Prenatal diagnosis of Fukuyama-type congenital muscular dystrophy by microsatellite analysis

We applied microsatellite analysis to prenatal diagnosis of Fukuyama- type congenital muscular dystrophy (FCMD), an autosomal recessive severe muscular dystrophy associated with brain malformations. Recent identification of the FCMD gene locus at 9q31-q33 provided the basis for prenatal diagnosis and carrier detection. We recently developed new microsatellite markers which are closer to the FCMD gene and improved the phenotype probability. Nine fetuses in eight unrelated FCMD families, including a twin pregnancy, were analysed using the newly developed markers. Four fetuses showed over 99% probability of being healthy either as normal homozygote (n = 1) or heterozygote carrier (n = 3) and were born without signs of FCMD. The other five fetuses were diagnosed with a probability of FCMD of 99% or greater; all of the latter parents decided to terminate the pregnancies. Brain malformations characteristic of FCMD in one of the aborted fetuses confirmed the diagnosis of FCMD at 19 weeks of gestation.      

Haplotype–Phenotype correlation in Fukuyama congenital muscular dystrophy

In typical Fukuyama congenital muscular dystrophy (FCMD), peak motor function is usually only unassisted sitting or sliding on the buttocks, though a few patients are able to walk at some point. However, a few patients have a severe phenotype and never acquire head control. In addition, it is clinically difficult to differentiate this severe FCMD from Walker‐Warburg syndrome (WWS) or from muscle–eye–brain disease (MEBD). In order to establish a genotype–phenotype correlation, we performed haplotype analysis using microsatellite markers closest to the FCMD gene (FCMD) in 56 Japanese FCMD families, including 35 families whose children were diagnosed as FCMD with the typical phenotype, 12 families with a mild phenotype, and 9 families with a severe phenotype. Of the 12 propositi with the mild phenotype, 8 could walk and the other 4 could stand with support; 10 cases were homozygous for the ancestral founder (A‐F) haplotype whereas the other 2 were heterozygous for the haplotype. In the 9 severe cases, who had never acquired head control or the ability to sit without support, 3 had progressive hydrocephalus, 2 required a shunt operation, and 7 had ophthalmological abnormalities. Haplotype analysis showed that 8 of the 9 cases of the severe phenotype are heterozygous for the A‐F haplotype, and the other one homozygous for the haplotype. We confirmed that at least one chromosome in each of the 56 FCMD patients has the A‐F haplotype. The rate of heterozygosity for the A‐F haplotypes was significantly higher in severe cases than in typical or mild cases (P < 0.005). Severe FCMD patients appeared to be compound heterozygotes for the founder mutation and another mutation. Thus, the present study yielded molecular genetic evidence of a broad clinical spectrum in FCMD. Am. J. Med. Genet. 92:184–190, 2000. © 2000 Wiley‐Liss, Inc.     

Prenatal diagnosis of Fukuyama type congenital muscular dystrophy by polymorphism analysis

Fukuyama type congenital muscular dystrophy (FCMD) is an autosomal recessive disorder characterized by a combination of primary muscular dystrophy of early infantile onset and brain malformation (lissencephaly type II). The identification of the FCMD gene locus at 9q31 opened the theoretical possibility of prenatal diagnosis. The authors conducted prenatal diagnosis in two unrelated FCMD families by analysis using nine microsatellite CA-repeat polymorphic markers flanking the FCMD locus, and calculated phenotype probabilities in fetuses with a computer program, LINKAGE. The fetus in family 1 showed a 99% probability of being healthy either as a normal homozygote or a heterozygote carrier and was born without signs of FCMD. In family 2, the fetus was diagnosed to have FCMD with at least 86% probability. The parents of this family decided to terminate the pregnancy and an abortus showed brain malformations characteristic of an FCMD fetus. © 1996 Wiley-Liss, Inc.     

Haplotype-phenotype correlation in Fukuyama congenital muscular dystrophy

In typical Fukuyama congenital muscular dystrophy (FCMD), peak motor function is usually only unassisted sitting or sliding on the buttocks, though a few patients are able to walk at some point. However, a few patients have a severe phenotype and never acquire head control. In addition, it is clinically difficult to differentiate this severe FCMD from Walker-Warburg syndrome (WWS) or from muscle-eye-brain disease (MEBD). In order to establish a genotype-phenotype correlation, we performed haplotype analysis using microsatellite markers closest to the FCMD gene (FCMD) in 56 Japanese FCMD families, including 35 families whose children were diagnosed as FCMD with the typical phenotype, 12 families with a mild phenotype, and 9 families with a severe phenotype. Of the 12 propositi with the mild phenotype, 8 could walk and the other 4 could stand with support; 10 cases were homozygous for the ancestral founder (A-F) haplotype whereas the other 2 were heterozygous for the haplotype. In the 9 severe cases, who had never acquired head control or the ability to sit without support, 3 had progressive hydrocephalus, 2 required a shunt operation, and 7 had ophthalmological abnormalities. Haplotype analysis showed that 8 of the 9 cases of the severe phenotype are heterozygous for the A-F haplotype, and the other one homozygous for the haplotype. We confirmed that at least one chromosome in each of the 56 FCMD patients has the A-F haplotype. The rate of heterozygosity for the A-F haplotypes was significantly higher in severe cases than in typical or mild cases (P < 0.005). Severe FCMD patients appeared to be compound heterozygotes for the founder mutation and another mutation. Thus, the present study yielded molecular genetic evidence of a broad clinical spectrum in FCMD.     

福山型先天性肌营养不良基因型和表型分析

目的 通过单体型分析,对临术诊断为福山型先天性肌营不良（Ｆｕｋｕｙａｍａ ｃｏｎｇｅｎｉｔａｌ ｍｕｓｃｕｌａｒ ｄｙｓｔｒｏｐｈｙ,ＦＣＭＤ）的患者进行基因诊断,并探讨ＦＣＭＤ基因型和表型之间的关系。方法 应用Ｄ９Ｓ３０６,Ｄ９Ｓ２１０５,Ｄ９Ｓ２１７０,Ｄ９Ｓ２１７１,Ｄ９Ｓ２１０７,Ｄ９Ｓ１７２等６个微卫星ＤＮＡ,经聚合酶链反应（ＰＣＲ）,扩增片段长度多态性－内烯酰胺凝胶电泳,对１００个日本     

Homozygosity and linkage disequilibrium mapping of autosomal recessive distal myopathy (Nonaka distal myopathy)

Autosomal recessive distal myopathy or Nonaka distal myopathy (NM) is characterized by its unique distribution of muscular weakness and wasting. The patients present with spared quadriceps muscles even in a late stage of the disease. The hamstring and tibialis anterior muscles are affected severely in early adulthood. We have localized the NM gene to the region between markers D9S319 and D9S276 on chromosome 9 by linkage analysis. To further refine the localization of the NM gene, we conducted homozygosity and linkage disequilibrium analysis for 14 patients from 11 NM families using 18 polymorphic markers. All of the patients from consanguineous NM families were found to be homozygous for six markers located within the region between markers D9S2178 and D9S1859. We also provided evidence for significant allelic associations between the NM region and five marker loci. Examination of the haplotype analysis identified a predominant ancestral haplotype comprising the associated alleles 199-160-154-109 (marker order: D9S2179-D9S2180-D9S2181-D9S1804), present in 60% of NM chromosomes and in 0% of parent chromosomes. On the basis of the data obtained in this study, the majority of NM chromosomes were derived from a single ancestral founder, and the NM gene is probably located within the 1.5-Mb region between markers D9S2178 and D9S1791. Received: January 18, 2001 / Accepted: August 21, 2001     

Carrier detection of Batten disease (Juvenile neuronal ceroid-lipofuscinosis)

Batten disease, or the juvenile form of neuronal ceroid lipofuscinosis, is an autosomal recessive neurodegenerative disorder manifesting with progressive blindness, seizures, and dementia, leading to an early death. The CLN3 locus which is involved in Batten disease had been localized to chromosome 16p11.2. Linkage disequilibrium has been observed between CLN3 and polymorphic microsatellite markers D16S288, D16S299, and D16S298, making carrier detection and prenatal diagnosis by haplotype analysis possible. For the purpose of carrier detection, haplotypes from Dutch Batten patients and their families were constructed. Most patients share the same D16S298 allele, suggesting the presence of a founder effect in the Dutch population. In a large inbred Dutch family, in which Batten disease occurs with high frequency, haplotype analysis has been carried out with high accuracy for carrier detection. © 1995 Wiley-Liss, Inc.     

Linkage disequilibrium at the SCA2 locus

Spinocerebellar ataxia type 2 (SCA2) is caused by the expansion of an unstable CAG repeat encoding a polyglutamine tract. Repeats with 32 to 200 CAGs are associated with the disease, whereas normal chromosomes contain 13 to 33 repeats. We tested 220 families of different geographical origins for the SCA2 mutation. Thirty three were positive (15%). Twenty three families with at least two affected subjects were tested for linkage disequilibium (LD) between the SCA2 mutation and three microsatellite markers, two of which (D12S1332-D12S1333) closely flanked the mutation; the other (D12S1672) was intragenic. Many different haplotypes were observed, indicating the occurrence of several ancestral mutations. However, the same haplotype, not observed in controls, was detected in the German, the Serbian, and some of the French families, suggesting a founder effect or recurrent mutations on an at risk haplotype.     

Refining the primary open-angle glaucoma GLC1C region on chromosome 3 by haplotype analysis

The GLC1C locus for primary open-angle glaucoma (POAG) is inherited as an autosomal dominant trait. This region on chromosome 3 is 11 cM long. DNA samples from members of a Greek and an American GLC1C family were obtained to determine whether additional typing of microsatellite markers in family members might narrow the region. GLC1C family members were evaluated clinically for POAG on the basis of open angles, intraocular pressures, cupping of discs, and visual fields. DNA samples from the Greek and Oregon GLC1C families were used to further refine the GLC1C region using microsatellite markers. A total of 22 affected members were identified in the two families. Common alleles for D3S3637 and D3S3612 were present in the disease haplotype from both families, suggesting that they may have a common founder. A newly diagnosed patient in the American family had a recombination in the distal portion of the GLC1C haplotype. This recombination narrows the GLC1C region from 11 to 4 cM.     

Genetic fine mapping of the gene for nonsyndromic congenital retinal nonattachment

Autosomal recessive nonsyndromic congenital retinal nonattachment (NCRNA) comprises congenital insensitivity to light, massive retrolental mass, shallow anterior chamber, microphthalmia, and nystagmus in otherwise normal individuals. Polymerase chain reaction-based linkage analyses of polymorphic microsatellite markers in the 10q21 region on DNA samples from 106 individuals provide evidence that the NCRNA locus is within an interval of approximately 0.6-1.5 cM, flanked by the markers D10S522 and D10S1418. Haplotype analysis demonstrated a unique founder haplotype shared by 100% of the NCRNA chromosomes. These results indicate a founder effect and the strong possibility of a single mutation as the cause of the disease in the affected population. Based on these findings, it is now possible to provide relatively accurate carrier detection and prenatal diagnostic testing for families with NCRNA based on close flanking markers and the capacity to identify NCRNA chromosomes by their haplotypes.     

A rapid diagnostic method for a retrotransposal insertional mutation into the FCMD gene in Japanese patients with Fukuyama congenital muscular dystrophy

Fukuyama-type congenital muscular dystrophy (FCMD) is characterized by congenital muscular dystrophy in combination with central nervous system (CNS) abnormalities. Differential diagnosis of FCMD from Duchenne and Becker muscular dystrophies (DMD/BMD) or other types of congenital muscular dystrophy is occasionally difficult, because of their phenotypic similarity. The gene (FCMD) responsible for FCMD at 9q31 was isolated in 1998. In Japan, most FCMD-bearing chromosomes (87%) have a 3-kb retrotransposal insertion into the 3'-untranslated region (UTR) of the gene that could be derived from a single ancestral founder. Nine non-founder mutations have been identified in Japanese FCMD patients. Severe phenotype was significantly more frequent in patients who were compound heterozygotes for a point mutation and the founder mutation, than in homozygotes for the founder mutation. We developed a PCR-based diagnostic method for a rapid detection of the retrotransposal insertion mutation. Using this system, we screened 18 FCMD patients, and found 16 homozygotes and two heterozygotes for the insertion. We also evaluated the carrier frequency in the normal Japanese population. Six of 676 persons were recognized as a heterozygous carrier. Furthermore, we found three homozygotes for the FCMD founder mutation among 97 patients who had been said to have probable DMD/BMD without any DMD mutations. On the other hand, there were no FCMD homozygotes but four heterozygous carriers among 335 patients with DMD mutations. The diagnostic method we developed will provide a rapid and reliable diagnosis of FCMD, which can bring important information in genetic counseling, such as the accurate mode of inheritance, recurrence risk and a life expectancy.     

An ancestral core haplotype defines the critical region harbouring the North Carolina macular dystrophy gene (MCDR1).

Autosomal dominant North Carolina macular dystrophy (NCMD) or central areolar pigment epithelial dystrophy (CAPED) is an allelic disorder that maps to an approximately 7.2 cM interval between DNA markers at D6S424 and D6S1671 on 6q14-q16.2. The further refinement of the disease locus has been hindered by the lack of additional recombination events involving the critical region. In this study, we have identified three multigeneration families of German descent who express the NCMD phenotype. Genotyping was carried out with a series of markers spanning approximately 53 cM around the NCMD locus, MCDR1. Genetic linkage between the markers and the disease phenotype in each of the families could be shown. Disease associated haplotypes were constructed and provide evidence for an ancestral founder for the German NCMD families. This haplotype analysis suggests that a 4.0 cM interval flanked by markers at D6S249 and D6S475 harbours the gene causing NCMD, facilitating further positional cloning approaches.     

Prenatal diagnosis of autosomal recessive polycystic kidney disease (ARPKD): Molecular genetics,clinical experience,and fetal morphology

Autosomal recessive polycystic kidney disease (ARPKD) is one of the most common hereditary renal cystic diseases and has a high infant mortality. Prenatal diagnosis using fetal sonography can be unreliable, especially in early pregnancy. The ARPKD locus has been mapped to proximal chromosome 6p allowing haplotype-based prenatal diagnosis in “at-risk” families. From December 1994 to March 1997, we received 258 inquiries regarding prenatal evaluation and we have completed analyses in 212 families. To date, 65 prenatal analyses have been performed in 57 families. In the majority of the requesting families (45/57), the index children are deceased and their DNA was extracted from paraffin-embedded tissue. Eighteen fetuses were homozygous for the disease-associated haplotypes. In 12 of these fetuses, pathoanatomical examination demonstrated typical ARPKD changes consisting of dilated collecting ducts and the characteristic hepatic ductal plate malformation. These changes were detected in two fetuses as early as 13 weeks gestational age. These cases represent the earliest demonstration of ARPKD-associated histopathology reported to date. One high risk fetus was carried to term and turned out to be unaffected. However, the diagnosis of ARPKD remained doubtful in the index patient. Forty-three fetuses were either heterozygous or homozygous for a nondisease-associated haplotype and all infants born were phenotypically unaffected at birth. In four cases, a recombination event occurred between the flanking markers and no genotypic prediction was possible. Three of these pregnancies were terminated and necropsy of the fetuses confirmed ARPKD, while one fetus was carried to term and showed no abnormalities at birth. These results show that haplotype-based prenatal testing is feasible and reliable in pregnancies “at risk” for ARPKD. An absolute prerequisite for these studies is an accurate diagnosis of ARPKD in previously affected sib(s). Am. J. Med. Genet. 76:137–144, 1998. © 1998 Wiley-Liss, Inc.     

The M53I mutation in CDKN2A is a founder mutation that predominates in melanoma patients with Scottish ancestry

Germline mutations in the tumor suppressor gene CDKN2A have been shown to predispose to cutaneous malignant melanoma. The M53I mutation is the most common CDKN2A mutation identified in Scottish melanoma patients and is also found in a small number of families in other countries. The aim of this study was to determine whether the occurrence of this mutation is due to a common ancestor originating from Scotland, and if so, to estimate how long ago the mutation arose. We examined 18 families carrying the M53I mutation: six from Scotland, five from Canada, four from Australia, and three from America. Haplotypes derived from segregation of seven informative microsatellite markers flanking CDKN2A were constructed in each family. Our findings show that 14 of 18 families carry a common ancestral haplotype on which the mutation arose approximately 88 generations ago (1-LOD-unit support interval 44-198 generations). This haplotype is very rare in controls, which supports the idea that it is a common founder mutation haplotype. The four M53I families that do not share the consensus haplotype may in fact have arisen from the same founder, but this is potentially obscured by presumed replication slippage for some of the microsatellite markers tested.     

Clouston hidrotic ectodermal dysplasia (HED): genetic homogeneity, presence of a founder effect in the French Canadian population and fine genetic mapping

HED is an autosomal dominant skin disorder that is particularly common in the French Canadian population of south-west Quebec. We previously mapped the HED gene to the pericentromeric region of chromosome 13q using linkage analysis in eight French Canadian families. In this study, we extend our genetic analysis to include a multiethnic group of 29 families with 10 polymorphic markers spanning 5.1 cM in the candidate region. Two-point linkage analysis strongly suggests absence of genetic heterogeneity in HED in four families of French, Spanish, African and Malaysian origins. Multipoint linkage analysis in all 29 families generated a peak lod score of 53.5 at D13S1835 with a 1 lod unit support interval spanning 1.8 cM. Recombination mapping placed the HED gene in a 2.4 cM region flanked by D13S1828 proximally and D13S1830 distally. We next show evidence for a strong founder effect in families of French Canadian origin thereby representing the first example of a founder disease in the south-west part of the province of Quebec. Significant association was found between HED in these families and all markers analysed (Fisher's exact test, P < 0.001). Complete allelic association was detected at D13S1828, D13S1827, D13S1835, D13S141 and D13S175 (P(excess) = 1) spanning 1.3 cM. A major haplotype including all 10 associated alleles was present on 65% of affected chromosomes. This haplotype most likely represents the founder haplotype that introduced the HED mutation into the French Canadian population. Luria-Delbrück equations and multipoint likelihood linkage disequilibrium analysis positioned the gene at the D13S1828 locus (likely range estimate: 1.75 cM) and 0.58 cM telomeric to this marker (support interval: 3.27 cM) respectively.     

Fine mapping of a gene responsible for regulating dietary cholesterol absorption; founder effects underlie cases of phytosterolaemia in multiple communities

Sitosterolaemia (also known as phytosterolaemia, MIM 210250) is a rare recessive autosomal inherited disorder, characterised by the presence of tendon and tuberous xanthomas, accelerated atherosclerosis and premature coronary artery disease. The defective gene is hypothesised to play an important role in regulating dietary sterol absorption and biliary secretion, thus defining a molecular mechanism whereby this physiological process is carried out. The disease locus was localised previously to chromosome 2p21, in a 15 cM interval between microsatellite markers D2S1788 and D2S1352 (based upon 10 families, maximum lodscore 4.49). In this study, we have extended these studies to include 30 families assembled from around the world. A maximum multipoint lodscore of 11.49 was obtained for marker D2S2998. Homozygosity and haplotype sharing was identified in probands from non-consanguineous marriages from a number of families, strongly supporting the existence of a founder effect among various populations. Additionally, based upon both genealogies, as well as genotyping, two Amish/Mennonite families, that were previously thought not to be related, appear to indicate a founder effect in this population as well. Using both homozygosity mapping, as well as informative recombination events, the sitosterolaemia gene is located at a region defined by markers D2S2294 and Afm210xe9, a distance of less than 2 cM.     

A linkage disequilibrium at the candidate gene locus for 16q-linked autosomal dominant cerebellar ataxia type III in Japan

We previously mapped the gene responsible for autosomal dominant cerebellar ataxia (ADCA) type III to a 10.9-cM interval between D16S3089 and D16S515 on chromosome 16q. This region, however, was identical to the candidate locus of spinocerebellar ataxia type 4 (SCA4). In this study, we extended our research to refine the gene locus of the disease by applying linkage disequilibrium with 20 microsatellite DNA markers. With 9 markers flanked by D16S3031 and D16S3107, we found that the affected individuals in six families had a common haplotype on their disease chromosomes. Furthermore, linkage disequilibrium was demonstrated with 5 informative markers: D16S3019 (P = 0.013), D16S3067 (P = 0.008), D16S3141 (P = 0.011), D16S496 (P = 0.032), and D16S3107 (P = 0.000). These results indicate that the disease could have originated from a common ancestor harboring a mutation within a less than 3-cM region between D16S3043 and D16S3095. The founder alleles were also observed in other patients with ADCA type III unrelated to the six families. Received: October 25, 2000 / Accepted: January 5, 2001     

Molecular studies in Finnish patients with familial juvenile nephronophthisis exclude a founder effect and support a common mutation causing mechanism.

Familial juvenile nephronophthisis (NPH) is an autosomal recessive tubulointerstitial kidney disease associated with formation of medullary and corticomedullary cysts. It progresses to end stage renal failure and its biochemical defect is unknown. An NPH locus has been assigned to a 2 cM interval on chromosome 2q13 by linkage studies. Homozygous deletions of approximately 250 kb have been detected in 80% of familial cases and 65% of sporadic cases and a common mutation mechanism has been suggested. We examined 14 Finnish families for the presence or absence of a deletion. After detecting a deletion in 12 patients belonging to nine families, we studied a possible founder effect by haplotype analysis using markers D2S340, D2S1889, and D2S1893. No common ancestral disease associated haplotype was found suggesting no founder effect. Results of pairwise linkage analyses were suggestive of linkage in the nine families with a deletion (lod scores of 1.39-3.89 at a recombination fraction of 0). Negative lod scores were obtained in the five families without a deletion suggesting that the disease locus in these families lies elsewhere. The end stage renal disease occurred at a more advanced age in patients without a deletion compared to patients with a deletion, indicating a phenotypic difference between these two groups.     

Haplotype analysis of the BRCA2 9254delATCAT recurrent mutation in breast/ovarian cancer families from Spain

A frame-shift 9254del5 mutation was independently identified in 12 families, eleven of them with Spanish ancestors, in a BRCA2 screening performed in 841 breast and/or ovarian cancer families and in 339 women with breast cancer diagnosed before the age of 40 at different centers in France and Spain. We sought to analyze in detail the haplotype and founder effects of the 9254del5 and to estimate the time of origin of the mutation. Eight polymorphic microsatellite markers and two BRCA2 polymorphisms were used for the haplotype analyses. The markers were located flanking the BRCA2 gene spanning a region of 6.1 cM. Our results suggest that these families shared a common ancestry with BRCA2 9254del5, which is a founder mutation originating in the Northeast Spanish, with an estimated age of 92 (95% CI 56-141) generations.     

Dutch myotonic dystrophy type 2 patients and a North-African DM2 family carry the common European founder haplotype

Myotonic dystrophy type 2 (DM2) is a progressive multisystem disease with muscle weakness and myotonia as main characteristics. The disease is caused by a repeat expansion in the zinc-finger protein 9 (ZNF9) gene on chromosome 3q21. Several reports show that patients from European ancestry share an identical haplotype surrounding the ZNF9 gene. In this study, we investigated whether the Dutch DM2 population carries the same founder haplotype. In all, 40 Dutch DM2 patients from 16 families were genotyped for eight short tandem repeat markers surrounding the ZNF9 gene. In addition, the single-nucleotide polymorphism (SNP) rs1871922 located in the first intron of DM2 was genotyped. Results were compared with previously published haplotypes from unrelated Caucasian patients. The repeat lengths identified in this study were in agreement with existing literature. In 36 patients of our population, we identified three common haplotypes. One patient showed overlap with the common haplotype for only one marker closest to the ZNF9 gene. The haplotype from a family originating from Morocco showed overlap with that of the patients of European descent for a region of 222 kb. All patients carried at least one C allele of SNP rs1871922 indicating that all patients carry the European founder haplotype. We conclude that DM2 patients from the Netherlands, including a North-African family, harbor a common haplotype surrounding the ZNF9 gene. This data show that the Dutch patients carry the common founder haplotype and strongly suggest that DM2 mutations in Europe and North Africa originate from a single ancestral founder.