Elizabeth Spriggs

Expression of X-linked bulbospinal muscular atrophy (Kennedy disease) in two homozygous women

The authors describe the novel occurrence of homozygosity for the CAG expansion in the androgen receptor gene causing Kennedy disease in two sisters (ages 34 and 42). Symptoms were limited to occasional muscle cramps and twitches. Physical examinations were normal apart from mild hand tremor in both women and rare perioral fasciculations in the older sibling. Electrodiagnostic studies were normal except for evidence of mild motor axonal loss in the sternocleidomastoid muscle of the older sibling.

Large genomic deletions in CACNA1A cause episodic ataxia type 2

Episodic ataxia (EA) syndromes are heritable diseases characterized by dramatic episodes of imbalance and incoordination. EA type 2 (EA2), the most common and the best characterized subtype, is caused by mostly nonsense, splice site, small indel, and sometimes missense mutations in CACNA1A. Direct sequencing of CACNA1A fails to identify mutations in some patients with EA2-like features, possibly due to incomplete interrogation of CACNA1A or defects in other EA genes not yet defined. Previous reports described genomic deletions between 4 and 40 kb in EA2. In 47 subjects with EA (26 with EA2-like features) who tested negative for mutations in the known EA genes, we used multiplex ligation-dependent probe amplification to analyze CACNA1A for exonic copy number variations. Breakpoints were further defined by long-range PCR. We identified distinct multi-exonic deletions in three probands with classic EA2-like features: episodes of prolonged vertigo and ataxia triggered by stress and fatigue, interictal nystagmus, with onset during infancy or early childhood. The breakpoints in all three probands are located in Alu sequences, indicating errors in homologous recombination of Alu sequences as the underlying mechanism. The smallest deletion spanned exons 39 and 40, while the largest deletion spanned 200 kb, missing all but the first three exons. One deletion involving exons 39 through 47 arose spontaneously. The search for mutations in CACNA1A appears most fruitful in EA patients with interictal nystagmus and onset early in life. The finding of large heterozygous deletions suggests haploinsufficiency as a possible pathomechanism of EA2.

A large novel deletion in the APC promoter region causes gene silencing and leads to classical familial adenomatous polyposis in a Manitoba Mennonite kindred

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome caused by the inheritance of germline mutations in the APC tumour suppressor gene. The vast majority of these are nonsense and frameshift mutations resulting in a truncated protein product and abnormal function. While APC promoter hypermethylation has been previously documented, promoter-specific deletion mutations have not been reported. In a large Canadian Mennonite polyposis kindred, we identified a large novel germline deletion in the APC promoter region by linkage analysis and MLPA. By RT-PCR and sequence analysis, this mutation was found to result in transcriptional silencing of the APC allele. A few genetic disorders have been characterized as over-represented in the Manitoba Mennonite population, however, the incidence of cancer has not been recognized as increased in this population as compared to other Manitoba ethnic groups. This study strengthens the likelihood that this novel APC promoter mutation is linked to this unique population as a founder mutation.

An Intronic Polymorphism of the hMLH1 Gene Contributes Toward Incomplete Genetic Testing for HNPCC

Hereditary non-polyposis colorectal cancer (HNPCC) is a common hereditary cancer. Genetic testing is complicated by the multiple DNA mismatch repair genes that underlie the disorder. Many suspected HNPCC families have no germ-line mutation identified. We reassessed an unusual family that appeared to have 2 individuals homozygous for a germline mutation within exon 1 of the hMLH1 gene. A few rare individuals with two inherited mutations in one of the mismatch repair genes have been reported and appear to have a distinct clinical appearance. However, there were no clinical features in the family discussed here that were consistent with constitutive lack of hMLH1. Redesigning the intronic primers for exon 1 identified a common polymorphism located within the original intronic primer site. The polymorphism prevented amplification of the wild-type allele, giving the erroneous appearance of homozygous inheritance of the mutated allele. Likewise, common intronic polymorphisms, if located within primer sequences on the chromosome harboring the HNPCC germ-line mutation could restrict amplification to only the wild-type allele, which may contribute significantly to the low success rate of identifying mutations in HNPCC families.

A Case of an Infant With Compound Heterozygous Mutations for Hypertrophic Cardiomyopathy Producing a Phenotype of Left Ventricular Noncompaction

A male infant was born to a 38-year-old G1P0 mother with hypertrophic cardiomyopathy (HCM). Fetal echocardiography was suspicious for HCM; however, postnatal echocardiography demonstrated features consistent with left ventricular noncompaction (LVNC). The infant was initially stable but presented at 2 months of age in cardiogenic shock. On genetic analysis, both parents were heterozygous for mutations associated with HCM. The proband was a compound heterozygote. This case, in which 2 mutations for HCM produced a phenotype of LVNC, has not been demonstrated in humans and raises the question of whether HCM and LVNC represent a continuum of pathologic processes.

SETX gene novel mutations in a non-French Canadian with ataxia-oculomotor apraxia type 2

The patient is a 24-year-old college-graduate male who presentedwith an insidious and a protracted course of balance difficulties since seven years of age. His initial symptoms were very mild however these slowly progressed through his junior and senior school years preventing him from participating in many sports activities. By 20 years of age, his symptoms advanced to a noticeably unsteady gait with occasional falls and deterioration in manual dexterity. The patient was born to a healthy non-consanguineous couple of English descent on the father’s side and Ukrainian ethnic background on the mother’s side. He has a younger healthy brother and there is no family history of ataxia. On examination, he scored 23/30 on the Montreal Cognitive Assessment (MoCA) testing, losing1pointoncopyingacube, 3points for repetitionof sentences andwordfluency,1point forabstraction,1 point for delayed recall and 1 point for orientation. There was no evidence of ideomotor or construction apraxia. His speech was dysarthric and scanning in nature. Ocular pursuit was saccadic in all directions and volitional saccades were markedly slowed. There was ocular apraxia with initiation of saccades with a head thrust maneuver. Therewas sustained gaze-evoked nystagmuswith lateral gaze. Therewas no ocular ataxia or dysmetric eyemovements. There were no conjunctival telangiectasias. Both axial and appendicular tone was normal. There was no pronator drift and strength was normal in the upper and lower extremities. The deep tendon reflexes were globally absent with normal plantar responses. The fine finger movements and rapid alternating movements were bilaterally impaired in the upper extremities, more so on the left side. He displayed symmetric dysmetria on finger-nose-finger and heel-toshin testing. There was impaired sensation in the feet to sharp pain and to temperature in a stocking pattern. Vibration and joint position sense were normal. He was able to sit independently and transfer without assistance. His gait and stance were broad in base. Stride length varied and he preferred to walk with his arms held rigidly at his sides. He had difficulty turning without losing his balance. He was unable to perform tandem walking. A “pull test” was normal. He did not exhibit evidence of gait apraxia. The biochemical work up included serum AFP level which was four times the upper limit of normal at 34 ug/L (normal 0.0–7 ug/ L). Magnetic resonance imaging of the brain revealed mild to moderate cerebellar atrophy predominantly affecting the vermis. A nerve conduction study showed an axonal, sensory more than motor, peripheral neuropathy. Chromosome breakage studies did not show any evidence of chromosome instability, ruling out the

Development of a diagnostic DNA chip to screen for 30 autosomal recessive disorders in the Hutterite population

The Hutterites are a religious isolate living in colonies across the North American prairies. This population originated from approximately 90 founders, resulting in a number of genetic diseases that are overrepresented, underrepresented, or unique. The founder effect in this population increases the likelihood that Hutterite couples carry the same recessive mutations. We have designed a diagnostic chip on a fee‐for‐service basis with Asper Biotech to provide Hutterites with the option of comprehensive carrier screening.

Ataxia with oculomotor apraxia type 2 in the Canadian aboriginal population.

To the Editor: Ataxia with oculomotor apraxia type 2 (AOA2) (OMIM 606002) is an autosomal recessive disorder, representing approximately 8% of non-Friedreich autosomal recessive cerebellar ataxias. It is characterized by ataxia onset between 11 and 22 years, and associated with oculomotor apraxia and elevated serum alpha fetoprotein. It was first described in Japanese (1), Pakistani (2) and French Canadian patients (3). We report on affected siblings from a consanguineous family of Ojibwe Canadian Aboriginal descent. The proband presented at age 16 years with insidious and protracted balance difficulties since age 11 years. By 16 years, his symptoms advanced to a noticeably unsteady gait with occasional falls and deterioration in manual dexterity. He was born to healthy parents who are second cousins. His older sister had similar gait abnormality. Reportedly, a paternal first cousin and two maternal first cousins once removed have a similar phenotype. The parents of these individuals are second cousins. These relatives have not presented for a formal evaluation. On examination, his speech was dysarthric and scanning. There was ocular apraxia with initiation of saccades with a head thrust maneuver. He had sustained gaze-evoked nystagmus with lateral gaze. There were no conjunctival telangiectasias. The fine finger and rapid alternating movements were impaired. He displayed symmetric dysmetria on finger-nose-finger and heel-to-shin testing. His gait and stance were broad in base. He was unable to perform tandem walking. The work up included serum alpha fetoprotein (AFP) which was elevated at 20 μg/l (normal 0.0–7.0 μg/l). Brain magnetic resonance imaging revealed cerebellar atrophy affecting the vermis. Chromosome breakage studies did not show evidence of chromosome instability. Mutation analysis of the SETX gene (Prevention Genetics, Marshfield, WI) was performed by polymerase chain reaction amplification of genomic DNA followed by automated sequencing of all the coding exons, as well as 50 bases of flanking non-coding sequences. This revealed a homozygous c.1406A>G (NM_015046.5) mutation predicted to result in the amino acid substitution p.His469Arg. His affected sister was also homozygous for this mutation. Since the early reports of AOA2 in Japanese (1), Pakastani (2) and French Canadian (3) families, it has now been reported in a wide range of populations. This report is the first to document the disease presence in the Canadian Aboriginal population. To date more than 75 mutations have been identified in more than 100 reported patients worldwide. The vast majority of these mutations are distributed across the entire gene without any reported hot spots. Our patients were homozygous for a c.1406A>G, a mutation that has been reported to be causative of AOA2 in a consanguineous family from Southern Italy (4). This substitution was not found in 200 Italian control chromosomes (4) nor did we identify this change in any of the population databases, including dbSNP, 1000Genomes and Exome Aggregation Consortium. In silico analysis using PolyPhen-2, SIFT and MutationTaster predict p.His469Arg change to be ‘probably damaging’, ‘not tolerated’ and ‘disease causing’, respectively (5–7). Based on the recent ACMG guidelines for interpreting sequence variants (8), the c.1406A>G is likely pathogenic. Consanguinity in this family favors the idea of a founder mutation. The presence of the same mutation in the family from Southern Italy is likely a recurrent event and not derived from a single ancestral mutation. This report supports the panethnic presence of AOA2.

Variable expressivity of a novel mutation in the SCN1A gene leading to an autosomal dominant seizure disorder.

Mutations in the SCN1A gene can cause a variety of dominantly inherited epilepsy syndromes. Severe phenotypes usually result from loss of function mutations, whereas missense mutations cause a milder phenotype by altering the sodium channel activity. We report on a novel missense variant (p.Val1379Leu) in the SCN1A gene segregating in an autosomal dominant pattern in a family exhibiting a variable epilepsy phenotype ranging from generalized epilepsy with febrile seizures during infancy to a well controlled seizure disorder in adulthood. This report supports the importance of SCN1A mutation analysis in families in which seizure disorders segregate in an autosomal dominant fashion.