Nail patella syndrome: a review of the phenotype aided by developmental biology

LMX1B is essential for the maintenance of differentiated podocytes in adult kidneys

Mutations of the LMX1B gene cause nail-patella syndrome, a rare autosomal-dominant disorder affecting the development of the limbs, eyes, brain, and kidneys. The characterization of conventional Lmx1b knockout mice has shown that LMX1B regulates the development of podocyte foot processes and slit diaphragms, but studies using podocyte-specific Lmx1b knockout mice have yielded conflicting results regarding the importance of LMX1B for maintaining podocyte structures. In order to address this question, we generated inducible podocyte-specific Lmx1b knockout mice. One week of Lmx1b inactivation in adult mice resulted in proteinuria with only minimal foot process effacement. Notably, expression levels of slit diaphragm and basement membrane proteins remained stable at this time point, and basement membrane charge properties also did not change, suggesting that alternative mechanisms mediate the development of proteinuria in these mice. Cell biological and biophysical experiments with primary podocytes isolated after 1 week of Lmx1b inactivation indicated dysregulation of actin cytoskeleton organization, and time-resolved DNA microarray analysis identified the genes encoding actin cytoskeleton-associated proteins, including Abra and Arl4c, as putative LMX1B targets. Chromatin immunoprecipitation experiments in conditionally immortalized human podocytes and gel shift assays showed that LMX1B recognizes AT-rich binding sites (FLAT elements) in the promoter regions of ABRA and ARL4C, and knockdown experiments in zebrafish support a model in which LMX1B and ABRA act in a common pathway during pronephros development. Our report establishes the importance of LMX1B in fully differentiated podocytes and argues that LMX1B is essential for the maintenance of an appropriately structured actin cytoskeleton in podocytes.

LMX1B mutations cause hereditary FSGS without extrarenal involvement

LMX1B encodes a homeodomain-containing transcription factor that is essential during development. Mutations in LMX1B cause nail-patella syndrome, characterized by dysplasia of the patellae, nails, and elbows and FSGS with specific ultrastructural lesions of the glomerular basement membrane (GBM). By linkage analysis and exome sequencing, we unexpectedly identified an LMX1B mutation segregating with disease in a pedigree of five patients with autosomal dominant FSGS but without either extrarenal features or ultrastructural abnormalities of the GBM suggestive of nail-patella-like renal disease. Subsequently, we screened 73 additional unrelated families with FSGS and found mutations involving the same amino acid (R246) in 2 families. An LMX1B in silico homology model suggested that the mutated residue plays an important role in strengthening the interaction between the LMX1B homeodomain and DNA; both identified mutations would be expected to diminish such interactions. In summary, these results suggest that isolated FSGS could result from mutations in genes that are also involved in syndromic forms of FSGS. This highlights the need to include these genes in all diagnostic approaches to FSGS that involve next-generation sequencing.

Nail-patella syndrome-a novel mutation in the LMX1B gene

Nail-patella syndrome (NPS) is an autosomal-dominant pleiotropic disorder characterized by dyplasia of finger nails, skeletal anomalies and frequently renal disease. In the reported case, genetic analysis revealed a new missense mutation in the homeodomain of LMX1B, presumed to abolish DNA binding (c.725T>C, p.Val242Ala). A missense mutation at codon 725 was identified, where thymine was replaced by cytosine which led to the replacement of valine by alanine at position 242. It was not detected in both parents. A 2005 study by Bongers et al. described a significant association between the presence of clinically relevant renal involvement in an NPS patient and a positive family history of nephropathy, which was lacking in our case.

A hypoplastic patella fracture in nail patella syndrome: a case report

Introduction

Nail patella syndrome is a rare autosomal dominant hereditary condition, with an incidence of 22 per million in the United Kingdom. The syndrome’s most common features include iliac horns, hypoplastic patella and nail dysplasia.

Case presentation

We report the case of a 26-year-old Caucasian man with nail patella syndrome who sustained a fracture of his right hypoplastic patella after a fall. His right knee became swollen and he was unable to extend against gravity immediately post fall. Radiographs revealed a fracture of the lower pole of his right patella with associated complete disruption of the extensor mechanism of the knee. He underwent operative fixation and his post operative course was uneventful. He was further treated post operatively with a full knee cast and graded immobilization. At six months he had regained the full range of motion at the knee joint.

Conclusions

To the best of our knowledge, this is the only case report in the literature describing a patella fracture in an individual with nail patella syndrome. We hypothesize that given the extent of pre-existing knee joint impairment in these individuals, functional outcome may be inferior, suggesting the need for more frequent follow-up.

Progress in pathogenesis of proteinuria

Aims. Proteinuria not only is a sign of kidney damage, but also is involved in the progression of renal diseases as an independent pathologic factor. Clinically, glomerular proteinuria is most commonly observed, which relates to structural and functional anomalies in the glomerular filtration barrier. The aim of this paper was to describe the pathogenesis of glomerular proteinuria. Data Sources. Articles on glomerular proteinuria retrieved from Pubmed and MEDLINE in the recent 5 years were reviewed. Results. The new understanding of the roles of glomerular endothelial cells and the glomerular basement membrane (GBM) in the pathogenesis of glomerular proteinuria was gained. The close relationships of slit diaphragm (SD) molecules such as nephrin, podocin, CD2-associated protein (CD2AP), a-actinin-4, transient receptor potential cation channel 6 (TRPC6), Densin and membrane-associated guanylate kinase inverted 1 (MAGI-1), α3β1 integrin, WT1, phospholipase C epsilon-1 (PLCE1), Lmx1b, and MYH9, and mitochondrial disorders and circulating factors in the pathogenesis of glomerular proteinuria were also gradually discovered. Conclusion. Renal proteinuria is a manifestation of glomerular filtration barrier dysfunction. Not only glomerular endothelial cells and GBM, but also the glomerular podocytes and their SDs play an important role in the pathogenesis of glomerular proteinuria.

A case of ectopic cilia in nail-patella syndrome

Both ectopic cilia and nail-patella syndrome (NPS) are rare entities. To our knowledge we report the first case of the two anomalies coexisting in one patient. We present the case of a 2-year-old girl, with no other ophthalmic complication of NPS, who had an excellent cosmetic outcome and no lesion recurrence following surgical excision of ectopic cilia.

A case of nail-patella syndrome associated with thyrotoxicosis

Nail-patella syndrome, also known as hereditary onycho-osteodystrophy, is a rare autosomal dominant disorder with pleiotropic phenotypic expression.The present report is of a nail-patella syndrome patient, a 26-year-old female, admitted to our NeuroMuscular Rehabilitation Clinic Division for neurological symptoms, secondary to a severe spondylolysthesis with bilateral L5 pedicle fracture. During hospitalization, she was also diagnosed with mild thyrotoxicosis, but interestingly enough, the bone mineral density, assessed at multiple sites, was quasi-normal.

c.194 A>C (Q65P) mutation in the LMX1B gene in patients with nail-patella syndrome associated with glaucoma

PURPOSE

To report the clinical, ophthalmic, extraophthalmic, and genetic characteristics of nail-patella syndrome (NPS) in a Chilean family and to investigate the expressivity of open angle glaucoma (OAG) and ocular hypertension (OHT) in the family members.

METHODS

Five family members affected with NPS and two unaffected members underwent a complete ophthalmologic examination, including computerized visual field, optical coherence tomography (OCT) of the optic disc and ultrasound pachymetry. Renal function was assessed by urinalysis and blood tests. Orthopedic evaluations were also performed, including radiological studies of the wrist, elbow and hip joints. Genomic DNA was extracted from peripheral leukocytes of the five affected and two unaffected family members. Exons 2-6 of the LIM homeobox transcription factor 1-beta (LMX1B) gene were screened for mutations by DNA sequencing of the proband. We also screened for mutations in exon 2 by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) of the other participants and 91 blood donors.

RESULTS

Five living family members from three generations were positively diagnosed with NPS, three of them with varying degrees of OAG and one with OHT. Retinal nerve fiber layer (RNFL) thickness measured by spectral domain OCT was below normal values in three individuals. All subjects evaluated had normal nephrologic function. Orthopedic, clinical, and radiological alterations were compatible with NPS. Screening for mutations in exons 2- 6 of LMX1B showed a heterozygous missense mutation c.194 A>C changing glutamine to proline within exon 2 in codon 65 (Q65P) of the coding sequence. This mutation was present in all NPS subjects and absent in the unaffected family members and in 91 Chilean blood donors.

CONCLUSIONS

This is the first report of c.194 A>C mutation in LMX1B in a Chilean family with NPS and the second worldwide. The phenotype associated with this mutation is variable within the family, although we noted a close connection between the presence of the c.194 A>C mutation and the presence of OHT or OAG and probably also with an early onset of OHT in patients with NPS. All subjects older than 21 years had either OHT or OAG. We also suggest that the LMX1B mutation may be related to affective disorders.

Increased symptoms of attention deficit hyperactivity disorder and major depressive disorder symptoms in Nail-patella syndrome: potential association with LMX1B loss-of-function

Nail-Patella syndrome (NPS) is an autosomal dominant disorder that is the result of heterozygous loss-of-function mutations in LMX1B, coding for a LIM homeobox (LIM-HD) transcription factor. Analyses of lmx1b mutant mice have revealed the role of Lmx1b in the development of mesencephalic dopaminergic neurons and the serotonergic system; these areas have been linked with symptoms of attention deficit hyperactivity disorder (ADHD) and major depressive disorder (MDD). Fifty adults (38 females, 12 males) with NPS completed the Conners' Adult ADHD Rating Scales-Self-report: Long Version (CAARS) and Beck Depression Inventory-II (BDI-II). The objective was to describe the neurobehavioral phenotype of these subjects and examine possible relationships between neurobehavioral symptoms and NPS. Elevated levels of DSM-IV-TR ADHD Inattentive symptoms were reported on the CAARS by 22% of the NPS sample. The BDI-II Total score was elevated for 40% of the NPS sample. There was a significant increase in the odds of an elevated BDI-II Total score when any of the three CAARS scales were elevated (odds ratios ranging from 11.455 to 15.615). The CAARS and BDI-II did not significantly differ with gender, age, or education level. There was no significant association between genetic mutation-predicted protein status and elevations on CAARS or BDI-II. Individuals with NPS reported co-occurring symptoms of ADHD and MDD, with higher levels of co-occurrence than reported in the literature for the general population. The co-occurrence of these symptoms may be related to mesencephalic dopaminergic neurologic pathway abnormalities that are a consequence of LMX1B loss of function.

Identification of genes controlled by LMX1B in E13.5 mouse limbs

During limb development, the dorsal limb mesenchyme expression of the transcription factor LMX1B is required for dorsoventral limb patterning. In mice, Lmx1b mutations result in the mirror-image duplication of ventral limb structures and loss of dorsal limb structures. Heterozygous LMX1B mutations in humans cause the Nail-Patella Syndrome characterized by limb, kidney, and eye developmental defects. We used DNA microarrays to compare the mRNAs in E13.5 mouse Lmx1b mutant and wild-type limbs. We report 14 genes that require Lmx1b for their normal expression in the dorsal limb or the restriction of their expression to the ventral limb.

Prevalence and complications of single-gene and chromosomal disorders in craniosynostosis

OBJECTIVES

We describe the first cohort-based analysis of the impact of genetic disorders in craniosynostosis. We aimed to refine the understanding of prognoses and pathogenesis and to provide rational criteria for clinical genetic testing.

METHODS

We undertook targeted molecular genetic and cytogenetic testing for 326 children who required surgery because of craniosynostosis, were born in 1993-2002, presented to a single craniofacial unit, and were monitored until the end of 2007.

RESULTS

Eighty-four children (and 64 relatives) had pathologic genetic alterations (86% single-gene mutations and 14% chromosomal abnormalities). The FGFR3 P250R mutation was the single largest contributor (24%) to the genetic group. Genetic diagnoses accounted for 21% of all craniosynostosis cases and were associated with increased rates of many complications. Children with an initial clinical diagnosis of nonsyndromic craniosynostosis were more likely to have a causative mutation if the synostoses were unicoronal or bicoronal (10 of 48 cases) than if they were sagittal or metopic (0 of 55 cases; P = .0003). Repeat craniofacial surgery was required for 58% of children with single-gene mutations but only 17% of those with chromosomal abnormalities (P = .01).

CONCLUSIONS

Clinical genetic assessment is critical for the treatment of children with craniosynostosis. Genetic testing of nonsyndromic cases (at least for FGFR3 P250R and FGFR2 exons IIIa/c) should be targeted to patients with coronal or multisuture synostoses. Single-gene disorders that disrupt physiologic signaling in the cranial sutures often require reoperation, whereas chromosomal abnormalities follow a more-indolent course, which suggests a different, secondary origin of the associated craniosynostosis.

Bilateral absence of patella

A 20-year-old man with bilateral absence of patella, thinness of the left femoral neck, femoral and tibial shaft was reported. This clinical presentation has not been reported in the English language literature. We propose that the unusual association observed in our patient may represent a distinguishing clinical presentation from previously reported aplastic patella syndromes.

Familial forms of nephrotic syndrome

The recent discovery of genes involved in familial forms of nephrotic syndrome represents a break-through in nephrology. To date, 15 genes have been characterized and several new loci have been identified, with a potential for discovery of new genes. Overall, these genes account for a large fraction of familial forms of nephrotic syndrome, but they can also be recognized in 10-20% of sporadic cases. These advances increase diagnostic and therapeutic potentials, but also add higher complexity to the scenario, requiring clear definitions of clinical, histopathological and molecular signatures. In general, genetic forms of nephrotic syndrome are resistant to common therapeutic approaches (that include steroids and calcineurin inhibitors) but, in a few cases, drug response or spontaneous remission suggest a complex pathogenesis. Finally, syndromic variants can be recognized on the basis of the associated extra-renal manifestations. In this educational review, clinical, histological and molecular aspects of various forms of familial nephrotic syndrome have been reviewed in an attempt to define a rational diagnostic approach. The proposed model focuses on practical and economic issues, taking into consideration the impossibility of using genetic testing as starting diagnostic tool. The final objective of this review is to outline a diagnostic flow-chart for clinicians and geneticists and to generate a rational scheme for molecular testing.

Kidney disease in nail-patella syndrome

Nail-patella syndrome (NPS) is a pleiotropic autosomal-dominant disorder due to mutations in the gene LMX1B. It has traditionally been characterized by a tetrad of dermatologic and musculoskeletal abnormalities. However, one of the most serious manifestations of NPS is kidney disease, which may be present in up to 40% of affected individuals. Although LMX1B is a developmental LIM-homeodomain transcription factor, it is expressed in post-natal life in the glomerular podocyte, suggesting a regulatory role in that cell. Kidney disease in NPS seems to occur more often in some families with NPS, but it does not segregate with any particular mutation type or location. Two patterns of NPS nephropathy may be distinguished. Most affected individuals manifest only an accelerated age-related loss of filtration function in comparison with unaffected individuals. Development of symptomatic kidney failure is rare in this group, and proteinuria (present in approximately one-third) does not appear to be progressive. A small minority (5-10%) of individuals with NPS develop nephrotic-range proteinuria as early as childhood or young adulthood and progress to end-stage kidney failure over variable periods of time. It is proposed that this latter group reflects the effects of more global podocyte dysfunction, possibly due to the combination of a mutation in LMX1B along with an otherwise innocuous polymorphism or mutation involving any of several genes expressed in podocytes (e.g. NPHS2, CD2AP), the transription of which is regulated by LMX1B.

Clinico-genetic study of nail-patella syndrome

Nail-patella syndrome (NPS) is an autosomal dominant disease that typically involves the nails, knees, elbows and the presence of iliac horns. In addition, some patients develop glomerulopathy or adult-onset glaucoma. NPS is caused by loss-of-function mutations in the LMX1B gene. In this study, phenotype-genotype correlation was analyzed in 9 unrelated Korean children with NPS and their affected family members. The probands included 5 boy and 4 girls who were confirmed to have NPS, as well as 6 of their affected parents. All of the patients (100%) had dysplastic nails, while 13 patients (86.7%) had patellar anomalies, 8 (53.3%) had iliac horns, 6 (40.0%) had elbow contracture, and 4 (26.7%) had nephropathy including one patient who developed end-stage renal disease at age 4.2. The genetic study revealed 8 different LMX1B mutations (5 missense mutations, 1 frame-shifting deletion and 2 abnormal splicing mutations), 6 of which were novel. Genotype-phenotype correlation was not identified, but inter- and intrafamilial phenotypic variability was observed. Overall, these findings are similar to the results of previously conducted studies, and the mechanism underlying the phenotypic variations and predisposing factors of the development and progression of nephropathy in NPS patients are still unknown.

The lmx1b gene is pivotal in glomus development in Xenopus laevis

We have previously shown that lmx1b, a LIM homeodomain protein, is expressed in the pronephric glomus. We now show temporal and spatial expression patterns of lmx1b and its potential binding partners in both dissected pronephric anlagen and in individual dissected components of stage 42 pronephroi. Morpholino oligonucleotide knock-down of lmx1b establishes a role for lmx1b in the development of the pronephric components. Depletion of lmx1b results in the formation of a glomus with reduced size. Pronephric tubules were also shown to be reduced in structure and/or coiling whereas more distal tubule structure was unaffected. Over-expression of lmx1b mRNA resulted in no significant phenotype. Given that lmx1b protein is known to function as a heterodimer, we have over-expressed lmx1b mRNA alone or in combination with potential interacting molecules and analysed the effects on kidney structures. Phenotypes observed by over-expression of lim1 and ldb1 are partially rescued by co-injection with lmx1b mRNA. Animal cap experiments confirm that co-injection of lmx1b with potential binding partners can up-regulate pronephric molecular markers suggesting that lmx1b lies upstream of wt1 in the gene network controlling glomus differentiation. This places lmx1b in a genetic hierarchy involved in pronephros development and suggests that it is the balance in levels of binding partners together with restricted expression domains of lmx1b and lim1 which influences differentiation into glomus or tubule derivatives in vivo.

Identification of genes controlled by LMX1B in the developing mouse limb bud

In the developing limb, dorsal-ventral patterning is controlled by the transcription factor LMX1B, expressed in the dorsal mesenchyme. Loss of Lmx1b function in mice or humans results in the loss of dorsal limb structures and Nail-Patella syndrome, but the effectors through which LMX1B controls limb patterning are virtually unknown. Using microarrays to analyze the differential expression of mRNAs in wild-type vs. Lmx1b(-/-) limb buds, we have identified hundreds of genes as putative LMX1B targets. Analysis of a subset of these candidates by in situ mRNA localization has identified eight genes previously unknown to require Lmx1b for their dorsal-ventral restriction of expression in the limb. Furthermore, our results suggest that LMX1B controls different targets along the proximal-distal axis of the limb, and suggest the existence of a dorsal proximal limb region that is rich in mRNAs requiring Lmx1b for their expression.

Role of homeobox genes in the patterning, specification, and differentiation of ectodermal appendages in mammals

Homeobox genes are an evolutionarily conserved class of transcription factors that are key regulators during developmental processes such as regional specification, patterning, and differentiation. In this review, we summarize the expression pattern, loss- and/or gain-of-function mouse models, and naturally occurring mouse and human mutations of known homeobox genes required for the development of ectodermal appendages.

Nail-Patella syndrome: a case report and anesthetic implications

PURPOSE

To report a case of asystole during combined epidural and general anesthesia occurring in a patient with Nail-Patella syndrome (NPS), and to review the management and anesthetic implications of this rare genetic syndrome.

CLINICAL FEATURES

A 64-yr-old male with NPS, renal impairment and coronary artery disease presented for right hemicolectomy for colon cancer. Following initiation of surgery and during insertion of a nasogastric tube there was sudden loss of the patient's pulse oxymetry, and arterial pressure waveforms with an asystolic electrocardiogram signal. Atropine 0.6 mg i.v. was administered and after an asystolic period of 20-30 sec, myocardial activity commenced at 110 beatsxmin(-1) with return of normal vital signs and no further sequelae.

CONCLUSIONS

Nail-Patella syndrome can present with an array of anomalies that may be associated with perioperative complications. Glaucoma, nephropathy, vasomotor dysfunction, fragile teeth, abnormal muscle, skeletal and nerve anatomy as well as involvement of the central and/or peripheral nervous systems are common findings. In this setting it is postulated that a vasovagal reflex from esophageal stimulation by nasogastric tube placement may have caused the asystolic event. This response could have been exaggerated by the sympatholytic combination of neuraxial block, preoperative beta-blockade, and potential autonomic dysfunction secondary to NPS. Awareness of this uncommon disease and its presentation may serve to caution the anesthesiologist regarding the perioperative implications of patients with this syndrome.

Fingertip dermatitis refractory to topical corticosteroids associated with nail-patella syndrome

A 14-year-old girl and her 47-year-old father presented with fingernails that were hypoplastic, spoon-shaped and ridged since birth. Fingertip dermatitis and paronychia were also observed in the daughter, which had been present since birth and had progressively worsened. The daughter denied trauma to her fingernails or chronic exposure to irritants and allergens. She had previously tried topical corticosteroids for 18 months without any benefit. We put forward the possibility of chronic paronychia and fingertip dermatitis, refractory to topical corticosteroids, as associations of digital nail-patella syndrome.

Renal phenotype in heterozygous Lmx1b knockout mice (Lmx1b +/−) after unilateral nephrectomy

The nail-patella syndrome (NPS) is a rare autosomal-dominant disorder which is caused by loss-of-function mutations in the transcription factor LMX1B. NPS is characterized by dysplastic nails, absent or hypoplastic patellae, minor skeletal abnormalities and nephropathy (in 20-40% of the cases), which is the most severe aspect of the disorder. The current data suggest that genetic modifiers in the outbred human genetic background are responsible for this variable phenotype. Preliminary work on the function of Lmx1b in the kidney has been performed using Lmx1b knockout mice (Lmx1b (-/-)). Although Lmx1b (-/-) mice die within 24 h after birth, they exhibit the characteristic NPS features including the renal abnormalities. But in contrast to the situation in human, no phenotype could so far be detected in heterozygous Lmx1b (+/-) mice. This indicates that our understanding of the pathomechanism underlying the nephropathy is still very limited. In an attempt to further evaluate these mechanisms, we tried to induce a renal phenotype in Lmx1b (+/-) mice, and thus model the human (NPS) situation. We applied unilateral nephrectomy as a model to induce nephron loss and detected a significant (p = 0.02) reduction in compensatory renal growth in heterozygous knockout animals (Lmx1b (+/-)) compared to Lmx1b (+/+) animals, which was correlated with a significantly lower increase in glomerular volume (V(G)) (p = 0.0034) and an increase in glomerulosclerosis (p = 0.085). Thus, Lmx1b deficiency in heterozygous Lmx1b (Lmx1b (+/-)) knockout mice profoundly affects the compensatory response to nephron loss. Moreover, this is the first report of a phenotype in heterozygous Lmx1b (Lmx1b ( +/-)) knockout animals.

Role of transcription factors in podocytes

Despite a wealth of information on structural proteins, comparatively little is known on the transcriptional regulation of podocyte structure and function. In this review we will highlight those transcription factors which, by gene inactivation or classical transgenic experiments, have been shown to be essential for podocytes or probably will turn out to be so. The tumor suppressor protein WT1 is not only indispensable for the initial stages of kidney development, but also very likely maintains the integrity of the fully differentiated podocyte. In the kidney, the LIM homeodomain transcription factor LMX1B is specifically synthesized in podocytes, and mutations in LMX1B lead to nail-patella syndrome and the associated nephropathy. Other transcription factors such as hypoxia-inducible factors and PAX2 are likely to play a role in podocytes, whereas the significance of others, e.g. of POD1 and CITED2, is more speculative at this point.

Surgical Options for Patellar Stabilization in the Skeletally Immature Patient

Patellar dislocations in children and youth are estimated to occur in 29 of 100,000 individuals. Recurrent patellar dislocations in the skeletally immature patient are often associated with distinct pathoanatomies, which include patella alta, trochlear dysplasia, and contractures of the central and/or lateral structures of the extensor mechanism. This paper discusses the features of patellar instabilities classified as traumatic versus atraumatic, congenital versus acquired, and fixed dislocations versus habitual dislocations. Suggestions for the surgical management of these various classifications of patellar instabilities, on the basis of the principle of identification and correction of the pathoanatomies unique to the individual, are provided.

Novel LMX1B mutation in familial nail-patella syndrome with variable expression of open angle glaucoma

PURPOSE

To describe the genetic and clinical findings in a large Spanish pedigree with nail-patella syndrome (NPS) and to investigate the expressivity of open angle glaucoma (OAG) in the family members.

METHODS

All individuals underwent a complete ophthalmologic examination, including optical coherence tomography (OCT) of the optic disc and peripapillary region and ultrasound pachymetry. Screening for mutations in the LMX1B gene was performed by denaturing gradient gel electrophoresis and direct genomic sequencing analysis.

RESULTS

Ten family members had NPS, seven with varying degrees of ocular hypertension (OHT). Only one of these had advanced OAG. The others showed high pachymetry values and OCT retinal nerve fiber layer (RNFL) thickness above the normal values. Screening for mutations in the exonic and flanking sequences of the LMX1B gene showed a deletion of one G (289delG) within the coding sequence of exon 3 at codon 97, resulting in a frame shift that creates a premature stop at codon 105 (E97fsX105), predicting a truncated protein. This mutation was present in all NPS patients and absent in the unaffected family members.

CONCLUSIONS

A novel mutation in the homeobox transcription factor LMX1B causes NPS in a family with variable expressivity of the syndrome, including OAG. The pathogenic mechanism resulting from the mutation is presumably haploinsufficiency rather than a dominant negative effect, which would explain the clinical variability in this family. All NPS OHT patients had considerably thick corneas and RNFL.

The podocyte-specific inactivation of Lmx1b, Ldb1 and E2a yields new insight into a transcriptional network in podocytes

Patients with nail-patella syndrome, which among other symptoms also includes podocyte-associated renal failure, suffer from mutations in the LMX1B gene. The disease severity among patients is quite variable and has given rise to speculations on the presence of modifier genes. Promising candidates for modifier proteins are the proteins interacting with LMX1B, such as LDB1 and E47. Since human kidney samples from patients are difficult to obtain, conventional Lmx1b knock-out mice have been extremely valuable to study the role of Lmx1b in podocyte differentiation. In contrast to findings in these mice, however, in which a downregulation of the Col4a3, Col4a4 and Nphs2 genes has been described, no such changes have been detected in kidney biopsies from patients. We now report on our results on the characterization of constitutive podocyte-specific Lmx1b, Ldb1 and E2a knock-out mice. Constitutive podocyte-specific Lmx1b knock-out mice survive for approximately 2 weeks after birth and do not present with a downregulation of the Col4a3, Col4a4 and Nphs2 genes, therefore they mimic the human disease more closely. The podocyte-specific Ldb1 knock-out mice survive longer, but then also succumb to renal failure, whereas the E2a knock-out mice show no renal symptoms for at least 6 months after birth. We conclude that LDB1, but not E2A is a promising candidate as a modifier gene in patients with nail-patella syndrome.

Síndrome unha-patela: Evolução da instabilidade da patela

A síndrome da unha-patela é uma doença de caráter autossômico dominante, com algumas características clássicas dermatológicas, músculoesqueléticas e, eventualmente, renais, oculares e gastrointestinais. Tem como principal sintoma ortopédico dor patelofemoral associada com instabilidade da patela desde a primeira infância. A melhor maneira de obter bons resultados nestes casos é um tratamento precoce da instabilidade do joelho. Tratada tardiamente, pode levar a uma artrose precoce, com limitação funcional da articulação do joelho. O presente caso mostra uma paciente que, tem se apresentado com essa síndrome, foi submetida a tratamento cirúrgico tardio e evoluiu com degeneração articular e limitação funcional do joelho. O objetivo deste trabalho é atentar para as características fenotípicas sindrômicas da doença e relacioná-las com as queixas ortopédicas comuns no consultório (tais como dor e instabilidade do joelho e, possivelmente, do cotovelo) e, finalmente, poder tratar esses sintomas precocemente, garantindo uma evolução favorável para a paciente.

Missing Creases of Distal Finger Joints as a Diagnostic Clue of Nail-Patella Syndrome

Nail-patella syndrome (NPS, OMIM 161200) is an autosomal dominant disorder with a clinical characteristic tetrad consisting of fingernail dysplasia, hypoplastic or absent patellae, bony protuberances of the ilia (iliac horns) and dislocation of the radial head. Kidney involvement may lead to renal failure, and there is an increased risk for glaucoma. Clinical diagnostic skin clues are triangular lunulae especially on the thumbs which are highly predictive for the NPS. A less known but even more important sign is the absence of skin creases on the dorsal aspects of the distal interphalangeal joints. Even in patients with normal nails the absence of distal interphalangeal creases was noted. Less specific skin changes are webbing between digits, within the popliteal fossae, hyperextensible joints, absent or fragile nails and grooved nails and longitudinal ridging with splitting. With increasing costs in the health care system, it is important to recognize diseases by specific clinical findings which are often as predictive and precise as expensive technical investigations.

Steroid-responsive nephrotic syndrome in a patient with nail-patella syndrome

Nail-patella syndrome (NPS) is a rare disorder with autosomal dominant mode of inheritance. We report a child with NPS and steroid-responsive, frequently relapsing nephrotic syndrome. The child had dystrophic nails, flexion contractures of both elbows and normal renal functions. X-rays of the knees and pelvis showed hypoplastic patellae and iliac horns. Renal histology was unremarkable with mild focal increase in mesangial cellularity compatible with minimal change disease. Ultrastructural features of NPS including thickening of the glomerular basement membrane with electron-lucent areas were not found.

Genitopatellar syndrome: Expanding the phenotype and excluding mutations inLMX1B andTBX4

Genitopatellar syndrome is a newly described disorder characterized by absent/hypoplastic patellae, lower extremity contractures, urogenital anomalies, dysmorphic features, skeletal anomalies, and agenesis of the corpus callosum. More recently, cardiac anomalies and ectodermal dysplasia have been suggested as additional features of this syndrome. We report on two additional patients with genitopatellar syndrome and expand the spectrum of anomalies to include radio-ulnar synostosis. Since there exists significant overlap in the skeletal phenotype between genitopatellar syndrome and both the nail-patella and short patella syndromes, mutation screening of their causative genes, LMX1B and TBX4, was performed. Although there still does not appear to be an identifiable molecular etiology in genitopatellar syndrome, mutations in these two candidate genes have been excluded in our patients. Since both LMX1B and TBX4 are involved in a common molecular pathway, it is likely that the causative gene of genitopatellar syndrome functions within the same developmental process.

Nail-patella syndrome and its association with glaucoma: a review of eight families

BACKGROUND

Nail-patella syndrome (NPS) is a rare autosomal dominant syndrome, characterised by dysplasia of the nails, patellae, elbows and iliac horns. Mutations in the LMX1B gene were found in four North American families in whom glaucoma cosegregated with NPS.

AIMS

To investigate the association of glaucoma with NPS in Australian families and to determine how common NPS is in Australia.

METHODS

One family with NPS and glaucoma was identified from the Glaucoma Inheritance Study in Tasmania. A further 18 index cases of NPS were identified from the genetics database for southeastern Australia. Eight of these pedigrees were available for comprehensive glaucoma examination on available family members. DNA was sequenced for mutations in LMX1B.

RESULTS

In total, 52 living cases of NPS were identified suggesting a minimum prevalence of at least 1 in 100 000. 32 subjects from eight NPS pedigrees (four familial and four sporadic cases) were examined. 14 subjects had NPS alone. 4 subjects had NPS and glaucoma or ocular hypertension. Five pedigrees with NPS had a reported family history of glaucoma, although some of these people with glaucoma did not have NPS. LMX1B mutations were identified in 5 of the 8 index cases-three sporadic and two familial. Two of the six (33%) participants over 40 years of age had developed glaucoma, showing increased risk of glaucoma in NPS.

CONCLUSION

Patients with NPS should be examined regularly for glaucoma. However, because the families with NPS are ascertained primarily from young probands or probands who are isolated cases, the exact level of risk is unclear.

Nail patella syndrome revisited: 50 years after linkage

Nail Patella Syndrome (NPS; OMIM #161200) is a pleiotropic condition, with a classical clinical tetrad of involvement of the nails, knees, elbows and the presence of iliac horns. Kidney disease and glaucoma are now recognised as part of the syndrome. Fifty years ago, James Renwick chose NPS to develop methods of linkage analysis in humans and revealed the third linkage group identified in man--that between NPS and the ABO blood group loci. After a fallow period of some forty years, the gene mutated in NPS has been identified (LMX1B) and the condition serves as a model for understanding the complex relationships between disease loci, modifier genes and the resultant clinical phenotype.

Klinische, radiologische und arthroskopische Aspekte des Nagel-Patella-Syndroms (NPS): Literaturübersicht am Beispiel einer betroffenen Familie

Nail patella syndrome (NPS) is an autosomal dominant hereditary disorder affecting the nails, skeletal system, kidneys, and eyes. Skeletal features include absent or hypoplastic patellae, patella dislocations, elbow abnormalities, talipes and iliac horns on plain films. The existing literature focuses on clinical and radiographic findings in patients with NPS. We also report the case of a 40-year-old male patient and his family affected by NPS and includes clinical, radiographic as well as arthroscopic findings. Arthroscopic findings in this case are characterized by multiple synovial plicae in the knee joint leading to cartilage defects on the corresponding cartilage surfaces. A review of the recent literature suggests that the occurrence of synovial plicae might be related to NPS and might account for at least part of the characteristic symptoms of these patients. Therefore, in cases of unspecific knee pain associated with NPS arthroscopy of the knee joints and plicae resection seems to be recommendable.

LIM-homeodomain genes in mammalian development and human disease

The human and mouse genomes each contain at least 12 genes encoding LIM homeodomain (LIM-HD) transcription factors. These gene regulatory proteins feature two LIM domains in their amino termini and a characteristic DNA binding homeodomain. Studies of mouse models and human patients have established that the LIM-HD factors are critical for the development of specialized cells in multiple tissue types, including the nervous system, skeletal muscle, the heart, the kidneys, and endocrine organs such as the pituitary gland and the pancreas. In this article, we review the roles of the LIM-HD proteins in mammalian development and their involvement in human diseases.

Human syndromes with congenital patellar anomalies and the underlying gene defects

Genetic disorders characterized by congenital patellar aplasia or hypoplasia belong to a clinically diverse and genetically heterogeneous group of lower limb malformations. Patella development involves different molecular and cellular mechanisms regulating dorso-ventral patterning, cartilage and bone formation along endochondral ossification pathways, and growth. Several human genes that are important for patella development have been uncovered by the study of human limb malformation syndromes, yet causative genes for many more such disorders await to be identified and their complex interactions in the developmental pathways deciphered. Mutant animal models of congenital patellar aplasia or hypoplasia are certainly instrumental to create more insight into this aspect of limb development. Moreover, investigation of the complete phenotype of human syndromes and animal models may reveal novel insights into the pleiotropic roles of the responsible genes in the normal developmental of other organ systems. In this review, the phenotype and gene defects of syndromes with congenital patellar aplasia or hypoplasia will be discussed, including the nail patella syndrome, small patella syndrome, isolated patella aplasia hypoplasia, Meier-Gorlin syndrome, RAPADILINO syndrome, and genitopatellar syndrome.

Interaction of the LMX1B and PAX2 gene products suggests possible molecular basis of differential phenotypes in Nail-Patella syndrome

The LMX1B gene, encoding a protein involved in limb, kidney and eye development, is mutated in patients affected by Nail-Patella syndrome. Inter- and intrafamilial variability is common in this disorder for skeletal abnormalities, presence and severity of nephropathy and ocular anomalies. Phenotypic variability might depend on interactions of the LMX1B causative gene with other genes during development of both kidney and eye, which might act as modifier genes. Results are presented on the interaction between LMX1B and PAX2 proteins, obtained by both direct yeast two-hybrid assay and coimmunoprecipitation. Such interaction provides support to further studies on pathways underlying important developmental processes.

A neurological phenotype in nail patella syndrome (NPS) patients illuminated by studies of murine Lmx1b expression

Nail patella syndrome (NPS) is an autosomal dominant disorder affecting development of the limb, kidney and eye. NPS is the result of heterozygous loss-of-function mutations in the LIM-homeodomain transcription factor, LMX1B. Recent studies suggest that the NPS phenotype may be more extensive than recognized previously including neurologic and neurobehavioral aspects. To determine whether these findings correlated with the expression of Lmx1b during development, an internal ribosomal entry site-LacZ reporter was inserted into the 3'UTR of the endogenous murine gene. The pattern of Lmx1b expression during the development of the limb, eye and kidney correlates with the NPS phenotype. Additional sites of expression were observed in the central nervous system (CNS). The effects of the absence of Lmx1b in the CNS were determined in lmx1b-/- mice by histology and immunocytochemistry. Lmx1b is required for the differentiation and migration of neurons within the dorsal spinal cord. The inability of afferent sensory neurons to migrate into the dorsal horn is entirely consistent with diminished pain responses in NPS patients.

Koilonychia, dome-shaped epiphyses, and vertebral platyspondylia

A 2.5-year-old girl presented with koilonychia since birth and was subsequently found to have dome-shaped femoral epiphyses and platyspondylia with anterior central tongues on a skeletal survey.

Congenital dislocation of the patella

OBJECTIVE

Our objective was to present the imaging findings for congenital dislocation of the patella, an uncommon condition with variable clinical manifestations in patients of different ages.

CONCLUSION

Sonography can clearly illustrate the presence and location of the laterally displaced patella and the anatomy of adjacent joint structures. The high resolution for soft-tissue, cartilaginous, and bony structures of the immature skeleton makes sonography a valuable tool in the management of congenital dislocation of the patella. Conventional radiography is a simple method for diagnosis once ossification of the patella has commenced and for postoperative follow-up. MRI allows visualization of fine anatomic details and relationships between the involved structures of the extensor mechanism and is the technique of choice for preoperative planning.

Functional characterization of LMX1B mutations associated with nail-patella syndrome

Nail-patella syndrome (NPS) is an autosomal dominant disease characterized by dysplastic nails, absent or hypoplastic patellae, elbow dysplasia, and nephropathy. Recently, it was shown that NPS is the result of heterozygous mutations in the LIM-homeodomain gene, LMX1B. Subsequently, many mutations of the LMX1B gene have been reported in NPS patients. However, functional analyses of the mutant proteins have been performed in only a few mutations. Furthermore, the mechanisms of dominant inheritance in humans have not been established. In the present study, we analyzed the LMX1B gene in three Japanese patients with NPS and identified two novel mutations, 6 nucleotide deletion (Delta246N 247Q) and V242L. These two mutations are located in the homeodomain of LMX1B. Functional analyses of the LMX1B mutants revealed that these mutants had diminished transcriptional activity and had lost DNA binding ability. Furthermore, we demonstrated that each mutant did not manifest a dominant-negative effect on the transcriptional activity of wild-type LMX1B. These results suggested that NPS is caused by loss-of-function mutations of LMX1B, and haploinsufficiency of LMX1B should be the predominant pathogenesis of NPS in humans.