Analysis of chromosome 1 microsatellite markers and the FHM2-ATP1A2 gene mutations in migraine pedigrees

OBJECTIVES: The aims of the study were: (i) to extend our linkage analysis of chromosome 1q microsatellite markers in predominantly migraine with aura pedigrees and (ii) to test the novel FHM-2 ATP1A2 gene for involvement in these migraine affected pedigrees and a previous pedigree (MF14) showing evidence of linkage of markers to C1q31.METHODS: A chromosome 1 scan (31 markers) was performed in 21 multiplex pedigrees affected predominantly with migraine with aura (MA). The known FHM-2 ATP1A2 gene mutations were tested, by sequencing, for the involvement in MA and migraine without aura (MO) in these pedigrees. Sequencing was performed in the coding areas of the ATP1A2 gene through three MA individuals from MF14.RESULTS: Evidence for linkage was obtained at C1q23 to markers spanning the ATP1A2 gene. However, testing of the known ATP1A2 gene mutations (for FHM) in common migraine probands of pedigrees showing excess allele sharing was negative. Sequencing of the entire coding areas of the gene through all the three MA affected from MF14 was also negative for mutations.DISCUSSION: Microsatellite markers on chromosome 1q23 show evidence of excess allele sharing in MA and some MO pedigrees, suggesting linkage to the common forms of migraine and the presence of a susceptibility gene in this region. The FHM-2 (ATP1A2 gene) does not seem to be involved in the common types of migraine. Despite certain clinical characteristics, the genetic correlation between FHM and familial typical migraine remains unclear. Several candidate genes lie within the C1q23 and C1q31 cytogenetic regions; therefore, further studies are needed.     

Familial hemiplegic migraine: linkage to chromosome 14q32 in a Spanish kindred

We sought to map the disease-causing gene in a large Spanish kindred with familial hemiplegic migraine (FHM). Patients were classified according to the ICHD-II criteria. After ruling out linkage to known migraine genetic loci, a single nucleotide polymorphism-based, 0.62-cM density genome-wide scan was performed. Among 13 affected subjects, FHM was the prevailing migraine phenotype in six, migraine with aura in four and migraine without aura in three. Linkage analysis revealed a disease locus in a 4.15-Mb region on 14q32 with a maximum two-point logarithm of odds (LOD) score of 3.1 and a multipoint parametric LOD score of 3.8. This genomic region does not overlap with the reported migraine loci on 14q21–22. Sequence analysis of three candidate genes in the region, SLC24A4, ATXN3 and ITPK1, failed to show disease-causing mutations in our patients. Genetic heterogeneity in FHM may be greater than previously suspected. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A genome-wide scan provides evidence for loci influencing a severe heritable form of common migraine

Migraine is a prevalent neurovascular disease with a significant genetic component. Linkage studies have so far identified migraine susceptibility loci on chromosomes 1, 4, 6, 11, 14, 19 and X. We performed a genome-wide scan of 92 Australian pedigrees phenotyped for migraine with and without aura and for a more heritable form of severe migraine. Multipoint non-parametric linkage analysis revealed suggestive linkage on chromosome 18p11 for the severe migraine phenotype (LOD*=2.32, P=0.0006) and chromosome 3q (LOD*=2.28, P=0.0006). Excess allele sharing was also observed at multiple different chromosomal regions, some of which overlap with, or are directly adjacent to, previously implicated migraine susceptibility regions. We have provided evidence for two loci involved in severe migraine susceptibility and conclude that dissection of the migraine phenotype may be helpful for identifying susceptibility genes that influence the more heritable clinical (symptom) profiles in affected pedigrees. Also, we concluded that the genetic aetiology of the common (International Headache Society) forms of the disease is probably comprised of a number of low to moderate effect susceptibility genes, perhaps acting synergistically, and this effect is not easily detected by traditional single-locus linkage analyses of large samples of affected pedigrees.     

Partial Cosegregation of Familial Hemiplegic Migraine and a Benign Familial Infantile Epileptic Syndrome

: Purpose: We studied a large Dutch-Canadian family, in which two very rare hereditary paroxysmal neurologic disorders, familial hemiplegic migraine (FHM) and a “benign familial infantile epileptic syndrome” concur and partially cosegregate. FHM is a dominantly inherited subtype of migraine with attacks of hemiparesis, linked to chromosome 19p13 in 50% of the families tested. Recently mutations in a brain-specific P/Q-type Ca²⁺ channel α1 subunit gene (CACNLlA4) were identified in families with chromosome 19-linked FHM. The infantile epileptic syndrome resembles to two other dominantly inherited benign epilepsies occurring in the first year of life, benign familial neonatal convulsions (BFNC), assigned to chromosomes 20q13.2 and 8q, and benign infantile familial convulsions (BIFC), as yet unlinked. Methods: Linkage analysis was performed for the known locations of FHM and BFNC. The question whether the two conditions in this family can be caused by a single gene defect was addressed by additional linkage analysis. Results: We excluded linkage of the infantile convulsions to markers on chromosome 20q13.2, Sq, or 19p13. This indicates the existence of a third locus for benign familial convulsions in the first year of life. Linkage of FHM to these markers was not formally excluded but seems very unlikely. Statistical analysis of whether, in this family, both conditions are caused by a single gene defect was inconclusive. Conclusions: We describe a “benign familial infantile epileptic syndrome“ with attacks of FHM at a later age. Further genetic studies in this family may help to unravel the genetic basis of epilepsy or migraine or both.     

Mapping of a second locus for familial hemiplegic migraine to 1q21–q23 and evidence of further heterogeneity

Familial hemiplegic migraine (FHM) is an autosomal dominant variety of migraine with aura. We previously mapped an FHM gene on the short arm of chromosome 19. Mutations in this gene, recently shown to be the α1 subunit of a P/Q-type voltage-dependent calcium channel, CACNL1A4, are involved in approximately 50% of unselected FHM families and in all families where migraine attacks are associated with permanent cerebellar ataxia. As a first step toward the identification of other FHM genes, we conducted a genetic linkage analysis in one large French pedigree and showed significant linkage to two microsatellite markers D1S2635 (Z_max: 3.33 at = 0.05) and D1S2705 (Z_max: 3.64 at = 0.05), establishing the existence of a second locus for FHM (FHM2) on chromosome 1q21–q23. Analysis of six additional FHM families favored linkage to this locus in two of them; linkage was excluded in the last four families, indicating further heterogeneity. Chromosome 1–linked families differ from the ones linked to chromosome 19, because penetrance in those families is much lower, and in some of their members, epileptic seizures occur during severe migraine attacks.     

Familial hemiplegic migraine: clinical features and probable linkage to chromosome 1 in an Italian family

We describe an Italian family with familial hemiplegic migraine (FHM), subtle cerebellar signs and probable linkage to chromosome 1. FHM is genetically heterogeneous; in about 50% of families it is caused by mutations within the CACNA1A gene on chromosome 19. Linkage to 1q31 and 1g21–23 has also been established. Other families do not link either to chromosome 19 or 1. Chromosome 19-linked FHM may display nystagmus and cerebellar ataxia. Affected family members were neurologically examined; linkage analysis was performed with markers for chromosomes 19p13, 1q21–23, and 1q32. Five family members had hemiplegic migraine, and 3 displayed additional cerebellar signs (scanning speech and nystagmus). In 1 patient, episodes of hemiplegic migraine triggered by mild head trauma. Epilepsy and mental retardation were also found in 1 affected relative each. Lod scores for linkage to 19p13 were negative, while the maximum two-point lod score was 1.81 to 1q21–23. This family with FHM and associated subtle cerebellar signs, epilepsy and mental retardation showed probable linkage to 1q21–23. Received: 27 December 2001 / Accepted in revised form: 27 February 2002     

hKCNN3 which maps to chromosome 1q21 is not the causative gene in periodic catatonia, a familial subtype of schizophrenia

The human calcium-activated potassium channel gene (hKCNN3, hSKCa3) contains two tandemly arranged, multiallelic CAG repeats located in exon 1 which result in short to moderate polyglutamine stretches of unknown functional significance. Case-control and family-based association studies suggested an association of hKCNN3 repeats with susceptibility for schizophrenia. Twelve multiplex pedigrees with periodic catatonia, a schizophrenia subtype with major gene effect and patterns of anticipation, were genotyped using the multiallelic hKCNN3 repeat polymorphism. Using a dominant model of inheritance with sex- and age-dependent penetrance classes, cumulative results showed exclusion of linkage of hKCNN3 to periodic catatonia under the assumption of genetic homogeneity with lod score of −48.01 at zero recombination fraction. Our results provide evidence that hKCNN3 is not the causative gene in the familial schizophrenia subtype of periodic catatonia. By fluorescent in situ hybridization we confirmed the assignment of hKCNN3 to chromosome 1q21 near the heterochromatin region. Linkage mapping showed segregation with marker DIS498 (θ=0.05) and placed hKCNN3 in the genetic linkage map in a cluster of genes near the centromeric region of chromosome 1. Received: 14 April 1999 / Accepted: 22 February 2000     

Confirmation that Xq27 and Xq28 are susceptibility loci for migraine in independent pedigrees and a case-control cohort

Investigations into migraine genetics have suggested that susceptibility loci exist on the X chromosome. These reports are supported by evidence that demonstrates male probands as having a higher proportion of affected first-degree relatives as well as the female preponderance of 3:1 that the disorder displays. We have previously implicated the Xq24-28 locus in migraine using two independent multigenerational Australian pedigrees that demonstrated excess allele sharing at the Xq24, Xq27 and Xq28 loci. Here, we expand this work to investigate a further six independent migraine pedigrees using 11 microsatellite markers spanning the Xq27–28 region. Furthermore, 11 candidate genes are investigated in an Australian case-control cohort consisting of 500 cases and 500 controls. Microsatellite analysis showed evidence of excess allele sharing to the Xq27 marker DXS8043 (LOD* 1.38 P00.005) in MF879 whilst a second independent pedigree showed excess allele sharing to DXS8061 at Xq28 (LOD* 1.5 P00.004). Furthermore, analysis of these key markers in a case control cohort showed significant association to migraine in females at the DXS8043 marker (T1 P00.009) and association with MO at DXS8061 (T1 P00.05). Further analysis of 11 key genes across these regions showed significant association of a three-marker risk haplotype in the NSDHL gene at Xq28 (P00.0082). The results of this study add further support to the presence of migraine susceptibility loci on chromosome Xq27 and Xq28 as well as point to potential candidate genes in the regions that warrant further investigation.     

A G301R Na<Superscript>+</Superscript>/K<Superscript>+</Superscript>-ATPase mutation causes familial hemiplegic migraine type 2 with cerebellar signs

Familial hemiplegic migraine (FHM) is an autosomal dominant subtype of migraine with hemiparesis during the aura. In over 50% of cases the causative gene is CACNA1A (FHM1), which in some cases produces a phenotype with cerebellar signs, including ataxia and nystagmus. Recently, mutations in ATP1A2 on chromosome 1q23 encoding a Na⁺/K⁺-ATPase subunit were identified in four families (FHM2). We now describe an FHM2 pedigree with a fifth ATP1A2 mutation coding for a G301R substitution. The phenotype was particularly severe and included hemiplegic migraine, seizure, prolonged coma, elevated temperature, sensory deficit, and transient or permanent cerebellar signs, such as ataxia, nystagmus, and dysarthria. A mild crossed cerebellar diaschisis during an attack further supported the clinical evidence of a cerebellar deficit. This is the first report suggesting cerebellar involvement in FHM2. A possible role for CACNA1A in producing the phenotype in this family was excluded by linkage studies to the FHM1 locus. The study of this family suggests that the absence of cerebellar signs may not be a reliable indicator to clinically differentiate FHM2 from FHM1.     

Association of progesterone receptor with migraine-associated vertigo

While migraine has been demonstrated to be familial and have genetic contributions, genome-wide linkage analyses and candidate gene studies have highlighted that migraine is genetically complex. Despite substantial efforts, no consistent replication of linkage or association has been reported for common migraine syndromes. Among the candidate genes tested for association with migraine by several groups were female sex hormone genes based on the observation of a much higher incidence of migraine in females. Migraine-associated vertigo (MAV) is a migraine syndrome also much more common in females than males. Because MAV is less common in the general population than migraine or migraine with aura, it may be a better migraine syndrome to detect susceptibility alleles. In this study, we tested the association of two female hormonal genes, progesterone receptor (PGR) and estrogen receptor (ESR1), which were previously reported to be associated with migraine in women. We typed 150 MAV subjects and 145 genomic matched control subjects. One SNP (rs1042838) within PGR, which is in high linkage disequilibrium with the functional PROGINS variant, was significantly associated with MAV (p = 0.0007). Two SNPs (rs2228480 and rs1801132) within ESR1 demonstrated no significant association. No synergistic effect between ESR1 variants and PGR variants was identified.     

Suggestive linkage to chromosomal regions 13q31 and 22q12 in families with psychotic bipolar disorder

OBJECTIVE: Linkage studies of bipolar disorder and schizophrenia have found overlapping evidence for susceptibility genes in four chromosomal regions-10p12-14, 13q32, 18p11.2, and 22q12-13. The authors previously demonstrated familial clustering of psychotic symptoms-defined as hallucinations and/or delusions-in some bipolar disorder pedigrees. In this study they used stratified linkage analysis to test the hypothesis that those bipolar disorder pedigrees most enriched for psychotic symptoms would show greater evidence of linkage to the regions of previous bipolar disorder/schizophrenia linkage overlap. METHOD: Nonparametric linkage analyses using GENEHUNTER and ASPEX were performed on 65 bipolar disorder families. Family subsets were defined by the number of family members with psychotic mood disorder. RESULTS: The 10 families in which three or more members had psychotic mood disorder showed suggestive evidence of linkage to 13q31 (nonparametric linkage score=3.56; LOD score=2.52) and 22q12 (nonparametric linkage score=3.32; LOD score=3.06). These results differed significantly from those for the entire study group of 65 families, which showed little or no linkage evidence in the two regions. The 10 families with three or more psychotic members did not show evidence of linkage to 10p12-14 or 18p11.2. The 95% confidence interval on 22q12 spanned 4.3 centimorgans (2.6 megabases) and was congruent with previous findings. CONCLUSIONS: Bipolar disorder families in which psychotic symptoms cluster may carry susceptibility genes on chromosomal regions 13q31 and 22q12. Replication should be attempted in similar families and perhaps in schizophrenia families in which mood symptoms cluster because these overlapping phenotypes may correlate most closely with the putative susceptibility genes. The localization of the 22q12 finding particularly encourages further study of this region.     

Molecular genetics of migraine

Migraine is a heterogeneous condition both clinically and genetically. Genetic and environmental factors are involved in migraine with and without aura. In most cases, genetic susceptibility has a polygenic pattern of inheritance with the exception of familial hemiplegic migraine (FHM) which is a mendelian, autosomal dominant, condition. Two genes have been identified so far in FHM, Cav2.1 and ATP1A2. The identification of these two genes have provided clues to understand the mechanisms of this condition, particularly through the analysis of murine animal models harboring mutations detected in human FHM patients. These two genes do not seem to be involved in the other forms of migraine. A number of association and linkage studies have pointed to several loci and/or genetic variants. However most of these data need confirmation.     

A novel missense ATP1A2 mutation in a Finnish family with familial hemiplegic migraine type 2

Familial hemiplegic migraine (FHM), a rare autosomal dominant subtype of migraine with aura, has been linked to two chromosomal loci, 19p13 and 1q23. Mutations in the Na⁺,K⁺-ATPase 2 subunit gene, ATP1A2, on 1q23 have recently been shown to cause familial hemiplegic migraine type 2 (FHM2). We sequenced the coding regions of this gene in a Finnish chromosome 1q23-linked FHM family with associated symptoms such as coma and identified a novel A1033G mutation in exon 9. This mutation results in a threonine-to-alanine substitution at codon 345. This residue is located in a highly conserved N-terminal region of the M4–5 loop of the Na⁺,K⁺-ATPase. Furthermore, the T345A mutation co-segregated with the disorder in our family and was not present in 132 healthy Finnish control individuals. For these reasons it is most likely the FHM-causing mutation in this family.     

Association between migraine and a functional polymorphism at the dopamine β-hydroxylase locus

Migraine is a common neurological disorder with a significant genetic component. Although a number of linkage and association studies have been undertaken, the number and identity of all migraine susceptibility genes has yet to be defined. The existence of dopaminergic hypersensitivity in migraine has been recognised on a pharmacological basis and some studies have reported genetic association between migraine and dopamine-related gene variants. Our laboratory has previously reported association of migraine with a promoter STR marker in the dopamine beta hydroxylase (DBH) gene. In the present study, we analysed two additional DBH markers in two independent migraine case–control cohorts. These two markers are putative functional SNPs, one within the promoter (−1021C→T) and another SNP (+1603C→T) in exon 11 of the DBH gene. The results showed a significant association for allelic and genotypic frequency distribution between the DBH marker in the promoter and migraine in the first (P = 0.004 and P = 0.012, respectively) and the second (P = 0.013 and P = 0.031, respectively) tested cohorts. There was no association observed between either genotype and/or allelic frequencies for the DBH marker located in exon 11 and migraine (P ≥ 0.05). The promoter DBH marker, reported associated with migraine in this study, has been shown to affect up to 52% of plasma DBH activity. Varying DBH activity levels have been postulated to be involved in migraine process with an increase of dopamine, resulting from a lower DBH activity shown positively correlated with migraine severity. It is plausible that the functional promoter variant of DBH may play a role in the migraine disorder.     

The genetics of migraine

The search for genes involved in the pathophysiology of migraine poses major difficulties. First, there is no objective diagnostic method to assess the status of the individuals studied. Second, migraine is a polygenic multifactorial disorder. Familial hemiplegic migraine (FHM) is the only known autosomal dominant subtype of migraine. In half the families with FHM who have been studied, there are mutations in the calcium-channel gene CACNA1A, located on chromosome 19. In other families, a locus has been mapped on chromosome 1. The role of these loci in typical migraine is still unknown. A susceptibility locus for migraine with aura has been located on chromosome 19 (but is distinct from CACNA1A) and a genome-wide linkage analysis has mapped a susceptibility locus on chromosome 4. Another locus for migraine may be on the X chromosome. Finally, many positive association studies have been published, but few have been replicated.     

Genetic heterogeneity in Italian families with familial hemiplegic migraine.

OBJECTIVE: To verify linkage to chromosome 19p13, to detect mutations in the CACNA1A gene, and to correlate genetic results to their clinical phenotypes in Italian families with familial hemiplegic migraine (FHM). BACKGROUND: FHM is an autosomal dominant disease, classified as a subtype of migraine with aura. Only a proportion of FHM patients have been associated with chromosome 19p13. Among these, four missense mutations within the CACNA1A gene in five unrelated families have been described. METHODS: A linkage study was performed in 19 patients affected by FHM from five families by studying microsatellite markers associated with the 19p13 region. All familial and seven additional sporadic patients with FHM were analyzed to search for mutations within the CACNA1A gene by applying the double gradient-denaturant gradient electrophoresis technique. RESULTS: Lod score values did not establish significantly linkage to chromosome 19. However, seven new genetic variants were detected: six were new polymorphisms. The seventh was a missense mutation present in family 1, and it was associated with a hemiplegic migraine phenotype without unconsciousness and cerebellar ataxia. Because this missense mutation is absent in the general population and cosegregates with the disease, it may be a pathologic mutation. CONCLUSIONS: Genetic heterogeneity of FHM has been shown in familial and sporadic FHM patients of Italian origin. The new missense mutation-G4644T-is associated with milder clinical features compared with typical FHM.     

Age-at-onset linkage analysis in Caribbean Hispanics with familial late-onset Alzheimer’s disease

The aim of the study was to identify chromosomal regions that may harbor putative genetic variants influencing age at onset in familial late-onset Alzheimer’s disease (LOAD). Data from a genome-wide scan that included genotyping of APOE were analyzed in 1,161 individuals from 209 families of Caribbean Hispanic ancestry with a mean age at onset of 73.3 years multiply affected by LOAD. Two-point and multipoint analyses were conducted using variance component methods using 376 microsatellite markers with an average intermarker distance of 9.3 cM. Family-based test of association was also conducted for the same set of markers. Age at onset of symptoms among affected individuals was used as the quantitative trait. Our results showed that the presence of APOE-ɛ4 lowered the age at onset by 3 years. Several candidate loci were identified. Using linkage analysis strategy, the highest logarithm of odds (LOD) scores were obtained using a conservative definition of LOAD at 5q15 (LOD = 3.1), 17q25.1 (LOD = 2.94), 14q32.12 (LOD = 2.36), and 7q36.3 (LOD = 2.29) in a model that adjusted for APOE-ɛ4 and other covariates. Both linkage and family-based association identified 17p13 as a candidate region. Family-based association analysis showed markers at 12q13 (p = 0.00002), 13q33 (p = 0.00043), and 14q23 (p = 0.00046) to be significantly associated with age at onset. The current study supports the hypothesis that there are additional genetic loci that could influence age at onset of late onset Alzheimer’s disease. The novel loci at 5q15, 17q25.1, 13q33, and 17p13 and the previously reported loci at 7q36.3, 12q13, 14q23, and 14q32 need further investigation. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Joseph H. Lee, Sandra Barral, Rong Cheng, and Inara Chacon contributed equally to this work.     

The genetic features of 24 patients affected by familial and sporadic hemiplegic migraine

Familial hemiplegic migraine (FHM) is the only migraine subtype for which a monogenic mode of inheritance, autosomal dominant has been clearly established. It is genetically heterogeneous and at least three different genes exist (CACNA1A, ATP1A2, and SCN1A), the so-called FHM1, FHM2, and FHM3 genes, respectively. Sporadic hemiplegic migraine (SHM) is a disorder, in which some patients may have their pathophysiology identical to FHM, but others, possibly the majority, may have different pathophysiology, probably related to the mechanisms of typical migraine with aura. In our study, we have screened the DNA of 24 patients affected by FHM and SHM. Only in three patients, 2 sporadic and 1 familial cases, we have described genetic mutations, all of them in the ATP1A2 gene. In our opinion, these results demonstrate a more frequent involvement of the ATP1A2 gene not only in the sporadic form, but probably also in the Italian FHM patients without permanent cerebellar signs. Moreover, the absence of CACNA1A, ATP1A2 and SCN1A mutations in the other 12 familial cases suggests the involvement of still unknown genes.

     

Habituation of evoked responses is greater in patients with familial hemiplegic migraine than in controls: a contrast with the common forms of migraine

Background: Familial hemiplegic migraine (FHM) is a rare, dominantly inherited subtype of migraine with transient hemiplegia during the aura phase. Mutations in at least three different genes can produce the FHM phenotype. The mutated FHM genes code for ion transport proteins that animal and cellular studies have associated with disturbed ion homeostasis, altered cellular excitability, neurotransmitter release, and decreased threshold for cortical spreading depression. The common forms of migraine are characterized interictally by a habituation deficit of cortical and subcortical evoked responses that has been attributed to neuronal dysexcitability. FHM and the common forms of migraine are thought to belong to a spectrum of migraine phenotypes with similar pathophysiology, and we therefore examined whether an abnormal habituation pattern would also be found in FHM patients. Methods: In a group of genotyped FHM patients (five FHM‐1, four FHM‐2), we measured habituation of visual evoked potentials (VEP), auditory evoked potentials including intensity dependence (IDAP), the nociception‐specific blink reflex (nsBR) and compared the results to a group of healthy volunteers (HV). Results: FHM patients had a more pronounced habituation during VEP (P = 0.025) and nsBR recordings (P = 0.023) than HV. There was no difference for IDAP, but the slope tended to be steeper in FHM. Conclusion: Contrary to the common forms of migraine, FHM patients are not characterized by a deficient, but rather by an increased habituation in cortical/brain stem evoked activities. These results suggest differences between FHM and the common forms of migraine, as far as central neuronal processing is concerned.     

Genetic heterogeneity for autosomal recessive pyridoxine-dependent seizures

Pyridoxine-dependent seizure (PDS) is a rare autosomal recessive intractable seizure disorder only controlled by a daily supplementation of pharmacological doses of pyridoxine (Vitamin B6). Although glutamate decarboxylase utilizes pyridoxal phosphate as a cofactor during conversion of the excitatory amino acid, glutamate, to the inhibitory neurotransmitter, γ-amino butyric acid (GABA), several studies have failed to demonstrate a linkage to either of the glutamate-decarboxylase-encoding genes (GAD1 and GAD2) and PDS excluding involvement of this functional candidate. However, in 2000, a locus for PDS was mapped to a 5 cM interval at chromosome 5q31 in four consanguineous and one multisib pedigree (Z _max=8.43 at θ=0 for marker D5S2017) [Cormier-Daire et al. in Am J Hum Genet 67(4):991–993 2000]. We undertook molecular genetic studies of six nonconsanguineous North American families, using up to ten microsatellite markers to perform haplotype segregation analysis of the 5q31 locus. Assignment to the chromosome 5q PDS locus was excluded in one of the six North American PDS pedigrees, as chromosome 5q31 haplotypes were incompatible with linkage to this locus. The remaining five PDS pedigrees showed haplotype segregation consistent with linkage to 5q31, generating a maximum combined lod score of 1.87 (θ=0) at marker D5S2011. In this study, we establish genetic heterogeneity for PDS, catalog 21 genes within the originally defined PDS interval, and identify additional recombinations that indicate a higher priority interval, containing just 11 genes.