Autosomal dominant congenital cataract and microphthalmia associated with a familial t(2;16) translocation

Biallelic variants in the small optic lobe calpain CAPN15 are associated with congenital eye anomalies, deafness and other neurodevelopmental deficits

Microphthalmia, coloboma and cataract are part of a spectrum of developmental eye disorders in humans affecting ~12 per 100 000 live births. Currently, variants in over 100 genes are known to underlie these conditions. However, at least 40% of affected individuals remain without a clinical genetic diagnosis, suggesting variants in additional genes may be responsible. Calpain 15 (CAPN15) is an intracellular cysteine protease belonging to the non-classical small optic lobe (SOL) family of calpains, an important class of developmental proteins, as yet uncharacterized in vertebrates. We identified five individuals with microphthalmia and/or coloboma from four independent families carrying homozygous or compound heterozygous predicted damaging variants in CAPN15. Several individuals had additional phenotypes including growth deficits, developmental delay and hearing loss. We generated Capn15 knockout mice that exhibited similar severe developmental eye defects, including anophthalmia, microphthalmia and cataract, and diminished growth. We demonstrate widespread Capn15 expression throughout the brain and central nervous system, strongest during early development, and decreasing postnatally. Together, these findings demonstrate a critical role of CAPN15 in vertebrate developmental eye disorders, and may signify a new developmental pathway.

A new locus for congenital cataract, microcornea, microphthalmia, and atypical iris coloboma maps to chromosome 2

OBJECTIVE

To report a novel phenotype of autosomal dominant atypical congenital cataract associated with variable expression of microcornea, microphthalmia, and iris coloboma linked to chromosome 2. Molecular analysis of this phenotype may improve our understanding of anterior segment development.

DESIGN

Observational case study, genome linkage analysis, and gene mutation screening.

PARTICIPANTS

Three families, 1 Egyptian and 2 Belgians, with a total of 31 affected were studied.

METHODS

Twenty-one affected subjects and 9 first-degree relatives underwent complete ophthalmic examination. In the Egyptian family, exclusion of PAX6, CRYAA, and MAF genes was demonstrated by haplotype analysis using microsatellite markers on chromosomes 11, 16, and 21. Genome-wide linkage analysis was then performed using 385 microsatellite markers on this family. In the 2 Belgian families, the PAX6 gene was screened for mutations by direct sequencing of all exons.

MAIN OUTCOME MEASURES

Phenotype description, genome-wide linkage of the phenotype, linkage to the PAX6, CRYAA, and MAF genes, and mutation detection in the PAX6 gene.

RESULTS

Affected members of the 3 families had bilateral congenital cataracts inherited in an autosomal dominant pattern. A novel form of hexagonal nuclear cataract with cortical riders was expressed. Among affected subjects with available data, 95% had microcornea, 39% had microphthalmia, and 38% had iris coloboma. Seventy-five percent of the colobomata were atypical, showing a nasal superior location in 56%. A positive lod score of 4.86 was obtained at theta = 0 for D2S2309 on chromosome 2, a 4.9-Mb common haplotype flanked by D2S2309 and D2S2358 was obtained in the Egyptian family, and linkage to the PAX6, CRYAA, or MAF gene was excluded. In the 2 Belgian families, sequencing of the junctions and all coding exons of PAX6 did not reveal any molecular change.

CONCLUSIONS

We describe a novel phenotype that includes the combination of a novel form of congenital hexagonal cataract, with variably expressed microcornea, microphthalmia, and atypical iris coloboma, not caused by PAX6 and mapping to chromosome 2.

FINANCIAL DISCLOSURE(S)

The authors have no proprietary or commercial interest in any materials discussed in this article.

Characterization of a familial t(16;22) balanced translocation associated with congenital cataract leads to identification of a novel gene, TMEM114, expressed in the lens and disrupted by the translocation

Molecular characterization of chromosomal rearrangements is a powerful resource in identification of genes associated with monogenic disorders. We describe the molecular characterization of a balanced familial chromosomal translocation, t(16;22)(p13.3;q11.2), segregating with congenital lamellar cataract. This led to the discovery of a cluster of lens-derived expressed sequence tags (ESTs) close to the 16p13.3 breakpoint. This region harbors a locus associated with cataract and microphthalmia. Long-range PCR and 16p13.3 breakpoint sequencing identified genomic sequence in a human genome sequence gap, and allowed identification of a novel four-exon gene, designated TMEM114, which encodes a predicted protein of 223 amino acids. The breakpoint lies in the promoter region of TMEM114 and separates the gene from predicted eye-specific upstream transcription factor binding sites. There is sequence conservation among orthologs down to zebrafish. The protein is predicted to contain four transmembrane domains with homology to the lens intrinsic membrane protein, LIM2 (also known as MP20), in the PMP-22/EMP/MP20 family. TMEM114 mutation screening in 130 congenital cataract patients revealed missense mutations leading to the exchange of highly-conserved amino acids in the first extracellular domain of the protein (p.I35T, p.F106L) in two separate patients and their reportedly healthy sibling and mother, respectively. In the lens, Tmem114 shows expression in the lens epithelial cells extending into the transitional zone where early fiber differentiation occurs. Our findings implicate dysregulation of expression of this novel human gene, TMEM114, in mammalian cataract formation.

The therapeutic potential of the calpain family: new aspects

The calpain family is a group of cysteine proteases unique in their dependency on calcium to attain functionally active forms. Calpains are involved in a wide range of cellular calcium-regulated functions, including signal transduction, cell proliferation and differentiation, and apoptosis. Moreover, altered calpain activity has been observed in several human diseases. Specific calpain inhibitors hold promise for the treatment of neuromuscular and neurodegenerative diseases in which calpains have been shown to be upregulated (e.g. Parkinson's disease and Duchenne muscular dystrophy). Conversely, calpain activators could be a useful approach for those diseases where reduced calpain activity has been observed, such as type 2 diabetes or metabolic syndrome.

Birth characteristics of different ocular congenital abnormalities in hungary

AIMS

The aim of the study was to estimate the prevalence at birth of different ocular congenital abnormalities and to describe their birth characteristics in Hungary.

METHODS

Two data sets were evaluated: the national-based Hungarian Congenital Abnormality Registry and the Hungarian Case-Control Surveillance of Congenital Abnormalities which include cases with ocular abnormalities and patient controls with other (non-ocular) congenital abnormalities, and population controls without abnormalities from the National Birth Registry.

RESULTS

Seven hundred twelve cases were found with ocular abnormalities in the data set of the Hungarian Congenital Abnormality Registry (2.62 per 10,000 live births), while that of the Hungarian Case-Control Surveillance of Congenital Abnormalities included 314 cases with ocular defects among 2.7 million live births in Hungary between 1980 and 2002. There was an obvious underascertainment and/or notification of cases with ocular defects because an extra effort to ascertain all cases with ocular abnormalities resulted in a birth prevalence of 6.31 per 10,000 live births in 1999. The main birth characteristics of cases were male excess, shorter mean gestational age and smaller mean birth weight with a larger proportion of preterm birth and low birthweight.

CONCLUSIONS

Earlier diagnosis of ocular abnormalities is necessary with a more complete notification of these cases to the Hungarian Congenital Abnormality Registry. The birth characteristics of cases with ocular abnormalities may have some associations with the origin of ocular defects; therefore, these variables will require further studies in case-control approach.

A newborn with anophthalmia and pulmonary hypoplasia (the Matthew–Wood syndrome)

The combination of anophthalmia and pulmonary hypoplasia with abnormal lobation is an extremely rare congenital disorder. We describe a case of a female newborn with these features that fits the recently described Matthew-Wood syndrome.

Factor VII deficiency and developmental abnormalities in a patient with partial monosomy of 13q and trisomy of 16p: case report and review of the literature

Background

Unbalanced chromosomal translocations may present with a variety of clinical and laboratory findings and provide insight into the functions of genes on the involved chromosomal segments.

Case Presentation

A 9 year-old boy presented to our clinic with Factor VII deficiency, microcephaly, a seizure disorder, multiple midline abnormalities (agenesis of the corpus callosum, imperforate anus, bilateral optic nerve hypoplasia), developmental delay, hypopigmented macules, short 5^th fingers, and sleep apnea due to enlarged tonsils. Cytogenetic and fluorescence in situ hybridization analyses revealed an unbalanced translocation involving the segment distal to 16p13 replacing the segment distal to 13q33 [46, XY, der(13)t(13;16)(q33;p13.3)]. Specific BAC-probes were used to confirm the extent of the 13q deletion.

Conclusion

This unique unbalanced chromosomal translocation may provide insights into genes important in midline development and underscores the previously-reported phenotype of Factor VII deficiency in 13q deletions.

Molecular genetic basis of inherited cataract and associated phenotypes

Congenital cataract is a leading cause of visual disability in children. Inherited isolated (non-syndromic) cataract represents a significant proportion of cases and recently many causative genetic mutations have been identified. Inherited cataract is known to be clinically and genetically heterogeneous. Eleven clear-cut cataract phenotypes have been described. Cataract may be inherited as autosomal dominant, autosomal recessive, or X-linked recessive traits, and 12 loci and 15 specific genes associated with inherited isolated cataract have been identified to date; it is likely that more genes remain to be discovered. The identification of remaining genes will not only improve our understanding of the mechanism of cataract formation but will shed new light on the developmental biology and biochemistry of the lens. Furthermore, it is possible that some of these genes will be implicated in the more common age related cataract, which also has a genetic component to its etiology.

Genetics of childhood cataract

PURPOSE OF REVIEW

Congenital cataracts, although much less common than their age-related counterparts, account for one-tenth of cases of childhood blindness. Approximately half are inherited, either in isolation or as part of a syndrome of ocular or systemic anomalies. This article reviews recent advances made in understanding the molecular genetic basis of isolated, nonsyndromic inherited cataract.

RECENT FINDINGS

New disease-causing mutations continue to be identified and now encompass genes encoding a wide variety of different lens proteins. More detailed investigations of the functional consequences of each mutation are being reported and suggest that lens opacification results not only from precipitation and amyloid-like accumulation of proteins essential for lens transparency but also from interference with their secondary functions.

SUMMARY

Improved functional characterization of mutations causing childhood cataract will improve understanding of lens development and physiology but will also have implications for the more common age-related cataract. This too has a significant genetic component to its etiology, and genes causing monogenic forms of childhood inherited cataract represent excellent candidate genes for age-related cataract. The identification of the genes conferring increased risk of developing age-related cataract will bring closer the development of a medical treatment to delay the onset of lens opacification and need for surgery.

Abnormal constitutional karyotypes in patients with neuroblastoma: a report of four new cases and review of 47 others in the literature

Anomalies of constitutional karyotype, which have led to the discovery of oncogenes and tumor-suppressor genes in embryonal tumors such as retinoblastoma and Wilms tumor, have, until recently, rarely been reported until recently in neuroblastoma. We present four new cases of neuroblastoma associated with (a) a mosaicism for monosomy 22; (b) an 11q interstitial deletion; (c) a pericentric inversion of chromosome 9 at band 9p21; and (d) a Robertsonian translocation t(13;14). These anomalies and 47 others in the literature are worthy of interest, because some are recurrent, involving the same chromosome regions (1p36, 2p23, 3q, 11q23, and 15q), and some anomalies are situated on chromosome regions known to contain genes involved in neuroblastoma development (1p, 2p, 9p, 11q, 16q, and 17q). Chromosome regions 3q and 15q, observed several times, may also contain genes significant for neuroblastoma onset or development. Furthermore, the lack of neuroblastoma in patients with Down syndrome and Klinefelter or triple-X syndromes, together with a probable excess of neuroblastoma in patients with Turner syndrome, suggests that genes of importance for neuroblastoma may map to chromosomes X and 21. A search for genes implicated in neuroblastoma biology should use these data.

Paradoxical eyelid movement in trisomy 2p

Paradoxical eyelid movement was reported in a 12-year-old female with 46,XX,dup(2)(p25.3p22.2). Alternating seesaw-like movement of the eyelids during lateral gazing had been observed at 5 months of age when she was first referred to our neuropediatric outpatient department, and the abnormal lid movement persisted without any change for 11 years. The differentiation of the features of the paradoxical lid movements in our patient from those of Duane syndrome were discussed, and a possible pathogenesis is discussed as well. Besides ophthalmologic abnormalities, the patient demonstrated severe psychomotor retardation, marked growth failure, symptomatic generalized epilepsy, and multiple anomalies. The dysmorphism consisted of a cleft lip, a narrow high-arched palate, malalignment, lowset ears, and kyphoscoliosis caused by fused thoracic vertebrae.

Molecular characterization of a ring chromosome 16 from a patient with bilateral cataracts

A four-month-old white female, who was referred to us for genetic evaluation because of severe developmental delay, dysmorphic features, and bilateral cataracts, was found by routine cytogenetic analysis to have ring chromosome 16 in almost all cells analyzed. Ring chromosome 16 was confirmed and further delineated by fluorescence in situ hybridization (FISH). Breakpoints between loci D16S521 and KG8 on the short arm and D16S3121 and D16S303 on the long arm of chromosome 16 were determined by polymerase chain reaction (PCR) analysis. The deleted chromosome was of maternal origin. To our knowledge, this is the first case of ring chromosome 16 associated with bilateral cataracts. Comparison of previously reported cases with deletion of chromosome 16 and our case suggests the presence of cataract locus within 1 Mb of the terminus of 16q.

Congenital progressive polymorphic cataract caused by a mutation in the major intrinsic protein of the lens, MIP (AQP0)

BACKGROUND

Congenital cataract, when inherited as an isolated abnormality, is phenotypically and genetically heterogeneous. Although there is no agreed nomenclature for the patterns of cataract observed, a recent study identified eight readily identifiable phenotypes.

METHODS

The Moorfields Eye Hospital genetic eye clinic database was used to identify a four generation family with isolated autosomal dominant congenital cataracts. All individuals (affected and unaffected) underwent a full ophthalmic assessment.

RESULTS

The results of the molecular linkage study identifying a missense mutation in the gene encoding the major intrinsic protein of the lens (MIP) have been published elsewhere. Affected individuals had bilateral discrete progressive punctate lens opacities limited to mid and peripheral lamellae with additional asymmetric polar opacification. One young female had predominantly cortical cataract and another had serpiginous nuclear opacities.

CONCLUSIONS

This phenotype has not been recorded in human families before and has been termed polymorphic. The pattern of opacification appears to reflect the distribution of MIP in the lens. Furthermore, this is the first clear evidence of allelic heterogeneity in this condition following the identification of a family with lamellar cataracts who have a different mutation within the MIP gene.

Phenotype of a patient with pure partial trisomy 2p(p23-->pter)

We present the case of a 7-month-old girl with the karyotype 46,XX, der(13) t(2;13)(p23;p11.2).ish der(13)(wcp2+) de novo. Painting confirmed that the additional segment on 13p was of chromosome 2 origin, resulting in trisomy 2p23 -->2pter. The child had a prominent forehead with a flat hemangioma, depressed nasal bridge, protruding tongue, posteriorly angulated ears, esotropia with poor abduction of the right eye, bilateral severe myopia (-5.5 D), retinal hypopigmentation, foveal hypoplasia, and striking left optic nerve hypoplasia. She also had pectus excavatum, a protruding abdomen with diastasis recti, generalized hypotonia, delayed fine and gross motor development, grade II reflux on the left side, and grade III-IV reflux on the right side. An EEG showed epileptiform discharges. Computed tomographic scan of the brain showed decreased white matter, but magnetic resonance imaging showed normal results.

Surgical management of congenital cataract associated with severe microphthalmos

PURPOSE

To report the results of cataract surgery in children with severe microphthalmos and congenital cataract.

SETTING

Seoul National University, Department of Ophthalmology, Seoul, Korea.

METHODS

Retrospective studies were conducted by reviewing the charts of 20 eyes of 11 patients with severe microcornea and microphthalmos or severe microcornea with a corneal diameter smaller than 9.0 mm. The patient pool was divided according to surgical method, specifically by incision site: an anterior group that had corneal limbal incisions and a posterior group treated via pars plicata incisions. Preoperative examinations included bilaterality, corneal diameter, axial length, and eye and systemic abnormalities. Postoperative results and complications of the 2 operative methods were compared.

RESULTS

All 11 patients had bilateral congenital cataract and microphthalmos. Except in 1 case, surgeries were done in patients ranging in age from 2 to 16 months. Mean follow-up was 2 years. Corneal diameter was smaller than 9.0 mm in all 20 eyes and smaller than 7.5 mm in 11 eyes. Ten eyes were categorized into the anterior group, and the other 10 eyes were placed in the posterior group. Postoperative complications included secondary membranes in 3 eyes in the posterior group and corneal opacity in 3 eyes in the anterior group.

CONCLUSION

The surgical management of children with congenital cataract and severe microphthalmos is recommended as a way to improve vision but must be performed carefully to avoid complications.

Human microphthalmia associated with mutations in the retinal homeobox gene CHX10

Isolated human microphthalmia/anophthalmia, a cause of congenital blindness, is a clinically and genetically heterogeneous developmental disorder characterized by a small eye and other ocular abnormalities. Three microphthalmia/anophthalmia loci have been identified, and two others have been inferred by the co-segregation of translocations with the phenotype. We previously found that mice with ocular retardation (the or-J allele), a microphthalmia phenotype, have a null mutation in the retinal homeobox gene Chx10 (refs 7,8). We report here the mapping of a human microphthalmia locus on chromosome 14q24.3, the cloning of CHX10 at this locus and the identification of recessive CHX10 mutations in two families with non-syndromic microphthalmia (MIM 251600), cataracts and severe abnormalities of the iris. In affected individuals, a highly conserved arginine residue in the DNA-recognition helix of the homeodomain is replaced by glutamine or proline (R200Q and R200P, respectively). Identification of the CHX10 consensus DNA-binding sequence (TAATTAGC) allowed us to demonstrate that both mutations severely disrupt CHX10 function. Human CHX10 is expressed in progenitor cells of the developing neuroretina and in the inner nuclear layer of the mature retina. The strong conservation in vertebrates of the CHX10 sequence, pattern of expression and loss-of-function phenotypes demonstrates the evolutionary importance of the genetic network through which this gene regulates eye development.

The genetics of childhood cataract

Human congenital cataract has a diverse aetiology. In the proportion of cases where the cause is genetic, the disease shows wide phenotypic and genetic heterogeneity. Over the past few years, much research has been devoted to mapping the genes that underlie the disorder. This has been helped by the extensive array of naturally occurring and genetically engineered mouse cataract models and the abundance of human candidate genes. Most progress to date has been in the identification of genetic mutations causing autosomal dominant congenital cataract where eight genes have been implicated in cataractogenesis. Overall there is good correlation between the genetic mutations so far identified and the resulting lens phenotype but it is clear that mutations at more that one locus may give rise to similar forms of cataract. The identification of genes causing inherited forms of cataract will improve our understanding of the mechanisms underlying cataractogenesis in childhood and provide further insights into normal lens development and physiology. Perhaps more importantly, it is likely that some of the genes causing early onset cataract will be implicated in age related cataract which remains the commonest cause of blindness in the world.

Molecular cytogenetic studies in three patients with partial trisomy 2p, including CGH from paraffin-embedded tissue

We report on three cases of partial trisomy 2p in which the identification and exact localization of the duplicated chromosome segment was possible only by application of molecular cytogenetic techniques. These included fluorescence in situ hybridization by use of wcp2, N-myc, and subtelomeric 2p probes and comparative genomic hybridization with DNA isolated from blood samples, frozen fetal tendon, and formalin fixed, paraffin-embedded fetal lung tissue. Two of the cases concerned fetuses of gestational week 20 and 24 with duplication of nonoverlapping terminal (2pter-->p24) and more proximal (2p25-->p23) segments and with distinctly different phenotypes. The third case was due to a de novo inverted duplication of 2p25-->p23, with loss of the subtelomeric region of 2p. This 53-month-old girl was a Bloom syndrome carrier. The patient had prenatal growth failure, borderline microcephaly, dilated lateral horns of the cerebral ventricles, transient cortical blindness, myopia, muscle hypotonia, and dilatation of the left renal collecting system. Dermal cysts were found on the glabella, the soles of both feet, and the vocal cord, causing respiratory embarrassment. Previously reported cases of pure trisomy 2p are reviewed, in an attempt to correlate clinical findings to overlapping regions in 2p. These cases illustrate the effectiveness of molecular cytogenetic methods in resolving subtle chromosomal aberrations in order to coordinate more accurately a chromosome regionspecific phenotype.

Solh, the mouse homologue of the Drosophila melanogaster small optic lobes gene: organization, chromosomal mapping, and localization of gene product to the olfactory bulb

The Drosophila melanogaster small optic lobes gene (sol) is required for normal development of the neuropiles of the medulla and lobula complexes of the adult optic lobes. The predicted protein products of sol and its human homologue SOLH contain zinc-finger-like repeats, a calpain-like protease domain, and a C-terminal domain of unknown function. Long-distance PCR was used to amplify genomic DNA for Solh, the mouse homologue of sol, following the identification of mouse Solh expressed sequence tags. The nucleotide sequence of the Solh coding region (6.0 kb) was determined. The predicted Solh protein of 1095 amino acid residues shows 89% identity (93% similarity) to the human homologue. Solh was localized by in situ hybridization to band A3.3 on mouse Chromosome 17, in a region of maintained homology with human 16p13.3. Antipeptide antibodies were prepared and verified by demonstration of specific reactivity with recombinant human SOLH protein prepared by in vitro transcription/translation and expression in insect cells using the baculovirus system. The antibodies were used to show that the Solh protein localizes to the olfactory bulb in mouse and rat brain, suggesting that it could have an analogous role in development of sensory system neurons in Drosophila and in mammals.

SOLH, a human homologue of the Drosophila melanogaster small optic lobes gene is a member of the calpain and zinc-finger gene families and maps to human chromosome 16p13.3 near CATM (cataract with microphthalmia)

Mutations in the Drosophila melanogaster small optic lobes (sol) gene cause a sever reduction in the neuropiles of the medulla and lobula complexes of the adult optic lobes. The predicted protein product of sol contains zinc-finger-like repeats, a calpain-like protease domain, and a C-terminal region of unknown function. We have isolated human brain cDNA for SOLH, a human homologue of sol. The human SOLH gene consists of 14 exons distributed over more than 45 kb of genomic DNA. The encoded SOLH protein of 1086 amino acids has strong similarity to the D. melanogaster protein. The calpain-like domain and C-terminal region are highly conserved (58% identity), and similar Cys2-Cys2 zinc fingers are present in the N-terminal region. A reported Caenorhabditis elegans homologue contains the calpain domain and C-terminal region, but appears to lack the zinc finger region. A single copy of the zinc finger sequence is present in adjacent C. elegans genomic cosmid DNA sequence, and we show that it is part of the C. elegans sol-like transcript. Northern analysis of human tissues revealed a SOLH transcript of approximately 5 kb that was strongest in human brain. We have mapped the SOLH gene to chromosome 16p13.3 by in situ hybridization. SOLH is a candidate gene for CATM (hereditary cataracts with microphthalmia), which maps in this region.

Cytogenetic and clinical findings in a patient with a deletion of 16q23.1: first report of bilateral cataracts and a 16q deletion

The most commonly reported manifestations of 16q deletions are severe growth and developmental disorders and anomalies of the craniofacial, visceral, and musculoskeletal systems. We reviewed the findings of patients reported with 16q- syndrome and compared them to our patient, a 4 1/2-year-old boy with a deletion of 16q23.1. Findings include psychomotor retardation, hypotonia, high forehead, hypertelorism, upslanting palpebral fissures, low-set abnormally modeled ears, and talipes equinovarus. Anomalies present in our patient not reported in others with 16q- syndrome include bilateral cataracts, iris coloboma, and autistic-like behavior. It is of note that a locus for autosomal dominant congenital cataract, known as Marner cataract, was mapped previously to 16q22. Because our patient has bilateral cataracts and a unilateral iris coloboma, it seems likely that a gene involved in ocular development is located within 16q23.1. Our patient's deletion may also include the gene involved in Marner cataract and may further assist in the isolation of this gene.

Two sibs with anophthalmia and pulmonary hypoplasia (the Matthew-Wood syndrome)

We describe two sibs with pulmonary hypoplasia and anophthalmia; one also had a number of other malformations. Only one other broadly similar case could be found in the literature, and it was an isolated occurrence. The condition is named the Matthew-Wood syndrome.

Assignment of congenital cataract Volkmann type (CCV) to chromosome 1p36

Congenital cataract, type Volkmann (McKusick no 115665, gene symbol CCV) is an autosomal dominant eye disease. The disease is characterized by a progressive, central and zonular cataract, with opacities both in the embryonic, fetal and juvenile nucleus and around the anterior and posterior Y-suture. We examined blood samples from 91 members of a Danish pedigree comprising 426 members, by using highly informative short tandem repeat polymorphisms and found the closest linkage of the disease gene (CCV) to a (CA)n dinucleotide repeat polymorphism at locus D1S243 (Zmax = 14.04 at theta M = 0.025 theta F = 0.000), at a penetrance of 0.90. Using two additional chromosome 1 markers, we were able to map the CCV gene in the sequence 1pter-(CCV, D1S243)-D1S468-D1S214. The (enolase 1) gene has been mapped to this area; however, a mutation described in this gene did not give eye disease.

Trisomy 2p: analysis of unusual phenotypic findings

We present three probands with partial trisomies 2p21-23 due to ins(4;2)(q21;p21p23) pat, 2p23-pter due to t(2;4)(p23;q35)mat, and 2p21-pter due to t(2;11)(p21;q23.3)mat. More than 50 cases of partial trisomy 2p have been reviewed and some abnormalities, unusual for most other types of structural autosomal imbalance, have been found in patients with inherited forms of 2p trisomy and in their non-karyotyped sibs. Neural tube defects (anencephaly, occipital encephalocele, and spina bifida) were found in five probands and 4/6 affected non-karyotyped sibs. The only triplicated segment common to all was 2p24. Different forms of "broncho-pulmonary a/hypoplasia" (including two cases of lung agenesis) were described in four patients (overlapping triplicated segment was 2p21-p25). Three patients (with overlapping triplicated segment 2p23-p25) had diaphragmatic hernia. Abnormal rotation of the heart or L-transposition of large vessels (with or without visceral heterotaxia) was found in two infants (overlapping triplicated segment 2p23-p24). In two patients with common triplicated segment 2p22.3-p25, neuroblastoma has been described. The occurrence of all these defects may be explained either by the action of the same gene(s) mapped to 2p24 or by action of some independent factors located in different segments of the short arm. Although the latter hypothesis is much less probable, it can not be rejected at the present time. We propose the existence of a genetic system controlling surveillance of an abnormal embryo to explain the phenotypic differences between patients with the same imbalance within a family. In some "restrictive" combinations the abnormal embryos will die, although in "permissive" combinations they can survive.