| Domain | Summary |
|---|---|
| Disease / identifiers | Hereditary spastic paraplegia 48 (SPG48); OMIM disease **613647**. Associated causal gene **AP5Z1**; OMIM gene **613653**. No Orphanet or MONDO identifier was available in the provided evidence snippets. (pqac-00000001, pqac-00000009) |
| Causal gene | **AP5Z1** (adaptor-related protein complex 5, zeta 1 subunit), encoding the **AP-5 ζ subunit** involved in intracellular membrane trafficking / vesicular cargo sorting. (pqac-00000001, pqac-00000006, pqac-00000021) |
| Inheritance | **Autosomal recessive** / biallelic AP5Z1-related disease. Reported as homozygous or compound heterozygous loss-of-function variants in affected individuals; asymptomatic relatives are often heterozygous carriers. (pqac-00000001, pqac-00000004, pqac-00000006, pqac-00000023) |
| Variant spectrum | Predominantly **loss-of-function** variants: nonsense, frameshift, splice-site, and exon-level deletions. In the 2021 multicenter study, 9 AP5Z1 variants (8 new) were reported, including **2 nonsense, 5 frameshift, 2 splice-site**, all predicted to lead to premature stop codons and nonsense-mediated decay. Examples include **c.1662_1672del;p.Glu554Hfs*15** and **c.1133-345_1311+249del;p.G378Vfs*93X**. (pqac-00000004, pqac-00000006, pqac-00000023, pqac-00000024) |
| Core phenotype | **Slowly progressive spastic paraplegia / spastic paraparesis** with lower-limb spasticity and weakness; often a **complicated HSP** with additional neurologic features. Wheelchair dependence may occur about **10 years after onset** in severe cases. (pqac-00000004, pqac-00000006, pqac-00000023) |
| Common additional features | Frequently reported: **axonal neuropathy**, **urinary incontinence**, **cognitive impairment / intellectual disability**, **hearing loss**, **visual impairment**, **ataxia**, **dystonia**, **parkinsonism**, **myoclonus**, and occasionally **seizures**. Azoospermia/infertility and deafness were reported in a 2023 case. (pqac-00000001, pqac-00000005, pqac-00000006, pqac-00000014, pqac-00000026) |
| Typical age at onset | Heterogeneous. In the multicenter AP5Z1 cohort, **mean onset 54.3 ± 5.3 years** (late-onset). Earlier onset is also documented, including ages **2 and 47 years** in a 2014 series; one case first showed shuffling gait at **47 years** and spastic gait by **50**. Overall, onset can “span many decades.” (pqac-00000001, pqac-00000010, pqac-00000023, pqac-00000026) |
| MRI / neuroimaging | Findings may be normal or abnormal. Reported abnormalities include **white-matter lesions / leukoencephalopathy**, **anterior/periventricular FLAIR hyperintensities**, **thinning/narrowing of the corpus callosum (TCC)**, **“ears of the lynx” sign**, **bifrontal/periventricular WM hyperintensities**, **dilated Sylvian fissures**, **moth-eaten basal ganglia appearance**, and **mild brain atrophy**. In one case, corpus callosum was normal despite WM changes. (pqac-00000001, pqac-00000004, pqac-00000006, pqac-00000023, pqac-00000026, pqac-00000027) |
| Electrophysiology | Supports peripheral nerve / motor neuron involvement. Reported findings include **axonal neuropathy**, **chronic neurogenic EMG pattern with reduced interference**, **decreased CMAP amplitudes**, **prolonged sural SNAP latency**, **prolonged F-wave latencies**, **prolonged H-reflexes**, and **prolonged somatosensory evoked potential latency**. (pqac-00000001, pqac-00000023, pqac-00000024, pqac-00000027) |
| Pathophysiology / mechanism | AP5Z1 loss disrupts the **AP-5/SPG11/SPG15** trafficking machinery on **late endosomes/lysosomes**. Mechanistic studies show impaired **late endosome-to-Golgi retrieval** of **CIMPR, GOLIM4, and GOLM1**, accumulation of **LAMP1-positive multilamellar endolysosomal structures**, and a **lysosomal storage–like phenotype**. Mouse and cellular models indicate impaired **autophagic flux** and **autophagic lysosome reformation (ALR)**, with buildup of autophagosomes/autolysosomes, intracellular waste, and ultimately **axon degeneration**. AP-5 may function as a **backup pathway for retromer**. (pqac-00000004, pqac-00000015, pqac-00000017, pqac-00000020, pqac-00000021, pqac-00000029) |
| Diagnostic approach | Diagnosis is based on phenotype-compatible **HSP evaluation** plus **molecular confirmation of biallelic AP5Z1 variants**. Reported methods include **targeted gene analysis**, **Sanger sequencing**, and **copy-number confirmation by fluorescence quantitative PCR** for exon deletions. In broader HSP workups, **multigene panels, WES, or WGS** are appropriate when a genetic spastic paraplegia is suspected. MRI and neurophysiology help characterize disease burden. Differential diagnostic overlap is especially noted with **SPG11** and **SPG15**. (pqac-00000023, pqac-00000024, pqac-00000025, pqac-00000027) |
| Management / treatment | No disease-modifying therapy is established in the provided evidence. Current care is **symptomatic/supportive**. In a 2023 case, **oral baclofen** and **tizanidine** improved symptoms; supportive mobility aids such as a **walking stick** were needed in progressive disease. Reviews note that HSP treatment is generally symptomatic, with rehabilitation/physiotherapy commonly used across HSP, though SPG48-specific controlled data were not identified in the provided snippets. (pqac-00000024, pqac-00000026, pqac-00000023) |
| Frequency / epidemiology notes | SPG48 is **ultra-rare**. Before the 2021 multicenter study, only **11 patients** had been reported; that study added **9 patients from 8 unrelated families** and noted **22 AP5Z1 variants** linked to SPG48 worldwide. A 2023 case report stated **14 cases worldwide** at that time. In a 61-patient complex HSP cohort, **2/61 (3%)** had SPG48/AP5Z1 variants. In a 127-patient European HSP cohort, AP5Z1 variants were very uncommon, leading authors to conclude AP5Z1 mutations are **rare, at least in Europeans**. (pqac-00000001, pqac-00000005, pqac-00000013, pqac-00000009) |
| Key primary references | **Breza et al., 2021, Movement Disorders** — multicenter AP5Z1 cohort expansion. DOI/URL: https://doi.org/10.1002/mds.28487 (pqac-00000001, pqac-00000004) ; **Hirst et al., 2015, Human Molecular Genetics** — AP-5 loss causes aberrant endolysosomes. DOI/URL: https://doi.org/10.1093/hmg/ddv220 (pqac-00000021) ; **Hirst et al., 2018, PLOS Biology** — AP-5 mediates late endosome-to-Golgi retrieval. DOI/URL: https://doi.org/10.1371/journal.pbio.2004411 (pqac-00000020) ; **Khundadze et al., 2019, Neurobiology of Disease** — mouse SPG48 model with blocked autophagic flux. DOI/URL: https://doi.org/10.1016/j.nbd.2019.03.026 (pqac-00000017) ; **Jin et al., 2023, Frontiers in Neurology** — SPG48 with deafness and azoospermia. DOI/URL: https://doi.org/10.3389/fneur.2023.1156100 (pqac-00000006, pqac-00000024) ; **Maruta et al., 2020, Clinical Neurology** — novel AP5Z1 frameshift case. DOI/URL: https://doi.org/10.5692/clinicalneurol.60.cn-001419 (pqac-00000023) |
| Evidence base type | Information in this summary is derived from **aggregated disease-level resources and primary literature**, including multicenter cohorts, case reports/series, and mechanistic studies in patient fibroblasts, HeLa CRISPR/siRNA models, and knockout mice. (pqac-00000001, pqac-00000017, pqac-00000020, pqac-00000021) |


*Table: This table summarizes the core disease knowledge-base facts for hereditary spastic paraplegia 48, including identifiers, genetics, phenotype, mechanism, diagnostics, and management. It is restricted to details directly supported by the provided evidence snippets and includes context-id citations in each cell.*