Alstrom syndrome other diagnostic studies
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1], Associate Editor(s)-in-Chief: Aarti Narayan, M.B.B.S [2]; Raviteja Guddeti, M.B.B.S. [3]
Overview
The diagnosis of Alström syndrome relies primarily on clinical findings and/or family history. In some instances the diagnosis can be confirmed by molecular genetic testing. Sequence analysis of the coding region should be performed: tiered testing with sequencing of select exons first, followed by analysis of the entire gene. The frequency of deletions is unknown but deletion/duplication analysis may be clinically indicated in some instances[1].
Other Diagnostic Studies
Molecular Genetic Testing[2]
| Gene | Testing Method | Detected Mutations |
| ALMS1[3] | Targeted mutation analysis | 19-bp insertion exon 16 |
| ALMS1 | Sequence analysis of select exons: 16, 10, and 8 | Sequence variants |
| ALMS1 | Sequence analysis of entire coding region | Sequence variants |
| ALMS1 | Deletion / duplication analysis | Exonic and whole-gene deletions |
Sensitivity and specificity of the above test are 96% and 100% respectively. Positive and negative predictive values reach 100% for this test. Given the current detection rate, failure to identify a disease-causing sequence variant does not preclude the diagnosis of Alström syndrome[4]. Family members who are possible carriers can be screened for the causative ALMS1 mutations if both mutated alleles have been identified in the index case.
Prenatal Testing
Prenatal diagnosis for at risk pregnancies is possible by analysis of DNA extracted from fetal cells obtained by amniocentesis usually performed at about 15 to 18 weeks' gestation or chorionic villus sampling (CVS) at about ten to 12 weeks' gestation. Both disease-causing alleles of an affected family member must be identified before prenatal testing can be performed.
For families in which both the disease-causing mutations have been identified preimplantation genetic diagnosis (PGD) may be available.
Renal Biopsy
Renal biopsy often shows interstitial fibrosis, glomerular hyalinosis, and tubular atrophy.
Liver Biopsy
Liver biopsy reveals varying degrees of steatohepatitis, hepatic fibrosis, cirrhosis, chronic nonspecific active hepatitis with lymphocytic infiltration, patchy necrosis, and fatty liver.
References
- ↑ Minton JA, Owen KR, Ricketts CJ; et al. (2006). "Syndromic obesity and diabetes: changes in body composition with age and mutation analysis of ALMS1 in 12 United Kingdom kindreds with Alstrom syndrome". J. Clin. Endocrinol. Metab. 91 (8): 3110–6. doi:10.1210/jc.2005-2633. PMID 16720663. Unknown parameter
|month=ignored (help) - ↑ Hearn T, Renforth GL, Spalluto C; et al. (2002). "Mutation of ALMS1, a large gene with a tandem repeat encoding 47 amino acids, causes Alström syndrome". Nat. Genet. 31 (1): 79–83. doi:10.1038/ng874. PMID 11941370. Unknown parameter
|month=ignored (help) - ↑ Collin GB, Marshall JD, Ikeda A; et al. (2002). "Mutations in ALMS1 cause obesity, type 2 diabetes and neurosensory degeneration in Alström syndrome". Nat. Genet. 31 (1): 74–8. doi:10.1038/ng867. PMID 11941369. Unknown parameter
|month=ignored (help) - ↑ Marshall JD, Hinman EG, Collin GB; et al. (2007). "Spectrum of ALMS1 variants and evaluation of genotype-phenotype correlations in Alström syndrome". Hum. Mutat. 28 (11): 1114–23. doi:10.1002/humu.20577. PMID 17594715. Unknown parameter
|month=ignored (help)