targeted gene panel sequencing or chromosomal microarray analysis. Overall, 80 patients (21.7%) received a molecular diagnosis due to 36 conditions, accounting for 32.7% of the patients who performed genetic testing. The diagnostic rates were highest for neuromuscular (58/186 patients [31.2%] in this group, 39.2% of 148 tested individuals) and movement disorders (14/79 [17.7%] patients, 29.2% of 48 tested), but lower for other disorders. Testing of nucleotide repeat expansions and ES provided a diagnosis to 28/73 (38.4%) and 19/132 (14.4%) individuals, respectively. Based on our findings, genetic workup and testing are useful in the diagnostic process of neurological patients aged ≥50 years, in particular for those with neuromuscular and movement disorders.

Mutations in the sarcosine dehydrogenase gene in patients with sarcosinemia.

Sarcosinemia is an autosomal recessive metabolic trait manifested by relatively high concentrations of sarcosine in blood and urine. Sarcosine is a key intermediate in 1-carbon metabolism and under normal circumstances is converted to glycine by the enzyme sarcosine dehydrogenase. We encountered six families from two different descents (French and Arab), each with at least one individual with elevated levels of sarcosine in blood and urine. Using the "candidate gene approach" we sequenced the gene encoding sarcosine dehydrogenase (SARDH), which plays an important role in the conversion of sarcosine to glycine, and found four different mutations (P287L, V71F, R723X, R514X) in three patients. In an additional patient, we found a uniparental disomy in the region of SARDH gene. In two other patients, we did not find any mutations in this gene. We have shown for the first time that mutations in the SARDH gene are associated with sarcosinemia. In addition, our results indicate that other genes are most probably involved in the pathogenesis of this condition.

Fundus albipunctatus: novel mutations and phenotypic description of Israeli patients.

PURPOSE: To characterize the genetic defects associated with fundus albipunctatus (FAP) in patients in Israel. METHODS: Twenty patients with FAP from diverse ethnicities underwent ophthalmic and electroretinogram tests following the International Society for Clinical Electrophysiology of Vision protocol. Genomic DNA was extracted from peripheral blood. Mutation analysis of the 11-cis retinol dehydrogenase (RDH5) gene was performed with direct sequencing of PCR-amplified exons. RESULTS: Four novel RDH5 gene mutations were identified. Of them, the null mutations c.343C>T (p.R54X) and c.242delTGCC were most prevalent. Macular involvement was present in two patients who carry different mutation types. CONCLUSIONS: Mutation analysis of the RDH5 gene in the present series revealed four novel mutations and a previously reported one. No significant genotype-phenotype correlation was found.

Carrier state for the nebulin exon 55 deletion and abnormal prenatal ultrasound findings as potential signs of nemaline myopathy.

OBJECTIVE: To increase awareness to the possibility of nemaline myopathy (NM) when abnormal prenatal ultrasound findings appear together with a carrier state for the common exon 55 deletion in the nebulin gene (NEB) of an Ashkenazi Jewish parent. METHODS: We describe four unrelated pregnancies with abnormal prenatal ultrasound findings resulting in the birth of newborns with NM, where one or both parents were of Ashkenazi Jewish origin. Data was collected retrospectively from the patients' medical files. Molecular analysis of NEB was performed on the DNA from the patients and parents. RESULTS: Prenatal ultrasound findings included polyhydramnios, decreased fetal movements, club feet, and arthrogryposis. A biopsy from two of the newborns was consistent with NM. In all of the newborns, the common NEB exon 55 deletion was detected in the heterozygote state and in three of them, a second novel mutation was found. CONCLUSIONS: Ultrasonographic findings suggestive of a myopathy and a carrier state for the NEB exon 55 deletion in one of the parents should trigger a thorough investigation for NM. The extreme size of NEB imposes great difficulties when searching for a second mutation, especially under the time constraints of an ongoing pregnancy.

Broadening the phenotype of LRRK1 mutations - Features of malignant osteopetrosis and optic nerve atrophy with intrafamilial variable expressivity.

Osteosclerotic metaphyseal dysplasia is a rare disorder which features osteosclerosis involving long bones, vertebrae, ribs, clavicles and the iliac crests. Additional features which have variably been reported include developmental delay, short stature, hypotonia and seizures. The disease is caused by pathogenic variants in the LRRK1 gene, and inherited in an autosomal recessive manner. We report three siblings (ages 14 years, 11.5 years and 0.9 years), born to consanguineous parents of Arab-Muslim descent, harboring a homozygous pathogenic variant in the LRRK1 gene (Chr15:101068759 AGGGGCT>A, c.5965_5970del TGGGGC, p.Trp1989Gly1990del). The patients displayed variable degrees of skeletal dysplasia, with the oldest sibling most severely affected, and the youngest infant with minor skeletal involvement. Two of the siblings exhibited normal neurological development, while the youngest sibling exhibited global developmental delay. None of the siblings had seizures; however, two of them exhibited nystagmus. Optic nerve involvement has not previously been reported to be part of the clinical spectrum of this disease. The degree of optic nerve involvement did not correlate with the degree of skeletal involvement. This indicates both intra-familial variable expressivity along with a broadening of the spectrum of LRRK1-associated disease. These findings warrant reconsideration of therapeutic strategies, including the possibility of hematopoietic stem cell transplantation (HSCT) as is performed in cases of malignant and intermediate forms of osteopetrosis.

Deleterious mutations in the Zinc-Finger 469 gene cause brittle cornea syndrome.

Brittle cornea syndrome (BCS) is an autosomal-recessive disorder characterized by a thin cornea that tends to perforate, causing progressive visual loss and blindness. Additional systemic symptoms such as joint hypermotility, hyperlaxity of the skin, and kyphoscoliosis place BCS among the connective-tissue disorders. Previously, we assigned the disease gene to a 4.7 Mb interval on chromosome 16q24. In order to clone the BCS gene, we first narrowed the disease locus to a 2.8 Mb interval and systematically sequenced genes expressed in connective tissue in this chromosomal segment. We have identified two frameshift mutations in the Zinc-Finger 469 gene (ZNF469). In five unrelated patients of Tunisian Jewish ancestry, we found a 1 bp deletion at position 5943 (5943 delA), and in an inbred Palestinian family we detected a single-nucleotide deletion at position 9527 (9527 delG). The function of ZNF469 is unknown. However, a 30% homology to a number of collagens suggests that it could act as a transcription factor involved in the synthesis and/or organization of collagen fibers.

Salt-Losing 21-Hydroxylase Deficiency Caused by Double Homozygosity for Two "Mild" Mutations.

CONTEXT: Congenital adrenal hyperplasia due to 21-hydroxylase deficiency presents with different severities that correlate with the genotype. The salt-losing phenotype requires 2 alleles with "severe" mutations. CASE DESCRIPTION: We present a case of salt-losing 21-hydroxylase deficiency that was found to be homozygous for 2 "mild" pathogenic variants: V281L and S301Y. Both in silico and heterologous expression functional analysis demonstrated that co-occurrence of these 2 mutations in cis severely impairs the function of the 21-hydroxylase enzyme. CONCLUSIONS: This case has important implications for genetic counseling. Regarding this combination of 2 "mild" variants as having mild phenotypic effects could lead to inappropriate counseling of heterozygote carriers.

Biallelic variants in ETV2 in a family with congenital heart defects, vertebral abnormalities and preaxial polydactyly.

The combination of congenital heart defects and vertebral anomalies with or without additional abnormalities has been reported in many genetic disorders. We describe a family in which four consecutive pregnancies were characterized by the combination of fetal congenital heart malformations and vertebral anomalies. In addition, preaxial polydactyly was detected in one of the fetuses. Reanalysis of the non-diagnostic clinical exome data revealed compound heterozygous variants c.350del, p.(Gly117AlafsTer90) and c.757G > T, p.(Asp253Tyr) in ETV2 which have previously not been known to be associated with a phenotype in humans. In mice, Etv2 encodes an obligatory transcription factor involved in the generation of hematopoietic and endothelial cells. Its homozygous disruption results in embryonic lethality due to severe blood and vessel defects. The Etv2 promoter may be bound by Nkx2-5, a key transcription factor in heart development. Pathogenic variants in the NKx2-5 homolog in humans (NKX2-5) are related to congenital heart defects. The identification of additional fetuses or live-born individuals with biallelic pathogenic variants in ETV2 will shed further light on this presumably novel gene-phenotype association and on the full phenotypic spectrum.

Early and late manifestations of neuropathy due to HSPB1 mutation in the Jewish Iranian population.

OBJECTIVE: Mutations in the HSPB1 gene are associated with a distal hereditary motor neuropathy type 2 (dHMN2) or Charcot-Marie-Tooth disease type 2F (CMT2F), usually with autosomal dominant inheritance. This study aimed to describe the phenotype of the HSPB1 c.407G>T (p.Arg136Leu) mutation at early and late stages of the disease course. METHODS: We identified this mutation (previously reported in patients from Italy) in a heterozygous state, among 14 individuals from eight families of Jewish Iranian descent. The clinical, electrophysiological and ultrasonographic features were evaluated during early (less than 5 years, N = 9) or late disease course (N = 5). RESULTS: The majority of subjects were males with a mean age at onset of 43.4 years (range 21-67). Common initial symptoms were gait imbalance, distal (often asymmetric) lower limb weakness and feet numbness. Neurological examination in early disease course showed distal lower extremity weakness in nearly all cases, and absent Achilles tendon reflex in about half. A minority had distal loss of pain, vibration or position sensation. These findings were more prevalent in late disease stage. Electrodiagnostic studies demonstrated a length-dependent axonal motor neuropathy, with typical preferential involvement of the tibial nerve. Muscle ultrasound showed a corresponding length-dependent increase of homogeneous echo-intensity, most noticeably in the gastrocnemius. One patient had a dual diagnosis of CMT2F and CMT2W. INTERPRETATION: The HSPB1 c.407G>G (p.Arg136Leu) mutation causes an adult-onset, predominantly motor, axonal neuropathy in individuals of Jewish Iranian descent. Variable manifestations are noticed, and sensory involvement is more prominent in prolonged disease duration.

A single center experience with publicly funded clinical exome sequencing for neurodevelopmental disorders or multiple congenital anomalies.

Exome sequencing (ES) is an important diagnostic tool for individuals with neurodevelopmental disorders (NDD) and/or multiple congenital anomalies (MCA). However, the cost of ES limits the test's accessibility for many patients. We evaluated the yield of publicly funded clinical ES, performed at a tertiary center in Israel, over a 3-year period (2018-2020). Probands presented with (1) moderate-to-profound global developmental delay (GDD)/intellectual disability (ID); or (2) mild GDD/ID with epilepsy or congenital anomaly; and/or (3) MCA. Subjects with normal chromosomal microarray analysis who met inclusion criteria were included, totaling 280 consecutive cases. Trio ES (proband and parents) was the default option. In 252 cases (90.0%), indication of NDD was noted. Most probands were males (62.9%), and their mean age at ES submission was 9.3 years (range 1 month to 51 years). Molecular diagnosis was reached in 109 probands (38.9%), mainly due to de novo variants (91/109, 83.5%). Disease-causing variants were identified in 92 genes, 15 of which were implicated in more than a single case. Male sex, families with multiple-affected members and premature birth were significantly associated with lower ES yield (p < 0.05). Other factors, including MCA and coexistence of epilepsy, autism spectrum disorder, microcephaly or abnormal brain magnetic resonance imaging findings, were not associated with the yield. To conclude, our findings support the utility of clinical ES in a real-world setting, as part of a publicly funded genetic workup for individuals with GDD/ID and/or MCA.

Clues and challenges in the diagnosis of intermittent maple syrup urine disease.

BACKGROUND: Maple syrup urine disease is a rare autosomal-recessive aminoacidopathy, caused by deficient branched-chain 2-keto acid dehydrogenase (BCKD), with subsequent accumulation of branched-chain amino acids (BCAAs): leucine, isoleucine and valine. While most cases of MSUD are classic, some 20% of cases are non-classic variants, designated as intermediate- or intermittent-types. Patients with the latter form usually develop normally and are cognitively intact, with normal BCAA levels when asymptomatic. However, intercurrent febrile illness and catabolism may cause metabolic derailment with life-threatening neurological sequelae. Thus, early detection and dietary intervention are warranted in intermittent MSUD. PATIENTS AND METHODS: We describe eight patients from four unrelated families, diagnosed with intermittent MSUD. Their presenting symptoms during metabolic crises varied from confusion and decreased consciousness, to ataxia, and acute psychosis. Molecular confirmation of MSUD was pursued via sequencing of the BCKDHA, BCKDHB and DBT genes. RESULTS: All affected individuals were found to harbor bi-allelic pathogenic variants in either BCKDHB or DBT. Of the seven variants, four variants in BCKDHB (p.G101D, p. V103A, p. A221D, p. Y195C) and one variant in DBT (p.K427E) were not previously described. CONCLUSIONS: While newborn screening programs allow for early detection of classic MSUD, cases of the intermittent form might go undetected, and present later in childhood following metabolic derailment, with an array of non-specific symptoms. Our experience with the families reported herein adds to the current knowledge regarding the phenotype and mutational spectrum of this unique inborn error of branched-chain amino acid metabolism, and underscore the high index of suspicion required for its diagnosis.

Reduction in Filamin C transcript is associated with arrhythmogenic cardiomyopathy in Ashkenazi Jews.

BACKGROUND: Filamin C is a cytoskeletal protein expressed in cardiac cells. Nonsense variations in the filamin C gene (FLNC) were associated with dilated and arrhythmogenic cardiomyopathies. METHODS AND RESULTS: We identified an intronic variation in FLNC gene (c.3791-1G > C) in three unrelated Ashkenazi Jewish families with variable expression of arrhythmia and cardiomyopathy. cDNA was prepared from a mutation carrier's cultured skin fibroblasts. Quantitative PCR demonstrated a reduction in total FLNC transcript, and no other FLNC splice variants were found. Single-nucleotide polymorphism (SNP) analysis revealed heterozygous variations in the genomic DNA that were not expressed in the messenger RNA. Immunohistochemical analysis of cardiac sections detected a normal distribution of filamin C protein in the heart ventricles. CONCLUSION: The transcript that included the FLNC variant was degraded. Haploinsufficiency in filamin C underlies arrhythmogenic cardiomyopathy with variable symptoms.

Cone-rod dystrophy and a frameshift mutation in the PROM1 gene.

PURPOSE: To identify the genetic cause underlying autosomal recessive cone-rod dystrophy (CORD) and high myopia. METHODS: Nine members of a consanguineous Arab family were clinically examined and were given fluorescein angiography (FA), biometry, and full field electroretinogram (ERG) testing. Blood samples were collected for DNA extraction. A homozygousity genome-wide scan was performed using >382 polymorphic microsatellite markers on genomic DNA from three affected family members. Regions of homozygosity were further analyzed in all members of the family. Mutation analysis of the PROM1 gene was performed by direct sequencing of PCR-amplified exons. RESULTS: The phenotype is characterized by severe visual impairment evident in the first decade of life. Affected family members have bull;s-eye macular appearance, peripheral retinal pigment clumps, and cone-rod type ERG changes. Additionally, they have high myopia with axial lengths exceeding 25.3 mm. A genome-wide scan detected a region of 2.1 Mb on chromosome 4p that fully segregates with the disease within the family. This region encompasses the PROML1 gene, mutations of which have been implicated in retinal dystrophies. PROML1 mutation analysis identified a novel single nucleotide insertion at position 1629 of the cDNA resulting in truncation of approximately one-third of the protein. CONCLUSIONS: The mutation described in this report further expands the clinical spectrum of PROM1 mutations.

Prenatal diagnosis for de novo mutations: Experience from a tertiary center over a 10-year period.

BACKGROUND: This study summarizes the results of prenatal diagnosis due to a history of de novo mutation in a previous pregnancy, in a tertiary center in Israel, over a 10-year period. METHODS: We sorted all cases of de novo mutations from a pool of 2,260 pregnancies for which prenatal molecular diagnosis was applied, between the years 2008 and 2017. We identified 122 molecular prenatal diagnosis performed for de novo mutations, in 90 women. RESULTS: While the total number of yearly prenatal diagnoses stayed stable, a linear increase was detected in the number of cases for which the procedure was done due to a previous de novo mutation: from 3 cases in 2008 to 24 cases in 2017. The most common diseases were Rett syndrome (19), neurofibromatosis Type-1 (12) and Tuberous sclerosis (5). Recurrence occurred in 3 of the 90 women (3.3%) and hotspot mutations were identified in two genes accounting for 11 cases. We did not find a difference in paternal age at first occurrence of the de novo mutation between the study group and the control group. CONCLUSION: The large increase in the annual number of prenatal diagnoses performed due to a previous pregnancy with a de novo mutation reflects the growing understanding regarding the role of these mutations in the pathogenesis of genetic diseases.