Features of Patients With Hereditary Mixed Polyposis Syndrome Caused by Duplication of GREM1 and Implications for Screening and Surveillance.

Hereditary mixed polyposis syndrome is a rare colon cancer predisposition syndrome caused by a duplication of a noncoding sequence near the gremlin 1, DAN family BMP antagonist gene (GREM1) originally described in Ashkenazi Jews. Few families with GREM1 duplications have been described, so there are many questions about detection and management. We report 4 extended families with the duplication near GREM1 previously found in Ashkenazi Jews; 3 families were identified at cancer genetic clinics in Israel and 1 family was identified in a cohort of patients with familial colorectal cancer. Their clinical features include extracolonic tumors, onset of polyps in adolescence, and rapid progression of some polyps to advanced adenomas. One family met diagnostic criteria for Lynch syndrome. Expansion of the hereditary mixed polyposis syndrome phenotype can inform surveillance strategies for carriers of GREM1 duplications.

Ultrasound findings provide clues to investigate founder mutations expressed as runs of homozygosity in chromosomal microarray studies.

OBJECTIVES: Chromosomal microarray analysis is effectively applied prenatally to detect copy number changes. Single nucleotide polymorphism (SNP) probes included in the microarray platform can detect regions of excessive homozygosity and identical-by-descent genomic stretches. The utility of the latter as part of prenatal diagnosis is not well established. Recessive founder mutations are well recognized within distinct ethnic groups. Combining these data with prenatal sonography provides accurate focused molecular diagnoses quickly. We aimed to evaluate the application of this approach in expectant families presenting to our unit. METHODS: Three unrelated gravidae presenting with specific fetal sonographic findings: (1) ventriculomegaly with encephalocele; (2) severe polyhydramnion; and (3) enlarged echogenic kidneys, underwent amniocentesis for chromosomal microarray analysis, and genome-wide human SNP array was used to analyze DNA from amniocytes. The Genomic Oligoarray and SNP array evaluation tool v3.0© was used to detect recessive loci associated with the reported clinical findings. Candidate genes were further interrogated using the Israeli National Genetic Database (INGD) and specifically searching and identifying a corresponding founder mutation within the defined ethnic group. RESULTS: Three fetuses from 3 distinct nuclear families in which the parents shared a similar ethnicity (either Ashkenazi or Bukharan Jews) albeit no reported consanguinity were assessed. We found no copy number changes; however, by evaluating regions of homozygosity, we were able to reveal relevant candidate gene for the specific phenotype for each fetus. Using the INGD led to targeted testing of a specific homozygous fetal mutation for which parents were found to be carriers. In the fetus with ventriculomegaly with encephalocele c.1167dupA mutation in the FKTN gene, in the fetus with severe polyhydramnion c.167ins6[TTTCCC] mutation in the BSND gene, and in the fetus with enlarged echogenic kidneys, c.3761_3762delCCinsG in the PKHD1 gene were identified. CONCLUSIONS: A tripartite approach integrating sonographic pathology with regions of excessive homozygosity data and INGD-based founder mutation repository yields a comprehensive streamlined approach to provide accurate genetic diagnosis and counselling within the time constraints of an ongoing pregnancy.

Constitutional Mismatch Repair Deficiency in Israel: High Proportion of Founder Mutations in MMR Genes and Consanguinity.

BACKGROUND: Heterozygous germline mutations in any of the mismatch repair (MMR) genes, MLH1, MSH2, MSH6, and PMS2, cause Lynch syndrome (LS), an autosomal dominant cancer predisposition syndrome conferring a high risk of colorectal, endometrial, and other cancers in adulthood. Offspring of couples where both spouses have LS have a 1:4 risk of inheriting biallelic MMR gene mutations. These cause constitutional MMR deficiency (CMMRD) syndrome, a severe recessively inherited cancer syndrome with a broad tumor spectrum including mainly hematological malignancies, brain tumors, and colon cancer in childhood and adolescence. Many CMMRD children also present with café au lait spots and axillary freckling mimicking neurofibromatosis type 1. PROCEDURE: We describe our experience in seven CMMRD families demonstrating the role and importance of founder mutations and consanguinity on its prevalence. Clinical presentations included brain tumors, colon cancer, lymphoma, and small bowel cancer. RESULTS: In children from two nonconsanguineous Ashkenazi Jewish (AJ) families, the common Ashkenazi founder mutations were detected; these were homozygous in one family and compound heterozygous in the other. In four consanguineous families of various ancestries, different homozygous mutations were identified. In a nonconsanguineous Caucasus/AJ family, lack of PMS2 was demonstrated in tumor and normal tissues; however, mutations were not identified. CONCLUSIONS: CMMRD is rare, but, especially in areas where founder mutations for LS and consanguinity are common, pediatricians should be aware of it since they are the first to encounter these children. Early diagnosis will enable tailored cancer surveillance in the entire family and a discussion regarding prenatal genetic diagnosis.

Myelin-associated glycoprotein gene mutation causes Pelizaeus-Merzbacher disease-like disorder.

Pelizaeus-Merzbacher disease is an X-linked hypomyelinating leukodystrophy caused by mutations or rearrangements in PLP1. It presents in infancy with nystagmus, jerky head movements, hypotonia and developmental delay evolving into spastic tetraplegia with optic atrophy and variable movement disorders. A clinically similar phenotype caused by recessive mutations in GJC2 is known as Pelizaeus-Merzbacher-like disease. Both genes encode proteins associated with myelin. We describe three siblings of a consanguineous family manifesting the typical infantile-onset Pelizaeus-Merzbacher disease-like phenotype slowly evolving into a form of complicated hereditary spastic paraplegia with mental retardation, dysarthria, optic atrophy and peripheral neuropathy in adulthood. Magnetic resonance imaging and spectroscopy were consistent with a demyelinating leukodystrophy. Using genetic linkage and exome sequencing, we identified a homozygous missense c.399C>G; p.S133R mutation in MAG. This gene, previously associated with hereditary spastic paraplegia, encodes myelin-associated glycoprotein, which is involved in myelin maintenance and glia-axon interaction. This mutation is predicted to destabilize the protein and affect its tertiary structure. Examination of the sural nerve biopsy sample obtained in childhood in the oldest sibling revealed complete absence of myelin-associated glycoprotein accompanied by ill-formed onion-bulb structures and a relatively thin myelin sheath of the affected axons. Immunofluorescence, cell surface labelling, biochemical analysis and mass spectrometry-based proteomics studies in a variety of cell types demonstrated a devastating effect of the mutation on post-translational processing, steady state expression and subcellular localization of myelin-associated glycoprotein. In contrast to the wild-type protein, the p.S133R mutant was retained in the endoplasmic reticulum and was subjected to endoplasmic reticulum-associated protein degradation by the proteasome. Our findings identify involvement of myelin-associated glycoprotein in this family with a disorder affecting the central and peripheral nervous system, and suggest that loss of the protein function is responsible for the unique clinical phenotype.

Genetic predisposition to radiation induced sarcoma: possible role for BRCA and p53 mutations.

The estimated incidence of radiation-associated sarcoma (RAS) is 0.03-0.2 % in 5 years post treatment. Most cancer predisposing genes are involved in DNA repair; therefore, elevated RAS risk in these patients is plausible. Cases of angiosarcoma post breast cancer treatment were reported in BRCA1 and BRCA2 carriers. We report the genetic evaluation of seven cases with suspected RAS from patients counseled in our cancer-genetic clinic. Of 2,885 breast cancer patient, 470 were BRCA1 or two mutation carriers and three were p53 mutation carriers. Of them seven developed sarcoma in the field of irradiation; five in the chest wall and two in other sites. Genetic evaluation revealed BRCA1 mutation in two, BRCA2 mutation in additional patient and a carrier of p53 mutation. The estimation of risk for RAS in patients with genetic predisposition is limited due to the rarity of this event, and the bias in referral to the clinic toward younger age. With these limitations the rate of RAS is 0.43 % (2/470, 95 % CI -0.17 to 1.02, SE = 0.3) in this group in a median follow-up of 8.2 years (range 1 month to 51 years). If we assume irradiation for the breast in 80 % of the patients than rate of RAS in group is proximately 0.53 % (2/376, 95 % CI -0.21 to 1.26, SE = 0.37). A BRCA1 carrier which had sarcoma after irradiation to head and neck carcinoma was not included in these analyses. In conclusion, we found a high frequency of BRCA1/2 mutation among our patients diagnosed with RAS. However, we estimated approximately twofold increase in the risk of RAS in BRCA1/2 carriers which was not significant compared to reports in general population. Therefore, RAS is a rare event in BRCA carriers as in the general population, and should not be considered in the decision regarding irradiation treatment in this population.

Unique Ataxia-Oculomotor Apraxia 2 (AOA2) in Israel with Novel Variants, Atypical Late Presentation, and Possible Identification of a Poison Exon.

AOA2 is a rare progressive adolescent-onset disease characterised by cerebellar vermis atrophy, peripheral neuropathy and elevated serum alpha-fetoprotein (AFP) caused by pathogenic bi-allelic variants in SETX, encoding senataxin, involved in DNA repair and RNA maturation. Sanger sequencing of genomic DNA, co-segregation and oxidative stress functional studies were performed in Family 1. Trio whole-exome sequencing (WES), followed by SETX RNA and qRT-PCR analysis, were performed in Family 2. Sanger sequencing in Family 1 revealed two novel in-frame SETX deletion and duplication variants in trans (c.7009_7011del; p.Val2337del and c.7369_7371dup; p.His2457dup). Patients had increased induced chromosomal aberrations at baseline and following exposure to higher mitomycin-C concentration and increased sensitivity to oxidative stress at the lower mitomycin-C concentration in cell viability test. Trio WES in Family 2 revealed two novel SETX variants in trans, a nonsense variant (c.568C > T; p.Gln190*), and a deep intronic variant (c.5549-107A > G). Intronic variant analysis and SETX mRNA expression revealed activation of a cryptic exon introducing a premature stop codon (p.Met1850Lysfs*18) and resulting in aberrant splicing, as shown by qRT-PCR analysis, thus leading to higher levels of cryptic exon activation. Along with a second deleterious allele, this variant leads to low levels of SETX mRNA and disease manifestations. Our report expands the phenotypic spectrum of AOA2. Results provide initial support for the hypomorphic nature of the novel in-frame deletion and duplication variants in Family 1. Deep-intronic variant analysis of Family 2 variants potentially reveals a previously undescribed poison exon in the SETX gene, which may contribute to tailored therapy development.

The H syndrome is caused by mutations in the nucleoside transporter hENT3.

The H syndrome is a recently reported autosomal-recessive disorder characterized by cutaneous hyperpigmentation, hypertrichosis, hepatosplenomegaly, heart anomalies, hearing loss, hypogonadism, short stature, hallux valgus, and fixed flexion contractures of the toe joints and the proximal interphalangeal joints. Homozygosity mapping in five consanguineous families resulted in the identification of mutations in the SLC29A3 gene, which encodes the equilibrative nucleoside transporter hENT3. Three mutations were found in 11 families of Arab and Bulgarian origin. The finding of several different mutations in a small geographic region implies that the H syndrome might be rather common. The identification of mutations in the SLC29A3 gene in patients with a mild clinical phenotype suggests that this is a largely underdiagnosed condition and strongly suggests that even oligosymptomatic individuals might have the disorder.

Familial hydrocephalus with normal cognition and distinctive radiological features.

Hydrocephalus is a clinically and genetically heterogeneous condition. Individuals with posterior fossa abnormalities have an increased risk of developing hydrocephalus. The Dandy-Walker malformation, Dandy-Walker variant, and mega-cisterna magna (MCM) seem to represent a continuum of developmental anomalies of the posterior fossa. Here we describe the natural clinical history and the radiological features of a family with autosomal or X-linked dominant inheritance of MCM and hydrocephalus of variable severity. The affected family members demonstrate similar structural brain abnormalities including midline cyst, colpocephaly, MCM with a large posterior fossa and minimal vermian hypoplasia. The cognitive development of the affected individuals is normal. L1CAM and FOXC1 gene involvement in the pathogenesis of the disease in this family was excluded. The rare possibility of autosomal dominant or X-linked dominant inheritance and variable penetrance and expressivity must always be considered in genetic counseling of families with hereditary hydrocephalus.

Mutations in SPG11 are frequent in autosomal recessive spastic paraplegia with thin corpus callosum, cognitive decline and lower motor neuron degeneration.

Hereditary spastic paraplegias (HSP) are neurodegenerative diseases mainly characterized by lower limb spasticity associated, in complicated forms, with additional neurological signs. We have analysed a large series of index patients (n = 76) with this condition, either from families with an autosomal recessive inheritance (n = 43) or isolated patients (n = 33), for mutations in the recently identified SPG11 gene. We found 22 truncating mutations, including the first four splice-site mutations, segregating in seven isolated cases and 13 families. Nineteen mutations were novel. Two recurrent mutations were found in Portuguese and North-African patients indicating founder effects in these populations. The mutation frequency varied according to the phenotype, from 41%, in HSP patients presenting with a thin corpus callosum (TCC) visualized by MRI, to 4.5%, in patients with mental impairment without a TCC. Disease onset occurred during the first to the third decade mainly by problems with gait and/or mental retardation. After a mean disease duration of 14.9 +/- 6.6 years, the phenotype of 38 SPG11 patients was severe with 53% of patients wheelchair bound or bedridden. In addition to mental retardation, 80% of the patients showed cognitive decline with executive dysfunction. Interestingly, the phenotype also frequently included lower motor neuron degeneration (81%) with wasting (53%). Slight ocular cerebellar signs were also noted in patients with long disease durations. In addition to a TCC (95%), brain MRI revealed white matter alterations (69%) and cortical atrophy (81%), which worsened with disease duration. In conclusion, our study reveals the high frequency of SPG11 mutations in patients with HSP, a TCC and cognitive impairment, including in isolated patients, and extends the associated phenotype.

MYORG is associated with recessive primary familial brain calcification.

Objective: To investigate the genetic basis of the recessive form of primary familial brain calcification and study pathways linking a novel gene with known dominant genes that cause the disease. Methods: Whole exome sequencing and Sanger-based segregation analysis were used to identify possible disease causing mutations. Mutation pathogenicity was validated by structural protein modeling. Functional associations between the candidate gene, MYORG, and genes previously implicated in the disease were examined through phylogenetic profiling. Results: We studied nine affected individuals from two unrelated families of Middle Eastern origin. The median age of symptom onset was 29.5 years (range 21-57 years) and dysarthria was the most common presenting symptom. We identified in the MYORG gene, a homozygous c.1233delC mutation in one family and c.1060_1062delGAC mutation in another. The first mutation results in protein truncation and the second in deletion of a highly conserved aspartic acid that is likely to disrupt binding of the protein with its substrate. Phylogenetic profiling analysis of the MYORG protein sequence suggests co-evolution with a number of calcium channels as well as other proteins related to regulation of anion transmembrane transport (False Discovery Rate, FDR < 10-8) and with PDCD6IP, a protein interacting with PDGFR ß which is known to be involved in the disease. Interpretation: MYORG mutations are linked to a recessive form of primary familial brain calcification. This association was recently described in patients of Chinese ancestry. We suggest the possibility that MYORG mutations lead to calcification in a PDGFR ß-related pathway.

Mutation spectrum in HNPCC in the Israeli population.

Hereditary non-polyposis colon cancer is caused by mutations in DNA mismatch repair genes. The mutation spectrum in the Israeli population is poorly documented except for the c.1906G>C Ashkenazi founder mutation in the hMSH2 gene. To report our experience in HNPCC screening, the mutations detected and the clinical features among a cohort of Israeli patients. Diagnostic work-up was done in a multi-step process guided by clinical and ethnic information. Tumors of suspected patients were tested for microsatellite instability and immunohistochemistry. Based on tumor analyses, we proceeded to mutation screening by DHPLC followed by sequence analysis and multiplex ligase dependent probe amplification. Ashkenazi Jews were first tested for the c.1906G>C founder mutation. Of the 240 families, 24, including Arabs and Jews from different ethnic origins, were tested positive. All tumors that lost expression of mismatch repair proteins also showed microsatellite instability. There was evidence for involvement of hMSH2 (15) hMLH1 (6) and hMSH6 (3) genes. Mutations were identified in 17/24 (71%) patients: 6 Ashkenazi families harbored the c.1906G>C mutation. Eleven other mutations (2 nonsense, 3 splice site and 6 small deletions) were detected. Three of the mutations are novel. No gross deletions or insertions were detected. This is the first report that characterizes the profile of HNPCC in a cohort of patients in Israel. Tumor testing indicated that the 3 main MMR genes are involved, and that mutation spectrum is broad.

The Genetics of Usher Syndrome in the Israeli and Palestinian Populations.

Purpose: Usher syndrome (USH) is the most common cause for deaf-blindness. It is genetically and clinically heterogeneous and prevalent in populations with high consanguinity rate. We aim to characterize the set of genes and mutations that cause USH in the Israeli and Palestinian populations. Methods: Seventy-four families with USH were recruited (23 with USH type 1 [USH1], 33 with USH2, seven with USH3, four with atypical USH, and seven families with an undetermined USH type). All affected subjects underwent a full ocular evaluation. A comprehensive genetic analysis, including Sanger sequencing for the detection of founder mutations, homozygosity mapping, and whole exome sequencing in large families was performed. Results: In 79% of the families (59 out of 74), an autosomal recessive inheritance pattern could be determined. Mutation detection analysis led to the identification of biallelic causative mutations in 51 (69%) of the families, including 21 families with mutations in USH2A, 17 in MYO7A, and seven in CLRN1. Our analysis revealed 28 mutations, 11 of which are novel (including c.802G>A, c.8558+1G>T, c.10211del, and c.14023A>T in USH2A; c.285+2T>G, c.2187+1G>T, c.3892G>A, c.5069_5070insC, c.5101C>T, and c.6196C>T in MYO7A; and c.15494del in GPR98). Conclusions: We report here novel homozygous mutations in various genes causing USH, extending the spectrum of causative mutations. We also prove combined sequencing techniques as useful tools to identify novel disease-causing mutations. To the best of our knowledge, this is the largest report of a genetic analysis of Israeli and Palestinian families (n = 74) with different USH subtypes.

Role of a founder c.201_202delCT mutation and new phenotypic features of congenital lipoid adrenal hyperplasia in Palestinians.

CONTEXT: Congenital lipoid adrenal hyperplasia (CLAH), caused by mutations in steroidogenic acute regulatory protein (StAR), is most frequent in Japanese and Palestinians. We report eight Palestinians from four unrelated families with CLAH. OBJECTIVE: The objective of the study was to identify the mutation(s) in StAR, correlate genotype with phenotype, and determine whether the common mutation represents a founder mutation. PATIENTS AND SETTING: Clinical, histopathological, and molecular genetic characterization was performed in these eight patients. RESULTS: All affected individuals (three XY, five XX) presented neonatally with undetectable adrenocortical hormones and are responding to replacement therapy. Only two sisters had neurodevelopmental deficits. Histopathological findings of excised XY gonads included accumulation of fat in Leydig cells. Significantly, already at 1 yr of age, positive placental alkaline phosphatase and octamer binding transcription factor staining indicated neoplastic potential. Sequence analysis of StAR revealed homozygosity for c.201_202delCT mutation in all eight cases, causing premature termination of the StAR protein. This mutation was confirmed to be a founder mutation using both an intragenic microsatellite and several single nucleotide polymorphism markers. Screening of 100 normal Jerusalem Palestinians detected no carriers of this mutation. CONCLUSION: CLAH is rare in the general Palestinian population. In most Palestinian cases, a founder c.201_202delCT mutation in StAR is the cause. The observed early neonatal presentation may reflect the major StAR protein truncation caused by this mutation. A crucial role for StAR in the central nervous system was not supported with normal neurological examinations in six of eight cases. Finally, we advocate early gonadectomy in XY CLAH cases, given the early onset of neoplastic changes observed histologically.

A novel BRCA-1 mutation in Arab kindred from east Jerusalem with breast and ovarian cancer.

BACKGROUND: The incidence of breast cancer (BC) in Arab women is lower compared to the incidence in the Jewish population in Israel; still, it is the most common malignancy among Arab women. There is a steep rise in breast cancer incidence in the Arab population in Israel over the last 10 years that can be attributed to life style changes. But, the younger age of BC onset in Arab women compared with that of the Jewish population is suggestive of a genetic component in BC occurrence in that population. METHODS: We studied the family history of 31 women of Palestinian Arab (PA) origin affected with breast (n = 28), ovarian (n = 3) cancer. We used denaturing high performance liquid chromatography (DHPLC) to screen for mutations of BRCA1/2 in 4 women with a personal and family history highly suggestive of genetic predisposition. RESULTS: A novel BRCA1 mutation, E1373X in exon 12, was found in a patient affected with ovarian cancer. Four of her family members, 3 BC patients and a healthy individual were consequently also found to carry this mutation. Of the other 27 patients, which were screened for this specific mutation none was found to carry it. CONCLUSION: We found a novel BRCA1 mutation in a family of PA origin with a history highly compatible with BRCA1 phenotype. This mutation was not found in additional 30 PA women affected with BC or OC. Therefore full BRCA1/2 screening should be offered to patients with characteristic family history. The significance of the novel BRCA1 mutation we identified should be studied in larger population. However, it is likely that the E1373X mutation is not a founder frequent mutation in the PA population.

Evidence for clinical and genetic heterogeneity in hereditary benign telangiectasia.

BACKGROUND: Telangiectases are abnormal dilatations of end vessels in the subpapillary plexus of the papillary dermis. Hereditary benign telangiectasia (HBT) (OMIM 187260) is a genetic skin disorder, characterized by multiple cutaneous telangiectases appearing in the first years of life in various locations. Several familial cases of HBT have been described displaying autosomal dominant inheritance. In some of the described pedigrees, telangiectases are limited to sun-exposed areas, whereas in others lesions are randomly distributed over the body. The disorder has been previously mapped to a 7Mb interval on chromosome 5q14 (CMC1 locus) in an Italian pedigree with randomly distributed telangiectases. OBJECTIVES: A large pedigree of HBT with photodistributed lesions is described. We sought to determine whether photodistributed HBT is linked to the CMC1 locus. METHODS: In all, 35 family members were examined. DNA was extracted from blood and saliva samples. Linkage analysis to CMC1 locus on chromosome 5q14 was screened by using 3 polymorphic markers. RESULTS: In all, 23 family members were found to have variable numbers of cutaneous radiating macular telangiectases, measuring 1 to 3 cm and distributed over the face, back of the hands, and forearms. HBT in this family is inherited in an autosomal dominant pattern with incomplete penetrance. Linkage to the CMC1 locus was excluded. LIMITATION: Only one family, although very large, was studied in this project. CONCLUSIONS: Clinical and genetic heterogeneity is evident in HBT. Photodistributed HBT is not related pathogenically to capillary malformations or to randomly distributed hereditary telangiectases and should be recognized as a separate entity.

[A new oncogenetic service of counseling and diagnosing for hereditary non-polyposis colorectal cancer (HNPCC)].

BACKGROUND: Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant cancer predisposition syndrome associated with a high risk for colorectal cancer (up to 80%), endometrial cancer (up to 60%), and increased risk for other malignancies, mostly ovarian and urinary system tumors. HNPCC is caused by a germline mutation in one of the mismatch repair (MMR) genes, mainly hMLH1, hMSH2 and hMSH6. The tumors present with microsatellite instability (MSI) associated with loss of heterozygosity of the affected gene, and with loss of expression of the gene product. Diagnosis of HNPCC involves tumor testing for MSI, immunohistochemistry staining and germ line mutation analysis of the suspected gene. Proper genetic counseling is based on the synthesis of the clinical, pathological and molecular data. Directed surveillance shows significant reduction in colon cancer incidence, cancer mortality and overall mortality among HNPCC patients. GOAL: To establish a multidisciplinary service for patients suspected of having HNPCC. METHODS: We have established a service which is based on tight collaboration between clinical departments and laboratories. The clinical work-up was conducted by a special oncogenetic clinic and the laboratory service consisted of tissue testing for MSI and immunohistochemistry, denaturing high performance liquid chromatography (DHPLC) for suspected genes, and mutation testing. RESULTS: The efficiency of detection of patients with HNPCC was high, completed in a multistep process. In the first year of our collaborative work, we have provided genetic counseling to over 100 families and performed suitable tests for 46 families. Among them we have identified more than 16 families with HNPCC; 4 showed absence of hMLH1, 1 showed absence of hMSH6, and 11 showed absence of hMSH2. All tumors that showed MSI also showed absence of either one of the three MMR proteins. We present the clinical, pathological and molecular features of our patients and discuss the implication of this data on future recommendations.

Hereditary spastic paraplegia with thin corpus callosum: reduction of the SPG11 interval and evidence for further genetic heterogeneity.

BACKGROUND: Hereditary spastic paraplegia (HSP) with thin corpus callosum (TCC) is an autosomal recessive form of complicated HSP mainly characterized by slowly progressive spastic paraparesis and mental deterioration beginning in the second decade of life. The locus for HSP-TCC, designated SPG11, was mapped to chromosome 15q13-15 in some of the affected families from Japan, Europe, and North America, spanning an interval of 17.5 megabases (Mb). OBJECTIVE: To perform a clinical and genetic study of HSP-TCC. DESIGN AND SETTING: Case series; multi-institutional study. PATIENTS: Seven patients with HSP-TCC who belong to 3 consanguineous families of Arab origin residing in Israel. RESULTS: The 7 patients manifested a relatively similar combination of adolescence-onset cognitive decline and spastic paraparesis with TCC on brain magnetic resonance imaging. After excluding the SPG7 locus, we tested the 3 families for linkage to the SPG11, SPG21/MAST, and ACCPN loci associated with autosomal recessive disorders with TCC. Two families showed evidence for linkage to SPG11 (Z(max) = 5.55) and reduced the candidate region to 13 Mb. CONCLUSIONS: Our findings in HSP-TCC further confirm its worldwide distribution and genetic heterogeneity, and they significantly reduce the candidate SPG11 interval.

An Ashkenazi founder mutation in the PKHD1 gene.

Autosomal recessive polycystic kidney disease (ARPKD) is usually detected late in pregnancies in embryos with large echogenic kidneys accompanied by oligohydramnios. Hundreds of private pathogenic variants have been identified in the large PKHD1 gene in various populations. Yet, because of the large size of the gene, segregation analysis of microsatellite polymorphic markers residing in the PKDH1 locus has commonly been utilized for prenatal diagnosis. Keeping in mind the limitations of this strategy, we utilized it for testing 7 families with affected fetuses or newborns, of which in 5 at least one parent was Ashkenazi, and identified that the same haplotype was shared by the majority of the Ashkenazi parents (7/9). This led us to suspect that they carry the same founder mutation. Whole Exome analysis of DNA from a fetus of one of the families detected an already known pathogenic variant c.3761_3762delCCinsG, an indel variant resulting in frameshift (p.Ala1254GlyfsX49). This variant was detected in 9 parents (5 families), of them 7 individuals were Ashkenazi and one Moroccan Jew who shared the same haplotype, and one Ashkenazi, who carried the same variant on a recombinant haplotype. Screening for this variant in 364 Ashkenazi individuals detected 2 carriers. These findings suggest that although c.3761_3762delCCinsG is considered one of the frequent variants detected in unrelated individuals, and was thought to have occurred independently on various haplotypes, it is in fact a founder mutation in the Ashkenazi population.

Early clinical heterogeneity in choreoacanthocytosis.

BACKGROUND: Choreoacanthocytosis (CHAC) is a slowly progressive multisystem disorder with involuntary movements, cognitive decline, behavioral changes, seizures, and polyneuropathy caused by mutations in the VPS13A gene. OBJECTIVE: To describe the early clinical features and possible genotype-phenotype correlation in CHAC. DESIGN AND SETTING: Case series in a tertiary care center. PATIENTS AND MAIN OUTCOME METHODS: Choreoacanthocytosis was diagnosed in 3 patients of Jewish origin from 3 unrelated families. We reviewed their medical histories and performed molecular analysis by screening all 73 exons of VPS13A. RESULTS: Trichotillomania, hypertrophic cardiomyopathy, and idiopathic hyperCKemia, in 1 patient each, preceded the development of the full clinical spectrum of CHAC by 2 to 20 years. At diagnosis, 2 patients manifested signs of overt neuromuscular involvement and were homozygous for the 6059delC mutation, whereas 1 patient had only hyporeflexia and was homozygous for the EX23del mutation. Because only 1 of the 2 patients with 6059delC had cardiomyopathy, its relevance to CHAC is unclear. CONCLUSIONS: These findings extend the knowledge of significant early clinical heterogeneity in CHAC and suggest a possible genotype-phenotype correlation. Awareness of the early manifestations may prevent misdiagnosis and enable appropriate genetic counseling.

Genetic screening in patients with Retinoblastoma in Israel.

Retinoblastoma (Rb) is a childhood tumor (~1 in 20,000 live births) developing in the retina due to mutations in the RB1 gene. Identification of the oncogenic mutations in the RB1 gene is important for the clinical management and for genetic counseling to families with a child or a parent affected with the tumor. Here we present our experience in detecting the pathogenic mutations in blood samples, from 150 unrelated Rb patients and highlight the relevant counseling issues. Mutation screening in the RB1 gene was based on Sanger sequencing, mosaicism of recurrent CpG transition mutations was detected by allele specific PCR and multiplex ligation dependent probe amplification for detecting of large deletions/duplications. The overall detection rate of mutations in our cohort was 55% (82/150). In the familial cases it was 100% (17/17), in bilateral and unilateral-multifocal sporadic cases 91% (50/55), and in the unilateral sporadic cases 19% (15/78). Nonsense mutations and small deletions or insertions that results in transcripts with premature termination codons that are subject to nonsense mediated decay were the most frequent, detected in 50/82 (61%) of the patients. The rest were large deletions detected in 14/82 (17%), splice site mutations detected in 11/82 (13%), missense mutations in four patients and mutations in the promoter sequence in three patients. Mutation mosaicism ranging from 10 to 30% was detected by allele specific PCR in ten patients, 9% (5/55) of patients with bilateral tumor and 33% (5/15) of the patients with unilateral tumor. In three patients rare variants were detected as the only finding which was also detected in other healthy family members. Allele specific amplification of recurrent mutations raises in our cohort the identification rate from 82 to 91% in the sporadic bilateral cases and from 13 to 19% in the unilateral sporadic cases. Most mosaic cases could not be identified by Sanger sequencing and therefore screening for recurrent CpG transition mutations by allele specific amplification is of utmost importance. Molecular screening is important for the genetic counseling regarding the risk for tumor development and the relevance for prenatal diagnosis but in several families is accompanied by detecting rare variants that might be rare polymorphisms or low penetrant mutations.