Duane's syndrome and focal segmental glomerulosclerosis

A mutation in transcription factor MAFB causes Focal Segmental Glomerulosclerosis with Duane Retraction Syndrome

Focal segmental glomerulosclerosis (FSGS) is a leading cause of end-stage renal disease in children and adults. Genetic factors significantly contribute to early-onset FSGS, but the etiologies of most adult cases remain unknown. Genetic studies of monogenic syndromic FSGS exhibiting extra-renal manifestations have uncovered an unexpected biological role for genes in the development of both podocytes and other cellular lineages. To help define these roles, we studied two unrelated families with FSGS associated with Duane Retraction Syndrome, characterized by impaired horizontal eye movement due to cranial nerve malformation. All four affected individuals developed FSGS and Duane Retraction Syndrome in their first to second decade of life, manifested as restricted abduction together with globe retraction and narrowed palpebral fissure on attempted adduction. Hypoplasia of the abducens nerves and hearing impairment occurred in severely affected individuals. Genetic analyses revealed that affected individuals harbor a rare heterozygous substitution (p.Leu239Pro) in MAFB, a leucine zipper transcription factor. Luciferase assays with cultured monocytes indicated that the substitution significantly reduced transactivation of the F4/80 promoter, the known MAFB recognition element. Additionally, immunohistochemistry indicated reduced MAFB expression in the podocytes of patients. Structural modeling suggested that the p.Leu239Pro substitution in the DNA-binding domain possibly interferes with the stability of the adjacent zinc finger. Lastly, podocytes in neonatal mice with p.Leu239Pro displayed impaired differentiation. Thus, MAFB mutations impair development and/or maintenance of podocytes, abducens neurons and the inner ear. The interactions between MAFB and regulatory elements in these developing organs are likely highly specific based on spatiotemporal requirements.

Adult familial nephrotic syndrome--Balkan variant of congenital nephrotic syndrome

We report on two families from the southern part of Former Yugoslav Republic of Macedonia (close to Mediterranean area) with autosomal dominant inherited nephrotic syndrome, documented with renal biopsy in three family members. Histopathological examination confirmed microcystic tubular changes and focal segmental glomerulosclerosis. In biopsied patients proteinuria was noted in the first decade, or second, but it was quantitatively documented as nephrotic in the second and third decade. The prognosis of the patients was poor: one patient died because of intracranial hemorrhage before developing end stage renal disease; the other two cases developed end stage chronic renal failure in the third and fourth decade.

Duane's retraction syndrome

Duane's retraction syndrome (DRS) has been a recognized clinical entity for nearly a century. It is a clinically well described ocular disorder consisting of retraction of the globe with narrowing of the lid fissure in attempted adduction, frequent abduction deficiency with variable limitation to adduction, and upshoot and/or downshoot of the affected eye on adduction. Among strabismus patients the incidence of DRS is probably not more than 5%. Most cases are sporadic, but familial cases have been estimated at 10% by most authors. Numerous theories concerning the etiology and pathogenesis of DRS have been proposed, including agenesis of the abducens nucleus, but the majority of investigators concur that the characteristic findings are best explained by a paradoxical innervation of the lateral rectus muscle, which subsequently causes a cocontraction of the horizontal rectus muscles. The frequent association of DRS with other congenital anomalies suggests a teratogenic event occurring between the fourth to eighth week of gestation as an etiological factor. In this review historical aspects and theories of the syndrome are studied and statistical data are compiled and analyzed. Clinical features, differential diagnoses and variants of the syndrome are examined. Testing and treatment objectives are discussed.