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Tay-Sachs disease (TSD) is an autosomal recessive lysosomal storage disorder caused by mutations of the HEXA gene resulting in the deficiency of hexosaminidase A (Hex A) and subsequent neuronal accumulation of G M2 gangliosides. Infantile TSD is a devastating and fetal neurodegenerative disease with death before the age of 3-5 years. A small proportion of TSD patients carry milder mutations and may present juvenile or adult onset milder disease. TSD is more prevalent among Ashkenazi Jewish (AJ) individuals and some other genetically isolated populations with carrier frequencies of approximately ~1:27 which is much higher than that of 1:300 in the general population. Carrier screening and prenatal testing for TSD are effective in preventing the birth of affected fetuses greatly diminishing the incidence of TSD. Testing of targeted HEXA mutations by genotyping or sequencing can detect 98% of carriers in AJ individuals; however, the detection rate is much lower for most other ethnic groups. When combined with enzyme analysis, above 98% of carriers can be reliably identified regardless of ethnic background. Multiplex PCR followed by allele-specific primer extension is one method to test for known and common mutations. Sanger sequencing or other sequencing methods are useful to identify private mutations. For prenatal testing, only predefined parental mutations need to be tested. In the event of unknown mutational status or the presence of variants of unknown significance (VUS), enzyme analysis must be performed in conjunction with DNA-based assays to enhance the diagnostic accuracy. Enzymatic assays involve the use of synthetic substrates 4-methylumbelliferyl-N-acetyl-β-glucosamine (4-MUG) and 4-methylumbelliferyl-6-sulfo-2-acetamido-2-deoxy-β-D-glucopyranoside (4-MUGS) to measure the percentage Hex A activity (Hex A%) and specific Hex A activity respectively. These biochemical and molecular tests can be performed in both direct specimens and cultured cells from chorionic villi sampling or amniocentesis.

Internationally, Tay-Sachs disease (TSD) preconception screening of Ashkenazi Jewish (AJ) individuals and couples has led to effective primary prevention of TSD. In Australia, adolescent preconception genetic screening programs operate mainly in Jewish community high schools. These existing programs offer an effective means of primary prevention of TSD, are cost effective and safe. However, in the broader Australian community TSD screening is not systematically performed and cases still occur in unscreened AJ individuals. In order to improve the effectiveness of Australian screening, there is a need for definitive guidelines for healthcare professionals to facilitate extension of the proven benefits of preconception TSD screening to all AJ individuals at risk. We performed a systematic review of the relevant literature relating to AJ pre-conception and antenatal screening for TSD. The evidence was assessed using an established National Health and Medical Research Council evidence grading system. Evaluations of efficacy of TSD screening programs design and execution, cost-benefit and cost-utility health economic evaluation, and population outcomes were undertaken. The results have been used to propose a model for universal AJ TSD preconception and antenatal screening for the primary care setting., (© 2014 The Authors. Journal of Paediatrics and Child Health © 2014 Paediatrics and Child Health Division (Royal Australasian College of Physicians).)

Tay-Sachs disease is an autosomal recessive storage disease caused by the impaired activity of the lysosomal enzyme hexosaminidase A. In this fatal disease, the sphingolipid GM2 ganglioside accumulates in the neurons. Due to high carrier rates and the severity of the disease, population screening and prenatal diagnosis of Tay-Sachs disease are routinely carried out in Israel. Laboratory diagnosis of Tay-Sachs is carried out with biochemical and DNA-based methods in peripheral and umbilical cord blood, amniotic fluid, and chorionic villi samples. The assay of hexosaminidase A (Hex A) activity is carried out with synthetic substrates, 4-methylumbelliferyl-6-sulfo-N-acetyl-beta-glucosaminide (4-MUGS) and 4-methylumbelliferil-N-acetyl-beta-glucosamine (4-MUG), and the DNA-based analysis involves testing for the presence of specific known mutations in the alpha-subunit gene of Hex A. Prenatal diagnosis of Tay-Sachs disease is accomplished within 24-48 h from sampling. The preferred strategy is to simultaneously carry out enzymatic analysis in the amniotic fluid supernatant or in chorionic villi and molecular DNA-based testing in an amniotic fluid cell-pellet or in chorionic villi.

The number of prenatal genetic tests that are being offered to women is constantly increasing. However, there is little national data as to who is performing the tests and the reasons for doing or not doing so. This study evaluated the proportion of Jewish women in Israel who perform the various prenatal genetic tests and the factors affecting the performance of these tests. It was found that 60.9% of the women performed the triple test, 50.8% of women older than 35 years performed amniocentesis, while 63.3 and 24.3% of women performed Tay-Sachs and fragile-X carrier testing respectively. Ninety-six percent of the secular women compared to only 6.7% of the ultrareligious women performed the triple test. It was also found that94.4% of the secular women, 36.4% of the religious, and none of the ultrareligious women older than 35 years performed amniocentesis. In the stepwise regression analysis, being secular, having a higher income, fewer children, and being of Ashkenazi origin remained significant factors in determining performance of Tay-Sachs carrier testing. As regards fragile-X carrier testing, being secular, having fewer than four children, and having a higher income and a supplementary medical insurance remained significant factors. The main reason reported by the women for not performing amniocentesis or the triple test was for religious or moral grounds (53.3 and 67% respectively). The main reason given for not performing Tay-Sachs or fragile-X testing was that they were not referred for the tests (76 and 82% respectively). Consideration should be given to providing first trimester prenatal diagnosis to the ultrareligious group, including state subsidized fragile-X testing and educating the primary care givers about the importance of prenatal genetic testing. The information from the present study is vital for the planning of an equitable prenatal genetic service and provides guidelines for the implementation of such services in other countries., (Copyright 2003 Wiley-Liss, Inc.)

Carrier testing for Tay-Sachs disease should be offered to couples when at least one individual is of Ashkenazi Jewish (carrier frequency 1/30), Pennsylvania Dutch, Southern Louisiana Cajun, or Eastern Quebec French Canadian descent. Ideally, testing is done prior to conception. For Ashkenazi Jews, in whom DNA testing identifies 99.9% of carriers, DNA testing is the preferred method to ascertain carriers [14]. For non-Jewish individuals seeking carrier testing, enzyme assay should be done initially and positive or indeterminate results should be confirmed by DNA mutation analysis. If only one partner is descended from a high-risk group, that person should be tested first; only if he/ she is a carrier should the other partner be tested. If the couple is pregnant at the time carrier testing is requested, both partners should have enzyme testing (leukocyte assay for the pregnant woman and serum assay for the father) and DNA testing sent concomitantly to expedite counseling and action. Carriers are individuals with a disease causing DNA mutation or carrier range enzyme analysis results on both serum and leukocytes with no detectable mutation and no pseudodeficiency alleles. Noncarriers are individuals with normal enzyme results or carrier range enzyme results and a pseudodeficiency allele on DNA mutation analysis. If both partners are found to be carriers they should be counseled of a 25% risk of having an affected child with each pregnancy. Options to modify this risk include prenatal diagnosis by amniocentesis or chorionic villus sampling, egg or sperm donation, preimplantation diagnosis or adoption.

Background: Tay-Sachs disease has been reported to be more prevalent in the Cajun population of Louisiana., Methods: Questionnaires were mailed to 744 obstetricians; 151 responded., Results: Of the 151 responding physicians, 95 (63%) reported that they do not routinely screen their prenatal patients for Tay-Sachs disease. Of the 52 responding obstetricians in New Orleans, 29 (58%) offer screening; 8 of 23 obstetricians (32%) in Acadiana (southwest Louisiana) and 19 of 72 (27%) of the remaining Louisiana obstetricians routinely screen their patients. Of 46 obstetricians in practice less than 10 years, 22 (48%) offer screening; of 105 in practice longer, 35 (33%) offer screening. Of 100 obstetricians trained in Louisiana, 32 (32%) offer screening, compared with 25 of 51 (49%) of those trained elsewhere., Conclusions: Most practicing obstetricians in Louisiana are not routinely offering Tay-Sachs screening to their prenatal patients. Screening may depend on location of practice, duration of practice, and place of training.

Tay-Sachs disease (TSD) is caused by mutation of the HEXA gene, which results in a deficiency of the alpha-subunit of hexosaminidase A. The major mutation in Japanese TSD is a G-to-T transversion at the 3'-splice site of intron 5. We established a fluorescent competitive allele-specific polymerase chain reaction (FCAS-PCR) method for detection of the mutation and applied it to prenatal diagnosis of a Japanese TSD family. FCAS-PCR distinguished the wild and mutant alleles clearly, with broad ranges in the amount of template DNA, the dNTP concentration, the MgCl2 concentration and the number of PCR cycles. After obtaining ethics committee approval and informed consent from the parents in the index family, chorionic villus sampling was performed. FCAS-PCR analysis using chorionic villus DNA disclosed that the fetus was homozygous for the mutation. To confirm the diagnosis, direct sequencing analysis of the genomic PCR fragment was performed, and showed the same results as those of the FCAS-PCR analysis. FCAS-PCR proved to be helpful for carrier screening and prenatal diagnosis in TSD families in the Japanese population. It would also be a useful DNA-diagnostic method for many other inherited disorders.

Preimplantation polar body diagnosis makes it possible to detect and avoid genetic and chromosomal disorders before pregnancy. We have shown that the polar body biopsy does not affect fertilization and viability of the resulting embryos. Our present experience of polar body diagnosis includes 187 clinical cycles, performed for preimplantation diagnosis of cystic fibrosis, alpha-1-antitrypsin deficiency, Tay-Sach's disease, retinitis pigmentosa, hemophilia A, Alport and sickle cell disease, and common aneuploidy, using the FISH technique. Over three-quarters of these cycles have resulted in embryo transfer, 38 in clinical pregnancy and 12 in the birth of an unaffected child. The present review describes the results of our clinical trial on the polar body diagnosis of genetic and chromosomal disorders, demonstrating the reliability of polar body genetic analysis for preimplantation diagnosis.

Purpose: The purpose was to evaluate methods of DNA preparation in a single cell to determine the ability to amplify and correctly diagnose a targeted gene., Methods: One- or two-cell lymphoblasts (n = 100/group), heterozygous for the normal and 4-base pair insertion on exon 11 of the beta-hexosaminidase A gene, were collected and prepared under the following conditions: (1) freeze-thaw liquid nitrogen, then boiling (LN2); (2) potassium hydroxide/dithiothreitol, heated to 65 degrees C, followed by acid neutralization (KOH); (3) boiling only (Bl); and (4) water only (H2O). Cells were analyzed by polymerase chain reaction using nested primers., Results: The total number of cells amplifying [in brackets] and the cells with amplification for both alleles (heterozygous), the normal allele, or the mutant allele were as follows, respectively: LN2 [38], 11, 16, 11; KOH [97], 91, 5, 1; Bl [41], 17, 13, 11; and H2O [85], 41, 16, 28. With two cells per reaction tube the results were as follows: LN2 [85], 53, 14, 18; and KOH [97], 96, 1, 0., Conclusions: KOH lysis was significantly greater than with all other methods (P < 0.006) and should be used for single cells. This study also demonstrates the importance of using heterozygous cells to determine the ability to amplify both alleles as a method of quality control for single-cell analysis.

Tay-Sachs disease is a lysosomal storage disease, which in its most severe form leads inexorably to death during infancy. We have developed a method for preimplantation diagnosis, using polymerase chain reaction (PCR) technology, by which the two most frequent mutations occurring in this disease can be amplified simultaneously. We have tested this method on single blastomeres and have compared four lysis methods: (i) boiling in water at 94 degrees C for 15 or (ii) 30 min, and (iii) incubation in an alkaline lysis buffer for 30 min at 94 degrees C or (iv) at 65 degrees C for 10 min. The amplification percentages were 21, 67, 71 and 91% respectively.

Assay of hexosaminidase A and B enzymes in four cases with developmental regression and cherry red spot on fundus examination confirmed that three cases had Tay-Sachs disease, and one case had Sandhoff disease. Prenatal diagnosis was carried out by hexosaminidase enzyme assay in amniotic fluid and cells in one family, and chorionic villus sample in the second family. The fetus was diagnosed to be unaffected in one, and affected in the other family. Assay of hexosaminidase A and B is useful for specific diagnosis of GM2 gangliosidosis, and for prenatal diagnosis to reduce the burden of these disorders.

Prenatal diagnosis in a pregnancy at risk for a juvenile B1 variant of GM2-gangliosidosis was carried out. The biochemical study of the cultured amniocytes and the affected fetal brain is reported. The results obtained show that the sulphated artificial substrate can be used in the diagnosis of B1 variant, but not the neutral one. The accumulation of GM2-ganglioside in the fetal brain of the B1 juvenile form and an infantile form of GM2-gangliosidosis (0 variant) was compared.

Objectives: Our purpose was to identify and evaluate practical methods within a preimplantation genetic diagnosis program that will increase the percentage of embryos for which a genetic diagnosis can be obtained, including clinical responses after failure of deoxyribonucleic acid amplification has occurred., Study Design: Known human lymphoblast cell lines and human embryo blastomeres were evaluated in a single-cell, nested primer polymerase chain reaction system with primer sequences for the specific locus surrounding the four base pair insertion mutation on exon 11 of beta-hexosaminidase A-Tay-Sachs disease, the delta F508 mutation of cystic fibrosis, and the sex-determining region on the Y chromosome. Reamplification polymerase chain reaction with standard polymerase chain reaction and primer extension preamplification was performed in deoxyribonucleic acid preparations after previous polymerase chain reaction amplification attempts had resulted in failure of amplification., Results: The amplification efficiency of Tay-Sachs disease, 51% (97/187), was significantly lower than that for cystic fibrosis, 85% (87/107), and for the sex-determining region on the Y chromosome, 85% (77/90). Tay-Sachs disease polymerase chain reaction amplification occurred in 51% of one-cell lymphoblasts, 89% of two-cell lymphoblasts, and 94% of samples when more than two cells were processed together. When previous amplification failure had occurred, standard Tay-Sachs disease polymerase chain reaction resulted in an amplification efficiency of 16% (three of 19), whereas primer extension preamplification polymerase chain reaction for Tay-Sachs disease resulted in amplification of 52% (31/59) lymphoblasts and 54% (13/24) of polyspermic human blastomeres. Four of six human blastomeres in which amplification failure occurred in a Tay-Sachs disease preimplantation genetic diagnosis cycle amplified by primer extension preamplification polymerase chain reaction, which increased the diagnostic information obtained from four to six of the seven embryos on which biopsy was performed., Conclusions: We suggest that practical approaches for consideration within a clinical preimplantation genetic diagnosis program to limit the net effect of amplification failure (i.e., reduced embryo transfer number) include increasing the deoxyribonucleic acid content in the polymerase chain reaction tube by using more than one blastomere and by using primer extension preamplification when the initial attempt at amplification fails.

A confocal laser scanning microscopic system was used to detect the storage of ganglioside GM2 in Tay-Sachs fibroblasts and amniocytes. The diagnosis of the disease was confirmed by counting immunoreactive cells or by digital imaging analysis. This novel system facilitates the prenatal diagnosis of GM2-gangliosidosis.

Objective: To demonstrate the use of the polymerase chain reaction in the amplification of deoxyribonucleic acid (DNA) from single human lymphoblasts and mouse blastomeres. Amplified target genes for diagnosis of sickle cell anemia and Tay-Sachs are shown. Similarly, the sparce fur mouse model for ornithine transcarbamylase deficiency was used as an X-linked system for demonstration of mutation detection after biopsy of a single blastomere. A new diagnostic method for the detection of the ornithine transcarbamylase mutation using the restriction enzyme Mse I is presented. Accuracy and reproducibility were assured., Design: Polymerase chain reaction proficiency test for amplification from single cells was studied. Also, accuracy of mutation detection systems was demonstrated., Setting: Laboratories of The Jones Institute for Reproductive Medicine, Department of Obstetrics and Gynecology, Eastern Virginia Medical School., Patients, Participants: We used the sparse fur mouse model and human blood cells., Interventions: Pre-embryo biopsy, polymerase chain reaction amplification, and mutation detection were performed., Main Outcome Measures: Accuracy and reproducibility of DNA amplification without contamination, as well as efficient diagnostic analysis, from both single somatic and embryonic cells were shown., Results: DNA amplification from single cells was uniformly rapid (6 to 10 hours) reproducible (n = 220) and accurate (n = 52)., Conclusions: Our findings support the feasibility of clinical application for pre-embryo biopsy and genetic diagnosis of specific heritable diseases.

Uncultured and cultured embryonic trophoblastic tissue obtained by chorionic villus sampling (CVS) displays enzyme activity towards 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranosyl-6-sulfate (MUGS), a specific substrate for Hexosaminidase A (Hex A), the enzyme deficient in Tay-Sachs disease (TSD). Specific activity is comparable to that found in cultured amniocytes and fibroblasts. The enzyme activity has a pH optimum of 4.1 and an apparent Km of 6 x 10(-4) mol/L. Thirteen pregnancies in eight families at risk for TSD were monitored by CVS using MUGS as the Hex A substrate. Four fetuses were proven affected by enzyme analysis of fetal tissues and cultured fetal fibroblasts obtained at the time of termination of the pregnancies. Nine fetuses were judged to be unaffected. Eight babies were clinically normal while the other pregnancy is continuing. The use of MUGS as substrate for Hex A makes prenatal diagnosis by CVS of families at risk for TSD simple, direct and accurate.

Prenatal diagnosis of Tay-Sachs disease was performed using the sulphated substrate 4-methylumbelliferyl-6-sulpho-2-acetamido-2-deoxy-beta-D-glucopyranoside to detect hexosaminidase A in chorionic villi. The presence or absence of hexosaminidase A in villi was detected by both a quantitative enzyme assay, and by a rapid, novel procedure which permitted visual discrimination between normal and affected villi.

Amniocentesis and subsequent tests are reported on a fetus conceived of a rare mating type: its mother has an intermediate level of beta hexosaminidase A (HEX A), characteristic of carriers of Tay-Sachs disease (TSD), while the father suffers from an adult-onset GM2 gangliosidosis (AOG) with severe HEX A deficiency. Activity of HEX A in the cultured fetal cells was very low when measured by the heat-inactivation method, thus showing the typical biochemical phenotype of TSD fetuses. However, upon separation of HEX isozymes by ion exchange chromatography, residual HEX A (17 per cent of total HEX) was demonstrated. Also in contrast to TSD fetuses, this fetus' fibroblasts were able to synthesize the precursor of alpha chains of HEX, and ultrastructural examination of its brain revealed few atypical lamellar bodies, unlike those found in TSD fetuses of the same gestational age. It is therefore concluded that the fetus was not affected with TSD, but rather with AOG.

Addition of serum derived from amniotic fluid cells (AFS) from Tay Sachs carrier to developing mouse cerebral cortex explants results in excessive accumulation of lipid in neuronal cytoplasm.

A large number of chorionic villi samples obtained from women undergoing elective first trimester termination of pregnancy was analysed by enzyme assays similar to those applied to cultured amniotic cells. The levels of 15 lysosomal enzymes were compared to those observed in tissue cultures of amniotic cells obtained through amniocentesis at 16-18 weeks of pregnancy and the results were discussed in order to assess the usefulness of trophoblast biopsy for first trimester diagnosis of hereditary lysosomal diseases. The data suggest the applicability of this source of fetal cells for prenatal diagnosis of fifteen respective genetically determined enzyme deficiencies with the probable exception of alpha-L-iduronidase deficiency. Enzyme determinations were performed on chorionic villi samples of two pregnancies at risk for Tay-Sachs disease, three pregnancies for GM1 gangliosidosis type 1, one for mucopolysaccharidosis type VI and one for Wolman's disease.

While there is no single best procedure for performing prenatal diagnosis, ther is a rationale or strategy which will produce correct, reliable results. The investigator should be experienced with all the tests and know what to expect from each. At least two of these tests should e used (more if there s ambiguity) on amniotic fluid and cultured cell extracts. Which tests, and how many, are not as important as the skill and experience of the investigator performing them. Proper controls should be used. Probably the biggest single factor in successful prenatal diagnosis is the use of both negative and positive controls run simultaneously. No method, no matter how good or how well performed, can be counted upon to give sufficiently reproducible results to interpret without these controls. Finally, it is necessary for the investigator to be thoroughly familiar with the enzyme and its isozymes and the clinical heterogeneity of the disease. Although the foregoing details pertain specifically to Tay-Sachs disease, similar or related problems exist in the prenatal diagnosis of any of the neurolipidoses. The need for care of the samples, appreciation of biochemical and clinical heterogeneity, the need for adequate techniques, and the importance of proper controls are requirements for diagnosing any of the neurolipidoses.

A method for preparing amniotic fluid cell culture has been developed. The optimal conditions for the culture involved the incubation period averaging 17.9 days. Normal activity values were obtained for 8 glycosidases whose deficiency is responsible for the development of hereditary accumulation diseases. The data obtained allow a prenatal diagnosis of glycolipidoses (Tay-Sachs, Fabrys, Gaucher's diseases, etc.). The evidence on prenatal diagnosis of Tay-Sach's disease is presented.

Prenatal diagnosis was carried out in 10 families suffering from lysosomal diseases: Tay-Sachs disease--5 families, Sandhoff disease--1 family, GM1-gangliosidosis--1 family and Hunter disease--3 families. Diagnosis of Tay-Sachs disease was excluded in fetuses of two families, Sandhoff disease--in one family, GM1-gangliosidosis--in one family, Hunter disease--in two families. Tay-Sachs disease was found in two fetuses and in one neonate. In two fetuses was found Hunter disease (twin pregnancy). The results of prenatal diagnosis were corroborated by postnatal studies of the neonates funicular blood and of autopsies of the aborted fetuses tissues. Application of several independent procedures for prenatal diagnosis of hereditary lysosomal diseases enabled to exclude erroneous diagnosis.

A case of infantile GM2 gangliosidosis with high residual beta-hexosaminidase A activity toward the synthetic substrate 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside was diagnosed prenatally. Extracts from cultured amniotic fluid cells of the fetus had a hexosaminidase A activity of 27% of total hexosaminidase but were almost completely unable to degrade [3H]ganglioside GM2 (less than 0.5% of control values) when assayed in the presence of the natural activator protein. These results were confirmed by analyses of fetal muscle fibroblasts, liver, and brain. All tissues examined showed a profound deficiency of ganglioside GM2 galactosaminidase despite hexosaminidase A levels in the heterozygote range. In brain tissue, ganglioside GM2 content was elevated more than 4-fold. Hydrolysis of p-nitrophenyl glucosaminide-6-sulfate, a substrate specific for hexosaminidases A and S, by tissue extracts was also markedly reduced but the residual activities found (5% in liver, 12% in fibroblasts, and 16% in brain) were much higher than those with the physiological lipid substrate, ganglioside GM2.

A preliminary report on the use of microtechniques for the detection of three lysosomal storage diseases (Tay-Sachs, GM1-gangliosidosis and Fabry disease) is presented. This microassay method uses from 100 to 300 cultured amniotic fluid cells or skin fibroblasts. A comparison between values for total activity and heat inactivated forms of hexosaminidase (in Tay-Sachs disease) is presented. The feasibility of the use of this microtechnique in prenatal diagnosis is discussed.

Hexosaminidase (Hex) A, B, and C/S were electrophoretically separated from cultured amniotic fluid cells, fetal brain, and white blood cells. Photographs of cellulose acetate zymograms were evaluated by reflectometric scanning. The usefulness and limitations of this rapid method were shown. Hex A was completely absent in the amniotic fluid cells of one out of three pregnancies at risk for Tay-Sachs disease, but Hex C/S was present in this case. The prenatal diagnosis of Tay-Sachs disease was made, and confirmed with the fetal material after abortion. Hex C/S was distinguishable from a residual or "heterozygous" Hex A activity. In the two other risk pregnancies, reflectometric Hex A activities were found to be 50 and 34% of control; the heterozygous stage was presumed for the fetuses.

Deficiency of glycosidases is a fundamental feature of the hereditary diseases of glycoconjugate accumulation. The data obtained on activity of glycosidases in cell culture of normal amnionic fluid might be used as standards in prenatal diagnostics of hereditary glycolipidoses and glycoproteinoses. Use of cell culture of amnionic fluid for prenatal diagnosis of Tay-Sachs disease is described.

Prenatal diagnosis for Tay-Sachs disease was performed on 25 patients using chorionic villus sampling (CVS). Nineteen were diagnosed as normal, and six were affected. Normal villus extracts had both hexosaminidase (hex) A and B activity, as determined by Cellogel and polyacrylamide gel electrophoresis, while extracts from affected fetuses had only hex B activity. Compared to cultured amniotic fluid cells or fibroblasts, villi contained less hex A. Hex A levels in fresh villi and cultured trophoblasts were roughly comparable.