Alport syndrome is a progressive, hereditary renal disease characterized by abnormalities in the glomerular basement membrane (GBM) and commonly associated with cochlear and/or ocular involvement.

Epidemiology

• Incidence – 1/50,000 live births
• Age – variable  
  • Autosomal recessive – earliest onset 
  • X-linked – next onset 
  • Autosomal dominant – onset in middle age
• Sex 
  • M>F for X-linked Alport syndrome – 100% penetrance in males, variable in females
  • M:F, equal for autosomal dominant and recessive forms

Inheritance

• Alport syndrome forms
  • 80% X-linked, 15% autosomal recessive, and <5% autosomal dominant
• Autosomal recessive and dominant forms are due to mutations in the COL4A3 and COL4A4genes
• X-linked form (end-stage renal disease after age 30) is due to mutations in the COL4A5 gene
  • Sequencing of COL4A5 identifies 70% of mutations in affected females and 80% of mutations in affected males regardless of age
  • 75% of adult X-linked Alport syndrome is caused by mutations C1564S, L1649R, and R1677Q
  • De novo mutations in 10-15% of affected males

Pathophysiology

• Type IV collagen laminin, nidogen and perlecan – major proteins of GBM
• Alport defects in type IV collagen alpha chain
  • Leads to loss of type IV collagen in the basal lamina
• Weakened basal lamina results in focal ruptures of glomerular capillary walls

Clinical Presentation

• Renal
  • Microscopic hematuria and proteinuria, progressive renal insufficiency, end-stage renal disease
    • 95% of females and 100% of males have microscopic hematuria in early childhood
  • 60% of males with X-linked Alport syndrome reach end-stage renal disease by age 30 and 90% by age 40
  • Most individuals with autosomal recessive Alport syndrome reach end-stage renal disease before age 30
  • End-stage renal disease is usually delayed until middle age in autosomal dominant Alport syndrome
• Cochlear
  • Sensorineural hearing loss
    • Usually presents in late childhood in X-linked Alport syndrome
    • 85% of males with X-linked Alport syndrome have sensorineural deafness by age 40
    • Individuals with autosomal recessive Alport syndrome have juvenile onset
    • Autosomal dominant Alport syndrome is associated with later adult onset
• Ocular – lenticonus, maculopathy, corneal endothelial vesicles and recurrent corneal abrasions
  • Ocular lesions are uncommon in adult-onset disease
• Gastrointestinal
  • Leiomyomatosis is occasionally associated with Alport syndrome

Treatment

• Early disease – antihypertensive drugs and angiotensin converting enzyme inhibitors
• Renal transplantation for end-stage disease
  • Antibodies may redevelop, but repeat renal failure is uncommon
  • Genetic testing of family members for Alport syndrome is critical when selecting eligible donors

Indications for Testing

• Unexplained hematuria or chronic kidney disease (particularly in men)
• Unexplained hematuria in women with a family history of chronic kidney disease

Laboratory Testing

• Genetic testing
  • Diagnostic testing for symptomatic individuals – COL4A5 sequencing, mutations and deletion/duplication
  • Exclude diagnosis of Alport syndrome in patients with positive thin basement membrane nephropathy on biopsy
  • Should not be used for prenatal testing
• Detailed family and personal history to rule out other possible diseases
• Audiologic and ophthalmologic exams – may be abnormal

Histology

• Immunohistochemical analysis of collagen IV expression using renal or skin biopsies
  • Skin biopsies have a higher incidence of false negatives than renal biopsies
• Electron microscopy of renal biopsy specimen

Differential Diagnosis

• Thin basement membrane nephropathy
• Other glomerular diseases
• Inherited hearing loss syndromes
• Fechtner-Epstein syndrome

• Presymptomatic and carrier testing for at-risk individuals who have previously diagnosed family members

Tests generally appear in the order most useful for common clinical situations

General

• Haas M. Alport syndrome and thin glomerular basement membrane nephropathy: a practical approach to diagnosis. Arch Pathol Lab Med. 2009; 133 (2) :224-232.PubMed
• Hudson BG, Tryggvason K, Sundaramoorthy M, Neilson EG. Alport's syndrome, Goodpasture's syndrome, and type IV collagen. N Engl J Med. 2003; 348 (25) :2543-2556.PubMed
• Joosten H, Strunk AL, Meijer S, Boers JE, Aries MJ, Abbes AP, Engel H, Beukhof JR. An aid to the diagnosis of genetic disorders underlying adult-onset renal failure: a literature review. Clin Nephrol. 2010; 73 (6) :454-472.PubMed
• Kashtan CE, Segal Y. Genetic disorders of glomerular basement membranes. Nephron Clin Pract. 2011; 118 (1) :c9-c18.PubMed
• Kashtan CE. Collagen IV-Related Nephropathies: Alport Syndrome and Thin Basement Membrane Nephropathy. In: GeneReviews at GeneTests: Medical Genetics Information Resource (database online). Copyright, University of Washington, Seattle. 1997-2010. Available at http://www.genetests.org [Last Updated: 15 Jul 2010; Accessed: 15 Dec 2010] 
• Kashtan CE. Familial hematuria. Pediatr Nephrol. 2009; 24 (10) :1951-1958.PubMed
• Thorner PS. Alport syndrome and thin basement membrane nephropathy. Nephron Clin Pract. 2007; 106 (2) :c82-c88.PubMed
• Tryggvason K, Patrakka J. Thin basement membrane nephropathy. J Am Soc Nephrol. 2006; 17 (3) :813-822.PubMed

ARUP Institute for Clinical and Experimental Pathology®

• Pont-Kingdon G, Sumner K, Gedge F, Miller C, Denison J, Gregory M, Lyon E. Molecular testing for adult type Alport syndrome. BMC Nephrol. 2009; 10 :38-.PubMed

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