Apparently changing patterns of inheritance in Alport's hereditary nephritis: genetic heterogeneity versus altered diagnostic criteria

Alport's syndrome: can carriers be identified by audiometry?

Alport's syndrome is characterized by familial nephropathy with haematuria, sensorineural hearing loss and ocular abnormalities. It is transmitted as an X-linked dominant condition. In the affected males the symptoms are severe compared with females who show a more variable clinical picture due to the effect of lyonization of the X-chromosome. The diagnosis of carriers of genetic disease is extremely valuable for the purpose of counselling the patients as well as their relatives. A number of attempts have been made in the past to diagnose these carriers. Some studies have shown that it is possible to diagnose carriers of conditions where hearing loss is a symptom, by sensitive audiometric techniques. In this study we examined obligate and possible carriers of Alport's syndrome with pure-tone audiometry (PTA) and the audioscan method. We found that all obligate carriers and a predictable proportion of possible carriers had either a hearing loss on PTA or a mid frequency notch in the audioscan.

Inherited diseases of the glomerular basement membrane

The inherited diseases of the glomerular basement membrane include Alport's syndrome (AS), nail-patella syndrome, and thin basement membrane nephropathy. Classical AS is inherited in an X-linked manner and accounts for approximately 85% of the cases. Its manifestations include hematuria, sensorineural hearing loss, ocular defects, and a progression to renal failure. A defect(s) in the alpha 5 (IV) chain of type IV collagen is believed to be the etiology of classic AS, and alterations in its encoding gene localized to the X-chromosome have been elucidated. Although isolated cases of anti-glomerular basement membrane glomerulonephritis have been reported following renal transplantation in patients with AS, it is considered an effective form of renal replacement therapy. Less is known regarding the genetic basis of the autosomal-dominant form of AS, which apparently accounts for the remaining 15% of the cases. Nail-patella syndrome is characterized by nail dysplasia, patellar hypoplasia or aplasia, and nephropathy. It is inherited in an autosomal-dominant fashion with the gene locus assigned to the long arm of chromosome 9. Possible linkage between the COL5A1 gene and the gene for nail-patella syndrome has been suggested. Approximately 30% of the patients progress to end-stage renal failure. Renal transplantation has been successful in treating patients who progress to end-stage renal failure. Thin basement membrane nephropathy is an autosomal dominant trait that accounts for approximately 30% of the cases presenting as persistent, asymptomatic hematuria. The cause of thin basement membrane nephropathy is unknown at present. No decline in renal function is associated with thin basement membrane nephropathy.

Laminin, fibronectin, and Goodpasture antigen detection in patients with Alport's syndrome

Indirect immunofluorescence study with laminin and fibronectin monoclonal antibodies on paraffin sections, as well as with serum from a patient with Goodpasture's syndrome with high titer of autoantibodies that recognize the antigenic determinants in human glomerular and tubular basement membrane, was performed on 14 patients with Alport's syndrome and 5 specimens of normal renal tissue obtained from donors in cases of renal transplantation (control group). We found no binding of Goodpasture antigen to glomerular and distal tubular basement membranes in renal biopsy tissue from all 14 patients with Alport's syndrome. In contrast, there was bright linear fluorescence of Goodpasture antigen on glomerular and tubular basement membranes of normal renal material. There was no difference in laminin and fibronectin binding in patients with Alport's syndrome and controls. In all the cases binding was strongly positive. These results suggest an abnormality or absence of immunoreactive autoantigen in the glomerular and distal tubular basement membrane in patients with Alport's syndrome. Therefore, Goodpasture antigen detection could be an important diagnostic method in early stages of Alport's syndrome when characteristic morphological changes are not yet developed.

A family with Alport syndrome and psychosis

A family is described with a history of both hereditary nephritis (Alport syndrome) and chronic psychosis in multiple family members. Although the disorders do not segregate together in all cases, the finding of this family may provide a clue for the location of a psychosis gene. Alport syndrome has been mapped to the long arm of the X chromosome. Some studies also support a genomic locus on the X chromosome in at least some cases of manic-depressive disorder and schizophrenia.

Identification of variant Alport phenotypes using an Alport-specific antibody probe

An antibody, which recognizes an epitope(s) on a 26 kD peptide of the noncollagenous domain of type IV collagen and which fails to bind to basement membranes of individuals with Alport syndrome, was used to characterize members of families representing phenotypic variants of the disorder. Ten of 11 families with juvenile-onset renal failure and 4 of 5 families with adult-onset renal failure exhibited loss of the epitope(s) from epidermal and/or renal basement membranes by indirect immunofluorescence. Two families with typical Alport nephropathy but normal hearing exhibited the same abnormality. This study provides strong evidence that a defect in the main noncollagenous domain of type IV collagen is common to the various phenotypes of Alport syndrome.

Fechtner syndrome: clinical and genetic aspects

Fechtner syndrome, a variant of Alport syndrome, was first reported by Peterson et al. [1985]. It is characterized by nephritis, hearing loss, eye abnormalities, macrothrombocytopenia, and leucocyte inclusions, present in varying combinations in several members of the same family. This is the second family reported; 16 relatives are affected. The clinical manifestations of the syndrome are delineated. The pattern of inheritance is autosomal dominant. The hematologic abnormalities are similar to those detected in May Hegglin anomaly. They are present in every affected relative and may be present at birth. The feasibility of prenatal diagnosis is discussed.

Alport's syndrome

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Genetics of Alport's syndrome

The pattern of inheritance of Alport's syndrome has been controversial for some time. Recent studies have clarified the mode of inheritance in this disease. Alport's syndrome is a heterogeneous disorder made up of a number of genetically distinct syndromes, with an autosomal dominant, an X-linked dominant and a rare autosomal recessive form. Clinical analysis shows that there are many distinct forms with or without nerve deafness, and with early or late occurrence of end-stage renal disease.

Ocular signs in Alport's syndrome

The eyes of sixty one patients with Alport's syndrome or its variant, and of 25 unaffected relatives, were examined. Details of ocular signs associated with Alport's syndrome are presented and related to renal prognosis and family history.

The Goodpasture antigen in Alport's syndrome: studies with a monoclonal antibody

A mouse monoclonal antibody (MCA-P1), which recognizes an antigenic determinant in human glomerular basement membrane against which autoantibodies are directed in Goodpasture's syndrome, was used in indirect immunofluorescence studies to investigate glomerular basement membrane structure in Alport's syndrome. We found reduced or absent binding of MCA-P1 to glomerular and distal tubular basement membranes in renal biopsy tissue from ten patients with Alport's syndrome. Antiglomerular basement membrane antibody eluted from the kidneys of a patient who had died from Goodpasture's syndrome was used to confirm these findings. In contrast, there was bright linear fluorescence of MCA-P1 on glomerular and tubular basement membranes of normal renal material and renal biopsy tissue obtained from patients with a variety of glomerulonephritides. These results suggest an abnormality or a variable quantity of the immunoreactive autoantigen in the glomerular basement membrane of patients with Alport's syndrome. Furthermore, MCA-P1 may be of value in the diagnostic interpretation of renal biopsies from patients with familial nephritis.

Genetic heterogeneity of Alport syndrome

Forty-one families have been studied with stringent diagnostic criteria of Alport syndrome: proven renal disease with hematuria affecting at least two relatives, neural hearing loss in at least one affected individual, and evolution to renal failure in at least one affected individual. The proportion of affected offsprings of affected females does not significantly differ from the ratio expected for a dominant trait. The descendance of affected males shows a lack of affected males. In four families, with parental consanguinity and nonaffected parents, the findings agree with an autosomal recessive inheritance. Study of quantitative traits such as death or renal death among brothers, uncle-nephew pairs and whole families shows evident intra-familial resemblances. We conclude that Alport syndrome seems to be a heterogeneous state composed of a number of genetically distinct syndromes, with an autosomal dominant, an X-linked dominant, and an autosomal recessive form.