A novel LIPE nonsense mutation found using exome sequencing in siblings with late-onset familial partial lipodystrophy.

BACKGROUND: Familial lipodystrophies are rare inherited disorders associated with redistribution of body fat and development of dyslipidemia, insulin resistance, and diabetes. We previously reported 2 siblings with unusual late-onset familial partial lipodystrophy in whom heretofore known causative genes had been excluded. We hypothesized they had a mutation in a novel lipodystrophy gene. METHODS: Our approach centred on whole exome sequencing of the patients' DNA, together with genetic linkage analysis and a bioinformatic prioritization analysis. All candidate variants were assessed in silico and available family members were genotyped to assess segregation of mutations. RESULTS: Our prioritization algorithm led us to a novel homozygous nonsense variant, namely p.Ala507fsTer563 in the hormone sensitive lipase gene encoding, an enzyme that is differentially expressed in adipocytes and steroidogenic tissues. Pathogenicity of the mutation was supported in bioinformatic analyses and variant cosegregation within the family. CONCLUSIONS: We have identified a novel nonsense mutation in hormone sensitive lipase gene, which likely explains the lipodystrophy phenotype observed in these patients.

Multiple sclerosis recurrence risk for siblings in an isolated population of Central Sardinia, Italy.

Studies of twins, adoptees, half siblings, and familial recurrence risk have shown that genetic and non-genetic factors are involved in multiple sclerosis (MS) etiology. Age at onset, gender, and parental MS status seem to influence sibling risk. We studied the recurrence risk in siblings of MS patients in an isolated population of Sardinia, Italy, which is genetically homogeneous, inbred, and very stable, with a high MS frequency. The Aalen-Nelson estimate of the recurrence risk in siblings is 4.7%, and the risk ratio compared with the general population is 31. Proportional hazards models were used to investigate the effect of sibling sex, sex, and age at onset of the proband, and number of affected relatives on a sibling's predicted MS risk. Sib's risk is influenced by age at onset (P = 0.02), and possibly by sex of the proband (P = 0.08). There is also a borderline significant interaction (P = 0.05) between the sex and age at onset of the proband: early age at onset influences sib's risk only if the proband is female. The number of affected relatives in the family is not found to influence sibling risk, but the power is lacking (95% CI 0.50-2.62). This result is consistent with a single dominant gene with an extremely low penetrance, a model that has not yet been disproved as a possible inheritance model for MS.