Spinocerebellar ataxia and hypergonadotropic hypogonadism associated with familial sensorineural hearing loss

Biallelic SQSTM1 mutations in early-onset, variably progressive neurodegeneration

OBJECTIVE

To characterize clinically and molecularly an early-onset, variably progressive neurodegenerative disorder characterized by a cerebellar syndrome with severe ataxia, gaze palsy, dyskinesia, dystonia, and cognitive decline affecting 11 individuals from 3 consanguineous families.

METHODS

We used whole-exome sequencing (WES) (families 1 and 2) and a combined approach based on homozygosity mapping and WES (family 3). We performed in vitro studies to explore the effect of the nontruncating SQSTM1 mutation on protein function and the effect of impaired SQSTM1 function on autophagy. We analyzed the consequences of sqstm1 down-modulation on the structural integrity of the cerebellum in vivo using zebrafish as a model.

RESULTS

We identified 3 homozygous inactivating variants, including a splice site substitution (c.301+2T>A) causing aberrant transcript processing and accelerated degradation of a resulting protein lacking exon 2, as well as 2 truncating changes (c.875_876insT and c.934_936delinsTGA). We show that loss of SQSTM1 causes impaired production of ubiquitin-positive protein aggregates in response to misfolded protein stress and decelerated autophagic flux. The consequences of sqstm1 down-modulation on the structural integrity of the cerebellum in zebrafish documented a variable but reproducible phenotype characterized by cerebellum anomalies ranging from depletion of axonal connections to complete atrophy. We provide a detailed clinical characterization of the disorder; the natural history is reported for 2 siblings who have been followed up for >20 years.

CONCLUSIONS

This study offers an accurate clinical characterization of this recently recognized neurodegenerative disorder caused by biallelic inactivating mutations in SQSTM1 and links this phenotype to defective selective autophagy.

Hypogonadism and neurological diseases

Affected patients with hypogonadism have unnaturally low amounts of sex hormones that produce male and female sex characteristics. Males who suffer from this condition lack testosterone, while females fail to produce enough estrogen. Hypogonadism may be present at birth, or it may take effect years later following injury or illness to the sex glands. Hypogonadism has remarkable associations with variable medical disorders; however, it is characterized by a distinctive association with variable neurological disorders: such as epilepsy, ataxia, dysmyelination, nerve muscle disease, movement disorders, mental retardation and deafness. The remarkable neurological diseases with hypogonadism should not basically be regarded as coincidental findings, but possibly related to an intrinsic pathophysiological association.

Hypergonadotropic hypogonadism, progressive early-onset spinocerebellar ataxia, and late-onset sensorineural hearing loss: case report and literature review

The association of ataxia, hypergonadotropic hypogonadism and hearing loss is extremely rare. Considerable heterogeneity exists in the literature of the neurological manifestations, age of onset, clinical severity and associated abnormalities. We describe a 24-year-old woman with secondary hypergonadotropic amenorrhea, early-onset progressive spinocerebellar ataxia (SCA), late-onset sensorineural hearing loss and normal intelligence and compare it with reported cases.

[A woman with cerebellar ataxia and hypergonadotropic hypogonadism]

A 26-year-old woman with primary amenorrhea in association with hypergonadotropinism, and lacking a vagina and uterus, suffered from a gradually progressive gait disturbance in her adolescence. The patient has no family history of ataxia and a chromosome study showed a normal karyotype (46,XX). Using the revised Hasegawa Dementia Scale, her cognitive function was measured as that of a normal adult, however, neurological examination revealed symptoms of scanning speech, horizontal gaze-evoked nystagmus, and ataxia. Bulging eyes, high-arched palate, scoliosis and ventricular septal defect were also observed. A brain MRI showed atrophy of the cerebellum. A 123I-IMP brain SPECT study showed hypoperfusion in the cerebellum. Previous studies show that among patients with cerebellar ataxia and hypergonadotropic hypogonadism, some show an autosomal recessive inheritance, while others have no family history. As a cause, a chromosomal abnormality is unlikely because all reported karyotypes were normal. This case is different from other reported cases in that she is not mentally impaired or deaf. The present case indicates that there is a close relationship between cerebellar ataxia and hypogonadism, and that other symptoms such as deafness and mental impairment could be an additional variable in patients with cerebellar ataxia arid hypergonadotropic hypogonadism.