Identification of novel mutations in WFS1 and genotype-phenotype correlation in Wolfram syndrome

Current developments in Wolfram syndrome

Wolfram syndrome (WS), an infrequent cause of diabetes mellitus, derives its name from the physician who first reported the combination of juvenile-onset diabetes mellitus and optic atrophy. Also referred to as DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy and deafness), it is an autosomal recessive neurodegenerative disease characterized by various clinical manifestations, such as diabetes mellitus, optic atrophy, diabetes insipidus, deafness, neurological symptoms, renal tract abnormalities, psychiatric manifestations and gonadal disorders. The condition is very rare with an estimated prevalence of one in 770,000 of the normal population, one out of 150 cases of juvenile-onset insulin-dependent diabetes mellitus, and with a carrier frequency of one in 354. This progressive neurodegenerative disease usually results in death before the age of 50 years and many patients lead a morbid life. The pathogenesis of the disorder although unknown is ascribed to mutation of a gene on chromosome 4p encoding a transmembrane protein of undetermined function called wolframin. This review summarizes the variable presentation of the disorder, its widespread complications, poor quality of life in affected individuals, and the problems in diagnosis and treatment of the syndrome.

WFS1 mutations are frequent monogenic causes of juvenile-onset diabetes mellitus in Lebanon

Most cases of juvenile-onset diabetes (JOD) are diagnosed as type 1 diabetes (T1D), for which genetic studies conducted in outbred Caucasian populations support the concept of multifactorial inheritance. However, this view may be partly challenged in particular population settings. In view of the suggestive evidence for a high prevalence of Wolfram syndrome (WFS) in Lebanon, the phenotypic variability associated with WFS1 mutations, and the high consanguinity rate in Lebanon, we aimed to evaluate the contribution of WFS1 mutations as monogenic determinants to JOD in Lebanon. We performed a family-based genetic study, with linkage analysis followed by systematic mutation screening of WFS1 exons in all JOD probands. The study population consisted of an unbiased recruitment of all juvenile-onset insulin-dependent diabetic patients from a specialized diabetes pediatric clinic in Beirut, Lebanon. Homozygous or compound heterozygous WFS1 mutations were found in 22 of the 399 JOD probands (5.5%), resulting in WFS (17 probands) or in non-syndromic non-autoimmune diabetes mellitus (DM, five probands). These accounted for 12.1% (21/174) of probands in consanguineous families, compared with 0.4% (1/225) in non-consanguineous families. Of the 38 patients identified with homozygous or compound heterozygous WFS1 mutations, 11 (29%) had non-syndromic DM, all of whom carried a particular WFS1 mutation, WFS1(LIB), encoding a protein with an extended C-terminal domain. This mutation resulted in a delayed onset or absence of extrapancreatic features. These results underscore the major impact of population-specific factors, such as population-specific mutations and founder effects, and family structure in the genetic determinism of JOD.

Autosomal dominant transmission of diabetes and congenital hearing impairment secondary to a missense mutation in the WFS1 gene

AIMS

Mutations of the WFS1 gene have been implicated in autosomal dominant diseases, such as low-frequency sensorineural hearing impairment (LFSNHI) and/or diabetes mellitus and/or optic atrophy. The aim was to investigate WFS1 gene sequences in a family with diabetes mellitus and hearing impairment.

METHODS

Three members of a family with a maternally inherited combination of diabetes mellitus and hearing impairment, but no specific mutations in its mitochondrial genome, were investigated for mutations in the WFS1 gene.

RESULTS

This pedigree, in which the proband had non-insulin-dependent diabetes mellitus and congenital hearing impairment and his mother a triple combination of diabetes mellitus, hearing impairment and optic atrophy, was found to be associated with autosomal dominant transmission of the E864K mutation of the WFS1 gene.

CONCLUSIONS

In the light of this confirmatory study, we recommend the systematic analysis of WFS1 gene sequences in patients with parentally inherited diabetes mellitus and deafness (+/- optic atrophy), in particular when diabetogenic mtDNA mutations have been excluded.