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Spectrum of pontocerebellar hypoplasia in 13 girls and boys with CASK mutations: confirmation of a recognizable phenotype and first description of a male mosaic patient.

Burglen L, Chantot-Bastaraud S, Garel C, Milh M, Touraine R, Zanni G, Petit F, Afenjar A, Goizet C, Barresi S, Coussement A, Ioos C, Lazaro L, Joriot S, Desguerre I, Lacombe D, des Portes V, Bertini E, Siffroi JP, de Villemeur TB, Rodriguez D - Orphanet J Rare Dis (2012)

Bottom Line: Other signs were frequently associated, such as growth retardation, ophthalmologic anomalies (glaucoma, megalocornea and optic atrophy), deafness and epilepsy.In our reference centre, CASK related PCH is the second most frequent cause of PCH.The identification of a de novo mutation in these patients enables accurate and reassuring genetic counselling.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre de Référence Maladies Rares « malformations et maladies congénitales du cervelet », Hôpital Trousseau-Paris, CHU de Lyon, CHU de Lille, Paris, France. lydie.burglen@trs.aphp.fr

ABSTRACT

Background: Pontocerebellar hypoplasia (PCH) is a heterogeneous group of diseases characterized by lack of development and/or early neurodegeneration of cerebellum and brainstem. According to clinical features, seven subtypes of PCH have been described, PCH type 2 related to TSEN54 mutations being the most frequent. PCH is most often autosomal recessive though de novo anomalies in the X-linked gene CASK have recently been identified in patients, mostly females, presenting with intellectual disability, microcephaly and PCH (MICPCH).

Methods: Fourteen patients (12 females and two males; aged 16 months-14 years) presenting with PCH at neuroimaging and with clinical characteristics unsuggestive of PCH1 or PCH2 were included. The CASK gene screening was performed using Array-CGH and sequencing. Clinical and neuroradiological features were collected.

Results: We observed a high frequency of patients with a CASK mutation (13/14). Ten patients (8 girls and 2 boys) had intragenic mutations and three female patients had a Xp11.4 submicroscopic deletion including the CASK gene. All were de novo mutations. Phenotype was variable in severity but highly similar among the 11 girls and was characterized by psychomotor retardation, severe intellectual disability, progressive microcephaly, dystonia, mild dysmorphism, and scoliosis. Other signs were frequently associated, such as growth retardation, ophthalmologic anomalies (glaucoma, megalocornea and optic atrophy), deafness and epilepsy. As expected in an X-linked disease manifesting mainly in females, the boy hemizygous for a splice mutation had a very severe phenotype with nearly no development and refractory epilepsy. We described a mild phenotype in a boy with a mosaic truncating mutation. We found some degree of correlation between severity of the vermis hypoplasia and clinical phenotype.

Conclusion: This study describes a new series of PCH female patients with CASK inactivating mutations and confirms that these patients have a recognizable although variable phenotype consisting of a specific form of pontocerebellar hypoplasia. In addition, we report the second male patient to present with a severe MICPCH phenotype and a de novo CASK mutation and describe for the first time a mildly affected male patient harboring a mosaic mutation. In our reference centre, CASK related PCH is the second most frequent cause of PCH. The identification of a de novo mutation in these patients enables accurate and reassuring genetic counselling.

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Sequence analysis of exon 4 amplified from DNA obtained from lymphocytes and cheek swab of patient 12 and from lymphocytes of his parents. The upper two sequence profiles (patient) show low signals for the mutant variant superimposed on the wild-type sequence (arrow). The lower two sequence profiles (parents) show the wild type sequence.
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Figure 2: Sequence analysis of exon 4 amplified from DNA obtained from lymphocytes and cheek swab of patient 12 and from lymphocytes of his parents. The upper two sequence profiles (patient) show low signals for the mutant variant superimposed on the wild-type sequence (arrow). The lower two sequence profiles (parents) show the wild type sequence.

Mentions: Ten CASK mutations, including eight novel mutations, were identified in 10 patients (eight females and two males). Several types of mutations were observed: five nonsense, one frameshift and four splice-site mutations (Table 2). In all cases, parental DNA analysis confirmed paternity and the de novo occurrence of the mutation. Three of the four intronic mutations (patients 5, 9 and 13) were localized at the consensus donor or acceptor canonical splice site and prediction software programs predicted that the respective donor or acceptor site was broken (Additional file 2). mRNA from these patients was not available to perform CASK transcript analysis. The splice mutation in patient 8 involved the fifth nucleotide of intron 24 and we used four different splice-site prediction software programs to predict the effect of this mutation. The results obtained from these in silico tools were consistent since they all predicted that the wild type donor site was broken (Additional file 2). RT-PCR performed on mRNA from lymphocytes of this patient revealed an aberrant transcript with skipping of exon 24 (Figure 1). This aberrant transcript is in-frame and is predicted to produce a protein which lacks 28 amino acids with the insertion of a Asp residue. The exact pathogenic mechanism of this mutation is unknown. In patient 12 a heterozygous profile was observed suggesting a mosaic nonsense mutation in this male patient. This profile was confirmed by analysis of a second tissue (cheek swab) (Figure 2). Finally, apart from the splice mutation in patient 8, all mutations were classified as truncating mutations. CASK sequencing in patients 2, 3 and 14 DNA was normal.


Spectrum of pontocerebellar hypoplasia in 13 girls and boys with CASK mutations: confirmation of a recognizable phenotype and first description of a male mosaic patient.

Burglen L, Chantot-Bastaraud S, Garel C, Milh M, Touraine R, Zanni G, Petit F, Afenjar A, Goizet C, Barresi S, Coussement A, Ioos C, Lazaro L, Joriot S, Desguerre I, Lacombe D, des Portes V, Bertini E, Siffroi JP, de Villemeur TB, Rodriguez D - Orphanet J Rare Dis (2012)

Sequence analysis of exon 4 amplified from DNA obtained from lymphocytes and cheek swab of patient 12 and from lymphocytes of his parents. The upper two sequence profiles (patient) show low signals for the mutant variant superimposed on the wild-type sequence (arrow). The lower two sequence profiles (parents) show the wild type sequence.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3351739&req=5

Figure 2: Sequence analysis of exon 4 amplified from DNA obtained from lymphocytes and cheek swab of patient 12 and from lymphocytes of his parents. The upper two sequence profiles (patient) show low signals for the mutant variant superimposed on the wild-type sequence (arrow). The lower two sequence profiles (parents) show the wild type sequence.
Mentions: Ten CASK mutations, including eight novel mutations, were identified in 10 patients (eight females and two males). Several types of mutations were observed: five nonsense, one frameshift and four splice-site mutations (Table 2). In all cases, parental DNA analysis confirmed paternity and the de novo occurrence of the mutation. Three of the four intronic mutations (patients 5, 9 and 13) were localized at the consensus donor or acceptor canonical splice site and prediction software programs predicted that the respective donor or acceptor site was broken (Additional file 2). mRNA from these patients was not available to perform CASK transcript analysis. The splice mutation in patient 8 involved the fifth nucleotide of intron 24 and we used four different splice-site prediction software programs to predict the effect of this mutation. The results obtained from these in silico tools were consistent since they all predicted that the wild type donor site was broken (Additional file 2). RT-PCR performed on mRNA from lymphocytes of this patient revealed an aberrant transcript with skipping of exon 24 (Figure 1). This aberrant transcript is in-frame and is predicted to produce a protein which lacks 28 amino acids with the insertion of a Asp residue. The exact pathogenic mechanism of this mutation is unknown. In patient 12 a heterozygous profile was observed suggesting a mosaic nonsense mutation in this male patient. This profile was confirmed by analysis of a second tissue (cheek swab) (Figure 2). Finally, apart from the splice mutation in patient 8, all mutations were classified as truncating mutations. CASK sequencing in patients 2, 3 and 14 DNA was normal.

Bottom Line: Other signs were frequently associated, such as growth retardation, ophthalmologic anomalies (glaucoma, megalocornea and optic atrophy), deafness and epilepsy.In our reference centre, CASK related PCH is the second most frequent cause of PCH.The identification of a de novo mutation in these patients enables accurate and reassuring genetic counselling.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre de Référence Maladies Rares « malformations et maladies congénitales du cervelet », Hôpital Trousseau-Paris, CHU de Lyon, CHU de Lille, Paris, France. lydie.burglen@trs.aphp.fr

ABSTRACT

Background: Pontocerebellar hypoplasia (PCH) is a heterogeneous group of diseases characterized by lack of development and/or early neurodegeneration of cerebellum and brainstem. According to clinical features, seven subtypes of PCH have been described, PCH type 2 related to TSEN54 mutations being the most frequent. PCH is most often autosomal recessive though de novo anomalies in the X-linked gene CASK have recently been identified in patients, mostly females, presenting with intellectual disability, microcephaly and PCH (MICPCH).

Methods: Fourteen patients (12 females and two males; aged 16 months-14 years) presenting with PCH at neuroimaging and with clinical characteristics unsuggestive of PCH1 or PCH2 were included. The CASK gene screening was performed using Array-CGH and sequencing. Clinical and neuroradiological features were collected.

Results: We observed a high frequency of patients with a CASK mutation (13/14). Ten patients (8 girls and 2 boys) had intragenic mutations and three female patients had a Xp11.4 submicroscopic deletion including the CASK gene. All were de novo mutations. Phenotype was variable in severity but highly similar among the 11 girls and was characterized by psychomotor retardation, severe intellectual disability, progressive microcephaly, dystonia, mild dysmorphism, and scoliosis. Other signs were frequently associated, such as growth retardation, ophthalmologic anomalies (glaucoma, megalocornea and optic atrophy), deafness and epilepsy. As expected in an X-linked disease manifesting mainly in females, the boy hemizygous for a splice mutation had a very severe phenotype with nearly no development and refractory epilepsy. We described a mild phenotype in a boy with a mosaic truncating mutation. We found some degree of correlation between severity of the vermis hypoplasia and clinical phenotype.

Conclusion: This study describes a new series of PCH female patients with CASK inactivating mutations and confirms that these patients have a recognizable although variable phenotype consisting of a specific form of pontocerebellar hypoplasia. In addition, we report the second male patient to present with a severe MICPCH phenotype and a de novo CASK mutation and describe for the first time a mildly affected male patient harboring a mosaic mutation. In our reference centre, CASK related PCH is the second most frequent cause of PCH. The identification of a de novo mutation in these patients enables accurate and reassuring genetic counselling.

Show MeSH
Related in: MedlinePlus