Verena Matejas

Mutations in the Human Laminin β2 (LAMB2) Gene and the Associated Phenotypic Spectrum

Mutations of LAMB2 typically cause autosomal recessive Pierson syndrome, a disorder characterized by congenital nephrotic syndrome, ocular and neurologic abnormalities, but may occasionally be associated with milder or oligosymptomatic disease variants. LAMB2 encodes the basement membrane protein laminin β2, which is incorporated in specific heterotrimeric laminin isoforms and has an expression pattern corresponding to the pattern of organ manifestations in Pierson syndrome. Herein we review all previously reported and several novel LAMB2 mutations in relation to the associated phenotype in patients from 39 unrelated families. The majority of disease‐causing LAMB2 mutations are truncating, consistent with the hypothesis that loss of laminin β2 function is the molecular basis of Pierson syndrome. Although truncating mutations are distributed across the entire gene, missense mutations are clearly clustered in the N‐terminal LN domain, which is important for intermolecular interactions. There is an association of missense mutations and small in frame deletions with a higher mean age at onset of renal disease and with absence of neurologic abnormalities, thus suggesting that at least some of these may represent hypomorphic alleles. Nevertheless, genotype alone does not appear to explain the full range of clinical variability, and therefore hitherto unidentified modifiers are likely to exist. Hum Mutat 31:992–1002, 2010.

SOS1 is the second most common Noonan gene but plays no major role in cardio-facio-cutaneous syndrome

Background: Heterozygous gain-of-function mutations in various genes encoding proteins of the Ras-MAPK signalling cascade have been identified as the genetic basis of Noonan syndrome (NS) and cardio-facio-cutaneous syndrome (CFCS). Mutations of SOS1, the gene encoding a guanine nucleotide exchange factor for Ras, have been the most recent discoveries in patients with NS, but this gene has not been studied in patients with CFCS. Methods and results: We investigated SOS1 in a large cohort of patients with disorders of the NS–CFCS spectrum, who had previously tested negative for mutations in PTPN11, KRAS, BRAF, MEK1 and MEK2. Missense mutations of SOS1 were discovered in 28% of patients with NS. In contrast, none of the patients classified as having CFCS was found to carry a pathogenic sequence change in this gene. Conclusion: We have confirmed SOS1 as the second major gene for NS. Patients carrying mutations in this gene have a distinctive phenotype with frequent ectodermal anomalies such as keratosis pilaris and curly hair. However, the clinical picture associated with SOS1 mutations is different from that of CFCS. These findings corroborate that, despite being caused by gain-of-function mutations in molecules belonging to the same pathway, NS and CFCS scarcely overlap genotypically.

Nineteen novel NPHS1 mutations in a worldwide cohort of patients with congenital nephrotic syndrome (CNS)

BACKGROUND Recessive mutations in the NPHS1 gene encoding nephrin account for approximately 40% of infants with congenital nephrotic syndrome (CNS). CNS is defined as steroid-resistant nephrotic syndrome (SRNS) within the first 90 days of life. Currently, more than 119 different mutations of NPHS1 have been published affecting most exons. METHODS We here performed mutational analysis of NPHS1 in a worldwide cohort of 67 children from 62 different families with CNS. RESULTS We found bi-allelic mutations in 36 of the 62 families (58%) confirming in a worldwide cohort that about one-half of CNS is caused by NPHS1 mutations. In 26 families, mutations were homozygous, and in 10, they were compound heterozygous. In an additional nine patients from eight families, only one heterozygous mutation was detected. We detected 37 different mutations. Nineteen of the 37 were novel mutations (approximately 51.4%), including 11 missense mutations, 4 splice-site mutations, 3 nonsense mutations and 1 small deletion. In an additional patient with later manifestation, we discovered two further novel mutations, including the first one affecting a glycosylation site of nephrin. CONCLUSIONS Our data hereby expand the spectrum of known mutations by 17.6%. Surprisingly, out of the two siblings with the homozygous novel mutation L587R in NPHS1, only one developed nephrotic syndrome before the age of 90 days, while the other one did not manifest until the age of 2 years. Both siblings also unexpectedly experienced an episode of partial remission upon steroid treatment.

Ophthalmological Aspects of Pierson Syndrome

PURPOSE To study the ocular phenotype of Pierson syndrome and to increase awareness among ophthalmologists of the diagnostic features of this condition. DESIGN Retrospective, observational case series. METHODS A multicenter study of 17 patients with molecularly confirmed Pierson syndrome. The eye findings were reviewed and compared to pertinent findings from the literature. RESULTS The most characteristic ocular anomaly was microcoria. A wide range of additional abnormalities were found, including posterior embryotoxon, megalocornea, iris hypoplasia, cataract, abnormal lens shape, posterior lenticonus, persistent fetal vasculature, retinal detachment, variable axial lengths, and glaucoma. There was high interocular and intrafamilial variability. CONCLUSIONS Loss-of-function mutations in laminin beta2 (LAMB2) cause a broad range of ocular pathology, emphasizing the importance of laminin beta2 in eye development. Patients with Pierson syndrome can initially present with ocular signs alone. In newborns with marked bilateral microcoria, Pierson syndrome should be considered and renal function investigated.

Neurodevelopmental deficits in Pierson (microcoria-congenital nephrosis) syndrome.

Pierson syndrome is an autosomal recessive disorder comprising congenital nephrotic syndrome with diffuse mesangial sclerosis and distinct eye abnormalities with microcoria reported as the most prominent clinical feature. LAMB2 mutations leading to lack of laminin β2 were identified as the molecular cause underlying Pierson syndrome. Although LAMB2 is known to be expressed in the neuromuscular system, and defects of the neuromuscular junctions had been found in laminin β2‐deficient mice, no consistent neurological phenotype has been described clinically in murine or human laminin β2‐deficiency before. This is likely due to the early lethality from renal failure. Here we provide a detailed description of neurological manifestations and development in four patients affected by Pierson syndrome, who survived until the age of 1.3–4.8 years owing to renal replacement therapy. Severe muscular hypotonia, psychomotor retardation, and blindness were present in three patients harboring truncating mutations on both LAMB2 alleles. These symptoms were not attributable to complications of chronic renal failure, thus representing a primary feature of the genetic disorder. Alterations in skeletal muscle tissue from one case were compatible with a chronic denervating process. One affected girl, however, exhibited a milder course of renal disease, normal development, and preserved vision, presumably owing to some residual LAMB2 function. Our findings indicate that severe neurodevelopmental deficits have to be considered as part of Pierson syndrome, at least in the presence of biallelic functional null mutations (complete lack of laminin β2). This is an important issue in the counseling of parents of an affected newborn or infant.

Mutation analysis of Son of Sevenless in juvenile myelomonocytic leukemia

retinoic acid receptor fusion oncoproteins generate acute promyelocytic leukemia? Cancer Cell 2006; 9: 73–74. 4 Cools J, DeAngelo DJ, Gotlib J, Stover EH, Legare RD, Cortes J et al. A tyrosine kinase created by fusion of the PDGFRA and FIP1L1 genes as a therapeutic target of imatinib in idiopathic hypereosinophilic syndrome. N Engl J Med 2003; 348: 1201–1214. 5 Kaufmann I, Martin G, Friedlein A, Langen H, Keller W. Human Fip1 is a subunit of CPSF that binds to U-rich RNA elements and stimulates poly(A) polymerase. EMBO J 2004; 23: 616–626. 6 Sainty D, Liso V, Cantu-Rajnoldi A, Head D, Mozziconacci MJ, Arnoulet C et al. A new morphologic classification system for acute promyelocytic leukemia distinguishes cases with underlying PLZF/ RARA gene rearrangements. Group Francais de Cytogenetique Hematologique, UK Cancer Cytogenetics Group and BIOMED 1 European Community-Concerted Action Molecular Cytogenetic Diagnosis in Haematological Malignancies. Blood 2000; 96: 1287–1296. 7 Hasle H, Niemeyer CM, Chessells JM, Baumann I, Bennett JM, Kerndrup G et al. A pediatric approach to the WHO classification of myelodysplastic and myeloproliferative diseases. Leukemia 2003; 17: 277–282. 8 Grisolano JL, Wesselschmidt RL, Pelicci PG, Ley TJ. Altered myeloid development and acute leukemia in transgenic mice expressing PML-RAR alpha under control of cathepsin G regulatory sequences. Blood 1997; 89: 376–387. 9 Zimonjic DB, Pollock JL, Westervelt P, Popescu NC, Ley TJ. Acquired, nonrandom chromosomal abnormalities associated with the development of acute promyelocytic leukemia in transgenic mice. Proc Natl Acad Sci USA 2000; 97: 13306–13311. 10 Sternsdorf T, Phan VT, Maunakea ML, Ocampo CB, Sohal J, Silletto A et al. Forced retinoic acid receptor alpha homodimers prime mice for APL-like leukemia. Cancer Cell 2006; 9: 81–94. 11 Kwok C, Zeisig BB, Dong S, So CW. Forced homo-oligomerization of RARalpha leads to transformation of primary hematopoietic cells. Cancer Cell 2006; 9: 95–108. 12 Palaniswamy V, Moraes KC, Wilusz CJ, Wilusz J. Nucleophosmin is selectively deposited on mRNA during polyadenylation. Nat Struct Mol Biol 2006; 13: 429–435. 13 Rego EM, Ruggero D, Tribioli C, Cattoretti G, Kogan S, Redner RL et al. Leukemia with distinct phenotypes in transgenic mice expressing PML/RAR alpha, PLZF/RAR alpha or NPM/RAR alpha. Oncogene 2006; 25: 1974–1979. 14 Kamashev D, Vitoux D, De The H. PML-RARA-RXR oligomers mediate retinoid and rexinoid/cAMP cross-talk in acute promyelocytic leukemia cell differentiation. J Exp Med 2004; 199: 1163–1174. 15 Stover EH, Chen J, Folens C, Lee BH, Mentens N, Marynen P et al. Activation of FIP1L1-PDGFRalpha requires disruption of the juxtamembrane domain of PDGFRalpha and is FIP1L1-independent. Proc Natl Acad Sci USA 2006; 103: 8078–8083. 16 Wodzinski MA, Watmore AE, Lilleyman JS, Potter AM. Chromosomes in childhood acute lymphoblastic leukaemia: karyotypic patterns in disease subtypes. J Clin Pathol 1991; 44: 48–51.

Analysis of genes encoding laminin β2 and related proteins in patients with Galloway–Mowat syndrome

Galloway–Mowat syndrome (GMS) is a rare autosomal recessive disorder characterized by early onset nephrotic syndrome and microcephaly with various anomalies of the central nervous system. GMS likely represents a heterogeneous group of disorders with hitherto unknown genetic etiology. The clinical phenotype to some extent overlaps that of Pierson syndrome (PS), which comprises congenital nephrotic syndrome and distinct ocular abnormalities but which may also include neurodevelopmental deficits and microcephaly. PS is caused by mutations of LAMB2, the gene encoding laminin β2. We hypothesized that GMS might be allelic to PS or be caused by defects in proteins that interact with laminin β2. In a cohort of 18 patients with GMS or a GMS-like phenotype we therefore analyzed the genes encoding laminin β2 (LAMB2), laminin α5 (LAMA5), α3-integrin (ITGA3), β1-integrin (ITGB1) and α-actinin-4 (ACTN4), but we failed to find causative mutations in these genes. We inferred that LAMA5, ITGA3, ITGB1, and ACTN4 are not directly involved in the pathogenesis of GMS. We excluded LAMB2 as a candidate gene for GMS. Further studies are required, including linkage analysis in families with GMS to identify genes underlying this disease.

Fraser and Ablepharon macrostomia phenotypes: Concurrence in one family and association with mutated FRAS1†

To date, Fraser syndrome (FS) and Ablepharon macrostomia syndrome (AMS) have been considered distinct disorders, but they share strikingly similar patterns of congenital abnormalities, specifically craniofacial anomalies. While recent research has led to the identification of the genes FRAS1 and FREM2 as the cause of FS, the genetic basis of AMS continues to be enigmatic. We report on the concurrence of AMS‐like and Fraser phenotypes in a Brazilian family. Both affected sibs were homozygous for a novel splice site mutation in the FRAS1 gene. Extensive studies on mRNA expression indicated that this mutation most likely leads to loss of function as most previously reported FRAS1 mutations associated with FS. We conclude that a phenotype resembling AMS is a rare clinical expression of FS with no obvious genotype–phenotype correlation. However, the molecular basis of “true” AMS which has been reported as a sporadic disorder in all cases but one, and so far with no relation to FS, is probably different and still needs to be further investigated.

Pierson syndrome in an adolescent girl with nephrotic range proteinuria but a normal GFR.

BackgroundPierson syndrome, caused by mutations in the LAMB2 gene, was originally described as a combination of microcoria and congenital nephrotic syndrome, rapidly progressing to end-stage renal failure.Case-Diagnosis/TreatmentWe report a minor variant of Pierson syndrome in a teenage girl with severe myopia since early infancy and proteinuria first detected at age 6. At the age of 11 she was found to carry a unique homozygous non-truncating LAMB2 mutation in exon 2: c.T240G (p.S80R). Renal biopsy revealed mild diffuse mesangial sclerosis and residual expression of laminin β2. Today at age 14, on treatment with angiotensin-converting enzyme inhibitors and angiotensin receptor blockers, she continues to have nephrotic range proteinuria, but a normal glomerular filtration rate.ConclusionsLAMB2 mutations should be considered in all patients with glomerular proteinuria and abnormal ocular phenotype, irrespective of age and disease severity.

Paternal isodisomy of chromosome 3 unmasked by autosomal recessive microcoria-congenital nephrosis syndrome (Pierson syndrome) in a child with no other phenotypic abnormalities.

Paternal Isodisomy of Chromosome 3 Unmasked by Autosomal Recessive Microcoria-Congenital Nephrosis Syndrome (Pierson Syndrome) in a Child With no Other Phenotypic Abnormalities Verena Matejas, Jutta Muscheites, Marianne Wigger, Hans-J€urgen Kreutzer, Horst Nizze, and Martin Zenker* Institute of Human Genetics, University Hospital Erlangen, University of Erlangen-Nuremberg, Erlangen, Germany Department of Pediatric Nephrology and Dialysis, Rostock, Germany Institute of Pathology, University Hospital Rostock, Germany Institute of Human Genetics, University Hospital Magdeburg, Germany