Power comparisons of the transmission/disequilibrium test and sib-transmission/disequilibrium-test statistics.

Brachydactyly type B (BDB), an autosomal dominant disorder, is the most severe of the brachydactylies and is characterized by hypoplasia or absence of the terminal portions of the index to little fingers, usually with absence of the nails. The thumbs may be of normal length but are often flattened and occasionally are bifid. The feet are similarly but less severely affected. We have performed a genomewide linkage analysis of three families with BDB, two English and one Portugese. The two English families show linkage to the same region on chromosome 9 (combined multipoint maximum LOD score 8.69 with marker D9S257). The 16-cM disease interval is defined by recombinations with markers D9S1680 and D9S1786. These two families share an identical disease haplotype over 18 markers, inclusive of D9S278-D9S280. This provides strong evidence that the English families have the same ancestral mutation, which reduces the disease interval to <12.7 cM between markers D9S257 and D9S1851 in chromosome band 9q22. In the Portuguese family, we excluded linkage to this region, a result indicating that BDB is genetically heterogeneous. Reflecting this, there were atypical clinical features in this family, with shortening of the thumbs and absence or hypoplasia of the nails of the thumb and hallux. These results enable a refined classification of BDB and identify a novel locus for digit morphogenesis in 9q22.     

Mapping of a gene determining familial partial epilepsy with variable foci to chromosome 22q11-q12

We identified two large French-Canadian families segregating a familial partial epilepsy syndrome with variable foci (FPEVF) characterized by mostly nocturnal seizures arising from frontal, temporal, and occasionally occipital epileptic foci. There is no evidence for structural brain damage or permanent neurological dysfunction. The syndrome is inherited as an autosomal dominant trait with incomplete penetrance. We mapped the disease locus to a 3. 8-cM interval on chromosome 22q11-q12, between markers D22S1144 and D22S685. Using the most conservative diagnostic scheme, the maximum cumulative LOD score was 6.53 at recombination fraction (straight theta) 0 with D22S689. The LOD score in the larger family was 5.34 at straight theta=0 with the same marker. The two families share an identical linked haplotype for >/=10 cM, including the candidate interval, indicating a recent founder effect. A severe phenotype in one of the probands may be caused by homozygosity for the causative mutation, as suggested by extensive homozygosity for the linked haplotype and a bilineal family history of epilepsy. An Australian family with a similar phenotype was not found to link to chromosome 22, indicating genetic heterogeneity of FPEVF.     

A new locus for a dominant form of multinodular goiter on 3q26.1-q26.3

A mass screening program for congenital hypothyroidism has markedly improved prognosis of children with congenital hypothyroidism and also revealed several cases with unknown pathogenesis. We here report two independent Japanese multigeneration families with multinodular goiter (MNG) with euthyroidism and with high TSH. The propositi, 3- and 8-year-old girls in two families, were found during a mass screening. An autosomal dominant pattern of inheritance was suggested in both families. The clinical examinations suggested impaired hormonogenesis but discarded known defects in iodine transport, organification, deficiency of hydrogen peroxide, and thyroid peroxidase. Linkage analysis of the two families including 10 members each using 343 microsatellite markers mapped a single locus independently at D3S1618 (theta = 0) on 3q26.1-q26.3 with a two-point LOD score 3.62 (1.81 for each family) and multipoint LOD score of 3.61 (1.80 for each family). Haplotype inspection delimited an 18-cM interval between D3S1565 and D3S3686.     

Autosomal dominant avascular necrosis of femoral head in two Taiwanese pedigrees and linkage to chromosome 12q13

Avascular necrosis of the femoral head (ANFH) is a debilitating disease that commonly leads to destruction of the hip joint in adults. The etiology of ANFH is unknown, but previous studies have indicated that heritable thrombophilia (increased tendency to form thrombi) and hypofibrinolysis (reduced ability to lyse thrombi), alcohol intake, and steroid use are risk factors for ANFH. We recently identified two families with ANFH showing autosomal dominant inheritance. By applying linkage analysis to a four-generation pedigree, we excluded linkage between the family and three genes related to thrombophilia and hypofibrinolysis: protein C, protein S, and plasminogen activator inhibitor. Furthermore, by a genomewide scan, a significant two-point LOD score of 3.45 (recombination fraction [theta] = 0) was obtained between the family with ANFH and marker D12S85 on chromosome 12. High-resolution mapping was conducted in a second family with ANFH and replicated the linkage to D12S368 (pedigree I: LOD score 2.47, theta = 0.05; pedigree II: LOD score 2.81, theta = 0.10). When an age-dependent-penetrance model was applied, the combined multipoint LOD score was 6.43 between D12S1663 and D12S85. Thus, we mapped the candidate gene for autosomal dominant ANFH to a 15-cM region between D12S1663 and D12S1632 on chromosome 12q13.     

The PARK8 locus in autosomal dominant parkinsonism: confirmation of linkage and further delineation of the disease-containing interval

Recently, a new locus (PARK8) for autosomal dominant parkinsonism has been identified in one large Japanese family. Linkage has been shown to a 16-cM centromeric region of chromosome 12, between markers D12S1631 and D12S339. We tested 21 white families with Parkinson disease and an inheritance pattern compatible with autosomal dominant transmission for linkage in this region. Criteria for inclusion were at least three affected individuals in more than one generation. A total of 29 markers were used to saturate the candidate region. One hundred sixty-seven family members were tested (84 affected and 83 unaffected). Under the assumption of heterogeneity and through use of an affecteds-only model, a maximum multipoint LOD score of 2.01 was achieved in the total sample, with an estimated proportion of families with linkage of 0.32. This LOD score is significant for linkage in a replication study and corresponds to a P value of.0047. Two families (family A [German Canadian] and family D [from western Nebraska]) reached significant linkage on their own, with a combined maximum multipoint LOD score of 3.33, calculated with an affecteds-only model (family A: LOD score 1.67, P=.0028; family D: LOD score 1.67, P=.0028). When a penetrance-dependent model was calculated, the combined multipoint LOD score achieved was 3.92 (family A: LOD score 1.68, P=.0027; family D: LOD score 2.24, P=.0007). On the basis of the multipoint analysis for the combined families A and D, the 1-LOD support interval suggests that the most likely disease location is between a CA repeat polymorphism on genomic clone AC025253 (44.5 Mb) and marker D12S1701 (47.7 Mb). Our data provide evidence that the PARK8 locus is responsible for the disease in a subset of families of white ancestry with autosomal dominant parkinsonism, suggesting that it could be a more common locus.     

A novel form of "central pouchlike" cataract, with sutural opacities, maps to chromosome 15q21-22

Congenital cataract is a clinically and genetically highly heterogeneous eye disorder, with autosomal dominant inheritance being most common. We investigated a large seven-generation family with 74 individuals affected by autosomal dominant congenital cataract (ADCC). The phenotype in this family can be described as "central pouchlike" cataract with sutural opacities, and it differs from the other mapped cataracts. We performed linkage analysis with microsatellite markers in this family and excluded the known candidate genes. A genomewide search revealed linkage to markers on chromosome 15, with a maximum two-point LOD score of 5.98 at straight theta=0 with marker D15S117. Multipoint analysis also gave a maximum LOD score of 5.98 at D15S117. Multipoint and haplotype analysis narrowed the cataract locus to a 10-cM region between markers D15S209 and D15S1036, closely linked to marker D15S117 in q21-q22 region of chromosome 15. This is the first report of a gene for a clinically new type of ADCC at 15q21-22 locus.     

A novel locus for autosomal dominant nonsyndromic hearing loss (DFNA44) maps to chromosome 3q28–29

Hereditary non-syndromic sensorineural hearing loss (NSSHL) is a genetically highly heterogeneous group of disorders. Autosomal dominant forms account for up to 20% of cases. To date, 39 loci have been identified by linkage analysis of affected families that segregate NSSHL forms in the autosomal dominant mode (DFNA). Investigation of a large Spanish pedigree with autosomal dominant inheritance of bilateral and progressive NSSHL of postlingual onset excluded linkage to known DFNA loci and, in a subsequent genome-wide scan, the disorder locus was mapped to 3q28-29. A maximum two-point LOD score of 4.36 at theta=0 was obtained for marker D3S1601. Haplotype analysis placed the novel locus, DFNA44, within a 3-cM genetic interval defined by markers D3S1314 and D3S2418. Heteroduplex analysis and DNA sequencing of coding regions and exon/intron boundaries of two genes (CLDN16 and FGF12) in this interval did not reveal disease-causing mutations.     

Evidence for a rare prostate cancer-susceptibility locus at chromosome 1p36

Combining data from a genomic screen in 70 families with a high risk for prostate cancer (PC) with data from candidate-region mapping in these families and an additional 71 families, we have localized a potential hereditary PC-susceptibility locus to chromosome 1p36. Because an excess of cases of primary brain cancer (BC) have been observed in some studies of families with a high risk for PC, and because loss of heterozygosity at 1p36 is frequently observed in BC, we further evaluated 12 families with both a history of PC and a blood relative with primary BC. The overall LOD score in these 12 families was 3.22 at a recombination fraction (theta) of .06, with marker D1S507. On the basis of an a priori hypothesis, this group was stratified by age at diagnosis of PC. In the younger age group (mean age at diagnosis <66 years), a maximum two-point LOD score of 3.65 at straight theta = .0 was observed, with D1S407. This linkage was rejected in both early- and late-onset families without a history of BC (LOD scores -7.12 and -6.03, respectively, at straight theta = .0). After exclusion of 3 of the 12 families that had better evidence of linkage to previously described PC-susceptibility loci, linkage to the 1p36 region was suggested by a two-point LOD score of 4.74 at straight theta = .0, with marker D1S407. We conclude that a significant proportion of these families with both a high risk for PC and a family member with BC show linkage to the 1p36 region.     

Dominant intermediate Charcot-Marie-Tooth neuropathy maps to chromosome 19p12-p13.2

The hereditary disorders of peripheral nerve form one of the most common groups of human genetic diseases, collectively called Charcot-Marie-Tooth (CMT) neuropathy. Using linkage analysis we have identified a new locus for a form of CMT that we have called "dominant intermediate CMT" (DI-CMT). A genomewide screen using 383 microsatellite markers showed strong linkage to the short arm of chromosome 19 (maximum LOD score 4.3, with a recombination fraction (straight theta) of 0, at D19S221 and maximum LOD score 5.28, straight theta=0, at D19S226). Haplotype analysis performed with 14 additional markers placed the DI-CMT locus within a 16.8-cM region flanked by the markers D19S586 and D19S546. Multipoint linkage analysis suggested the most likely location at D19S226 (maximum multipoint LOD score 6.77), within a 10-cM confidence interval. This study establishes the presence of a locus for DI-CMT on chromosome 19p12-p13.2.     

Localization of the gene causing keratolytic winter erythema to chromosome 8p22-p23, and evidence for a founder effect in South African Afrikaans-speakers.

Keratolytic winter erythema (KWE), also known as "Oudtshoorn skin disease," or "erythrokeratolysis hiemalis," is an autosomal dominant skin disorder of unknown etiology characterized by a cyclical erythema, hyperkeratosis, and recurrent and intermittent peeling of the palms and soles, particularly during winter. Initially KWE was believed to be unique to South Africa, but recently a large pedigree of German origin has been identified. The disorder occurs with a prevalence of 1/7,000 in the South African Afrikaans-speaking Caucasoid population, and this high frequency has been attributed to founder effect. After a number of candidate regions were excluded from linkage to KWE in both the German family and several South African families, a genomewide analysis was embarked on. Linkage to the microsatellite marker D8S550 on chromosome 8p22-p23 was initially observed, with a maximum LOD score (Z(max)) of 9.2 at a maximum recombination fraction (theta(max)) of .0 in the German family. Linkage was also demonstrated in five of the larger South African families, with Z(max) = 7.4 at theta(max) = .02. When haplotypes were constructed, 11 of 14 South African KWE families had the complete "ancestral" haplotype, and 3 demonstrated conservation of parts of this haplotype, supporting the hypothesis of founder effect. The chromosome segregating with the disease in the German family demonstrated a different haplotype, suggesting that these chromosomes do not have a common origin. Recombination events place the KWE gene in a 6-cM interval between D8S550 and D8S552. If it is assumed that there was a single South African founder, a proposed ancestral recombinant suggests that the gene is most likely in a 1-cM interval between D8S550 and D8S265.     

In Swedish families with hereditary prostate cancer, linkage to the HPC1 locus on chromosome 1q24-25 is restricted to families with early-onset prostate cancer.

Prostate cancer clusters in some families, and an estimated 5%-10% of all cases are estimated to result from inheritance of prostate cancer-susceptibility genes. We previously reported evidence of linkage to the 1q24-25 region (HPC1) in 91 North American and Swedish families each with multiple cases of prostate cancer (Smith et al. 1996). In the present report we analyze 40 (12 original and 28 newly identified) Swedish families with hereditary prostate cancer (HPC) that, on the basis of 40 markers spanning a 25-cM interval within 1q24-25, have evidence of linkage. In the complete set of families, a maximum two-point LOD score of 1.10 was observed at D1S413 (at a recombination fraction [theta] of.1), with a maximum NPL (nonparametric linkage) Z score of 1.64 at D1S202 (P=.05). The evidence of linkage to this region originated almost exclusively from the subset of 12 early-onset (age <65 years) families, which yielded a maximum LOD score of 2.38 at D1S413 (straight theta=0) and an NPL Z score of 1.95 at D1S422 (P=.03). Estimates from heterogeneity tests suggest that, within Sweden, as many as 50% of early-onset families had evidence of linkage to the HPC1 region. These results are consistent with the hypothesis of linkage to HPC1 in a subset of families with prostate cancer, particularly those with an early age at diagnosis.     

Mapping of a First Locus for Autosomal Dominant Myxomatous Mitral-Valve Prolapse to Chromosome 16p11.2-p12.1

Myxomatous mitral-valve prolapse (MMVP), also called Barlow disease, is a common cardiac abnormality and affects up to 5% of the population. It is characterized by an excess of tissue that leads to billowing of the mitral leaflets, sometimes complicated by prolapse. Typical histological findings include myxomatous degeneration and degradation of collagen and elastin. Previous reports have proposed an autosomal dominant inheritance of the trait, with age- and sex-dependent expression. By systematic echocardiographic screening of the first-degree relatives of 17 patients who underwent mitral-valve repair, we have identified four pedigrees showing such an inheritance. Genomewide linkage analysis of the most informative pedigree (24 individuals, three generations) showed a significant linkage for markers mapping to chromosome 16p, with a two-point maximum LOD score for D16S3068 (Zmax=3.30 at straight theta=0). Linkage to D16S3068 was confirmed in a second family (Zmax=2.02 at straight theta=0) but was excluded for the two remaining families, thus demonstrating the genetic heterogeneity of the disease. Multipoint linkage analysis performed, with nine additional markers, on the two families with linkage gave maximum multipoint LOD scores of 5.45 and 5.68 for D16S3133, according to a conservative and a stringent model, respectively. Haplotype analysis defined a 5-cM minimal MMVP-1 locus between D16S3068 (16p11.2) and D16S420 (16p12. 1) and a 34-cM maximal interval between D16S404 and D16S3068 when recombination events were taken into account only in affected individuals. The identification of this locus represents a first step toward a new molecular classification of mitral-valve prolapse.     

Mapping of a new locus for autosomal recessive demyelinating Charcot-Marie-Tooth disease to 19q13.1-13.3 in a large consanguineous Lebanese family: exclusion of MAG as a candidate gene

Autosomal recessive Charcot-Marie-Tooth disease (CMT) type 4 (CMT4) is a complex group of demyelinating hereditary motor and sensory neuropathies presenting genetic heterogeneity. Five different subtypes that correspond to six different chromosomal locations have been described. We hereby report a large inbred Lebanese family affected with autosomal recessive CMT4, in whom we have excluded linkage to the already-known loci. The results of a genomewide search demonstrated linkage to a locus on chromosome 19q13.1-13.3, over an 8.5-cM interval between markers D19S220 and D19S412. A maximum pairwise LOD score of 5.37 for marker D19S420, at recombination fraction [theta].00, and a multipoint LOD score of 10.3 for marker D19S881, at straight theta = .00, strongly supported linkage to this locus. Clinical features and the results of histopathologic studies confirm that the disease affecting this family constitutes a previously unknown demyelinating autosomal recessive CMT subtype known as "CMT4F." The myelin-associated glycoprotein (MAG) gene, located on 19q13.1 and specifically expressed in the CNS and the peripheral nervous system, was ruled out as being the gene responsible for this form of CMT.     

Paget disease of bone: mapping of two loci at 5q35-qter and 5q31

Paget disease of bone is characterized by focal increases of the bone-remodeling process. It is the second most common metabolic bone disease after osteoporosis. Genetic factors play a major role in the etiology of Paget disease of bone, and two loci have been mapped for the disorder: PDB1 and PDB2. The gene(s) causing the typical form of the disorder remains to be characterized. To decipher the molecular basis of Paget disease of bone, we performed genetic linkage analysis in 24 large French Canadian families (479 individuals) in which the disorder was segregating as an autosomal dominant trait. After exclusion of PDB2, a genomewide scan was performed on the three most informative family nuclei. LOD scores >1.0 were observed at seven locations. The 24 families were then used to detect strong evidence for linkage to chromosome 5q35-qter. Under heterogeneity, a maximum LOD score of 8.58 was obtained at D5S2073, at straight theta= .1. The same characteristic haplotype was carried by all patients in eight families, suggesting a founder effect. A recombination event in a key family confined the disease region within a 6-cM interval between D5S469 and the telomere. The 16 other families, with very low conditional probability of linkage to 5q35-qter, were further used, to map a second locus at 5q31. Under heterogeneity, a maximum LOD score of 3.70 was detected at D5S500 with straight theta=.00. Recombination events refined the 5q31 region within 12.2 cM, between D5S642 and D5S1972. These observations demonstrate the mapping of two novel loci for Paget disease of bone and provide further evidence for genetic heterogeneity of this highly prevalent disorder. It is proposed that the 5q35-qter and 5q31 loci be named "PDB3" and "PDB4," respectively.     

An autosomal recessive nonsyndromic-hearing-loss locus identified by DNA pooling using two inbred Bedouin kindreds.

Autosomal recessive nonsyndromic hearing loss (ARNSHL) is the most common form of severe inherited childhood deafness. We present the linkage analysis of two inbred Bedouin kindreds from Israel that are affected with ARNSHL. A rapid genomewide screen for markers linked to the disease was performed by using pooled DNA samples. This screen revealed evidence for linkage with markers D9S922 and D9S301 on chromosome 9q. Genotyping of individuals from both kindreds confirmed linkage to chromosome 9q and a maximum combined LOD score of 26.2 (recombination fraction [theta] .025) with marker D9S927. The disease locus was mapped to a 1.6-cM region of chromosome 9ql3-q2l, between markers D9S15 and D9S927. The disease segregates with a common haplotype in the two kindreds, at markers D9S927, D9S175, and D9S284 in the linked interval, supporting the hypothesis that both kindreds inherited the deafness gene from a common ancestor. Although this nonsyndromic-hearing-loss (NSHL) locus maps to the same cytogenetic interval as DFNB7, it does not overlap the currently defined DFNB7 interval and may represent (1) a novel form of NSHL in close proximity to DFNB7 or (2) a relocalization of the DFNB7 interval to a region telomeric to its reported location. This study further demonstrates that DNA pooling is an effective means of quickly identifying regions of linkage in inbred families with heterogeneous autosomal recessive disorders.     

A new locus for generalized epilepsy with febrile seizures plus maps to chromosome 2

Generalized epilepsy with febrile seizures plus (GEFS+) is a recently recognized but relatively common form of inherited childhood-onset epilepsy with heterogeneous epilepsy phenotypes. We genotyped 41 family members, including 21 affected individuals, to localize the gene causing epilepsy in a large family segregating an autosomal dominant form of GEFS+. A genomewide search examining 197 markers identified linkage of GEFS+ to chromosome 2, on the basis of an initial positive LOD score for marker D2S294 (Z=4.4, recombination fraction [straight theta] = 0). A total of 24 markers were tested on chromosome 2q, to define the smallest candidate region for GEFS+. The highest two-point LOD score (Zmax=5.29; straight theta=0) was obtained with marker D2S324. Critical recombination events mapped the GEFS+ gene to a 29-cM region flanked by markers D2S156 and D2S311, with the idiopathic generalized epilepsy locus thereby assigned to chromosome 2q23-q31. The existence of the heterogeneous epilepsy phenotypes in this kindred suggests that seizure predisposition determined by the GEFS+ gene on chromosome 2q could be modified by other genes and/or by environmental factors, to produce the different seizure types observed.     

Hereditary Vascular Retinopathy, Cerebroretinal Vasculopathy, and Hereditary Endotheliopathy with Retinopathy, Nephropathy, and Stroke Map to a Single Locus on Chromosome 3p21.1-p21.3

We performed a genomewide search for linkage in an extended Dutch family with hereditary vascular retinopathy associated with migraine and Raynaud phenomenon. Patients with vascular retinopathy are characterized by microangiopathy of the retina, accompanied by microaneurysms and telangiectatic capillaries. The genome search, using a high throughput capillary sequencer, revealed significant evidence of linkage to chromosome 3p21.1-p21.3 (maximum pairwise LOD score 5.25, with D3S1578). Testing of two additional families that had a similar phenotype, cerebroretinal vasculopathy, and hereditary endotheliopathy with retinopathy, nephropathy, and stroke, revealed linkage to the same chromosomal region (combined maximum LOD score 6.30, with D3S1588). Haplotype analysis of all three families defined a 3-cM candidate region between D3S1578 and D3S3564. Our study shows that three autosomal dominant vasculopathy syndromes with prominent cerebroretinal manifestations map to the same 3-cM interval on 3p21, suggesting a common locus.     

Autosomal recessive familial exudative vitreoretinopathy is associated with mutations in LRP5

Familial exudative vitreoretinopathy (FEVR) is a hereditary eye disorder that affects both the retina and vitreous body. Autosomal recessive FEVR was diagnosed in multiple individuals from three consanguineous families of European descent. A candidate-locus-directed genome scan shows linkage to the region on chromosome 11q flanked by markers D11S905 and D11S1314. The maximum LOD score of 3.6 at theta =0 is obtained with marker D11S987. Haplotype analysis confirms that the critical region is the 22-cM (311-Mb) interval flanked by markers D11S905 and D11S1314. This region contains LRP5 but not FZD4; mutations in both of these genes cause autosomal dominant FEVR. Sequencing of LRP5 shows, in all three families, homozygous mutations R570Q, R752G, and E1367K. This suggests that mutations in this gene can cause autosomal recessive as well as autosomal dominant FEVR.     

A Genomewide Search for Type 2 Diabetes–Susceptibility Genes in Indigenous Australians

The prevalence of type 2 diabetes among Australian residents is 7.5%; however, prevalence rates up to six times higher have been reported for indigenous Australian communities. Epidemiological evidence implicates genetic factors in the susceptibility of indigenous Australians to type 2 diabetes and supports the hypothesis of the "thrifty genotype," but, to date, the nature of the genetic predisposition is unknown. We have ascertained clinical details from a community of indigenous Australian descent in North Stradbroke Island, Queensland. In this population, the phenotype is characterized by severe insulin resistance. We have conducted a genomewide scan, at an average resolution of 10 cM, for type 2 diabetes-susceptibility genes in a large multigeneration pedigree from this community. Parametric linkage analysis undertaken using FASTLINK version 4.1p yielded a maximum two-point LOD score of +2.97 at marker D2S2345. Multipoint analysis yielded a peak LOD score of +3.9 <1 cM from marker D2S2345, with an 18-cM 3-LOD support interval. Secondary peak LOD scores were noted on chromosome 3 (+1.8 at recombination fraction [theta] 0.05, at marker D3S1311) and chromosome 8 (+1.77 at theta=0.0, at marker D8S549). These chromosomal regions are likely to harbor novel susceptibility genes for type 2 diabetes in the indigenous Australian population.     

A novel locus for Meckel-Gruber syndrome,MKS3, maps to chromosome 8q24

Meckel-Gruber syndrome (MKS), the most common monogenic cause of neural tube defects, is an autosomal recessive disorder characterised by a combination of renal cysts and variably associated features, including developmental anomalies of the central nervous system (typically encephalcoele), hepatic ductal dysplasia and cysts, and polydactyly. Locus heterogeneity has been demonstrated by the mapping of the MKS1locus to 17q21-24 in Finnish kindreds, and of MKS2 to 11q13 in North African-Middle Eastern cohorts. In the present study, we have investigated the genetic basis of MKS in eight consanguineous kindreds, originating from the Indian sub-continent, that do not show linkage to either MKS1 or MKS2. We report the localisation of a third MKS locus ( MKS3) to chromosome 8q24 in this cohort by a genome-wide linkage search using autozygosity mapping. We identified a 26-cM region of autozygosity between D8S586 and D8S1108 with a maximum cumulative two-point LOD score at D8S1179 ( Z(max)=3.04 at theta=0.06). A heterogeneity test provided evidence of one unlinked family. Exclusion of this family from multipoint analysis maximised the cumulative multipoint LOD score at locus D8S1128 ( Z(max)=5.65). Furthermore, a heterozygous SNP in DDEF1, a putative candidate gene, suggested that MKS3 mapped within a 15-cM interval. Comparison of the clinical features of MKS3-linked cases with reports of MKS1- and MKS2-linked kindreds suggests that polydactyly (and possibly encephalocele) appear less common in MKS3-linked families.