A new MRXS locus maps to the X chromosome pericentromeric region: a new syndrome or narrow definition of Sutherland-Haan genetic locus?

The Renpenning syndrome spectrum: new clinical insights supported by 13 new PQBP1-mutated males

Since the first reports of polyglutamine-binding protein 1 (PQBP1) mutations in Renpenning syndrome and related disorders, the spectrum of PQBP1-linked clinical manifestations has been outlined from rare published case reports. The phenotypic description is often obtained from medical archives, and therefore, heterogeneous. Moreover, some aspects such as brain imaging or cognitive and behavioral functioning are rarely described. In this study, 13 PQBP1-mutated French patients were subjected to a standardized clinical, cognitive and behavioral assessment. Physical measurements of their relatives were also collected. We report on a recognizable clinical and radiological phenotype. All patients presented with microcephaly, leanness and mild short stature, relative to familial measurements. Three new clinical features are described: upper back progressive muscular atrophy, metacarpophalangeal ankylosis of the thumb and velar dysfunction. The specific facial dysmorphic features included at least four of the following signs: long triangular face, large ridged nose, half-depilated eyebrows, dysplastic or protruding ears and rough slightly sparse hair. An over-aged appearance was noticed in elderly patients. Cortical gyrification was normal based on available magnetic brain imaging of six patients. PQBP1-linked microcephaly (or Renpenning syndrome) is an X-linked mental retardation syndrome, which has clinically recognizable features.

Genotype-phenotype studies in three families with mutations in the polyglutamine-binding protein 1 gene (PQBP1)

Recently, the polyglutamine-binding protein 1 (PQBP1) gene was found to be mutated in five of 29 families studied with X-linked mental retardation (XLMR) linked to Xp. The reported mutations include duplications or deletions of AG dinucleotides in the fourth coding exon that resulted in shifts of the open reading frame. Three of the five families with mutations in this newly identified XLMR gene have been reported previously. We characterized the phenotypic and neuropsychological features in the two unpublished families with aberrations in PQBP1 and in a family reported 10 years ago. In total, seven patients diagnosed with aberrations in this gene were examined, including a newly identified patient at 18 months of age. Additionally, the features were compared to those reported in the literature of three other families, comprising MRXS3 (Sutherland-Haan syndrome) MRX55 and MRXS8 (Renpenning syndrome). Characteristics seen in these patients are microcephaly, lean body habitus, short stature, striking facial appearance with long narrow faces, upward slant of the eyes, malar hypoplasia, prognathism, high-arched palate and nasal speech. In addition, small testes and midline defects as anal atresia or imperforate anus, clefting of palate and/or uvula, iris coloboma and Tetralogy of Fallot are seen in several patients. These observations contribute to the phenotypic knowledge of patients with PQBP1 mutations and make this XLMR syndrome well recognizable to clinicians.