Alport Syndrome

Excerpt

Clinical characteristics: Alport syndrome is characterized by kidney manifestations, sensorineural hearing loss (SNHL), and ocular manifestations. In the absence of treatment, kidney disease progresses from microhematuria to proteinuria, progressive kidney insufficiency, and end-stage kidney disease (ESKD) in most males with X-linked Alport syndrome (XLAS), and in most males and females with autosomal recessive Alport syndrome (ARAS). Progressive SNHL is usually present by late childhood or early adolescence. Ocular findings include anterior lenticonus (which is virtually pathognomonic), maculopathy (whitish or yellowish flecks or granulations in the perimacular region), corneal endothelial vesicles (posterior polymorphous dystrophy), and recurrent corneal erosion. In females with XLAS and individuals with autosomal dominant Alport syndrome (ADAS), ESKD is frequently delayed until later adulthood, SNHL is relatively late in onset, and ocular involvement is rare.

Diagnosis/testing: The molecular diagnosis of Alport syndrome is established in a proband with suggestive findings and a pathogenic variant(s) in COL4A3, COL4A4, or COL4A5 identified by molecular genetic testing. Kidney biopsy, skin biopsy (in some individuals with XLAS), or clinical diagnostic criteria may be used to establish the diagnosis in those without access to genetic testing or those with uninformative results.

Management: Treatment of manifestations: Angiotensin-converting enzyme inhibitor or angiotensin receptor blocker to delay onset of ESKD; standard treatment of hypertension; kidney transplantation for ESKD. Potential living related donors must be evaluated carefully to avoid nephrectomy in an affected individual. Hearing aids as needed for SNHL; cataract removal as needed; in those with deletions of COL4A5 extending into intron 2 of COL4A6, surgical intervention for symptomatic leiomyomas as needed.

Surveillance: Evaluation by a nephrologist including urinalysis, assessment of kidney function, and blood pressure every six to 12 months; monthly monitoring of at-risk transplant recipients for development of anti-glomerular basement membrane antibody-mediated glomerulonephritis for the first year post transplant; audiologic evaluation every one to two years beginning at age six to seven years; ophthalmology evaluation for ocular abnormalities every one to two years beginning in adolescence in males with a COL4A5 truncating pathogenic variant and in persons with ARAS.

Agents/circumstances to avoid: Drink adequate fluids as dehydration may accelerate the progression of nephropathy. Protection of corneas from minor trauma in those with recurrent corneal erosions. Minimize exposure to loud noise.

Evaluation of relatives at risk: Evaluate at-risk family members in order to identify as early as possible those who would benefit from initiation of treatment either by molecular genetic testing if the pathogenic variant(s) in the family are known or urinalysis and blood pressure if the pathogenic variant(s) in the family are not known.

Genetic counseling: COL4A5-related Alport syndrome is inherited in an X-linked manner (XLAS). COL4A3- and COL4A4-related Alport syndrome are inherited in an autosomal dominant (ADAS) or autosomal recessive (ARAS) manner. Digenic Alport syndrome is caused by pathogenic variants in more than one Alport syndrome-related gene: typically pathogenic variants in both COL4A3 and COL4A4 (on the same or on opposite chromosomes) or, more rarely, a pathogenic variant in COL4A5 in addition to a pathogenic variant in COL4A3 or COL4A4.

XLAS: The risk to sibs of a male proband depends on the genetic status of the mother: if the mother of the proband has a COL4A5 pathogenic variant, the chance of transmitting it in each pregnancy is 50%. The risk to the sibs of a female proband depends on the genetic status of the parents: if the mother of the proband has a COL4A5 pathogenic variant, the chance of transmitting it in each pregnancy is 50%; if the father of the proband has a COL4A5 pathogenic variant, he will transmit it to all of his daughters and none of his sons. Males and females who inherit the pathogenic variant will be affected.

ARAS: If both parents are known to be heterozygous for a COL4A3 or COL4A4 pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting biallelic pathogenic variants (and having ARAS), a 50% chance of being heterozygous (and at risk for ADAS), and a 25% chance of inheriting neither of the familial pathogenic variants.

ADAS: If a parent of the proband is affected and/or is known to have the COL4A3 or COL4A4 pathogenic variant identified in the proband, the risk to sibs of inheriting the pathogenic variant is 50%. The severity of clinical manifestations may vary greatly among heterozygous family members; some heterozygotes may be asymptomatic and some may develop ESKD.

Digenic Alport syndrome: The risk to sibs depends on the involved genes, the location of the pathogenic variants (i.e., on the same or on opposite chromosomes) in families segregating pathogenic variants in COL4A3 and COL4A4, and the sex of the proband (in families segregating pathogenic variants in COL4A5 and COL4A3 or COL4A4).

Once the Alport syndrome-related pathogenic variant(s) have been identified in an affected family member, prenatal and preimplantation genetic testing are possible.