Novel G6B gene variant causes familial autosomal recessive thrombocytopenia and anemia.

OBJECTIVE: To characterize the underlying genetic and molecular defects in a consanguineous family with lifelong blood disorder manifested with thrombocytopenia (low platelets count) and anemia. METHODS: Genetic linkage analysis, exome sequencing, and functional genomics were carried out to identify and characterize the defective gene. RESULTS: We identified a novel truncation mutation (p.C108*) in chromosome 6 open reading frame 25 (C6orf25) gene in this family. We also showed the p.C108* mutation was responsible for destabilizing the encoded truncated G6B protein. Unlike the truncated form, wild-type G6B expression resulted in enhanced K562 differentiation into megakaryocytes and erythrocytes. C6orf25, also known as G6B, is an effector protein for the key hematopoiesis regulators, Src homology region 2 domain-containing phosphatases SHP-1 and SHP-2. CONCLUSION: G6B seems to act through an autosomal recessive mode of disease transmission in this family and regarded as the gene responsible for the observed hematological disorder. This inference is well supported further by in vivo evidence where similar outcomes were reported from G6b-/- and SHP1/2 DKO mouse models.

The Endocrine and Metabolic Characteristics of a Large Bardet-Biedl Syndrome Clinic Population.

Context: Bardet-Biedl syndrome (BBS) is a rare autosomal recessive disorder in which previous reports have described obesity and a metabolic syndrome. Objective: We describe the endocrine and metabolic characteristics of a large BBS population compared with matched control subjects. Design: We performed a case-control study. Setting: This study was performed at a hospital clinic. Patients: Study patients had a clinical or genetic diagnosis of BBS. Main Outcome Measurements: Our study determined the prevalence of a metabolic syndrome in our cohort. Results: A total of 152 subjects were studied. Eighty-four (55.3%) were male. Mean (± standard deviation) age was 33.2 ± 1.0 years. Compared with age-, sex-, and body mass index-matched control subjects, fasting glucose and insulin levels were significantly higher in subjects with BBS (glucose: BBS, 5.2 ± 1.2 mmol/L vs control, 4.9 ± 0.9 mmol/L, P = 0.04; insulin: BBS, 24.2 ± 17.0 pmol/L vs control, 14.2 ± 14.8 pmol/L, P < 0.001). Serum triglycerides were significantly higher in subjects with BBS (2.0 ± 1.2 mmol/L) compared with control subjects (1.3 ± 0.8 mmol/L; P < 0.001), but total cholesterol, high-density lipoprotein, and low-density lipoprotein were similar in both groups. Systolic blood pressure was higher in the BBS group (BBS, 135 ± 18 mm Hg vs control subjects, 129 ± 16 mm Hg; P = 0.02). Alanine transaminase was raised in 34 (26.8%) subjects with BBS, compared with five (8.9%) control subjects (P = 0.01). The rate of metabolic syndrome, determined using International Diabetes Federation criteria, was significantly higher in the BBS group (54.3%) compared with control subjects (26% P < 0.001). Twenty-six (19.5%) of male subjects with BBS were hypogonadal (serum testosterone, 9.9 ± 5.3 mmol/L), but significant pituitary abnormalities were uncommon. Subclinical hypothyroidism was present in 24 of 125 (19.4%) patients with BBS, compared with 3 of 65 (4.6%) control subjects (P = 0.01). Conclusions: Insulin resistance and the metabolic syndrome are increased in adult patients with BBS compared with matched control subjects. Increased subclinical hypothyroidism in the BBS cohort needs further investigation.