Analysis of genes encoding laminin beta2 and related proteins in patients with Galloway-Mowat syndrome

Collapsing Glomerulopathy in a Child with Galloway-Mowat Syndrome

Galloway-Mowat syndrome (GMS) is an autosomal recessive disorder with a poor prognosis that was first defined as a triad of central nervous system involvement, hiatal hernia, and nephrotic syndrome. However, this syndrome is now known to have a heterogeneous clinical presentation. The nephrotic syndrome is steroid resistant and is responsible for the outcome. The combination of collapsing glomerulopathy and GMS is very rare. A 26-month-old boy presented with steroid-resistant nephrotic syndrome associated with neurologic findings, including microcephaly, psychomotor retardation, and nystagmus. Magnetic resonance imaging showed marked cerebral atrophy, optic atrophy, and hypomyelination. A renal biopsy was consistent with collapsing glomerulopathy. If collapsing glomerulopathy is associated with neurological abnormalities, especially with microcephaly, clinicians should consider GMS as a possible underlying cause.

The etiology of congenital nephrotic syndrome: current status and challenges

BACKGROUND

Congenital nephrotic syndrome (CNS), defined as heavy proteinuria, hypoalbuminemia, hyperlipidemia and edema presenting in the first 0-3 months of life, may be caused by congenital syphilis, toxoplasmosis, or congenital viral infections (such as cytomegalovirus). However, the majority of CNS cases are caused by monogenic defects of structural proteins that form the glomerular filtration barrier in the kidneys. Since 1998, an increasing number of genetic defects have been identified for their involvements in the pathogenesis of CNS, including NPHS1, NPHS2, WT1, PLCE1, and LAMB2.

DATA SOURCES

We searched databases such as PubMed, Elsevier and Wanfang with the following key words: congenital nephrotic syndrome, proteinuria, infants, neonate, congenital infection, mechanism and treatment; and we selected those publications written in English that we judged to be relevant to the topic of this review.

RESULTS

Based on the data present in the literature, we reviewed the following topics: 1) Infection associated CNS including congenital syphilis, congenital toxoplasmosis, and congenital cytomegalovirus infection; 2) genetic CNS including mutation of NPHS1 (Nephrin), NPHS2 (Podocin), WT1, LAMB2 (Laminin-β2), PLCE1 (NPHS3); 3) Other forms of CNS including maternal systemic lupus erythematosus, mercury poisoning, renal vein thrombosis, neonatal alloimmunization against neutral endopeptidase.

CONCLUSION

At present, the main challenge in CNS is to identify the cause of disease for individual patients. To make a definitive diagnosis, with the exclusion of infection-related CNS and maternal-associated disorders, pathology, family history, inheritance mode, and other accompanying congenital malformations are sometimes, but not always, useful indicators for diagnosing genetic CNS. Next-generation sequencing would be a more effective method for diagnosing genetic CNS in some patients, however, there are still some challenges with next-generation sequencing that need to be resolved in the future.

WDR73 Mutations Cause Infantile Neurodegeneration and Variable Glomerular Kidney Disease

Infantile-onset cerebellar atrophy (CA) is a clinically and genetically heterogeneous trait. Galloway-Mowat syndrome (GMS) is a rare autosomal recessive disease, characterized by microcephaly with brain anomalies including CA in some cases, intellectual disability, and early-infantile-onset nephrotic syndrome. Very recently, WDR73 deficiency was identified as the cause of GMS in five individuals. To evaluate the role of WDR73 mutations as a cause of GMS and other forms of syndromic CA, we performed Sanger or exome sequencing in 51 unrelated patients with CA and variable brain anomalies and in 40 unrelated patients with a diagnosis of GMS. We identified 10 patients from three CA and from two GMS families with WDR73 mutations including the original family described with CA, mental retardation, optic atrophy, and skin abnormalities (CAMOS). There were five novel mutations, of which two were truncating and three were missense mutations affecting highly conserved residues. Individuals carrying homozygous WDR73 mutations mainly presented with a pattern of neurological and neuroimaging findings as well as intellectual disability, while kidney involvement was variable. We document postnatal onset of CA, a retinopathy, basal ganglia degeneration, and short stature as novel features of WDR73-related disease, and define WDR73-related disease as a new entity of infantile neurodegeneration.

Loss-of-function mutations in WDR73 are responsible for microcephaly and steroid-resistant nephrotic syndrome: Galloway-Mowat syndrome

Galloway-Mowat syndrome is a rare autosomal-recessive condition characterized by nephrotic syndrome associated with microcephaly and neurological impairment. Through a combination of autozygosity mapping and whole-exome sequencing, we identified WDR73 as a gene in which mutations cause Galloway-Mowat syndrome in two unrelated families. WDR73 encodes a WD40-repeat-containing protein of unknown function. Here, we show that WDR73 was present in the brain and kidney and was located diffusely in the cytoplasm during interphase but relocalized to spindle poles and astral microtubules during mitosis. Fibroblasts from one affected child and WDR73-depleted podocytes displayed abnormal nuclear morphology, low cell viability, and alterations of the microtubule network. These data suggest that WDR73 plays a crucial role in the maintenance of cell architecture and cell survival. Altogether, WDR73 mutations cause Galloway-Mowat syndrome in a particular subset of individuals presenting with late-onset nephrotic syndrome, postnatal microcephaly, severe intellectual disability, and homogenous brain MRI features. WDR73 is another example of a gene involved in a disease affecting both the kidney glomerulus and the CNS.

Rare hereditary COL4A3/COL4A4 variants may be mistaken for familial focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a histological lesion with many causes including inherited genetic defects with significant proteinuria being the predominant clinical finding at presentation. Mutations in COL4A3 and COL4A4 are known to cause Alport syndrome, thin basement membrane nephropathy, and to result in pathognomonic glomerular basement membrane findings. Secondary FSGS is known to develop in classic Alport Syndrome at later stages of the disease. Here, we present seven families with rare or novel variants in COL4A3 or COL4A4 (six with single and one with two heterozygous variants) from a cohort of 70 families with a diagnosis of hereditary FSGS. The predominant clinical findings at diagnosis were proteinuria associated with hematuria. In all seven families, there were individuals with nephrotic range proteinuria with histologic features of FSGS by light microscopy. In one family, electron microscopy showed thin glomerular basement membrane, but four other families had variable findings inconsistent with classical Alport nephritis. There was no recurrence of disease after kidney transplantation. Families with COL4A3 and COL4A4 variants that segregated with disease represent 10% of our cohort. Thus, COL4A3 and COL4A4 variants should be considered in the interpretation of next-generation sequencing data from such patients. Furthermore, this study illustrates the power of molecular genetic diagnostics in the clarification of renal phenotypes.

Galloway-Mowat syndrome: neurologic features in two sibling pairs

Galloway-Mowat syndrome is an autosomal recessive disorder presenting as early-onset nephrotic syndrome and central nervous system abnormalities, including microcephaly and developmental delays. Neurologic findings are universal in children with this disorder, and often precede renal abnormalities. However, relatively few descriptions of associated neurologic features are available. We describe two pairs of siblings with Galloway-Mowat syndrome who illustrate the spectrum of neurologic findings, to increase awareness of this syndrome among pediatric neurologists.

Infantile nephrotic syndrome with microcephaly and global developmental delay: the Galloway Mowat Syndrome

The authors present the first case of Galloway Mowat Syndrome (GMS), a rare disorder comprising of nephrotic syndrome in association with microcephaly, from India. An 11-mo-old girl with microcephaly, developmental delay and nystagmus presented with nephrotic syndrome. The perinatal and neonatal periods had been uneventful. The renal biopsy revealed mesangial proliferation with IgM deposition, while MRI of the brain showed hypomyelination. Molecular diagnosis by polymerase chain reaction (PCR) did not reveal any pathogenic sequences in the exons and the flanking intronic regions of the NPHS2 gene and LAMB2 gene. The infant responded to prednisolone. GMS must be suspected whenever microcephaly and global developmental delay occurs in association with nephrotic syndrome, as this is important for prognostication and genetic counseling. The genetics of GMS remains an enigma and further research is required to delineate the pathogenesis of this disorder.

Galloway-Mowat syndrome: prenatal ultrasound and perinatal magnetic resonance imaging findings

OBJECTIVE

To present prenatal ultrasound and perinatal magnetic resonance imaging (MRI) findings of Galloway-Mowat syndrome.

CASE REPORT

A 31-year-old woman, gravida 3, para 2, was referred for genetic counseling at 29 weeks of gestation because of abnormal ultrasound findings and a previous child with Galloway-Mowat syndrome. During this pregnancy, microcephaly, intrauterine growth restriction (IUGR), and oligohydramnios were first noted at 27 weeks of gestation. Repeated ultrasounds showed microcephaly, IUGR, and oligohydramnios. MRI performed at 32 weeks of gestation showed reduced sulcation of the brain, pachygyria, poor myelination of the white matter, and cerebellar atrophy. A diagnosis of recurrent Galloway-Mowat syndrome was made. At 40 weeks of gestation, a 2,496-g female baby was delivered with microcephaly, a narrow slopping forehead, epicanthic folds, microphthalmos, a highly arched palate, a small midface, a beaked nose, thin lips, large low-set floppy ears, clenched hands, and arachnodactyly. Postnatal MRI findings were consistent with the prenatal diagnosis. Renal ultrasound showed enlarged bilateral kidneys with increased echogenicity. At the age of 2 weeks, the infant became edematous and developed nephrotic syndrome.

CONCLUSION

Microcephaly, IUGR, and oligohydramnios are significant ultrasound triad of fetal Galloway-Mowat syndrome. Prenatal ultrasound diagnosis of microcephaly, IUGR, and oligohydramnios in late second trimester or in early third trimester should alert clinicians to the possibility of Galloway-Mowat syndrome and prompt a detailed search of abnormal sulcation, cortical gyral maldevelopment, and cerebellar atrophy by fetal ultrafast MRI.

Neuropathological homology in true Galloway-Mowat syndrome

Galloway-Mowat syndrome is a rare condition that is likely hereditary though the underlying offending gene has not been identified, and is characterized by microcephaly and severe nephrotic syndrome culminating in childhood death. Some of the reported cases have abnormalities in neuronal migration and intractable seizures, but many of the described cases focus on the renal pathology and emphasize a diversity of clinical and pathological features. The case described herein includes a thorough neuropathological description, and when the neuroradiology and neuropathology of the previously published cases is scrutinized, a fairly consistent clinical and neuropathological phenotype emerges.

Mutations in the human laminin beta2 (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 beta2, 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 beta2 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.