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Purpose: Genomic test results, regardless of laboratory variant classification, require clinical practitioners to judge the applicability of a variant for medical decisions. Teaching and standardizing clinical interpretation of genomic variation calls for a methodology or tool., Methods: To generate such a tool, we distilled the Clinical Genome Resource framework of causality and the American College of Medical Genetics/Association of Molecular Pathology and Quest Diagnostic Laboratory scoring of variant deleteriousness into the Clinical Variant Analysis Tool (CVAT). Applying this to 289 clinical exome reports, we compared the performance of junior practitioners with that of experienced medical geneticists and assessed the utility of reported variants., Results: CVAT enabled performance comparable to that of experienced medical geneticists. In total, 124 of 289 (42.9%) exome reports and 146 of 382 (38.2%) reported variants supported a diagnosis. Overall, 10.5% (1 pathogenic [P] or likely pathogenic [LP] variant and 39 variants of uncertain significance [VUS]) of variants were reported in genes without established disease association; 20.2% (23 P/LP and 54 VUS) were in genes without sufficient phenotypic concordance; 7.3% (15 P/LP and 13 VUS) conflicted with the known molecular disease mechanism; and 24% (91 VUS) had insufficient evidence for deleteriousness., Conclusion: Implementation of CVAT standardized clinical interpretation of genomic variation and emphasized the need for collaborative and transparent reporting of genomic variation., Competing Interests: Conflict of Interest Julius O.B. Jacobsen and Damian Smedley are paid consultants to Congenica Ltd. All other authors declare no conflicts of interest., (Copyright © 2022 American College of Medical Genetics and Genomics. Published by Elsevier Inc. All rights reserved.)

Genome-wide sequencing (GWS) is a standard of care for diagnosis of suspected genetic disorders, but the proportion of patients found to have pathogenic or likely pathogenic variants ranges from less than 30% to more than 60% in reported studies. It has been suggested that the diagnostic rate can be improved by interpreting genomic variants in the context of each affected individual's full clinical picture and by regular follow-up and reinterpretation of GWS laboratory results. Trio exome sequencing was performed in 415 families and trio genome sequencing in 85 families in the CAUSES study. The variants observed were interpreted by a multidisciplinary team including laboratory geneticists, bioinformaticians, clinical geneticists, genetic counselors, pediatric subspecialists, and the referring physician, and independently by a clinical laboratory using standard American College of Medical Genetics and Genomics (ACMG) criteria. Individuals were followed for an average of 5.1 years after testing, with clinical reassessment and reinterpretation of the GWS results as necessary. The multidisciplinary team established a diagnosis of genetic disease in 43.0% of the families at the time of initial GWS interpretation, and longitudinal follow-up and reinterpretation of GWS results produced new diagnoses in 17.2% of families whose initial GWS interpretation was uninformative or uncertain. Reinterpretation also resulted in rescinding a diagnosis in four families (1.9%). Of the families studied, 33.6% had ACMG pathogenic or likely pathogenic variants related to the clinical indication. Close collaboration among clinical geneticists, genetic counselors, laboratory geneticists, bioinformaticians, and individuals' primary physicians, with ongoing follow-up, reanalysis, and reinterpretation over time, can improve the clinical value of GWS., Competing Interests: The authors declare no competing interests., (© 2022 The Authors.)

Many parents are motivated to pursue genome-wide (exome or genome) sequencing to find a diagnosis for their child with a suspected but undiagnosed genetic condition. However, the impact of the genomic test extends beyond the provision of results and the so-called 'diagnostic odyssey'. Our goal was to quantify post-test decisional regret and characterize long-term, post-test experiences and unmet needs of the parents of children with suspected genetic diseases after they had received the results of genome-wide sequencing. Study participants were parents of children who underwent trio genome-wide sequencing as part of the CAUSES research study at Children's & Women's Health Centre of British Columbia. About half of the participants received a definite or likely genetic diagnosis after clinical interpretation of the genome-wide sequencing results. Parents who participated in the current study (n = 121) completed the Decisional Regret Scale four weeks after receiving results. A subset of these parents (n = 32) had semi-structured interviews a median of 7 months (range 3-20 months) after results disclosure and post-test genetic counseling. Most parents expressed either no regret or mild regret about having undergone genome-wide sequencing on both the Decisional Regret Scale and in the interviews. Parents whose children did not receive a genetic diagnosis were slightly more likely to have decisional regret on this quantitative scale. Analysis of transcribed interviews revealed the following major themes: (a) a lack of decisional conflict around having the testing; (b) a lack of decisional regret post-testing; (c) expressions of both relief and continued uncertainty around the meaning of a genetic diagnosis; (d) expression of initial disappointment and evolving interpretation surrounding a result yielding no genetic diagnosis; and (e) needing time to absorb the test results. Our results suggest that parents need time to absorb the testing results and that long-term post-test counseling, including acknowledging feelings of relief, loss, and disappointment, may help parents adapt to the genomic test results and assist families to anticipate and plan for the next steps in their child's medical trajectory, whether or not a diagnosis is found., (© 2021 National Society of Genetic Counselors.)

Identifying genetic mosaicism is important in establishing a diagnosis, assessing recurrence risk, and providing accurate genetic counseling. Next-generation sequencing has allowed for the identification of mosaicism at levels below those detectable by conventional Sanger sequencing or chromosomal microarray analysis. The CAUSES Clinic was a pediatric translational trio-based genome-wide (exome or genome) sequencing study of 500 families (531 children) with suspected genetic disease at BC Children's and Women's Hospitals. Here we present 12 cases of apparent mosaicism identified in the CAUSES cohort: nine cases of parental mosaicism for a disease-causing variant found in a child and three cases of mosaicism in the proband for a de novo variant. In six of these cases, there was no evidence of mosaicism on Sanger sequencing-the variant was not detected on Sanger sequencing in three cases, and it appeared to be heterozygous in three others. These cases are examples of six clinical manifestations of mosaicism: a proband with classical clinical features of mosaicism (e.g., segmental abnormalities of skin pigmentation or asymmetrical growth of bilateral body parts), a proband with unusually mild manifestations of a disease, a mosaic proband who is clinically indistinguishable from the constitutive phenotype, a mosaic parent with no clinical features of the disease, a mosaic parent with mild manifestations of the disease, and a family in which both parents are unaffected and two siblings have the same disease-causing constitutional mutation. Our data demonstrate the importance of considering the possibility of mosaicism whenever exome or genome sequencing is performed and that its detection via genome-wide sequencing can permit more accurate genetic counseling., (© 2021 Cook et al.; Published by Cold Spring Harbor Laboratory Press.)

Purpose: Clinical diagnostic genome-wide (exome or genome) sequencing (GWS) in British Columbia requires funding approval by a provincial agency on a case-by-case basis. The CAUSES Clinic was a pediatric translational trio-based GWS study at BC Children's and Women's Hospitals. Referrals to the CAUSES Clinic were made through a Genomic Consultation Service (GCS), a multidisciplinary team led by genetic counsellors that provided advice regarding genomic testing for physicians considering GWS for their patients. Here we review the outcomes of the GCS, focusing on patients not recommended for the CAUSES Study., Methods: Demographic, clinical, and testing data were abstracted from patient charts. Logistic regression analysis was used to explore associations between demographic and clinical variables and two outcomes: the type of recommendation and referring physicians' decisions to follow the recommendation., Results: Of 972 GCS referrals, 248 patients were not referred to the CAUSES Study. GWS (vs. a targeted test; e.g. multi-gene panel) was more likely to be recommended to physicians of patients with ID than physicians of patients without ID (OR = 2.98; 95% CI = 1.46 to 6.27; n = 149). In total, 40% of physicians who were recommended to pursue clinical genomic testing submitted an application for funding approval; 71% of applications were approved for funding. Among approved tests, 50% resulted in a diagnosis, including 33% of targeted tests and 82% of GWS tests (χ 2 (1) = 5.0, p = 0.026)., Conclusion: The GCS provided an effective model in which physicians can interface with genetic specialists, including genetic counsellors, to facilitate appropriate genomic test selection., (Copyright © 2020 Elsevier Masson SAS. All rights reserved.)

Renpenning syndrome (OMIM: 309500) is a rare X-linked disorder that causes intellectual disability, microcephaly, short stature, a variety of eye anomalies, and characteristic craniofacial features. This condition results from pathogenic variation of PQBP1, a polyglutamine-binding protein involved in transcription and pre-mRNA splicing. Renpenning syndrome has only been reported in affected males. Carrier females do not usually have clinical features, and in reported families with Renpenning syndrome, most female carriers exhibit favorable skewing of X-chromosome inactivation. We describe a female with syndromic features typical of Renpenning syndrome. She was identified by exome sequencing to have a de novo heterozygous c.459_462delAGAG mutation in PQBP1 (Xp11.23), affecting the AG hexamer in exon 4, which is the most common causative mutation in this syndrome. Streaky hypopigmentation of the skin was observed, supporting a hypothesized presence of an actively expressed, PQBP1 mutation-bearing X-chromosome in some cells. X-inactivation studies on peripheral blood cells demonstrated complete skewing in both the proband and her mother with preferential inactivation of the maternal X chromosome in the child. We demonstrated expression of the PQBP1 mutant transcript in leukocytes of the affected girl. Therefore, it is highly likely that the PQBP1 mutation arose from the paternal X chromosome., (© 2019 Wiley Periodicals, Inc.)

Genetic disorders are one of the leading causes of infant mortality and are frequent in neonatal intensive care units (NICUs). Rapid genome-wide sequencing (GWS; whole genome or exome sequencing (ES)), due to its diagnostic capabilities and immediate impacts on medical management, is becoming an appealing testing option in the NICU setting. RAPIDOMICS was a trio-based rapid ES pilot study of 25 babies with suspected genetic disorders in the BC Women's Hospital NICU. ES and bioinformatic analysis were performed after careful patient ascertainment. Trio analysis was performed using an in-house pipeline reporting variants in known disease-causing genes. Variants interpreted by the research team as definitely or possibly causal of the infant's phenotype were Sanger validated in a clinical laboratory. The average time to preliminary diagnosis was 7.2 days. Sanger validation was pursued in 15 patients for 13 autosomal dominant and 2 autosomal recessive disorders, with an overall diagnostic rate (partial or complete) of 60%.Conclusion: In total, 72% of patients enrolled had a genomic diagnosis achieved through ES, multi-gene panel testing or chromosomal microarray analysis. Among these, there was an 83% rate of significant and immediate impact on medical decision-making directly related to new knowledge of the diagnosis. Health service implementation challenges and successes are discussed. What is Known: • Rapid genome-wide sequencing in the neonatal intensive care setting has a greater diagnostic hit rate and impact on medical management than conventional genetic testing. However, the impact of consultation with genetics and patient ascertainment requires further investigation. What is New: • This study demonstrates the importance of genetic consultation and careful patient selection prior to pursuing exome sequencing (ES). • In total, 15/25 (60%) patients achieved a diagnosis through ES and 18/25 (72%) through ES, multi-gene panel testing or chromosomal microarray analysis with 83% of those having immediate effects on medical management.

As genome-wide sequencing (GWS; exome sequencing [ES] and whole genome sequencing [WGS]) is implemented more frequently in the neonatal intensive care unit (NICU), it is important to understand parents' opinions regarding GWS, and views toward incidental findings (IFs) (also known as secondary findings). RAPIDOMICS was a pilot study of rapid trio-based (biological parents and neonate) ES for 25 neonates with a suspected genetic condition at the BC Women's Hospital NICU. As part of RAPIDOMICS, we explored parents' motivations and concerns regarding ES of their child, uptake of IFs for themselves, and rates of anxiety and depression at the time of pre-test genetic counseling via administration of the Generalized Anxiety Disorder Assessment 7 and Patient Health Questionnaire 8. These findings were compared to those from the Clinical Assessment of the Utility of Sequencing and Evaluation as a Service (CAUSES) study (outpatient trio-based GWS) that includes pediatric patients with suspected genetic disease (with an average age of 10 years). Parents in RAPIDOMICS were more likely to identify "diagnosis" as their primary motivation to pursue GWS (p = 0.011), less likely to identify "no concerns" (p = 0.003), and less likely to opt in to receive IFs (p = 0.003) than parents in CAUSES. Rates of depression and anxiety in both groups were higher relative to the general population. We present novel findings regarding the similarities and differences in parental opinions and decisions of these cohorts., (© 2018 National Society of Genetic Counselors.)

Purpose: This study aimed to generate benchmark estimates for the cost, diagnostic yield, and cost per positive diagnosis of diagnostic exome sequencing (ES) in heterogeneous pediatric patient populations and to illustrate how the design of an ES service can influence its cost and yield., Methods: A literature review and Monte Carlo simulations were used to generate benchmark estimates for singleton and trio ES. A cost model for the Clinical Assessment of the Utility of Sequencing and Evaluation as a Service (CAUSES) study, which is testing a proposed delivery model for diagnostic ES in British Columbia, is used to illustrate the potential effects of changing the service design., Results: The benchmark diagnostic yield was 34.3% (95% confidence interval (CI): 23.2-46.5) for trio ES and 26.5% (95% CI: 12.9-42.9) for singleton ES. The benchmark cost of delivery was C$6,437 (95% CI: $5,305-$7,704) in 2016 Canadian dollars (US$4,859; 4,391€) for trio ES and C$2,576 (95% CI: $1,993-$3,270) (US$1,944; 1,757€) for singleton ES. Scenario models for CAUSES suggest that alternative service designs could reduce costs but might lead to a higher cost per diagnosis due to lower yields., Conclusion: Broad conclusions about the cost-effectiveness of ES should be drawn with caution when relying on studies that use cost or yield assumptions that lie at the extremes of the benchmark ranges.

Background: Access to clinical diagnostic genome-wide sequencing (GWS; exome or whole genome sequencing) is limited in British Columbia. The establishment of a translational research initiative (CAUSES) to provide diagnostic genome-wide sequencing for 500 children necessitated the development of a genomic consultation service, a clinical service established to provide consultation for physicians considering GWS for their pediatric patients throughout British Columbia. The Genomic Consultation Service provides patient-specific genomic advice that may include: GWS, multi-gene panel, single gene test, referral to medical genetics for clinical evaluation, or no genetic testing. Here, we describe and evaluate this service., Methods: We analyzed referral patterns, patient demographics, clinical indications, and genomic advice provided during the first year of this service. Comparison of outcomes from the first 6 months versus the last 6 months was performed., Results: A total of 407 referrals (238 males and 169 females [p = .0006]) were processed in the first year. Only children were eligible for referral and average patient age was 8 years. Medical genetics was the most frequent referring discipline, followed by biochemical disease and pediatric neurology, respectively. Most patients (68%) had syndromic intellectual disability. There was a significant difference in the frequency of referrals not appropriate for GWS in the first versus the second 6 months of the service (75/220 vs. 42/187; p = .01) suggesting increasing awareness of testing criteria by referring physicians., Conclusion: This triage service is utilized throughout the province and appears to be an important factor in the high diagnostic rate (>40%) achieved in our GWS program., (© 2018 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.)

The forkhead box (FOX) transcription factors have roles in development, carcinogenesis, metabolism, and immunity. In humans FOXP1 mutations have been associated with language and speech defects, intellectual disability, autism spectrum disorder, facial dysmorphisms, and congenital anomalies of the kidney and urinary tract. In mice, Foxp1 plays critical roles in development of the spinal motor neurons, lymphocytes, cardiomyocytes, foregut, and skeleton. We hypothesized therefore that mutations of FOXP1 affect additional tissues in some humans. Supporting this hypothesis, we describe two individuals with novel variants of FOXP1 (NM_032682.5:c.975-2A>C and NM_032682.5:c.1574G>A) and additional features. One had a lung disease resembling neuroendocrine cell hyperplasia of infancy (NEHI), and the second had a skeletal disorder with undertubulation of the long bones and relapsing-remitting fevers associated with flushing and edema. Although attribution of these traits to mutation of FOXP1 requires ascertainment of additional patients, we hypothesize that the variable expression of these additional features might arise by means of stochastic developmental variation., (© 2017 Wiley Periodicals, Inc.)

Failure to thrive arises as a complication of a heterogeneous group of disorders. We describe two female siblings with spastic paraplegia and global developmental delay but also, atypically for the HSPs, poor weight gain classified as failure to thrive. After extensive clinical and biochemical investigations failed to identify the etiology, we used exome sequencing to identify biallelic UNC80 mutations (NM_032504.1:c.[3983-3_3994delinsA];[2431C>T]. The paternally inherited NM_032504.1:c.3983-3_3994delinsA is predicted to encode p.Ser1328Argfs*19 and the maternally inherited NM_032504.1:c.2431C>T is predicted to encode p.Arg811*. No UNC80 mRNA was detectable in patient cultured skin fibroblasts, suggesting UNC80 loss of function by nonsense mediated mRNA decay. Further supporting the UNC80 mutations as causative of these siblings' disorder, biallelic mutations in UNC80 have recently been described among individuals with an overlapping phenotype. This report expands the disease spectrum associated with UNC80 mutations. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Background: Mutations of TCF4, which encodes a basic helix-loop-helix transcription factor, cause Pitt-Hopkins syndrome (PTHS) via multiple genetic mechanisms. TCF4 is a complex locus expressing multiple transcripts by alternative splicing and use of multiple promoters. To address the relationship between mutation of these transcripts and phenotype, we report a three-generation family segregating mild intellectual disability with a chromosomal translocation disrupting TCF4., Results: Using whole genome sequencing, we detected a complex unbalanced karyotype disrupting TCF4 (46,XY,del(14)(q23.3q23.3)del(18)(q21.2q21.2)del(18)(q21.2q21.2)inv(18)(q21.2q21.2)t(14;18)(q23.3;q21.2)(14pter®14q23.3::18q21.2®18q21.2::18q21.1®18qter;18pter®18q21.2::14q23.3®14qter). Subsequent transcriptome sequencing, qRT-PCR and nCounter analyses revealed that cultured skin fibroblasts and peripheral blood had normal expression of genes along chromosomes 14 or 18 and no marked changes in expression of genes other than TCF4. Affected individuals had 12-33 fold higher mRNA levels of TCF4 than did unaffected controls or individuals with PTHS. Although the derivative chromosome generated a PLEKHG3-TCF4 fusion transcript, the increased levels of TCF4 mRNA arose from transcript variants originating distal to the translocation breakpoint, not from the fusion transcript., Conclusions: Although validation in additional patients is required, our findings suggest that the dysmorphic features and severe intellectual disability characteristic of PTHS are partially rescued by overexpression of those short TCF4 transcripts encoding a nuclear localization signal, a transcription activation domain, and the basic helix-loop-helix domain.

Chromosome 4q deletion syndrome is a rare intellectual disability disorder caused by a variety of non-recurrent deletions of 4q. We describe the evolution of the phenotypic features of a female patient with a previously unreported deletion of 4q12-4q21.21 (hg 18; 54,711,575-79,601,919). By review reported individuals with interstitial deletions extending telomeric from 4q12 have syndromic intellectual disability with variable piebaldism. We expand the phenotype to include dolichocephaly, pectus excavatum, hip dysplasia, pes planus, myopia, lens opacities, and an absence of spoken language but not of communication through sign. The proposita also did not have piebaldism suggesting again that piebaldism arises from a mechanism more complex than simple haploinsufficiency of KIT. Comparing deletions among affected individuals localizes the critical interval within 4q12-4q13.1, although the absence of molecular boundaries for nearly all reported cases precludes precise delineation and genotype-phenotype correlation., (© 2014 Wiley Periodicals, Inc.)

Coffin-Siris Syndrome (CSS) is an intellectual disability disorder caused by mutation of components of the SWI/SNF chromatin-remodeling complex. We describe the evolution of the phenotypic features for a male patient with CSS from birth to age 7 years and 9 months and by review of reported CSS patients, we expand the phenotype to include neonatal and infantile hypertonia and upper airway obstruction. The propositus had a novel de novo heterozygous missense mutation in exon 17 of SMARCA4 (NM_001128849.1:c.2434C>T (NP_001122321.1:p.Leu812Phe)). This is the first reported mutation within motif Ia of the SMARCA4 SNF2 domain. In summary, SMARCA4-associated CSS is a pleiotropic disorder in which the pathognomic clinical features evolve and for which the few reported individuals do not demonstrate a clear genotype-phenotype correlation., (© 2014 Wiley Periodicals, Inc.)

CK syndrome (CKS) is an X-linked recessive intellectual disability syndrome characterized by dysmorphism, cortical brain malformations, and an asthenic build. Through an X chromosome single-nucleotide variant scan in the first reported family, we identified linkage to a 5 Mb region on Xq28. Sequencing of this region detected a segregating 3 bp deletion (c.696_698del [p.Lys232del]) in exon 7 of NAD(P) dependent steroid dehydrogenase-like (NSDHL), a gene that encodes an enzyme in the cholesterol biosynthesis pathway. We also found that males with intellectual disability in another reported family with an NSDHL mutation (c.1098 dup [p.Arg367SerfsX33]) have CKS. These two mutations, which alter protein folding, show temperature-sensitive protein stability and complementation in Erg26-deficient yeast. As described for the allelic disorder CHILD syndrome, cells and cerebrospinal fluid from CKS patients have increased methyl sterol levels. We hypothesize that methyl sterol accumulation, not only cholesterol deficiency, causes CKS, given that cerebrospinal fluid cholesterol, plasma cholesterol, and plasma 24S-hydroxycholesterol levels are normal in males with CKS. In summary, CKS expands the spectrum of cholesterol-related disorders and insight into the role of cholesterol in human development., (Copyright © 2010 The American Society of Human Genetics. Published by Elsevier Inc. All rights reserved.)

X-linked mental retardation (XLMR) affects 1-2/1,000 males and accounts for approximately 10% of all mental retardation (MR). We have ascertained a syndromic form of XLMR segregating within a five-generation family with seven affected males. Prominent characteristics include mild to severe MR, cortical malformation, microcephaly, seizures, thin build with distinct facial features including a long and thin face, epicanthic folds, almond-shaped eyes, upslanting palpebral fissures and micrognathia and behavioral problems. Carrier females have normal physical appearance and intelligence. This combination of features is unreported and distinct from Lujan-Fryns syndrome, Snyder-Robinson syndrome, and zinc finger DHHC domain-containing 9-associated MR. We propose the name of this new syndrome to be CK syndrome., (Copyright 2009 Wiley-Liss, Inc.)

Psychiatric disease occurs with increased frequency in a number of malformation syndromes. We hypothesize that the study of these disorders is helpful for understanding the pathophysiology of psychiatric disease. With this objective, we have been screening for individuals with malformations and prominent psychiatric disease. We report on a man with visual and auditory hallucinations and behavioral problems who was the product of an incestuous relationship and had anomalies primarily of his face, hands and feet. His distinctive features define an undescribed acro-auricular malformation syndrome with a psychiatric component. The study of Mendelian syndromes such as the one presented will likely be helpful for isolating novel genes involved in psychiatric illness.

Unlabelled: Specific language impairment (SLI) or developmental dysphasia denotes the inability to acquire normal expression and/or comprehension of language in the absence of peripheral hearing impairment, neurological disorder, and mental retardation. The presence of attention deficit/hyperactivity in some SLI children has previously been documented. This family history study used 27 SLI families, identified through the parents from the Dysphasia Association, to examine the relationship between attention deficit/hyperactivity in SLI children and the risk to first-degree relatives. All SLI children were clinically diagnosed with speech/language disorder; medical records were searched for the presence of any of the exclusion criteria noted above. The 13 SLI children with medical record of attention deficit/hyperactivity had a significantly higher chance of having first-degree relatives with speech/language disorders than 14 SLI children without such record (15/27 and 4/46, respectively). This preliminary report suggests that additional study is warranted to investigate the relationship between speech/language disorders and attention deficit/hyperactivity in families of SLI children., Learning Outcomes: As a result of this activity, the participant will be able to describe the SLI phenotype, its prevalence, and complexity and to recognize the relationship between comorbid attention deficit/hyperactivity in SLI children and the risk of speech/language disorder in their relatives.

Familial hypercholesterolemia (FH) is caused by mutations in the LDL receptor (LDLR) gene and is usually associated with hypercholesterolemia, lipid deposition in tissues, and premature coronary artery disease (CAD). However, individuals with heterozygous FH in China exhibit a milder phenotype despite having deleterious mutations in the LDLR gene (X.-M. Sun et al, Arterioscler Thromb. 1994;14:85-94). Nineteen Chinese FH heterozygotes living in Canada were screened for the 11 mutations that had been described in FH patients living in China. One Chinese Canadian carried one of these mutations (Trp462Stop), 2 carried a previously unreported single-base substitution (Cysl63Arg), and 1 carried a mutation observed in French-Canadian patients (Glu207Lys). Twelve additional carriers of these mutations were identified in the families of the index patients. Significantly higher LDL cholesterol concentrations were observed in FH heterozygotes with defined mutations living in Canada (mean+/-SD, 7.46+/-1.29, n=16) than in those living in China (4.35+/-1.09, n=18; P<.0001). Six of the 16 FH heterozygotes residingin Canada had evidence of tendon xanthomata and 4 had a history of premature CAD, whereas none of those in China had tendon xanthomata or CAD. Complete segregation between hypercholesterolemia and inheritance of a mutant allele was observed in 3 Canadian Chinese FH families. Thus, Chinese FH heterozygotes living in Canada exhibit a phenotype similar to that of other FH patients in Western societies. The difference between patients living in Canada and those living in China could be ascribed to differences in dietary fat consumption, showing that environmental factors such as diet play a significant role in modulating the phenotype of heterozygous FH.