Novel and Recurrent KIF21A Mutations in Congenital Fibrosis of the Extraocular Muscles Type 1 and 3

OPHTHALMIC MOLECULAR GENETICS Novel and Recurrent KIF21A Mutations in Congenital Fibrosis of the Extraocular Muscles Type 1 and 3

Shasha Lu, MD, PhD; Chen Zhao, MD, PhD; Kanxing Zhao, MD, PhD; Ningdong Li, MD, PhD; Catharina Larsson, MD, PhD

Objective: To characterize the disease-causing muta- CFEOM1 families (2860CϾT) and the CFEOM3 family tions and associated clinical phenotypes in 5 Chinese fami- (2861GϾA). In another CFEOM1 family, a novel mis- lies with congenital fibrosis of the extraocular muscles sense mutation (84CϾG, C28W) was revealed. (CFEOM). Conclusions: The novel KIF21A mutation 84CϾG Methods: Ophthalmic investigations included visual acu- demonstrated in a CFEOM1 family affects the kinesin ity, levator function, documentation of compensatory head motor domain, supporting that mutations may also oc- position, ocular motility, and slitlamp and fundus ex- cur outside the commonly involved coiled-coil domain. aminations. The kinesin family member 21A gene The 2861GϾA mutation found in a CFEOM3 family (KIF21A) was sequenced for mutation detection. Geno- has been previously reported in CFEOM1, further sup- typing and linkage analysis were performed for the porting that different phenotypes can arise from identi- KIF21A/FEOM1 and FEOM3 loci. cal mutations. Results: Four families were clinically classified as hav- Clinical Relevance: Clinical and genetic characteriza- ing CFEOM type 1 (CFEOM1) with full expression of tion are complementary tools for diagnostic, prognos- severe ptosis and ophthalmoplegia. One family had tic, and treatment purposes in CFEOM. CFEOM type 3 (CFEOM3) with typically varying expression of phenotypes between individuals. Recurrent heterozygous KIF21A mutations were identified in 2 Arch Ophthalmol. 2008;126(3):388-394

ONGENITAL FIBROSIS OF The majority of CFEOM kindreds are the extraocular muscles caused by mutations in the kinesin fam- (CFEOM) is a group of ily member 21A gene (KIF21A)atthe developmental disorders FEOM1 locus in the chromosomal region in which defective inner- 12q12.7-9 KIF21A mutations have also been vationC by the oculomotor and/or troch- reported in CFEOM3 families6,10; how- lear nerves impairs the extraocular ever, most CFEOM3 families are as- muscles, leading to ophthalmoplegia and signed to the FEOM3 locus on 16qter,11 ptosis.1,2 Autosomal dominant CFEOM oc- where the causative gene remains to be curs in 2 clinical forms with varying ex- identified. CFEOM type 2 is a recessive pressivity.3 In CFEOM1 (OMIM #135700), form of the disease involving the PHOX2A 12,13 which is the most common, all affected gene at the FEOM2 locus in 11q13. Author Affiliations: family members are born with bilateral Herein, we have further investigated the Department of Molecular phenotype-genotype relationship in Medicine and Surgery, severe ptosis and ophthalmoplegia characterized by the chin-up position CFEOM by characterizing the clinical phe- Karolinska Institute, Karolinska notypes and KIF21A genotypes in 5 af- University Hospital–Solna, of the head and restricted vertical and Stockholm, Sweden (Drs Lu, horizontal ocular motility.4 By contrast, fected kindreds. C. Zhao, and Larsson); JiangSu the members of a CFEOM3 (OMIM Province Hospital, Nanjing, %600638) family demonstrate variable METHODS JiangSu (Dr Lu), and expressivity of CFEOM, and at least 1 af- Laboratory of Molecular fected individual should lack or have Genetics, Tianjin Eye Hospital, CLINICAL EVALUATIONS Tianjin Medical University, only unilateral ophthalmoplegia or pto- AND SAMPLE COLLECTIONS Tianjin (Drs C. Zhao, K. Zhao, sis or have 1 or both eyes fixed above the and Li), People’s Republic midline or the ability to raise 1 or both The 5 studied CFEOM families (families 1, 2, of China. eyes above the midline.5,6 3, 4, and 5) (Figure 1 and Figure 2) reside

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I:3 I:1 I:2 I:1 I:2 ∗∗ ∗∗ ∗ ∗∗ ∗ ∗

II:1 II:7 II:2 II:8 II:3 II:6 II:4 II:9 II:5 II:1 II:3 II:2 ∗∗ ∗ ∗ ∗ ∗ ∗∗

III:1 III:2 III:4 III:3 III:5 III:6 III:7 III:8 III:9 III:1 III:2 ∗

IV:1

Family 3 (CFEOM1) ∗ Family 4 (CFEOM1)

I:1 I:2 I:1 I:2

∗∗ ∗ ∗∗ ∗∗ ∗

II:6 II:1 II:7 II:2 II:3 II:4 II:5 II:1 II:3 II:2 II:4

∗ ∗ ∗ ∗ ∗∗ ∗∗∗

III:1 III:2 III:3 III:4 III:1 III:2 III:5 III:4 III:3

∗ Male Female ∗ Unaffected member Affected member Deceased (both sexes) IV:2 IV:1

B 2860 C>T 2861G>A

A A T A G C A A N G G G A G G A A C T C A A T A G C A A C N G G A G G A A C

Mutant

A A T A G C A A C G G G A G G A A C T C A A T A G C A A C G G G A G G A A C

Wild type

Figure 1. A, Pedigrees of families 1 through 4 with congenital fibrosis of the extraocular muscles (CFEOM) type 1 or 3. Individuals participating in the study are indicated by an asterisk to the left. Arrows indicate probands in each family. B, Sequencing chromatograms showing the recurrent KIF21A mutations in families 2 and 3 (2860CϾT) and family 1 (2861GϾA). The position of the mutation is marked by an arrow in the mutant and corresponding wild-type sequences shown. Both mutations are missense, leading to amino acid alterations at position 954, and have been previously described in other families.

in various regions of China and were clinically investigated in vidual underwent a detailed ophthalmic investigation to evalu- Tianjin Eye Hospital. None of the patients had been treated sur- ate corrected visual acuity, palpebral fissure size, levator function, gically at the time of examination. Each participating indi- compensatory head position, and ocular motility including ab-

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I:1 I:2

∗ ∗ ∗ ∗∗

II:4 II:1 II:2 II:5 II:3 2 3 2 2 2 4 1 3 3 4 1 2 5 1 ∗ ∗ ∗ ∗ 5 2 ∗ 3 3 2 2 2 3 4 1 4 3 4 3 1 3 5 2 1 5 1 1 2 4 4 1 III:1 III:2 III:5 III:3 III:4 ∗ 2 3 2 3 2 5 2 2 2 1 5 2 1 2 3 4 5 1 5 3 4 3 1 3 3 3 4 2 4 4 1 2 5 2 5 1 IV:1 1 5 1 2

Male Female 2 2 Unaffected member 5 3 Affected member 4 3 Deceased (both sexes) 1 5

B 84C>G Wild type

G A G A A G A T T G A A G G A T G N C A T A T T T G T A C A T C T G T C A C A G A G A A G A T T G A A G G A T G C C A T A T T T G T A C A T C T G T C A C A

C II:4 II:1 III:1 III:2 III:5 IV:1 III:3 II:2 III:4 II:5 II:3 Control Control Marker

Wild type 292 bp 204 bp Mutated 88 bp

D 5′ 3′

E944Q M947V 2861G>A R954Q M947R 84C>G M356T A1008P C28W M947T I1010T 2860C>T M947I R954W R954L

N C

Kinase motor domain Coiled-coil region WD40 domain

Figure 2. A, Pedigree of family 5 with congenital fibrosis of the extraocular muscles type 1 (CFEOM1) and haplotypes of the FEOM1/KIF21A region. The genotypes represent the microsatellite loci D12S1648, D12S59, D12S1029, and D12S1048 and the affected haplotype is indicated by a box. Individuals participating in the study are indicated by an asterisk to the left. Arrow indicates the proband. B, Sequencing chromatograms showing the novel mutation 84CϾGinexon2of KIF21A. C, Confirmation of the presence or absence of the 84CϾG mutation in affected and unaffected family members using BccI restriction cleavage. bp Indicates base pair. D, Location of KIF21A mutations on the genomic (top) and protein (below) levels. Mutations identified in this study are boxed. The novel C28W and the known M356T mutations affect the kinesin motor domain (green) while the other mutations affect amino acids in the coiled-coil region (yellow).

errant eye movements, together with examinations by slit- used for sequencing and genotyping analysis. The samples were lamp and direct funduscopy (Table 1). Genomic DNA was collected with informed consent from the participating indi- isolated from peripheral leukocytes by standard methods and viduals or their parents after explanation of the nature and pos-

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Visual Acuity Ptosis/Levator Function Ocular Motility Age, Compensatory Pedigree Member Sex y OD OS OD OSStrabismus Vertical Horizontal Head Position Family 1 (CFEOM3) II:1 M 70 0.2 0.2 Severe/3 mm Severe/3 mm Hypo Fixed Limited Yes II:3 F 67 0.1 0.2 Severe/0 mm Severe/0 mm Hypo Fixed Fixed Yes II:4 M 65 0.9 0.8 No/12 mm No/12 mm No Limited Normal No III:2 M 45 0.3 0.1 Severe/0 mm Severe/0 mm Hypo Fixed Limited Yes III:3 F 41 0.4 0.5 Severe/3 mm Mild/7 mm Hypo with exo Fixed Limited Yes III:5 F 40 0.1 0.1 Severe/0 mm Severe/0 mm Hypo Fixed Limited Yes III:7 M 26 0.7 0.3 Mild/8 mm Severe/4 mm Hypo Limited Limited No III:8 F 38 0.1 0.1 Severe/0 mm Severe/1 mm Hypo Fixed Limited Yes IV:1 M 17 0.1 0.3 Severe/3 mm Mild/7 mm Hypo with exo Fixed Limited No Family 2 (CFEOM1) II:1 M 60 0.3 0.2 Severe/2 mm Severe/2 mm Hypo with exo Limited Limited Yes III:1 M 33 0.4 0.3 Severe/2 mm Severe/3 mm Hypo with exo Limited Limited Yes III:2 M 29 0.4 0.5 Severe/1 mm Severe/3 mm Hypo with exo Limited Limited Yes Family 3 (CFEOM1) I:2 F 68 0.05 0.1 Severe/0 mm Severe/0 mm Hypo with exo Fixed Limited Yes II:1 F 42 0.1 0.3 Severe/1 mm Severe/2 mm Hypo with exo Limited Limited Yes II:2 F 39 0.2 0.2 Severe/0 mm Severe/0 mm Hypo with exo Fixed Fixed Yes II:4 M 34 0.2 0.3 Severe/0 mm Severe/1 mm Hypo with exo Fixed Limited Yes III:1 M 19 0.1 0.1 Severe/0 mm Severe/0 mm Hypo Fixed Limited Yes III:4 M 11 0.2 0.1 Severe/0 mm Severe/0 mm Hypo with exo Fixed Fixed Yes Family 4 (CFEOM1) II:1 M 67 0.1 FC Severe/0 mm Severe/0 mm Hypo with exo Fixed Limited Yes III:2 M 41 0.2 0.3 Severe/1 mm Severe/2 mm Hypo with exo Limited Limited Yes III:3 F 38 0.1 0.1 Severe/0 mm Severe/0 mm Hypo with exo Limited Limited Yes IV:1 M 20 0.2 0.2 Severe/0 mm Severe/0 mm Hypo with exo Fixed Fixed Yes IV:2 M 16 0.4 0.1 Severe/3 mm Severe/1 mm Hypo with exo Fixed Limited Yes Family 5 (CFEOM1) II:1 M 73 FC 0.1 Severe/0 mm Severe/0 mm Hypo with exo Fixed Limited Yes II:2 M 69 0.05 0.1 Severe/0 mm Severe/0 mm Hypo with exo Fixed Limited Yes III:1 M 50 0.1 0.2 Severe/0 mm Severe/1 mm Hypo with exo Fixed Limited Yes III:3 F 41 0.2 0.2 Severe/2 mm Severe/4 mm Hypo with exo Limited Limited Yes III:4 M 44 0.1 0.1 Severe/0 mm Severe/0 mm Hypo with exo Fixed Fixed Yes IV:1 M 19 0.2 0.1 Severe/1 mm Severe/3 mm Hypo with exo Limited Limited Yes

Abbreviations: CFEOM, congenital fibrosis of the extraocular muscles; CFEOM1, CFEOM type 1; CFEOM3, CFEOM type 3; FC, finger count within 30 cm; Hypo, hypotropia; Exo, exotropia.

sible consequence of the study and with local ethics approval (New England Biolabs, Ipswich, Massachusetts) according to according to the tenets of the Declaration of Helsinki. the instructions of the manufacturer. At electrophoresis in 3% agarose gels, the wild-type allele resulted in a single approxi- MUTATION ANALYSIS OF KIF21A mately 292–base pair (bp) fragment and the mutated allele, in 2 fragments of approximately 88 bp and approximately 204 bp. The 38 exons and flanking exon-intron boundaries of the KIF21A gene were sequenced using primers and conditions detailed else- LINKAGE ANALYSES where (data not shown). The polymerase chain reaction am- plicons were sequenced in both directions and analyzed in an Genotyping of microsatellite markers was carried out in fami- automated ABI 3730 Genetic Analyzer system (Applied Bio- lies 4 and 5 using previously described methods.14 Possible link- systems, Foster City, California) using methods previously de- age to the FEOM1 locus was analyzed by markers D12S1648, scribed.14 Initially, exons 8, 20, and 21, with reported muta- D12S59, D12S1029, and D12S1048, and the FEOM3 locus was tions,6,9,10,15-19 were sequenced in the probands of the 5 families. represented by markers D16S486, D16S498, D16S689, D16S3121, Subsequently, all 38 exons of KIF21A were sequenced in fami- and D16S303 (ENSEMBL human genome browser map, http: lies 4 and 5. Exons with novel variations were sequenced in all //www.ensembl.org). Two-point linkage analyses were per- members of the concerned families to determine cosegrega- formed using the LINKAGE software package of SimWalk2 tion with the affected status. A putative novel mutation de- (Version 3.35; E. Sobel, University of California, Los Ange- tected in exon 2 in family 5 was sequenced in 100 unrelated les), under the assumption of an autosomal dominant trait with control DNA samples of the same ethnicity to evaluate whether 99% penetrance and a disease-allele frequency of 0.000001. Each it represented disease-associated mutation. Moreover, this novel marker was assumed to have equally frequent alleles, with equal mutation was further verified in a restriction cleavage assay in recombination frequencies in males and females. Pedigrees were family 5 and in another group of 50 normal controls. The cor- drawn and haplotypes were generated using Cyrillic software responding region of exon 2 was polymerase chain reaction am- (version 2.1; CyrillicSoftware, Oxfordshire, England) and con- plified by new primer (data not shown) and cleaved with BccI firmed by inspection.

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Linkage to KIF21A Mutations Clinical Mode of Pedigree No. Phenotype Inheritance FEOM 1 FEOM 3 Sequence Exon Amino Acid Family 1 CFEOM3 AD ND ND 2861GϾA/wt Exon 21 R954Q Family 2 CFEOM1 AD ND ND 2860CϾT/wt Exon 21 R954W Family 3 CFEOM1 AD ND ND 2860CϾT/wt Exon 21 R954W Family 4 CFEOM1 AD Suggestive Suggestive wt/wt Family 5 CFEOM1 AD Suggestive Not linked 84CϾG/wt Exon 2 C28W

Abbreviations: AD, autosomal dominant; CFEOM, congenital fibrosis of the extraocular muscles; CFEOM1, CFEOM type 1; CFEOM3, CFEOM type 3; ND, not determined; wt, wild type. a Mutations were numbered according to complementary DNA sequence reference number AM177179.

RESULTS teration from arginine to tryptophan (R954W). Family 1 with CFEOM3 harbored another heterozygous base substitution (2861GϾA) (Figure 1) giving an amino acid shift CHARACTERIZATION OF CFEOM1 from arginine to glutamine (R954Q). These 2 missense AND CFEOM3 PHENOTYPES mutations were shown to cosegregate with the CFEOM phenotype in the respective families. To date, they are The 5 families studied were diagnosed with autosomal the 2 most commonly reported mutations, with 2860CϾT dominant CFEOM based on the inheritance patterns and having been reported in both CFEOM1 and CFEOM3 clinical phenotypes (Figure 1 and Figure 2) (Table 1). pedigrees and 2861GϾA having been previously re- Slitlamp and funduscopy examination results were nor- ported in CFEOM1 pedigrees.6,9,10,15-19 mal in all the affected individuals. All affected members of families 2 through 5 presented similar phenotypes with bilateral severe ptosis, compensatory head position with IDENTIFICATION OF typical chin-up appearance, hypotropia with or without A NOVEL KIF21A MUTATION IN EXON 2 exotropia, and severely impaired vertical and horizontal ocular motility (Table 1). All affected members had Families 4 and 5 were genotyped for markers at the poor visual acuity, which might have resulted from de- KIF21A/FEOM1 and FEOM3 loci. Both families had posi- prived amblyopia secondary to congenital ptosis. In ad- tive logarithm of odds scores for markers at KIF21A/ dition, patients II:1 and III:3 in family 4 had aberrant eye FEOM1 in agreement with a possible involvement of movements in the form of synergistic convergence when KIF21A (data not shown). FEOM3 was excluded in fam- attempting upgaze. Based on these findings, families 2 ily 5 and gave inconclusive results in family 4. The am- through 5 were classified as having CFEOM1. biguity of linkage data in family 4 is likely because of the The members of family 1 showed variable involvement relatively limited number of family members. and severity of ophthalmoplegia and ptosis consistent with Sequencing of all 38 exons of KIF21A in families 4 and a diagnosis of CFEOM3 (Table 1). For example, individu- 5 revealed a heterozygous base transition at nucleotide als II:1, II:3, III:2, III:5, and III:8 presented a classical phe- 84 in exon 2 (84CϾG) (Figure 2) in the proband of fam- notype with bilateral severe ptosis, restricted upgaze, and ily 5. This alteration is predicted to give an alteration of compensatory head position. By contrast, in individuals III:3, amino acid 28 from cysteine to tryptophan (C28W; III:7, and IV:1, at least 1 eye had mild ptosis with residual complementary DNA reference number, AM177179). In upgaze or the ability to elevate above the midline. Simi- addition, a novel silent single-nucleotide polymor- larly, individuals III:7 and IV:1 had varying ptosis with- phism (3118CϾT) was identified in exon 22 in pro- out compensatory head position. Individual II:4, who is an band IV:1 and a spouse, III:5, but not in the other indi- obligate carrier, had only subtle symptoms in the form of viduals in family 5. The mutation 84CϾG creates a mild limitation of vertical ocular motility without ptosis, cleavage site for BccI, which was evaluated in the entire strabismus, or compensatory head position (Table 1). The family 5 (Figure 2). Based on sequencing as well Bcc I uneven visual acuity observed in this family is possibly due cleavage, the novel mutation was shown to be present to variable severity of ptosis. in all affected individuals, in agreement with the inheritance of the affected haplotype (Figure 2). However, the DETECTION OF RECURRENT KIF21A mutation was not detected in any of the unaffected mem- MUTATIONS IN CFEOM1 bers in family 5 or in 150 normal controls by either se- AND CFEOM3 FAMILIES quencing or BccI cleavage assay. In family 4, no sequence alterations were found in the coding regions or flanking The initial screening of exons 8, 20, and 21 of the KIF21A exon-intron boundaries of the KIF21A gene. However, 2 gene identified 2 missense mutations in exon 21 in 3 of intronic alterations were revealed, including single- the 5 families. In families 2 and 3, the same heterozy- nucleotide polymorphism rs3736466 in intron 7 and a novel gous base substitution 2860CϾT was observed (Figure 1). 4-bp deletion in intron 25 (IVS25ϩ245-248) that did not These substitutions are predicted to give a missense al- cosegregate with the affected status. Table 2 summa-

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 rizes all clinical and genetic findings in the 5 studied CFEOM could interfere with motor function through similar families. mechanisms remains to be determined. Two recurrent mutations (2860CϾT, 2861GϾA) were identified in 3 of the 5 studied families. The mutation COMMENT 2860CϾT, found in families 2 and 3 with CFEOM1, rep- resents the most frequent KIF21A mutation and is found In this study, we report a novel (84CϾG) and 2 recur- in approximately 70% of all kindreds with a demon- rent (2860CϾT, 2861GϾA) missense KIF21A muta- strated mutation.9 The CFEOM3 family (family 1) seg- tions identified in 4 Chinese families with CFEOM1 and regated a 2861GϾA mutation, which, to our knowl- CFEOM3 phenotypes. In support of their pathogenic na- edge, has not been previously reported. However, the same ture, the mutations were shown to cosegregate with the mutation has previously been described in families and CFEOM phenotype in the respective families, and in ad- isolated cases with CFEOM1. The present findings thus dition, the novel mutation was absent in 150 normal con- are supportive of previous findings that identical muta- trols. Our findings add to the knowledge about KIF21A tions can give rise to distinct phenotypes, suggesting that mutation spectra and support the genetic heterogeneity additional genetic factors determine the expressivity of of CFEOM1 and CFEOM3. CFEOM. Taken together with previous reports,6,10 3 dif- The KIF21A gene spans 150 kilobases of genomic DNA ferent KIF21A mutations have presently been associ- and consists of 38 exons encoding an amino acid 1674 pro- ated with CFEOM3 families. These mutations are all pre- tein, which is part of the kinesin superfamily involved in dicted to give substitutions at amino acid 947 or amino transportation of vesicles and organelles.9,20,21 Its N termi- acid 954, similar to CFEOM1. nal kinesin motor domain interacts with microtubules and In family 4, no KIF21A mutation was demonstrated tends to be highly conserved,19 the coiled-coil domain is implicating the involvement of a different disease gene important for dimer formation, and the tail with 7 WD40 in support of genetic heterogeneity for CFEOM1. Re- repeats is assumed to interact with the presently uniden- sults from linkage analysis were consistent with a puta- tified cargo based on functional study of another kinesin tive involvement of the FEOM1 as well as the FEOM3 loci. family member KIF21B.21 Despite the large size of KIF21A, On precise identification of the still elusive disease gene only a small number of different mutations have been re- at the FEOM3 locus, it will be worthwhile to screen for ported. Nine of the 11 published mutations were found in mutations in this strong candidate gene. families with the CFEOM1 phenotype (1067TϾC, Taken together with the results of previously pub- 2830GϾC, 2839AϾG, 2840TϾG, 2840TϾC, 2861GϾA, lished studies,6,10,28,29 our present findings clearly sup- 2861GϾT, 3022GϾC, 3029TϾC), 1 was identified in a port a genetic heterogeneity in CFEOM1 as well as CFEOM3 kindred (2841GϾA), and 1 has been associated CFEOM3. This underlines the need to base classifica- with both CFEOM1 and CFEOM3 (2860CϾT).6,9,10,18,19 tion of CFEOM in clinical practice on both genetic Figure 2 illustrates the known KIF21A mutations, includ- findings and clinical presentations. Furthermore, the ing those described herein.6,9,10,15-19 Intriguingly, 10 of the possibility of KFI21A mutations occurring outside the published mutations are clustered, resulting in substitu- previously reported exons 8, 20, and 21 needs to be tions of 5 amino acid residues in the coiled-coil region taken into account in genetic diagnostic procedures. (944Glu, 947Met, 954Arg, 1008Ala, 1010Ile), and the 11th Further analyses of the molecular effects of different mutation, involving amino acid 356 at the ␣-helix 6 of the KIF21A mutations are expected to provide insights KIF21A motor domain, is close to the neck-linker region, into KIF21A functions and the possibility of genetic which is located between the motor domain and the coiled- treatment. coil region. Because the C terminal of ␣-helix 6 is the base of the neck linker, it has been proposed that all these re- Submitted for Publication: July 22, 2007; final revision reported mutations could impair protein dimerization and ceived September 21, 2007; accepted September 25, 2007. thus interfere with the transportation of cargos from the Correspondence: Chen Zhao, MD, PhD, Department of oculomotor neurons to the synapse of the developing neu- Molecular Medicine and Surgery, Karolinska Institute, romuscular junction of the extraocular muscle.22 By con- Karolinska University Hospital–Solna, CMM L8:01, trast, the novel mutation reported herein, 84CϾG, is lo- SE-171 76 Stockholm, Sweden ([email protected]). cated in exon 2, which encodes the beginning of the Author Contributions: Drs Lu and Zhao contributed kinesin motor domain. This finding would further sup- equally to this work. port a role for dysfunction of the kinesin motor domain Financial Disclosure: None reported. in the etiology of CFEOM because the previous muta- Funding/Support: This study was financially supported tion 356MϾT was close to the linker region and could by the Swedish Research Council, Go¨ran Gustavsson have interfered with its function. Point mutations affect- Foundation for Research in Natural Sciences and Medi- ing motor domains of other kinesin family genes have cine, the Stockholm County Council, and the Chinese been reported in spastic paraplegia (KIF5A) and Charcot- National Natural Science Foundation Awards. Marie-Tooth disease (KIF1Bβ) and have been shown to prevent stimulation of the motor adenosine triphospha- REFERENCES tase by microtubule binding.23,24 Furthermore, specific point mutations in kinesin motor orthologs have been 1. Gutowski NJ, Bosley TM, Engle EC. 110th ENMC International Workshop: the 25-27 associated with loss of kinesin motor function. congenital cranial dysinnervation disorders (CCDDs): Naarden, the Nether- Whether the KIF21A mutation identified herein, 84CϾG, lands, 25-27 October, 2002. Neuromuscul Disord. 2003;13(7-8):573-578.

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©2008 American Medical Association. All rights reserved. Downloaded From: https://jamanetwork.com/ on 09/28/2021 2. Brown HW. Congenital structural muscle anomalies. In: Allen JH, ed. Strabis- 16. Tiab L, d’Allèves Manzi V, Borruat FX, Munier FL, Schorderet DF. Mutation analy- mus Opthalmic Symposium. St Louis, MO: CV Mosby Co. 1950:205-236. sis of KIF21A in congenital fibrosis of the extraocular muscles (CFEOM) patients. 3. Engle EC, Goumnerov BC, McKeown CA, et al. Oculomotor nerve and muscle Ophthalmic Genet. 2004;25(4):241-246. abnormalities in congenital fibrosis of the extraocular muscles. Ann Neurol. 1997; 17. Shimizu S, Okinaga A, Maruo T. Recurrent mutation of the KIF21A gene in Japa- 41(3):314-325. nese patients with congenital fibrosis of the extraocular muscles. Jpn J Ophthalmol. 4. Engle EC, McIntosh N, Yamada K, et al. CFEOM1, the classic familial form of con- 2005;49(6):443-447. genital fibrosis of the extraocular muscles, is genetically heterogeneous but does 18. Yamada K, Hunter DG, Andrews C, Engle EC. A novel KIF21A mutation in a pa- not result from mutations in ARIX. BMC Genet. 2002;3:3. tient with congenital fibrosis of the extraocular muscles and Marcus Gunn jaw- 5. Engle EC. The molecular basis of the congenital fibrosis syndromes. Strabismus. winking phenomenon. Arch Ophthalmol. 2005;123(9):1254-1259. 2002;10(2):125-128. 19. Chan WM, Andrews C, Dragan L, et al. Three novel mutations in KIF21A high- 6. Yamada K, Chan WM, Andrews C, et al. Identification of KIF21A mutations as a light the importance of the third coiled-coil stalk domain in the etiology of CFEOM1. rare cause of congenital fibrosis of the extraocular muscles type 3 (CFEOM3). BMC Genet. 2007;8:26. Invest Ophthalmol Vis Sci. 2004;45(7):2218-2223. 20. Miki H, Setou M, Kaneshiro K, Hirokawa N. All kinesin superfamily protein, KIF, 7. Engle EC, Kunkel LM, Specht LA, Beggs AH. Mapping a gene for congenital fi- genes in mouse and human. Proc Natl Acad Sci U S A. 2001;98(13):7004- brosis of the extraocular muscles to the centromeric region of chromosome 12. 7011. Nat Genet. 1994;7(1):69-73. 21. Marszalek JR, Weiner JA, Farlow SJ, Chun J, Goldstein LS. Novel dendritic ki- 8. Engle EC, Marondel I, Houtman WA, et al. Congenital fibrosis of the extraocular nesin sorting identified by different process targeting of two related kinesins: KIF21A muscles (autosomal dominant congenital external ophthalmoplegia): genetic ho- and KIF21B. J Cell Biol. 1999;145(3):469-479. mogeneity, linkage refinement, and physical mapping on chromosome 12. Am 22. Engle EC. The genetic basis of complex strabismus. Pediatr Res. 2006;59(3):343- J Hum Genet. 1995;57(5):1086-1094. 348. 9. Yamada K, Andrews C, Chan WM, et al. Heterozygous mutations of the kinesin 23. Reid E, Kloos M, Ashley-Koch A, et al. A kinesin heavy chain (KIF5A) mutation in KIF21A in congenital fibrosis of the extraocular muscles type 1 (CFEOM1). Nat hereditary spastic paraplegia (SPG10). Am J Hum Genet. 2002;71(5):1189- Genet. 2003;35(4):318-321. 10. Lin LK, Chien YH, Wu JY, Wang AH, Chiang SC, Hwu WL. KIF21A gene c.2860CϾT 1194. mutation in congenital fibrosis of extraocular muscles type 1 and 3. Mol Vis. 2005; 24. Zhao C, Takita J, Tanaka Y, et al. Charcot-Marie-Tooth disease type 2A caused 11:245-248. by mutation in a microtubule motor KIF1Bbeta. Cell. 2001;105(5):587-597. 11. Doherty EJ, Macy ME, Wang SM, Dykeman CP, Melanson MT, Engle EC. CFEOM3: 25. Hirokawa N, Noda Y, Okada Y. Kinesin and dynein superfamily proteins in or- a new extraocular congenital fibrosis syndrome that maps to 16q24.2-q24.3. In- ganelle transport and cell division. Curr Opin Cell Biol. 1998;10(1):60-73. vest Ophthalmol Vis Sci. 1999;40(8):1687-1694. 26. Nakata T, Hirokawa N. Point mutation of adenosine triphosphate-binding motif 12. Wang SM, Zwaan J, Mullaney PB, et al. Congenital fibrosis of the extraocular generated rigor kinesin that selectively blocks anterograde lysosome mem- muscles type 2, an inherited exotropic strabismus fixus, maps to distal 11q13. brane transport. J Cell Biol. 1995;131(4):1039-1053. Am J Hum Genet. 1998;63(2):517-525. 27. Rhee DK, Cho BA, Kim HB. ATP-binding motifs play key roles in Krp1p, kinesin- 13. Nakano M, Yamada K, Fain J, et al. Homozygous mutations in ARIX(PHOX2A) related protein 1, function for bi-polar growth control in fission yeast. Biochem result in congenital fibrosis of the extraocular muscles type 2. Nat Genet. 2001; Biophys Res Commun. 2005;331(2):658-668. 29(3):315-320. 28. Sener EC, Lee BA, Turgut B, Akarsu AN, Engle EC. A clinically variant fibrosis 14. Zhao C, Lu S, Zhou X, Zhang X, Zhao K, Larsson C. A novel locus (RP33) for syndrome in a Turkish family maps to the CFEOM1 locus on chromosome 12. autosomal dominant retinitis pigmentosa mapping to chromosomal region Arch Ophthalmol. 2000;118(8):1090-1097. 2cen-q12.1. Hum Genet. 2006;119(6):617-623. 29. Traboulsi EI. Congenital abnormalities of cranial nerve development: overview, 15. Ali M, Venkatesh CP, Ragunath A, Kumar A. Mutation analysis of the KIF21A gene molecular mechanisms, and further evidence of heterogeneity and complexity in an Indian family with CFEOM1: implication of CpG methylation for most fre- of syndromes with congenital limitation of eye movements. Trans Am Ophthal- quent mutations. Ophthalmic Genet. 2004;25(4):247-255. mol Soc. 2004;102:373-389.

From the Archives of the Archives

In the sixties, de Wecker, Stellwag, and others, believ- ing that scleral section alone was sufficient to relieve the tension in glaucoma, introduced into ophthalmology sclerotomy to take the place of iridectomy. From what has been said it is evident that incision of the chamber angle, like sclerotomy, is to be regarded as an operation which for a short time provides an artifi- cial channel of exit for the aqueous humor, and prob- ably exercises only an indirect influence upon the res- toration of the normal channels. Reference: Andogsky N, Selensky P. The role of scleral scars in operations for glaucoma. Arch Ophthalmol. 1902; 31:450, 459.

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