Huppke-Brendel Syndrome
Summary
Clinical characteristics.
Huppke-Brendel syndrome (HBS) is characterized by bilateral congenital cataracts, sensorineural hearing loss, and severe developmental delay. To date, six individuals with HBS have been reported in the literature. All presented in infancy with axial hypotonia; motor delay was apparent in the first few months of life with lack of head control and paucity of limb movement. Seizures have been reported infrequently. In all individuals described to date serum copper and ceruloplasmin levels were very low or undetectable. Brain MRI examination showed hypomyelination, cerebellar hypoplasia mainly affecting the vermis, and wide subarachnoid spaces. None of the individuals reported to date were able to sit or walk independently. All affected individuals died between age ten months and six years.
Diagnosis/testing.
The diagnosis of HBS is established in a proband with characteristic features (bilateral congenital cataracts, sensorineural hearing loss, severe developmental delay, very low serum copper and ceruloplasmin levels) and biallelic (compound heterozygous or homozygous) pathogenic variants in SLC33A1 identified by molecular genetic testing.
Management.
Treatment of manifestations: Cataract extraction is indicated in the first few months of life; early feeding tube placement to manage difficulties with swallowing, ensure adequate nutrition, and reduce the risk of aspiration; developmental intervention; physiotherapy to maintain muscle function and prevent contractures.
Surveillance: Periodic developmental and neurologic assessment; nutritional and growth evaluation; hearing evaluation; ophthalmologic evaluation; orthopedic evaluation for increased risk of scoliosis and contractures.
Genetic counseling.
HBS is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Once the SLC33A1 pathogenic variants have been identified in an affected family member, carrier testing for at-risk relatives, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible.
Diagnosis
Formal diagnostic criteria for Huppke-Brendel syndrome (HBS) have not been established.
Suggestive Findings
HBS should be suspected in individuals with the following clinical, radiographic, electrophysiologic, and laboratory findings.
Clinical findings
- Bilateral congenital cataract
- Nystagmus
- Sensorineural hearing loss
- Severe developmental delay / intellectual disability
- Hypotonia
- Seizures, hypopigmented hair, and hypogenitalism (reported infrequently)
Radiographic findings on brain MRI examination
- Cerebellar hypoplasia
- Hypomyelination
- Wide subarachnoid spaces
Electrophysiologic findings. Brain stem auditory evoked potentials show absent wave forms.
Laboratory findings
- Low serum copper (usually 10%-20% of normal for age)
- Low serum ceruloplasmin (undetectable or very low)
Note: Identification of low serum copper and ceruloplasmin levels may be problematic in infants younger than age six months given the normally low serum concentration in all children at this age.
Establishing the Diagnosis
The diagnosis of HBS is established in a proband with the above Suggestive Findings and identification of biallelic pathogenic variants in SLC33A1 by molecular genetic testing (see Table 1).
Molecular genetic testing approaches can include a combination of gene-targeted testing (single-gene testing, multigene panel) and comprehensive genomic testing (exome sequencing, genome sequencing) depending on the phenotype.
Gene-targeted testing requires that the clinician determine which gene(s) are likely involved, whereas genomic testing does not. Because the phenotype of HBS is broad, individuals with the distinctive findings described in Suggestive Findings are likely to be diagnosed using gene-targeted testing (see Option 1), whereas those in whom the diagnosis of HBS has not been considered are more likely to be diagnosed using genomic testing (see Option 2).
Option 1
When the phenotypic and laboratory findings suggest the diagnosis of HBS, molecular genetic testing approaches can include single-gene testing or use of a multigene panel.
- Single-gene testing. Sequence analysis of SLC33A1 detects small intragenic deletions/insertions and missense, nonsense, and splice site variants; typically, exon or whole-gene deletions/duplications are not detected. Perform sequence analysis first. If only one or no pathogenic variant is found, perform gene-targeted deletion/duplication analysis to detect intragenic deletions or duplications.
- A multigene panel that includes SLC33A1 and other genes of interest (see Differential Diagnosis) is most likely to identify the genetic cause of the condition at the most reasonable cost while limiting identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. Note: (1) The genes included in the panel and the diagnostic sensitivity of the testing used for each gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests.For an introduction to multigene panels click here. More detailed information for clinicians ordering genetic tests can be found here.
Option 2
When the diagnosis of HBS is not considered because an individual has atypical phenotypic features, comprehensive genomic testing (which does not require the clinician to determine which gene[s] are likely involved) is the best option. Exome sequencing is most commonly used; genome sequencing is also possible.
For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.
Table 1.
Gene 1 | Method | Proportion of Probands with Pathogenic Variants 2 Detectable by Method |
---|---|---|
SLC33A1 | Sequence analysis 3 | 6/6 probands |
Gene-targeted deletion/duplication analysis 4 | Unknown 5 |
- 1.
See Table A. Genes and Databases for chromosome locus and protein.
- 2.
See Molecular Genetics for information on allelic variants detected in this gene.
- 3.
Sequence analysis detects variants that are benign, likely benign, of uncertain significance, likely pathogenic, or pathogenic. Variants may include small intragenic deletions/insertions and missense, nonsense, and splice site variants; typically, exon or whole-gene deletions/duplications are not detected. For issues to consider in interpretation of sequence analysis results, click here.
- 4.
Gene-targeted deletion/duplication analysis detects intragenic deletions or duplications. Methods used may include quantitative PCR, long-range PCR, multiplex ligation-dependent probe amplification (MLPA), and a gene-targeted microarray designed to detect single-exon deletions or duplications.
- 5.
No data on detection rate of gene-targeted deletion/duplication analysis are available.
Clinical Characteristics
Clinical Description
Huppke-Brendel syndrome (HBS) is characterized by cataract, sensorineural deafness, and severe developmental delay in all reported individuals. To date, six individuals with HBS have been reported in the literature [Horváth et al 2005, Huppke et al 2012, Chiplunkar et al 2016].
Ocular features. Bilateral congenital cataracts were reported in all affected individuals. Affected individuals presented with poor visual fixation and rotary nystagmus. Two individuals underwent cataract extraction in early infancy; there was improvement in visual fixation and nystagmus in one child [Horváth et al 2005] and no improvement in vision in the other [Chiplunkar et al 2016].
Sensorineural hearing loss manifests during infancy. Brain stem auditory evoked potentials in two individuals showed absent waveforms. Otoacoustic emissions were absent bilaterally in one individual.
Neurologic features. Axial hypotonia was present in all infants. Motor delay was apparent in the first few months of life in all reported individuals. Lack of head control and paucity of movements in the limbs were evident. None of the individuals reported to date were able to sit or walk independently. None learned to speak. Developmental progress has been reported only in one individual who received copper histidinate therapy from age five months [Horváth et al 2005]. Follow up at age 13 months in this individual showed good head control, rolling over, reaching out for objects, and improved alertness and communication.
Deep tendon reflexes were normal and symmetric.
Two of the six reported individuals had seizures.
Orthopedic complications. Affected individuals are at increased risk for scoliosis and joint contractures [Author, personal communication].
Other. Hypopigmented hair and hypogenitalism were reported in one individual [Chiplunkar et al 2016]. This child had micropenis with bilaterally descended testes. The hair was uniformly hypopigmented and sparse. Hair analysis under polarized light microscopy showed uniform and finely granulated melanin pigment and no clumps. There was no kinking or abnormal polarization.
Prognosis. All affected individuals died between age ten months and six years. Causes of death included pneumonia, renal failure, and multiorgan failure. The cause of multiorgan failure was not reported.
Neuroimaging. Brain MRI showed hypomyelination, cerebellar hypoplasia mainly affecting the vermis, hypoplasia of the temporal lobes, and wide subarachnoid spaces (see Figure 1) [Horváth et al 2005, Huppke et al 2012, Chiplunkar et al 2016].
Figure 1.
Histopathology on muscle biopsy
- Subsarcolemmal proliferation and vacuolization in few type 1 fibers are reported. No typical ragged red fibers or ragged blue fibers or COX-negative fibers are seen [Horváth et al 2005, Chiplunkar et al 2016].
- Biochemical measurements of the respiratory chain enzymes showed significantly reduced activity of COX with 30% residual activity in one individual [Horváth et al 2005] and 35% residual activity in another [Chiplunkar et al 2016].
Genotype-Phenotype Correlations
The number of individuals with confirmed pathogenic variants in SLC33A1 is too small to make any conclusive genotype-phenotype correlations.
Nomenclature
HBS may also be referred to as congenital cataracts, hearing loss, and neurodegeneration (CCHLND).
Prevalence
Prevalence of HBS is unknown. Only six affected individuals have been reported to date.
Differential Diagnosis
Table 2.
Disorder | Gene(s) | MOI | Overlapping Clinical /Laboratory Features | Distinguishing Clinical Features |
---|---|---|---|---|
Disorders w/overlapping clinical & laboratory features | ||||
SUCLG1-related mtDNA depletion syndrome, encephalomyopathic form w/methylmalonic aciduria | SUCLG1 | AR |
| Dystonia, other extrapyramidal features, & basal ganglia signal changes on MRI differentiate this disorder from HBS. |
SUCLA2-related mtDNA depletion syndrome, encephalomyopathic form w/methylmalonic aciduria | SUCLA2 | AR |
| Dystonia, extrapyramidal features, & basal ganglia signal changes differentiate this disorder from HBS. |
Combined oxidative phosphorylation deficiency 11 (OMIM 614922) | RMND1 | AR |
| Systemic features incl cardiac abnormalities & nephropathy differentiate this disorder from HBS. |
Hypomyelination and congenital cataract | FAM126A | AR |
| Normal early development & normal hearing distinguish this disorder from HBS. |
Menkes syndrome (see ATP7A-Related Copper Transport Disorders) | ATP7A | AR |
| Kinky hair, seizures as a predominant manifestation, normal hearing, white matter signal changes on brain MRI, & tortuous blood vessels on brain MR angiogram differentiate this disorder from HBS. |
Disorders w/overlapping laboratory features | ||||
Wilson disease | ATP7B | AR |
| Liver disease, movement disorder, & Kayser-Fleischer rings help to differentiate this disorder from HBS. |
Congenital disorder of glycosylation, type IIo (OMIM 616828) | CCDC115 | AR |
| Cataracts & deafness are not characteristic of CDG-IIo. |
Congenital disorder of glycosylation, type IIp (OMIM 616829) | TMEM199 | AR | ↓ serum ceruloplasmin | Psychomotor development can be normal, & cataracts & deafness are not characteristic of CDG-IIp. |
MEDNIK syndrome (OMIM 609313) | AP1S1 | AR |
| Cutaneous manifestations (icthyosis & keratodermia) & enteropathy differentiate this disorder from HBS. |
AR = autosomal recessive; CDG = congenital disorder of glycosylation; DD = developmental delay; MOI = mode of inheritance
Management
Evaluations Following Initial Diagnosis
To establish the extent of disease and needs in an individual diagnosed with Huppke-Brendel syndrome (HBS), the following evaluations are recommended if they have not already been completed:
- Ophthalmologic evaluation
- Assessment of feeding and nutrition
- Developmental assessment
- Audiologic evaluation including brain stem auditory evoked response and otoacoustic emissions testing
- Complete neurologic assessment
- Electroencephalography if seizures are suspected
- Consultation with a clinical geneticist and/or genetic counselor
Treatment of Manifestations
The following are indicated:
- Cataract extraction in the first few months of life
- Early feeding tube placement to manage difficulties with swallowing, ensure adequate nutrition, and reduce the risk of aspiration
- Developmental intervention
- Physiotherapy to maintain muscle function and prevent contractures
Surveillance
Individuals with HBS require the following periodically:
- Developmental and neurologic assessment
- Nutritional and growth evaluation
- Hearing evaluation
- Ophthalmologic evaluation
- Orthopedic evaluation because of increased risk for scoliosis and contractures
Evaluation of Relatives at Risk
It is appropriate to evaluate infants at risk for HBS in order to identify as early as possible those who would benefit from prompt removal of cataracts as well as feeding and developmental support. Evaluations can include the following:
- Clinical exam, ophthalmologic exam for cataracts, and audiologic evaluation in an at-risk newborn prior to molecular testing or while waiting for molecular resultsNote: Serum copper and ceruloplasmin levels may not be informative in a newborn because serum ceruloplasmin and, to a lesser degree, serum copper are very low in normal neonates (even more so in premature infants); further, the depletion of copper stores may not be noticeable in the first few months of life even in patients with known disorders of copper transport.
- Molecular genetic testing if the pathogenic variants in the family are known
See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.
Therapies Under Investigation
Treatment with copper histidinate in three affected individuals did not result in an increase in serum copper or ceruloplasmin. Clinical improvement was reported in one individual, who died at age four years.
Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions.