Ellen Taub

Fragile-X Carrier Screening and the Prevalence of Premutation and Full-Mutation Carriers in Israel

Fragile-X syndrome is caused by an unstable CGG trinucleotide repeat in the FMR1 gene at Xq27. Intermediate alleles (51-200 repeats) can undergo expansion to the full mutation on transmission from mother to offspring. To evaluate the effectiveness of a fragile-X carrier-screening program, we tested 14,334 Israeli women of child-bearing age for fragile-X carrier status between 1992 and 2000. These women were either preconceptional or pregnant and had no family history of mental retardation. All those found to be carriers of premutation or full-mutation alleles were offered genetic counseling and also prenatal diagnosis, if applicable. We identified 207 carriers of an allele with >50 repeats, representing a prevalence of 1:69. There were 127 carriers with >54 repeats, representing a prevalence of 1:113. Three asymptomatic women carried the fully mutated allele. Among the premutation and full-mutation carriers, 177 prenatal diagnoses were performed. Expansion occurred in 30 fetuses, 5 of which had an expansion to the full mutation. On the basis of these results, the expected number of avoided patients born to women identified as carriers, the cost of the test in this study (U.S.

The CC2D1A, a member of a new gene family with C2 domains, is involved in autosomal recessive non-syndromic mental retardation

100), and the cost of lifetime care for a mentally retarded person (>

Mutated nup62 causes autosomal recessive infantile bilateral striatal necrosis

350,000), screening was calculated to be cost-effective. Because of the high prevalence of fragile-X premutation or full-mutation alleles, even in the general population, and because of the cost-effectiveness of the program, we recommend that screening to identify female carriers should be carried out on a wide scale.

Diagnostic utility of array‐based comparative genomic hybridization (aCGH) in a prenatal setting

Background: The molecular basis of autosomal recessive non-syndromic mental retardation (NSMR) is poorly understood, mostly owing to heterogeneity and absence of clinical criteria for grouping families for linkage analysis. Only two autosomal genes, the PRSS12 gene on chromosome 4q26 and the CRBN on chromosome 3p26, have been shown to cause autosomal recessive NSMR, each gene in only one family. Objective: To identify the gene causing autosomal recessive NSMR on chromosome 19p13.12. Results: The candidate region established by homozygosity mapping was narrowed down from 2.4 Mb to 0.9 Mb on chromosome 19p13.12. A protein truncating mutation was identified in the gene CC2D1A in nine consanguineous families with severe autosomal recessive NSMR. The absence of the wild type protein in the lymphoblastoid cells of the patients was confirmed. CC2D1A is a member of a previously uncharacterised gene family that carries two conserved motifs, a C2 domain and a DM14 domain. The C2 domain is found in proteins which function in calcium dependent phospholipid binding; the DM14 domain is unique to the CC2D1A protein family and its role is unknown. CC2D1A is a putative signal transducer participating in positive regulation of I-κB kinase/NFκB cascade. Expression of CC2D1A mRNA was shown in the embryonic ventricular zone and developing cortical plate in staged mouse embryos, persisting into adulthood, with highest expression in the cerebral cortex and hippocampus. Conclusions: A previously unknown signal transduction pathway is important in human cognitive development.

Genetic screening for autosomal recessive nonsyndromic mental retardation in an isolated population in Israel

The objective of this study was to identify the gene causing autosomal recessive infantile bilateral striatal necrosis.

Genetic carrier screening for spinal muscular atrophy and spinal muscular atrophy with respiratory distress 1 in an isolated population in Israel.

Array‐based comparative genomic hybridization (aCGH) is a new technique for detecting submicroscopic deletions and duplications. There is limited information regarding its use in the prenatal setting. Here, we present our experience of 269 prenatal aCGHs between 2006 and 2009.

Low Estriol Levels in the Maternal Triple-Marker Screen as a Predictor of Isolated Adrenocorticotropic Hormone Deficiency Caused by a New Mutation in the TPIT Gene

Nonsyndromic mental retardation (NSMR) is the diagnosis of exclusion in mentally retarded individuals without additional abnormalities. We have recently identified a protein-truncating mutation, G408fsX437, in the gene CC2D1A on chromosome 19p13.12 in nine consanguineous Israeli Arab families with severe autosomal recessive NSMR, and have developed a comprehensive prevention program among the at-risk population in the village. The subjects tested were healthy women who were invited to undergo the genetic screening test as a part of their routine pregnancy monitoring. One hundred and seventeen subjects reported a family history positive for mental retardation. We tested 524 pregnant or preconceptional women and found 47 carriers (∼1/11), whose spouses were then recommended to undergo testing. We identified eight carrier couples, who were given genetic counseling and offered prenatal diagnosis. Of all the marriages, 28.6% were consanguineous; 16.5% of the total were between first cousins. The high prevalence of the mutation can be explained both by the founder effect owing to the generally high consanguinity rate among the inhabitants of the village, and also because two families with excessive numbers of mentally retarded offspring were unacceptable as marriage partners by the rest of the families. This is the first example of the establishment of a large-scale genetic screening program for autosomal recessive NSMR, which was made possible owing to the high frequency of the specific causative mutation in this isolated population.

Increased transmission of intermediate alleles of the FMR1 gene compared with normal alleles among female heterozygotes

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by progressive muscle weakness. It is caused by a mutation in the survival motor neuron gene 1 (SMN1) gene. SMA with respiratory distress 1 (SMARD1), an uncommon variant of infantile SMA also inherited in an autosomal recessive manner, is caused by mutations in the immunoglobulin mu-binding protein 2 (IGHMBP2) gene. We carried out genetic carrier screening among the residents of an isolated Israeli Arab village with a high frequency of SMA in order to identify carriers of SMA type I and SMARD1. During 2006, 168 women were tested for SMA, of whom 13.1% were found to be carriers. Of 111 women tested for SMARD1, 9.9% were found to be carriers. Prenatal diagnosis was performed in one couple where both spouses were carriers of SMARD1; the fetus was found to be affected, and the pregnancy was terminated. To the best of our knowledge, this is the first example of the establishment of a large-scale carrier-screening program for SMA and SMARD1 in an isolated population. SMA has a carrier frequency of 1:33-1:60 in most populations and should be considered for inclusion in a population-based genetic-screening program.

Prenatal diagnosis in Li-Fraumeni syndrome.

Isolated adrenocorticotropic hormone (ACTH) deficiency (IAD) is a rare cause of adrenocortical insufficiency, especially in children, and may be an underestimated cause of neonatal death. Early postnatal diagnosis may prevent hypoglycemic seizures, Addisonian crises, and death. There are also occasional reports of prenatal diagnosis of IAD by findings on the maternal triple-marker screen (TMST), a combined serum analyte test that measures levels of α-fetoprotein, human chorionic gonadotropin, and unconjugated estriol for the detection of Down syndrome and open neural-tube defects. An isolated low estriol level is usually correlated with compromised uteroplacental perfusion and frequently associated with fetal death. A low estriol level in the context of normal fetal sonography and growth, after exclusion of placental sulfatase deficiency and Smith-Lemli-Opitz syndrome, should raise the suspicion of deficient fetal steroidogenesis, which leads to decreased production of adrenal dehydroepiandrosterone sulfate. We describe 2 brothers with adrenal insufficiency resulting from IAD. The parents are first cousins whose first son is healthy. During the pregnancy of the second son, who died at the age of 7 weeks as a result of presumed cardiomyopathy, a low estriol level on the TMST was ignored because of a normal fetal ultrasound. In the third pregnancy, a low level was found again, and the mother was referred to our tertiary center. Ultrasonography revealed no abnormalities, and karyotype was normal. Normal levels of steroid sulfatase activity and 7-dehydrocholesterol ruled out X-linked ichthyosis and Smith-Lemli-Opitz syndrome, respectively. Postnatally, basal and stimulated cortisol and ACTH levels were low. Other pituitary functions were normal, suggesting the diagnosis of IAD. The patient was treated with a stress dose of hydrocortisone on day 2 of life, which was tapered to a maintenance dose. At the time of this writing, he was 7 months old, with normal growth and development. Recently, loss-of-function mutations in the human TPIT gene were detected in autosomal recessive IAD. TPIT is a cell-restricted T-box transcription factor that is important for the terminal differentiation of pituitary corticotrophs. Therefore, we performed molecular analysis of the TPIT gene, which revealed a new mutation (IVS4+1G>A) that affects the first nucleotide of the splice site at the 5′ end of the fourth intron. This stop codon probably leads to loss of TPIT function by nonsense-mediated mRNA decay, as it does for other TPIT nonsense mutations. We recommend that pregnant women with an isolated low estriol level of unexplained etiology be referred for additional evaluation by a multidisciplinary team that includes a geneticist and pediatric endocrinologist. Prompt ACTH testing in the first postnatal days will allow for early diagnosis. The immediate institution of glucocorticoid therapy, with proper instructions for stress management, can prevent unnecessary neonatal death secondary to an easily treatable disease.

New syndrome of simplified gyral pattern, micromelia, dysmorphic features and early death

Fragile X syndrome (Fra X) is the most common heritable disease accounting for mental retardation and is caused by an expanded CGG repeat in the first exon of the FMR1gene. Previous studies have shown an increased fertility rate among fragile X carrier mothers and a preponderance of mentally retarded boys among the male offspring. In this study, we examined the transmission of the intermediate allele in the lower range of CGG repeats in carrier mothers found randomly in a screening program of the normal population. We tested 10,587 healthy women with no family history of mental retardation and identified 138 (1.3%) who were carriers of the intermediate allele (51-200 CGG repeats). Of these, 107 underwent prenatal testing during 108 pregnancies for Fra X in the fetus. Of the 108 pregnancies, the abnormal allele was transmitted in 67 (segregation ratio = 0.62, P < 0.012). We found a significant increase in the transmission of the abnormal allele by mothers who had between 51 and 60 repeats (segregation ratio = 0.69 [P < 0.007] for the group with 51-55 repeats, and 0.74 [P < 0.04] for the group with 56-60 repeats), but no increase by mothers who had more than 61 repeats. This suggests a genetic advantage for the abnormal allele in the 51- to 60-repeat range.