General Practice Care for Patients with Rare Diseases in Belgium. A Cross-Sectional Survey.

There are almost no studies about rare diseases in general practice. This study examined care characteristics of active rare disease patients in the Belgian Network of Sentinel General Practices (SGP) and the importance of rare diseases in general practice by its caseload, general practitioner (GP)⁻patient encounter frequency and nationwide prevalence. The SGP reported data about: (i) the number of active rare disease patients in 2015; and (ii) characteristics of one to three most recently seen patients. Rare diseases were matched against Orphanet (www.orpha.net). GP encounter frequency and patients' age were compared to the total general practice population. Details from 121 active patients (median age: 44, interquartile range (IQR) 24⁻60) showed that for 36.9% the GP had been the first caregiver for the rare disease and for 35.8% the GP established a diagnostic referral. GPs rated their knowledge about their patients' disease as moderate and used Orphanet for 14.9% of patients. Any active rare disease patients (median: 1, IQR 0⁻2) were reported by 66 of 111 SGP. Compared to the total general practice population, the mean GP encounter frequency was higher (7.3; 95% confidence intervals (CI) 6.1⁻8.5 versus 5.4; 95% CI 5.4⁻5.4). The prevalence of rare diseases in the Belgian general practice population was estimated at 12.0 (95% CI 10.3⁻13.9) per 10,000. This study acknowledges the important role of GPs in rare disease care. Knowledge and use of Orphanet by GPs could be improved.

Kinetochore KMN network gene CASC5 mutated in primary microcephaly.

Several genes expressed at the centrosome or spindle pole have been reported to underlie autosomal recessive primary microcephaly (MCPH), a neurodevelopmental disorder consisting of an important brain size reduction present since birth, associated with mild-to-moderate mental handicap and no other neurological feature nor associated malformation. Here, we report a mutation of CASC5 (aka Blinkin, or KNL1, or hSPC105) in MCPH patients from three consanguineous families, in one of which we initially reported the MCPH4 locus. The combined logarithm of odds score of the three families was >6. All patients shared a very rare homozygous mutation of CASC5. The mutation induced skipping of exon 18 with subsequent frameshift and truncation of the predicted protein. CASC5 is part of the KMN network of the kinetochore and is required for proper microtubule attachment to the chromosome centromere and for spindle-assembly checkpoint (SAC) activation during mitosis. Like MCPH gene ASPM, CASC5 is upregulated in the ventricular zone (VZ) of the human fetal brain. CASC5 binds BUB1, BUBR1, ZWINT-1 and interestingly it binds to MIS12 through a protein domain which is truncated by the mutation. CASC5 localized at the equatorial plate like ZWINT-1 and BUBR1, while ASPM, CEP152 and PCTN localized at the spindle poles in our patients and in controls. Comparison of primate and rodent lineages indicates accelerated evolution of CASC5 in the human lineage. Our data provide strong evidence for CASC5 as a novel MCPH gene, and underscore the role of kinetochore integrity in proper volumetric development of the human brain.

Subtelomeric imbalances in phenotypically normal individuals.

Subtelomeric imbalances are identified in approximately 5% of patients with idiopathic mental retardation (MR) and multiple congenital anomalies (MCA). Because of this high incidence, screening for subtelomeric anomalies became part of the routine genetic evaluation of MCA/MR patients. In contrast to the general view that subtelomeric imbalances cause MCA/MR, we report here 15 subtelomeric copy-number changes in 12 families in which the imbalance is inherited from a phenotypically normal parent. We detected inherited deletions at subtelomeres 2q, 3p, 4p, 4q, 6q, 10q, 17p, 17q, Xp, and Yq and duplications at 1q, 4q, 10q, and 11q. Interestingly, in addition to small deletions (<1 Mb) also unexpected large deletions and duplications up to 7.8 Mb were detected. Taken together with previous reports, a total of 16 subtelomeric duplications and 18 deletions inherited from a phenotypically normal parent have now been reported. Clearly, more extensive genotype-phenotype correlations are needed to better understand the phenotypic consequences of these subtelomeric copy number variations and to resolve the current uncertainty for genetic counseling in postnatal and prenatal diagnosis.